Improving crop production for food security and improved livelihoods on the East India Plateau. I. Rainfall-related risks with rice and opportunities for improved cropping systems

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Improving crop production for food security and improved livelihoods on the East India Plateau. I. Rainfall-related risks with rice and opportunities for improved cropping systems Peter S. Cornish a,*, Dinabandhu Karmakar b, Ashok Kumar b,1, Sudipta Das b,2, Barry Croke c a

University of Western Sydney, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW 1797, Australia Professional Assistance for Development Action (PRADAN), Dumdum Road, Kolkata, India c Integrated Catchment Assessment and Management Centre, The Australian National University, Canberra, ACT 0200, Australia b

A R T I C L E

I N F O

Article history: Received 22 August 2014 Received in revised form 24 December 2014 Accepted 2 January 2015 Available online Keywords: Rice-based cropping system Purulia Watershed development Water balance model Climate risk

A B S T R A C T

Rainfed transplanted rice (Oryza sativa) is the staple crop of the East India Plateau (EIP), where it is low yielding and drought-prone despite high annual rainfall (>1200 mm). Although grown traditionally on lowlands associated with drainage lines, population pressure has forced rice onto terraced slopes (mediumuplands) that now comprise >80% of the rice area, and the only rice land for many families. Crop monitoring, soil water measurement and soil water-balance modelling in Pogro watershed (West Bengal) were used to explore rainfall-related risks associated with rice-fallow on medium-upland and to examine opportunities for using rainfall more effectively. The analysis was extended to three more EIP locations by using the model with long-term rainfall. Rice depends on sustained ponding for transplanting and good yields, but in Pogro, failure to meet this condition on medium-uplands led to delayed or failed transplanting and/or periodic or premature draining of fields in five years from 2005 to 2011. Modelled ponding duration was more variable than rainfall. Most farmers have adapted to variable ponding by growing mediumduration varieties on medium-uplands, rather than the longer types grown in lowlands. However, the average ponding duration of 65 days over all four locations was well short of the ~90 days required. Even shorter-duration varieties would provide only a partial solution as ponding was <50 days in ~25% of years, and transplanting impossible in 10% of years. Watershed development (WSD) is unlikely to deliver food security from transplanted rice, because in dry years there is little or no runoff to capture for irrigation and shallow groundwater becomes available too late; although modelling confirmed the potential for WSD to promote post-monsoon cropping in wetter years. Significantly, in every year at all locations there was enough soil water for non-flooded crops (rarely <140 continuous days of >30 mm available soil water). Duration of available soil water was the least variable measure of water security, confirming that perceptions of ‘drought’ arise from experience with transplanted rice that depends on ponding. We conclude that ‘aerobic’ (un-puddled) rice culture on medium-uplands should provide food security from this staple crop. Modelling identified opportunities to intensify and diversify cropping systems with manageable climate risk, even without WSD, by opportunistically using residual water after rice, shorter-duration varieties to maximise residual water, and minimal supplementary irrigation from shallow groundwater that apparently is recharged every year. The suggested developments have implications for river basin hydrology and WSD that require research and a reappraisal of policy. Crown Copyright © 2015 Published by Elsevier Ltd. All rights reserved.

1. Introduction Eastern India is the most densely populated, least developed and poorest region of the Sub-Continent, and rural poverty has been

* Corresponding author. Tel./Fax: +61 2 4573 1663. E-mail address: [email protected] (P.S. Cornish). 1 Present address: PRADAN, 3rd Floor, Rukmini Tower, Harmu Rd, Ranchi, Jharkhand, India. 2 Present address: Collectives for Integrated Livelihood Initiative, Jamshedpur, Jharkhand, India.

linked to social unrest (Bonnerjee and Koehler, 2010; Dixit, 2010; Edmonds et al., 2006). Of the 220 million people in Eastern India, 70% are subsistence farmers who depend on rainfed mono-cropped transplanted rice in a rice-fallow cropping system (ICRISAT/CARE, April 2002; unpublished joint report). The region accounts for about half the rice area in India, but impressive yield improvements in irrigated rice since the 1960’s have generally not been replicated in rainfed Eastern India (Anon, 2010a). The reasons for low yield and slow adoption of ‘improved’ practices have received little attention (Fuwa et al., 2007) although ‘drought’ is often said to be a factor, even with modern rice varieties (Pandey et al., 2012). Despite variable rainfall and susceptibility

http://dx.doi.org/10.1016/j.agsy.2015.01.008 0308-521X/Crown Copyright © 2015 Published by Elsevier Ltd. All rights reserved.

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to drought, the region is regarded as having great potential because of high average monsoon precipitation (1100–1600 mm) that provides excess water to be captured through watershed development (WSD) and made available for irrigation (e.g. Sikka et al., 2009). WSD is a major programme in India for improving livelihoods where there is little irrigation infrastructure, although apparently it has been unable to insure against ‘bad years’ (Joy et al., 2004). The task of implementing WSD is vast, and progress is limited by the availability of funds and expertise. So there remains a need for less risky and more productive rainfed cropping systems based on existing water resources, including any residual soil water left by rice in the traditional rice-fallow and any accessible annually-recharged shallow groundwater. This study relates to the elevated region of East India, the Chota Nagpur Plateau (or East India Plateau, EIP), comprising the States of Jharkhand and Chhattisgarh and parts of West Bengal, Bihar and Odisha. Despite undulating topography, rainfed transplanted rice is by far the most important crop, with average paddy yields of <2 t ha−1 (Anon, 2010a). Rice traditionally has been grown on lowlands associated with drainage lines, but population pressure has forced expansion onto terraced slopes (medium-uplands) where most of the rice is now grown (Pangare and Karmakar, 2003). Average yields hide important differences related to the toposequence, with greater yields low in the landscape (Fuwa et al., 2007) where rice is favoured by runoff and seepage and farmers grow longer-duration varieties accordingly (Pandey et al., 2012). The vast majority of families have not yet benefitted from WSD, so few have significant irrigation capacity although small ‘water-harvesting’ structures (seepage pits, ponds) are common. There is a large representation of Tribal people without a long tradition of settled (arable) agriculture (Edmonds et al., 2006; Verma, 2007). Against this background, the rainfall-related risks and opportunities for cropping on the EIP were considered by a combination of soil water measurement and water balance modelling. This approach accounted for evapotranspiration as well as rainfall, plus the potential storage of rainfall when it exceeds evapotranspiration, either in the soil or above the soil when fields are ponded for rice. Soil water measurements in a case-study watershed in Purulia District (West Bengal) were used to parameterise a daily water balance model that was then run using daily weather data from the watershed and subsequently applied to longer-term rainfall from the nearby Shaharajore dam and to long-term data from three other locations in West Bengal and Jharkhand. The objectives were to: (i) characterise the rainfall-related risks for the rice-fallow system, (ii) suggest options for managing these risks, and (iii) identify opportunities for more intensive and diverse cropping systems.

2. Materials and methods

Recharge zone

Upland

Runoff

Medium upland Terraced/bunded uplands & hillslopes

Drainage

Medium lowland Terraced & bunded foot-slopes Lowland Variable discharge

Seasonally-recharged shallow ground water

Discharge zone

Fig. 1. Landscape schematic.

The acid, infertile soils are developed mainly on gneiss or granite parent materials and are mainly Alfisols and Inseptisols (Agarwal et al., 2010), or more correctly Anthroposols because of the soil moved in association with terracing, and modification by wet tillage for rice production (Gong, 1983). Season names in this paper refer to summer (March to Mid-June), monsoon (Mid-June to September/ October) and winter (November to February). Warm-season crops (mainly rice) are grown in the kharif (monsoon), whilst coolseason crops may be grown (infrequently) in the rabi (winter). 2.2. Case study watershed The Pogro watershed (area 2 km2) in Purulia District (West Bengal), on the eastern fall of the EIP (elevation ~380 m), was used to characterise soil for modelling and to support agronomic interpretation. PRADAN facilitated the engagement of every family in Pogro, primarily through women’s self-help groups leading ultimately to watershed development. From 2006 to 2008, about 20% of the farmers (~50 families) were engaged more directly in soil and crop surveys in a participatory process described by Cornish et al. (2015). Soils are developed mostly on gneiss (Sahu and Dey, unpublished data for 13 soil profiles). Medium-uplands comprise >80% of the rice area and about 60% of the total area, which is representative of the Plateau area except where steep and heavily forested. Average family land holdings are <1 ha and fragmented across the landscape. Poor families own smaller areas, mostly of upland or medium-upland, and better-off families generally own somewhat larger areas that include a greater proportion of lowlands and medium-lowlands. Pogro has two large community-owned ponds and numerous open wells for domestic use, and numerous small ponds that also appeared to be for domestic use. Rice is monocropped in the kharif, when small areas of vegetables are also grown for home consumption on uplands near homesteads. Secondcropping is confined to small areas of wet lowlands where winter rice may be grown, and negligible areas of vegetables may be irrigated from ephemeral streams or dug wells.

2.1. The plateau landscape 2.3. The water balance model The EIP rises south from the eastern Indo-Gangetic Plain and west of the coastal plain of the Bay of Bengal, and comprises a series of plateaus, hills and valleys with an average elevation ~500 m and occasional higher peaks. Drainage lines and low-lying areas near streams comprise the lowlands which rise to nearby uplands with local topographic relief typically <30 m. Much of the original hillslope area has been terraced and bunded over time to create mediumlowlands and medium-uplands for rice (Fig. 1). Uplands and medium-uplands behave hydrologically as recharge areas for the seasonally recharged shallow groundwater. Discharge occurs in lowlands and, in wetter years, the narrow band of medium-lowland. (Drainage to deeper regional aquifers is slow. These aquifers are sometimes tapped for irrigation, but this consideration is beyond the scope of the present paper).

The intention was to characterise risks and opportunities for the Plateau region rather than predict crop yield. This avoided the need to parameterise and validate a rice model, which would have been impracticable as the study region has little research infrastructure, the research locations are remote, and the research was onfarm to maximise relevance. The region experiences security issues (Dixit, 2010) that sometimes restricted the research team. The research reflected these realities, requiring simplifying assumptions where reliable data were absent and not readily collectable. A single-layer daily water balance model run in Microsoft Excel was used, based on Cornish and Murray (1989) but modified to include drainage beyond the root zone and to allow water to pond above the soil surface with rice. Evapotranspiration (ET) was

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Bunds over-top

400 Ponded water

Upper Limit (UL)/Saturation

300

Ponded water 100 mm + PAWC (UL-CLL) 190 mm (range 150-230) = AW 290 mm

Drainable soil water (>’field capacity’) ‘Field capacity’

210

Maximum available water (AW) for rice

Plant-extractable soil water (range 60-140 mm) Crop Lower Limit (CLL)

110 Unavailable soil water (range 70-130 mm) 0

Oven dry UL = 300 mm total water in soil to 90 cm depth (at saturation) (range 220-360 mm)

Fig. 2. Components of water (mm) measured or estimated for lowland rice in medium-uplands of the East India Plateau.

modelled as a function of reference evapotranspiration (Eo) estimated by the Penman–Monteith equation (Allen et al., 1998). The model is described briefly below. Details of parameterisation and the underlying assumptions are given in the Supplementary Material. Sensitivity testing and verification are discussed in Section 3.2. The water balance from June 2006 to December 2011 was computed for a rainfed system of rice in the kharif and grazed weeds in the subsequent fallow (Equation 1). Only medium-uplands were modelled as these are the most widespread rice lands. The soil water balance was:

AWC time 2 = AWCtime 1 + (rainfall + irrigation + run-on) − (ET + runoff + drainage)

(1)

AWC is the plant-available water content between an upper limit (UL) determined by soil properties and a crop-specific lower limit (CLL); ET is evapotranspiration; drainage (D) is downward flux beyond the root-zone to annually recharged shallow aquifers (with some subsequently draining to deeper aquifers). All run-on is assumed to run off so nett run-on equals zero. Maximum AWC is termed the potential available water capacity (PAWC). During rice growth, water may pond above the soil surface, effectively adding to available water. The model thus estimated ‘Available Water’ (AW), which had a maximum value of PAWC plus the maximum depth of ponded water (Fig. 2). Model output included daily AW, ET, runoff and drainage. As this is a point model, runoff and drainage estimates cannot be scaled up directly. Field measurements were made of UL and CLL during on-farm research where rice management, soil properties and yields were observed from 2006 to 2008. UL for medium-upland soil was 300 mm for the 90 cm root-zone. This is the water held at saturation not the ‘upper drained limit’ (Burk and Dalgliesh, 2008), because soil is usually near saturation under transplanted rice. CLL was 110 mm. The difference between UL and CLL (the PAWC) averaged 190 mm (range 150–230 mm), comprising 100 mm between the CLL and FC plus 90 mm between FC and the UL (saturation). The importance of the range in PAWC was assessed in model applications. The concept of FC has been largely superseded in agronomy, but a value was needed in the model to support estimates of ET and D. Total and available water at FC were set at 210 mm and 100 mm. D was set at 3 mm d−1 when the profile was wetter than FC, based on limited field observation (see Supplementary Material). The model was tested for sensitivity to values from 2 to 10 mm d−1. The model assumed ET = Eo when AWC > 0.5 (FC-CLL) and ET = 0.5 Eo when AWC ≤ 0.5 (FC-CLL) (after Allen et al., 1998). The threshold AWC of 0.5 (FC-CLL) was 50 mm.

Pond depth was typically 100 mm in Pogro, but varied between farmers and landscape position. Sensitivity to this value was assessed by running the model with depths of 75, 100 and 125 mm, which also allowed evaluation of deeper ponds as an option to reduce the risk of fields draining in dry years. Rainfed non-flooded alternative crops were simulated with no ponding. The only water data for model validation were the values for UL and CLL. So in addition, model output was tested for ‘sense’ with farmers and development professionals to see that it adequately captured seasonal water dynamics. Cardinal agronomic dates derived from the modelling (dates for seedbed preparation, transplanting and when fields drain of free water) were evaluated against actual field observation from 2006 to 2008 (Section 2.5). Observed water levels in wells and piezometers and stream gauging (Croke et al., 2015) provided independent data for runoff and drainage. 2.4. Climate data An automatic weather station (Onset Computer Corporation) was installed at Pogro, providing daily rainfall and estimated Eo for June 2006–November 2011. The 1994–2000 rainfall data from Shaharajore dam (2 km from Pogro) were used to extend Pogro modelling. No other meteorological data were available from Shaharajore dam, so average evaporation for each day of the year was used from the 6 years at Pogro, possibly over-estimating Eo in wet conditions and under-estimating it in dry periods. Examination of average and actual Eo over 6 years at Pogro showed no bias, as days of under-estimated Eo were typically followed by days of over-estimated Eo. The spatial and temporal relevance of Pogro results was examined by calculating the water balance using long-term rainfall (1971– 2009) from the Indian Meteorology Department for three locations on the EIP: Purulia, West Bengal (50 km SE of Pogro); Bokaro, Jharkhand (30 km N of Pogro) and West Singhbhum, Jharkhand (120 km SW of Pogro). No evaporation data were available for these locations so daily Pogro averages were used to provide daily Eo for use with the model. 2.5. Field monitoring – agronomic data relevant to model verification and interpretation From discussions with farmers engaged in the soil and crop monitoring, the following consensus ‘rules’ were determined to allow key dates to be predicted from modelled water to compare with field observations. Cultivation follows pre-monsoon rains of ~50 mm or more at any time after late May and nurseries would be sown after mid-June. Further cultivation, including ‘puddling’, occurs with onset

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of the monsoon. Transplanting commences once seedlings are ≥ 21 days old (typically >28 days) and fields hold standing water (AW > 190 mm). Fields remain ponded until bunds are opened (if necessary) to drain them prior to harvest. Bunds are restored at the next monsoon. Each year from 2006 to 2008, observations in ~60 fields (~50 farmers) distributed amongst land classes were made of the dates of cultivation, planting of the rice nursery (and variety), puddling, transplanting, anthesis and harvest. Mean dates were used to interpret or verify agronomic conclusions based on modelled water availability. Transient draining of fields was noted, and the date when fields drained prior to harvest. Farmers were asked to qualitatively assess the rice season (poor, average, good) and comment if this assessment reflected (i) late cultivation and nursery preparation, (ii) insufficient early monsoon rain that delayed transplanting, (iii) periodic draining of fields during the monsoon, or (iv) early recession of the monsoon and draining of fields. A late monsoon delays nursery planting and may lead to lateseason drought or cold stress. Faltering rains after planting may lead to transplanting with over-mature seedlings and reduced yield (Sarwar et al., 2011). Transplanted rice needs continuous ponding of sufficient duration determined by variety. Ponding is needed for weed control (Bhager et al., 1999), P-availability (Willett et al., 1978),

free-living N-fixation (Roger and Ladha, 1992), and droughtavoidance where crops are shallow rooted (Henry et al., 2011). More than 90 days ponding was deemed necessary for good yields of medium-duration rice (25 days in the dry nursery + 90 days submergence + 10 days to physiological maturity). 2.6. Measures of variability The coefficient of variation (CV) was used to express dispersion in the rainfall data and all variables derived from use of the model. This dimensionless measure allowed comparison between variables with different units (e.g. rainfall and the duration of ponding). 3. Results and discussion 3.1. Rainfall Average rainfall at Pogro for the study period was 1233 mm (CV 0.29) (Table 1). Rainfall in the nominal monsoon period (June– September) averaged 1072 mm (CV 0.29), or 87% of the annual average. Annual rainfall for the study period varied from 723 mm to 1774 mm, which covered the range of expectations from the

Table 1 Hydrologic and agronomic assessments for transplanted rice-fallow in Pogro medium-uplands.

Rainfall (mm) Total June–Sept (monsoon) May (pre monsoon) Oct (post monsoon) Modelled water balance components for the rice-fallow system (mm yr−1)a Annual ET Rice ETb Predicted runoff Predicted drainage Modelled water for plants Avail. waterd at: 30 Sept. Rice maturity Ponding duration (d)e Within-season drainingf Duration of available water (days)g Date at CLL + 10 mmh Date rice maturityi Rabi irrigationj (mm) Farmer’s summary of each year for rice

2006

2007

2008

2009

2010

2011

Mean

CV

1303 1140 103 27

1774 1518 64 41

1139 1004 68 20

1029 944 38 40

723 603 74 33

1429 1225 68 59

1233 1072 69 37

0.29 0.29 0.30 0.37

797 488 122 360

846 482 568 366

663 465 167 327

576 453 131 316

641 433 0c 69

768 441 290 401

715 460 213 307

0.15 0.05 0.93 0.39

193 111 68

0.41 0.62 0.55

166 7 Jan 25 Oct 71

0.13

281 239 79 Yes 200 19/01/07 10/10/06 23 Bad on some med-upland. Delayed transplanting some fields, periodic draining

266 109 103 No 169 9/01/08 2/11/07 77 Good

96 79 62 No 151 25/11/08 10/10/08 108 Moderately bad. Early monsoon and transplanting but early end to monsoon

193 76 65 Yes 160 5/01/10 2/11/09 92 Bad transplanting delayed in most fields, plus early end to monsoon

102 41 0 No ponding 138 26/01/11 12/11/10 70 Bad No rice transplanted

219 123 99 No 180 17/01/12 18/10/11 53 Good (but 3 wks. dry in Aug–Sept, some fields drained briefly)

0.42

a Weather data in 2011 end 5 Nov, so subsequent water-use was estimated by assuming no further rainfall and the average ET from 2006–2010, for each day during Nov–Dec. b ET from the first opportunity to sow rice nursery (after 1 June), to 125 days after sowing (equivalent to medium duration rice (e.g. Lalat). c The only runoff observed in 2010 was from relatively impermeable surfaces (e.g. roads, degraded land). The absence of significant runoff was confirmed by stream gauging (Croke, unpublished data). d Available water (AW) at the nominal end of monsoon (30 Sept) and at maturity for a 125-day rice sown at the first opportunity after 1st of June. This indicates residual water for a later crop. e Days AW >190 mm from transplanting to maturity, ignoring drained periods between transplanting and 1 Sept. Defines the ponding period for transplanted rice. Assumes growth will not end if ponds drain before Sept. (although yield may be reduced). f Ponds observed to drain after transplanting but before 1 Sept. g The period between sowing rice in the nursery and when AW reached 30 mm after the monsoon. It is the period over which a rainfed cropping system (e.g. rice + rabi crop) may be grown with no irrigation and mature with water remaining (i.e. no water stress). h Day/month/year when AW reached 10 mm above the CLL (remaining water will contribute little to production). This is a less conservative estimate for the duration of rainfed cropping. i Day/month/year when a 125 d variety would mature if planted at first opportunity (assumed to apply to any rainfed crop or to weeds). This represents the start of harvest and the earliest date for sowing a rabi crop. j Irrigation required to keep AW >0.3 FC (30 mm) for 90 days following rice harvest (also see footnote g).

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Probability of exceedance

1

locally within a region that is otherwise enjoying good rainfall. We observed similar variation in the region during fieldwork during 2006–11.

2010

2009

0.8

3.2. Model verification and sensitivity testing 2008

0.6

2006

0.4 2011

0.2 2007

0

0

500

1000

1500

2000

2500

Annual rainfall (mm) Fig. 3. Annual rainfall exceedence curves for the Pogro study site. Long-term data are from the Indian Meteorology Department gridded dataset. Annual rainfall (mm) at Pogro was 1153 (2006), 1774 (2007), 1139 (2008), 1029 (2009), 723 (2010) and 1429 (2011). Table 2 Rainfall and modelled water balance components for transplanted rice-fallow at Shaharajore dam, near Pogro (1994–2001).

Annual rainfall (mm) Runoff (mm) Drainage (mm) Ponding durationa (days)

Mean

CV

1488 369 380 77

0.37 0.90 0.29 0.58

Days AW >190 mm from transplanting to maturity, ignoring drained periods between transplanting and 1 Sept. a

long-term frequency distribution of rainfall for the surrounding area, based on the 0.5 × 0.5 degree gridded data from the Indian Meteorology Department (Fig. 3). Average annual rainfall at Shaharajore dam (1994–2001) was 1488 mm (724–2270 mm) (Table 2). Although greater than Pogro, 3 years had rainfall that was in the wettest 5% of years in the gridded data (Fig. 3). Shaharajore dam rainfall CV (0.37) was greater than at Pogro. Average annual rainfall for the 14 years of Shaharajore/ Pogro data combined was 1352 mm. Of the locations with long-term rainfall used for modelling, Bokaro had the lowest rainfall (1128 mm), then West Singhbhum (1332 mm) and Purulia (1360 mm) (Table 3). There was substantial variation between locations within years, showing that ‘drought’ may occur

Table 3 The long-term water balance components modelled for a transplanted rice-based cropping system. Values are means (coefficient of variation).

Rainfall (mm) Runoff (mm) Drainage (mm) Ponding duration (days)a Plant-available waterb (days)

Bokaro

Purulia

West Singhbhum

1128 (0.25) 116 (1.28) 307 (0.35) 48 (0.83) 177 (0.19)

1360 (0.22) 223 (1.03) 364 (0.21) 75 (0.50) 200 (0.13)

1332 (0.22) 189 (0.97) 364 (0.22) 67 (0.57) 198 (0.16)

Days AW >190 mm from transplanting to maturity, ignoring drained periods between transplanting and 1 Sept. b The period between sowing of rice in the nursery and when AW reached 30 mm after the monsoon. a

5

3.2.1. Verification With ponding depth of 100 mm and drainage rate of 3 mm d−1, actual dates for transplanting agreed well with dates derived from modelled water (see Section 3.3.1), supporting infiltration assumptions and model predictions for the early monsoon. The model predicted AW of 17 mm for the 100 mm pond depth in midNovember 2008, when fields were sampled to estimate the CLL (zero AW). This relatively small over-prediction is unlikely to be of practical significance. Farmers and local development professionals verified that the model credibly captured the variation in water between and within seasons in ‘average’ medium-uplands, and could be used to derive approximate dates of important agronomic events (e.g. time of ploughing and transplanting) and predict when fields drained during and at the end of the monsoon. Farmer’s subjective assessments of each year (Table 1) matched researcher expectations based on water. 3.2.2. Sensitivity testing Sensitivity to pond depth and drainage rate was assessed by running the model for 6 years (2006–11). Data for 2008 are given as an example. Annual rainfall in 2008 (1139 mm) approached the 6-year average (1208 mm). Farmers assessed 2008 as a ‘moderately bad’ year (Table 1) despite good early rain that enabled timely sowing of nurseries and transplanting. Their rating reflected early cessation of the monsoon, premature draining of fields, and low yields in much of the medium-upland. 3.2.2.1. Pond depth. Varying pond depth between 75–125 mm made little difference to predicted AW (15–21 mm) in mid-November 2008 when CLL was measured (Fig. 4). With shallow ponds (75 mm), the model indicated fields draining briefly during the 2008 monsoon that was not observed. Over all years, 75 mm depth tended to overpredict draining events. The model predicted an early end to ponding in 2008, as farmers observed, whilst increased pond depth delayed field draining by 4 d per 25 mm depth (Fig. 4). Greater water depth in ponds evidently offset the 6 mm d−1 loss; viz. 3 mm d−1 assumed drainage plus September ET of ~3 mm d−1. Over 6 years, increasing depth by 50 mm extended ponding by an average 10 d (range 0–16 d), but this possible drought mitigation measure had no effect in the dry year of 2010, or during the dry early monsoon in 2009 when ponding was intermittent until 154 mm rain fell on 6th September. 3.2.2.2. Drainage rate. Drainage rate had little effect on predicted planting dates. All except 10 mm d−1 captured what farmers said about early transplanting in 2008 (Fig. 5). Estimated AW was above the CLL in mid-November 2008 with drainage rates of 1 and 2 mm d−1 (Fig. 5). Only the 3 mm d−1 rate gave a reasonable estimate of AW in mid-November and also captured what farmers reported in 2008 about ‘early draining of fields’ without periodic draining during the monsoon. Draining of fields during the 2006 monsoon and the ‘dry finish’ reported by farmers in 2011 were both captured best with 3 mm d−1 (Fig. 6). 3.3. Model predictions and their agronomic interpretation 3.3.1. The risks with growing rice – Pogro case study Variable rainfall led to variation in the planting time for rice nurseries, large variation in the time that ponding commenced (AW > 190 mm), and to variation in when surface water drained after

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350

Water (mm)

300 250

75 mm 100 mm 125 mm

200

Sat

150 FC

100 50

CLL

0 1/1/08

1/4/08

1/7/08

1/10/08

Fig. 4. Model sensitivity to variation in pond depth (at drainage rate of 3 mm d−1) at Pogro in 2008. Saturation (Sat), ‘field capacity (FC) and the crop lower limit of water extraction for rice (CLL).

350

1 mm/d

2 mm/d

3 mm/d mm

5 mm/d

Water (mm)

300 250

10 mm/d Rice CLL (zero AW) measured here

Nursery planted

200 150 100

Earliest transplanting

50 0 1/01/08

1/04/08

1/07/08

1/10/08

Fig. 5. Model sensitivity to drainage rate (pond depth of 100 mm), Pogro 2008.

300

Water (mm)

250

No rice transplanted

200

Sat

150 100

FC

50 0 1/6/06

CLL rice

1/12/06

1/6/07

1/12/07

1/6/08

1/12/08

1/6/09

1/12/09

1/6/10

1/12/10

1/6/11

1/12/11

Fig. 6. Available water in a rice-fallow system, modelled in medium-uplands at Pogro from June 2006 to December 2011, showing saturation (Sat), ‘field capacity’ (FC) and the crop lower limit of water extraction for rice (CLL rice), with observed transplanting dates (solid arrow) and dates derived from modelled water (dashed arrow). The nominal onset of the monsoon is mid-June.

the monsoon (AW ≤ 190 mm) (Fig. 6). Consequently, ponding duration varied from zero in 2010 (723 mm rainfall) to 103 d in 2007 (1774 mm) (Table 1). Ponding duration (mean 68 d, CV 0.55) varied more than rainfall (CV 0.29). Given the crucial role of ponding in rice culture (Section 2.5), we took this variability as a key indicator of ‘drought’ risk. Farmers’ observations (Table 1) confirmed the conclusion derived from modelling that rice would have suffered in 4 of the 6 years; from delayed transplanting and periodic draining of fields (2006), short ponding duration despite timely transplanting (2008), delayed transplanting with short ponding duration (2009), or no ponding and transplanting at all (2010). We also observed widespread failure of rice in the medium-uplands in 2005 due to an early end of the monsoon. Little or no rice was harvested from medium-uplands in 2005, 2009 and 2010. Thus during a 7-year period when rainfall represented the range of longer-term expectations (Fig. 3), rice on medium-upland was ‘drought-affected’ in 5 years and essentially failed in 3 of them. Note that rice was still harvested in Pogro in 2005 and 2009, from lowlands

and medium-lowlands (Fig. 1), but not in 2010 when ‘drought’ affected much of East India (Anon, 2010b). Modelling using rainfall from nearby Shaharajore dam extended Pogro results by 8 years (Table 2). Mean ponding duration (77 d) was longer than at Pogro (68 d) but just as variable. Results were skewed by three years in the top 5% for rainfall, yet ponding duration in 3 of the 8 years was only 4, 30 and 40 d. Ponding duration for the combined Pogro/Shaharajore data averaged 73 d. A complex picture emerges of the ‘drought’ risk for transplanted rice in medium-uplands. It includes delayed nursery planting that increases the risk of terminal drought or cold stress, delayed transplanting with over-mature seedlings, insufficient ponding to transplant at all, within-monsoon draining of fields leading to weed and nutritional issues, and terminal drought arising from premature draining of fields. Without irrigation, there will be no simple solution to this suite of problems. Although rainfall was often insufficient for transplanted rice, abundant water always remained in the soil at harvest (Table 1), showing that drought per se was not the problem, and even

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suggesting the possibility of a second crop in some years. At maturity of a 125-day rice, the estimated residual water averaged 111 mm (41–239 mm, CV 0.62) (Table 1). Further, the period when water was available for rainfed crops, between planting the nursery and when AW fell to 30 mm after the monsoon, averaged 166 d, far exceeding the 125 d needed for medium-duration rice (Table 1). (The limit of 30 mm provided a conservative estimate of when crops could grow without significant water stress.) 3.3.2. The wider applicability of Pogro findings, long-term simulations (1971–2009) Having verified the utility of model predictions (Section 3.2), we simulated the water balance at three more locations to explore the wider applicability of the Pogro analysis, using ponding duration as an indicator of ‘drought’ risk for transplanted rice. Average ponding duration at Bokaro, Purulia and West Singhbhum was 48, 75 and 67 d (Table 3) compared with 68 d at Pogro (73 d including Shaharajore dam). The overall mean of 65 days was much less than the 90 days required for medium-duration rice (Section 2.5). Over all locations, estimated ponding duration exceeded 90 d in only onethird of years and it was <50 d in 25% of years (Fig. 7). There was little chance of ponding at all when rainfall was less than 1000 mm (Fig. 7), which, from the gridded long-term rainfall data (Fig. 3), occurs in >10% of years. Ponding duration was much more variable than rainfall at all locations (Table 3). Ponding duration was also a good indicator of delayed transplanting. At Purulia for example, ponding duration was <70 d in 15 of 39 years simulated (Fig. 7). In 14 of these years, seedlings were >28 d old at the first opportunity to transplant. In 5 of these 14 years, seedlings were from 52 to 83 d old at possible transplanting, and judged to be ‘over-mature’. In an additional 5 years there was no opportunity to transplant at all (as at Pogro in 2010). In a linear regression, transplanting was delayed 1.4 d d−1 ponding was <70 d (P < 0.05, r2 = 0.74). These quantified rainfall-related risks for transplanted rice in medium-uplands confirm the widely held qualitative view that rice in the region is often drought affected (Fuwa et al., 2007; Sikka et al., 2009) and broadly support estimates from household surveys in Purulia, that drought occurs one year in two or three causing yield losses of 20–70% (Pandey et al., 2012). It is notable that variability in agronomic terms (ponding duration) was much greater than rainfall statistics alone suggest.

Duration of ponding or available water (days)

Purulia

7

Farmers recognise the vulnerability of rice to drought in mediumuplands compared with lowlands and use shorter-duration varieties in an attempt to match variety to field hydrology (Pandey et al., 2012). In Pogro, a common variety in medium-upland was Lalat (125 days), requiring ~90 days of ponding. Even shorter-duration varieties (e.g. Bullet) were grown occasionally. Long-duration varieties were typical of lowlands (e.g. Swarna, 140 days). Short duration leading to early maturity is a sensible strategy for addressing terminal water stress arising from premature draining of fields, because the soil is invariably wetter at the nominal end of the monsoon than later (Table 1). However, the chances of terminal water stress remain high with medium- or even shortduration varieties, given that ponding duration is <50 days in 25% of years. Short duration does nothing to address the risk of being unable to transplant. Some farmers manage the risk of delayed transplanting by establishing additional (late) nurseries, but these need quick maturing varieties to address the short ponding period that mostly follows late transplanting, and cannot help when there is no chance to transplant. Greater drought tolerance in rice has been advocated for the region (Pandey et al., 2012), but even successful breeding for drought avoidance (short maturity, deep rooting) or physiological drought resistance would provide only partial solutions to the problems arising from inadequate ponding (Section 2.5). Increasing pond depth may reduce the risk, but not remove it (Section 3.2.2.1). 3.3.3. Opportunities for watershed development – ‘rescue irrigation’ of rice Although point-scale estimates of runoff and drainage are not directly scalable to the watershed, modelling provided an initial assessment of the water that WSD may ‘harvest’ for irrigation. WSD uses structural works to increase the capture and storage of runoff water, and sometimes to increase flow to the annually-recharged groundwater that is accessed via shallow dug wells or ‘seepage pits’ low in the landscape or in drainage lines (Verma, 2007). Over the study period at Pogro, the estimated annual rice-fallow ET averaged only 715 mm, little more than half the annual rainfall (Table 1). Consequently, average predicted runoff (213 mm yr−1) and drainage (307 mm yr−1) from this dominant land-use were high, apparently justifying a focus on WSD. Our initial question was whether WSD can help to manage the drought-risk associated with transplanted rice.

Bokaro

West Singhbuum

300 Ponding

Available water

250 200 150 100 50 0 0

500

1000

1500

2000

0

500

1000

1500

2000

0

500

1000 1500 2000

Annual rainfall (mm) Fig. 7. Duration of ponding and available water (>30 mm) in response to rainfall in a cropping system based on transplanted rice at three locations on the East India Plateau (1971–2009).

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Fig. 8. Runoff and drainage from bunded medium-uplands in response to rainfall at three locations on the East India Plateau (1971–2009).

Runoff at Pogro was more variable than ponding duration (CV 0.93 versus 0.55) and did not occur every year (Table 1). Stream gauging confirmed there was no significant runoff in 2010 (Croke et al., 2015). Runoff from medium-uplands can be low despite high rainfall because bunded terraces retain water that may otherwise run off. With little or no runoff in some years, WSD interventions designed to capture runoff cannot reliably provide rescue irrigation for rice (assuming ponds empty each year). This may explain why WSD has been ‘unable to insure against bad years’ (Joy et al., 2004) and why the ‘5% pit’ used in WSD to capture local runoff for rescue irrigation of rice in medium-uplands is not always effective (Pangare and Karmakar, 2003). It also suggests that WSD based on runoff capture may only benefit farmers in wetter years, through irrigation of crops following the monsoon. Drainage was predicted every year at Pogro, and detected in piezometers installed in the watershed, although in medium-upland the shallow groundwater generally arose late in the monsoon and persisted for only a short time after the monsoon (Croke et al., 2015). Average predicted drainage exceeded runoff (Table 1). It was also less variable (CV 0.39 versus 0.93) because drainage occurs whenever the root zone is wetter than FC, which is common even in lowrainfall years (Fig. 6). Similar findings for runoff and drainage were made at Shaharajore dam (Table 2); and in the long-term modelling (Table 3) where runoff rose linearly above about 1200 mm rainfall, below which there was little runoff (Fig. 8). There was negligible runoff in over onequarter of years; but there was >150 mm drainage every year at all locations, except for the three extremely dry years at Bokaro (Fig. 8). The reliable recharge of shallow groundwater suggests that access to this water for irrigation may contribute more to food security in dry years than planning to capture runoff. Unfortunately, this water becomes available too late in the kharif to save rice in the event of ‘drought’. In any case, seepage water can’t be transferred easily from the point of extraction to medium-uplands. However, the ‘5% pit’ designed to capture runoff to irrigate rice in medium-upland may briefly allow access to shallow groundwater (Croke et al., 2015), potentially providing short-term irrigation of early-sown rabi crops that could contribute to food security in dry years and cash income in other years. Our analysis suggests that neither shallow groundwater nor runoff appear able to deliver food security from transplanted rice, nor, as we have discussed, can any strategy for adapting lowland rice technology to medium-uplands, including deeper ponds and short-

season, drought resistant varieties (Section 3.3.2). Therefore, additional strategies are needed for food security. 3.3.4. A foundation for food security – non-flooded kharif crops including ‘aerobic’ rice This section considers if there is enough rainfall to base food security on alternative kharif crops in rainfed medium-upland, requiring bunds to be left open to avoid flooding. The options include ‘aerobic’ rice that is direct-sown without puddling and grown as any field crop (Sridhara et al., 2012). The potential for alternative kharif crops to deliver food security depends on the duration of available soil water, as distinct from transplanted rice that depends on the duration of ponding. In transplanted rice at Pogro, water was available (AW >30 mm) for an average of 166 days (Table 1). At Bokaro, Purulia and West Singhbhum it was 177, 200 and 198 d (Table 3), enough for even long-duration rice. It was rarely <140 d and it rose with rainfall to a maximum of about 220 d (Fig. 7). However, removing bunds from terraced fields must reduce water storage on hill slopes, generate more runoff, and potentially leave less water for crops. Moreover, soil structure may improve over time when soil is no longer puddled, possibly leading to increased drainage rates, also resulting in less water for crops. Therefore the rice-fallow water balance in Pogro was simulated with no ponding, although soils could saturate during wet periods. Drainage scenarios simulated were 3 mm d−1 as for puddled rice, and a hypothetical 10 mm d−1 to gauge the possible effects of improved soil management on drainage rate (refer to Supplementary Material). With no ponding and the higher drainage rate, simulations should apply to crops in upland fields with PAWC of 100 mm, assuming saturation-excess runoff still applies (untrue for degraded areas). The 100 mm of plant-extractable water is midrange for sandy-loam to clay-loam soils with an effective rooting depth of 90 cm (e.g. Burk and Dalgliesh, 2008). When calculating the duration of available soil water for crops, two scenarios for the lower limit of water-use were used: the CLL + 10 mm; and a more conservative 0.3 FC (30 mm) which minimised water stress. Available water simulated for 6 years is given in Fig. 9 whilst runoff, drainage and relevant agronomic information derived from the water balance are given in Table 4. Leaving bunds open increased annual runoff from 213 mm to 296 mm (with drainage rate 3 mm d−1), but reduced annual drainage from 307 mm to 254 mm, resulting in 30 mm less annual ET (cf. Tables 1 and 4) and 43 mm less residual water at

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9

200

Soil water (mm)

3 mm/d 10 mm/d

150

100

FC

50

0 1/6/06

CLL

1/12/06

1/6/07

1/12/07

1/6/08

1/12/08

1/6/09

1/12/09

1/6/10

1/12/10

1/6/11

1/12/11

Fig. 9. Soil water in a crop-fallow on Pogro medium-upland where the crop is not puddled and ponded. Assumes drainage rates of 3 mm d−1 (solid line) or 10 mm d−1 (dashed line). Soil water may rise above ‘field capacity’ (FC), saturating the soil profile during wet periods.

Table 4 Water balance components for a 125-day non-ponded crop-fallow system, predicted without ponding using alternative drainage rates (3, 10 mm d−1) and lower limits of extraction (10, 30 mm).

Drainage rate 3 mm d−1 Runoff (mm yr−1) Drainage (mm yr−1) Annual ET (mm) Rice ET (mm) Date CLL + 10 mm AW (mm) at: 30 Septa Crop maturity Duration available water (days)b to: CLL (+10 mm) 1/3 of FC (30 mm) Drainage rate 10 mm d−1 Runoff (mm yr-1) Drainage (mm yr-1) Annual ET (mm) Rice ET (mm) Date CLL + 10 mm AW (mm) at: 30 Septa Crop maturity Duration available water (days)c to: CLL (+10 mm) 1/3 of FC (30 mm)

2006

2007

2008

2009

2010

2011

Mean

CV

222 309 772 489 18 Dec

668 311 796 483 11 Dec

267 250 623 466 15 Nov

231 262 543 454 2 Dec

0 69 626 437 26 Jan

390 324 752 448 6 Dec

296 254 685 463 13 Dec

0.75 0.38 0.15 0.04

181 132

166 63

80 63

99 38

102 41

134 71

127 68

0.32 0.50

194 168

166 145

162 145

156 132

201 175

192 166

179 155

0.11 0.11

9 560 739 488 25 Nov

271 738 768 473 28 Nov

107 436 598 466 12 Nov

113 394 530 435 25 Nov

0 107 600 432 13 Jan

187 552 724 448 30 Nov

115 465 660 457 2 Dec

0.90 0.46 0.15 0.05

142 81

117 43

74 57

69 32

65 30

86 46

92 48

0.33 0.39

171 150

153 134

159 138

149 128

188 162

179 156

167 145

0.09 0.09

a

Available water at the nominal end of the monsoon (30 Sept), and at maturity for a 125-day crop sown at the earliest opportunity. Assumes no ponding, maximum AW = 190 mm (saturation), drainage rate 3 mm d−1. Days from the date when AW first reaches 50 mm after 1st May to either the CLL (+10 mm) or 0.3 FC (30 mm). Weather data in 2011 end 5 Nov, so subsequent rice water-use was estimated by assuming no further rainfall and the average ET from 2006 to 2010 for each day during Nov–Dec. c Assumes a hypothetical drainage rate of 10 mm d−1 following soil remediation. Other assumptions are as for the 3 mm d−1 drainage rate. b

rice maturity. With 10 mm d−1 of drainage, annual runoff was reduced to 115 mm and drainage increased to 465 mm, resulting in 55 mm less ET and 63 mm less residual water than bunded fields. Despite the large effects on runoff and drainage, soil water would have been available continuously for >5 months every year on mediumupland at Pogro. This was regardless of drainage rate, although the 10 mm d–1 rate did result in ~10 days earlier drying than 3 mm d−1 averaged over the two lower limits used (Table 4). With 3 mm d−1 drainage rate, water was available for 179 d with water used down to the CLL + 10 mm, and for 155 d with the more conservative scenario of water use to 0.3 FC. With 10 mm d−1 of drainage, water was available for 167 and 145 d with the two lower limits. In all scenarios there was more than enough water in all years for medium-duration rice or other kharif crops of comparable duration. This conclusion also applies to some uplands (see above), where a range of crops could be safely grown. The duration of available water for non-ponded crops is by far the least variable of all the measures of water security in Pogro, with CV ≤ 0.11 (Table 4). Available water at harvest is a further measure of water-security, indicating the likelihood and degree of any terminal water stress.

At Pogro it averaged 68 mm (range 38–132 mm) and 48 mm (range 30–81 mm) for a 125-day non-ponded crop sown at the earliest opportunity assuming drainage rates of 3 and 10 mm d−1 (Table 4). All of these values suggest that terminal water stress would be unlikely in non-ponded kharif crops. Had a short-duration kharif crop been grown, maturing by 30th September, soil water would have averaged 127 mm (80–181 mm) and 92 mm (69–142 mm) for 3 and 10 mm d−1 drainage rates. These values confirm the security of soil water for un-ponded crops and demonstrate useful starting water for a following crop. The wider relevance of un-bunded Pogro simulations was evaluated using long-term rainfall and running the model with a drainage rate of 3 mm d−1 and water-use to 0.3 FC. Average available water duration was 168, 182 and 180 d for Bokaro, Purulia and West Singhbhum (Table 5), with all years >125 d (Fig. 10). Short- to medium-duration aerobic rice or un-ponded alternatives could have been grown securely in all years with regard to rainfall and soil water. It is notable that removing bunds and particularly increasing drainage rates had large effects on the partitioning between runoff

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Fig. 10. The duration of available water in an un-bunded rice-based cropping system at three locations on the East India Plateau.

and drainage (cf. Tables 1 and 4), even though the effects on soil water and crop production in the kharif were small. Hydrologic responses are discussed further in Section 3.5. The inescapable conclusion is that although ‘drought’ occurs on the EIP as a rainfall statistic, agriculturally it is only a perception based on transplanted rice. Drought would not occur for rainfed kharif crops that require no ponding. Many crops including vegetables can be grown in the kharif, but ‘aerobic’ rice will be the key to ricebased food security for poor families with little or no lowlands for safe rice production. SRI rice enjoys growing popularity in India (Basu and Leeuwis, 2012), but it requires puddling for transplanting so is still subject to variability in early monsoon rainfall. With aerobic rice, bunds may be reinstated after crop establishment, affecting the water balance. As soil is not puddled, any ponding will not occur exactly as it does with transplanted rice, but it may still provide more water for the crop than if bunds are left open. This will not improve the reliability of aerobic rice, as there is abundant water anyway, but periodic ponding may increase the soil water at maturity. This could not be simulated without knowing more about ponding in un-puddled fields that have previously grown rice. Also, with short-duration rice, bunds will be opened near maturity in wetter years anyway, to facilitate harvest, so reducing any benefit for residual soil water. 3.4. Opportunities to intensify cropping systems by using existing water resources more effectively This section investigates opportunities for generating cash income by intensifying rice-based cropping systems in the absence of WSD. Residual soil water following both bunded and un-bunded rice

Table 5 The long-term modelled water balance for un-bunded cropping. Values are means (CV).

Annual runoff (mm) Annual drainage (mm) Plant-available water (days)a

Bokaro

Purulia

West Singhbhum

186 (0.96) 267 (0.34) 168 (0.17)

308 (0.79) 310 (0.21) 182 (0.15)

259 (0.79) 310 (0.21) 180 (0.17)

a Days of available water from sowing an alternative kharif crop (including aerobic rice) to when AW falls to 30 mm after the monsoon.

provides the foundation. Since no crops are sown after rice it is presently ‘lost’ through drainage (when AW > 100 mm) and soil evaporation, or it is used by weeds. Early rice maturity increases the amount of residual water (cf. Tables 1 and 4) and should increase the potential for a second crop. Two scenarios were considered, one with supplementary irrigation (Section 3.4.1) based on the observation that many farmers have small water bodies that could be used for limited irrigation, and the other without any irrigation (Section 3.4.2). 3.4.1. Cropping system intensification using residual water and supplemental irrigation – Pogro 3.4.1.1. Rabi cropping after transplanted rice in medium-upland – minimal system change. Residual soil water at Pogro following 125day transplant rice averaged 111 mm, ranging between years from 41 to 239 mm (Table 1) with the mean PAWC of 190 mm. However, PAWC ranged from 150 to 230 mm (Fig. 2), so the residual water will also vary between fields. The average residual water in fields with a PAWC of 150 mm was 88 mm (39–192 mm), and with PAWC of 230 mm it was 132 mm (41–272 mm). The greatest difference between fields was in wetter years. It follows that second-cropping requires flexibility in choosing when and where to grow the second crop if irrigation is limited and soil water is important. The model was used to estimate the supplementary irrigation needed to keep crops unstressed (AW > 0.3 FC) for an arbitrary 90 d following harvest of a 125-day transplanted rice (with PAWC 190 mm). An average of 71 mm irrigation was needed, ranging from 23 mm in 2006 to 108 mm in 2008 (Table 1). This small average requirement results from good residual water at planting combined with low Eo. Even the driest year (2010) required only 70 mm irrigation. Farmers apply ~50 mm per irrigation (Cornish et al., 2015), so only 1–2 irrigations could secure a 90-day rabi crop. To value the residual water and limited irrigation on a 90-day crop (total 182 mm), we used published estimates of water-use efficiency (WUE, yield/ET) in rainfed crops with limited water. Australian estimates suggest possible yields of ~1.0 t ha−1 for canola (Brassica napus) (Robertson and Kirkegaard, 2005) and ~1.9 t ha−1 for wheat (Triticum aestivum) (Hochman et al., 2009). Experiments in India suggest ~1.3 t ha−1 for mustard (Singh et al., 1991). WUE and therefore yields could be higher than this on the EIP because rainfed rabi crops grow mainly on residual soil water, so soil evaporation will be relatively low. These are not high yields,

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but they could be achieved by farmers with minimal irrigation resources who want to try multiple cropping without changing their rice variety or growing methods. Planting a rabi crop requires enough soil water for germination or planting rainfall, or irrigation. To assess if irrigation would have been required for establishment in the Pogro case study, we assumed that either ≥25 mm rain must fall soon after harvest, or AW must be >100 mm (FC) to ensure moist surface soil from upward water flux from the shallow groundwater (Cornish, 1983). One or both of these conditions were met after 125-day rice in 2006, 2007 and 2011 (Table 1). 3.4.1.2. Rabi cropping after un-bunded rice (or other kharif crop) – more radical system change. Simulations in this section relate to farmers making a radical system change based on un-ponded kharif crops. They reflect the potentially reduced soil water when fields are not bunded. Farmers have two options for adapting to reduced soil water without developing additional water resources for irrigation (or opting for shorter-duration, lower-yielding rabi crops). They may grow shorter-duration rice in fields intended for rabi cropping and/or target their wetter fields. To explore these options, the irrigation needed to keep soil >0.3 FC was estimated for 90-day rabi crops at Pogro following a kharif crop of either 90- or 125-day duration, in fields with PAWC of 150, 190 and 230 mm. The average irrigation required by a 90-day rabi crop following 125-day rice on un-bunded average medium-upland (190 mm PAWC) was 102 mm (Table 6), compared with 71 mm when bunded (Table 1). The increase is the price paid to eliminate the risk of transplanted rice failing. Aerobic rice may leave more residual water than alternative kharif crops resulting in a smaller inrease in irrigation requirement, but this could not be quantified. Soil PAWC had surprisingly little effect on average irrigation requirement. It was ~10 mm less in fields with high PAWC than in fields with average PAWC and ~10 mm more in fields with low PAWC, whether the preceding rice was a 90- or 125-day variety (Table 6). Conversely, growing 90-day rice reduced the average irrigation requirement by 55 mm, regardless of PAWC. It also increased the likelihood that planting could utilise post-monsoon rainfall, which in October at Pogro averaged 37 mm (Table 1). Whilst choosing fields with wetter soil will always be a good strategy, in terms of reducing the need for irrigation it would be better to opt for shorter-

Table 6 Estimates of the irrigation requireda for a 90-day rabi crop on un-bunded fields with PAWCb of 150, 190 or 230 mm, following a short (90 days) or medium duration (125 days) kharif cropc from 2006/07 to 2011/12 at Pogro. Assumed drainage rate was 3 mm d−1. PAWC (mm)

150

190

230

Planting possibled

Rice maturity (days)

90

125

90

125

90

125

90

125

Irrigation requirement (mm) 2006/07 2007/08 2008/09 2009/10 2010/11 2011/12 Mean

42 78 84 86 18 38 58

94 134 133 144 80 93d 113

20 65 75 84 10 23 46

72 123 126 144 70 76 102

2 46 70 62 7 28 36

54 103 119 121 68 83e 91

Y Y Y Y Y Y

Y N N N N Y

Irrigation required to keep AW >0.3 FC for 90 days following rice harvest. Assumes irrigation is at Eo and rabi crops have the same CLL as rice. b Potential plant available water content of soil (Fig. 2). c Alternatives to transplanted rice, including ‘aerobic’ rice. d Yes/no assessment if planting was possible without irrigation following rice of 90 or 125 days duration, requiring either a wet soil surface (AW > FC) and/or rainfall after rice harvest (>25 mm). PAWC was 190 mm. e Last 15 days used average evaporation data for 2006–2011. a

11

season rice varieties. A 90-day rabi crop could have been grown with 1 or 2 irrigations every year following a 90-day rice variety on unbunded medium-upland fields with average or better PAWC, and sometimes with no irrigation at all as in 2006/07 and 2010/11 (Table 6). Either one or both of the requirements for being able to plant without irrigation were met every year after short-duration rice, but in only 2 out of 6 years following 125-day rice (Table 6), supporting the case for growing shorter-duration rice to facilitate multiple cropping. Section 3.4.1 has stressed minimal irrigation from the shallow aquifer (Fig. 1) that appears to be recharged to some degree every year (Fig. 8). It can be accessed with only small capital outlay (Pangare and Karmakar, 2003; Verma, 2007) and is potentially available to most families even without WSD and without the risk of over-exploiting deep groundwater. It also suggested a second crop may sometimes be grown at Pogro without irrigation after short duration rice (Table 6). 3.4.2. Cropping system intensification without irrigation – long-term simulations Without irrigation, the important question is whether shorterduration rabi crops would enable more frequent and widespread second-cropping. Simulations using long-term rainfall from three locations determined the probability of sowing, and growing to harvest without water stress, a 60-day or 90-day rainfed rabi crop after 125- or 90-day rice on either bunded or un-bunded fields. 3.4.2.1. Rainfed cropping systems based on transplanted (bunded) rice. After 90-day rice, there was a 96% probability of sowing a crop without irrigation (averaged over locations), and 96% and 72% probabilities of both sowing and harvesting 60-day and 90-day rabi crops, respectively (Table 7, top). After 125-day rice, the probability of

Table 7 Agronomic opportunities with non-irrigated cropping systems based on either transplanted rice (bunded) or alternative crop (un-bunded)a. Model predictions of probabilities are based on long-term rainfall (1971–2009) from three locations. Assumed drainage rate was 3 mm d−1.

Transplanted rice-based system – with bunds Probability (%) of sowingb a crop after: 90-day rice 125-day rice Probability of harvestingc a rabi crop: 60-d crop after 90-d rice 60-d crop after 125-d rice 90-d crop after 90-d rice 90-d crop after 125-d rice Alternative kharif crop – bunds removed Probability (%) of sowing a crop after: 90-d rice 125-d rice Probability (%) of harvesting a rabi crop: 60-d crop after 90-d rice 60-d crop after 125-d rice 90-d crop after 90-d rice 90-d crop after 125-d rice

Bokaro

Purulia

West Singhbhum

Mean

92 56

100 79

97 79

96 71

90 41 56 21

100 72 82 41

97 64 77 49

96 59 72 37

90 33

100 64

97 69

96 55

85 18 41 5

90 44 59 13

90 46 51 21

88 36 50 13

a The estimates of probabilities will also apply to ‘aerobic’ rice that has no obligatory ponding period (see text). b Sowing possible if AW >100 mm and/or 25 mm rain within 21 days of rice harvest. c Crop is harvestable when (i) sowing possible and (ii) AW >30 mm for at least 60 days or at least 90 days.

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sowing a rabi crop was reduced to 71%, and the probabilities of both sowing and harvesting 60-day and 90-day rabi crops were reduced to only 59% and 37%, respectively. 3.4.2.2. Rainfed cropping systems based on non-bunded alternative kharif crops. Modelling shows it is still possible to sow a second crop after a 90-day non-ponded kharif crop almost every year without irrigation (Table 7, bottom) despite reduced residual water in the un-bunded system. Sowing is much less likely after a 125-day crop. The only realistic option for second cropping without irrigation is to follow a short-duration kharif crop (~90 days) with a shortduration rabi crop (~60 days), which had an 88% chance of growing to harvest without significant water stress. 3.4.2.3. The use of pre-monsoon rainfall. Potentially useful rains fall before the nominal monsoon and planting of rice nurseries. May rainfall in Pogro averaged 65 mm from 2006 to 2011, with lower variability (CV 0.22) than annual or monsoon rainfall (Table 1). This explains why farmers at the time of project inception asked what could be done to make better use of this rainfall, much of which is lost unproductively. Although reliable, it is risky to plant on premonsoon rainfall because Eo is high and the arrival of the monsoon is unpredictable. The risk could be managed with irrigation (unlikely at the end of summer), but also by controlling fallow weeds to conserve water left by rice in the subsoil (‘fallow’ as defined by Freebairn et al., 2006). Selected fields could be set aside for premonsoon cropping if rainfall allowed. 3.5. Significant implications for watershed development on the EIP That WSD appears unable to ‘drought-proof’ transplanted rice should lead to a reappraisal of policies relating to rural development. Moreover, the strategies for providing food security, suggested here, have important hydrologic implications. Removing bunds to grow an alternative kharif crop could slightly increase the total of drainage + runoff and significantly increase runoff at the cost of drainage. Modelling predicts this for both Pogro (cf. Tables 1 and 4) and more broadly (cf. Tables 3 and 5). As medium-uplands comprise ~80% of the rice area and a significant proportion of the total area of watersheds, a change in the medium-upland water balance has the potential for large impacts on WSD design and watershed hydrology. Although the modelled drainage and runoff results cannot be scaled up directly to watersheds, they indicate that further research is needed with more appropriate models. For example, re-partitioning of runoff and drainage could increase the need for surface water storage capacity in WSD (although there will still be years with little runoff) and reduce the effectiveness of measures taken to increase the use of the annuallyrecharged groundwater. Re-partitioning also has implications for river basin hydrology. It is sometimes said that widespread WSD in watersheds in upper reaches reduces water yield for downstream irrigators (Kiersch, 2002), but this may not be the case on the EIP, especially if farmers switch to un-bunded culture over a wide area. Conversely, improving soil structure over time has the potential to increase annual drainage and reduce runoff. For example, assuming D of 10 mm d−1 resulted in little or no modelled runoff in 2 of 6 years at Pogro (Table 4). Increasing D alters the balance between quick flow and slow flow from the watershed, reducing runoff peaks and extending base-flow following the monsoon. It may reduce the water that can be harvested and stored in ponds, but increase accessions to shallow groundwater. Research is needed to experimentally determine drainage rates, their response to changed soil management, and the impact of this on hydrology. These are potentially large but opposing effects that may result from replacing transplanted rice with alternative kharif crops over

a large proportion of medium-uplands in a small watershed. Cumulative impact of this on larger watersheds is unknown and needs research. However, increasing cropping intensity by drawing mainly on residual water is not likely to have significant effects on either small watershed or river basin hydrology, as the practice should merely divert ET from weeds to crops. 4. Concluding discussion Poverty and social unrest on the EIP (Bonnerjee and Koehler, 2010; Dixit, 2010) is underpinned by variable rainfall and the effects of drought on rice (Pandey et al., 2012; Sikka et al., 2009). Our analysis leads to the conclusion that revolutionary cropping systems have the potential to use existing water resources much more effectively, providing both food security and greater cash incomes with manageable climate risk, without WSD. The knowledge and skills gained in doing so could be invaluable once WSD is implemented. The questions addressed by our research, and the main findings leading to the conclusion, are summarised in Table 8. 4.1. The inevitability of failure with transplanted rice on the East India Plateau The Pogro case study and long-term modelling of three other locations lead to the conclusion that low yields of transplanted rice and crop failures on medium-uplands are inevitable on the EIP because of insufficient continuity or duration of ponding, which is much more variable than rainfall. Transplanting is not even possible in ~10% of years. The shorter-duration varieties used by farmers and widely promoted to avoid drought (Pandey et al., 2012) cannot alone ensure food security. Yet there is no lack of water. It is the un-met need for ponding that lies at the heart of low yields and rice crop failures on the EIP, regardless of any other management issues. 4.2. WSD unlikely to ‘drought-proof’ rice despite potential to increase post-monsoon production WSD may not be able to deliver food security from transplanted rice in all years. There is little runoff to ‘harvest’ for rescue irrigation in dry years, and shallow aquifer recharge becomes available too late. However, there is abundant water to ‘harvest’ through WSD in wetter years, with the potential to substantially increase overall agricultural production following the monsoon. 4.3. Food security from alternative kharif crops – the case for aerobic rice Despite the failure of transplanted rice there is ample water for rainfed kharif crops, even in the driest years. Many kharif crops including vegetables could provide a low climate-risk alternative to transplanted rice; but as rice is the staple crop, ‘aerobic rice’ seems to be the most likely candidate to provide a basis for food security. It can be grown as any field crop, with no puddling, transplanting and obligatory ponding (Sridhara et al., 2012). Aerobic rice has been investigated as a resource and labour saving technology, especially for water efficiency in irrigated rice, but in East India it also offers climate risk management in rainfed rice. The literature is inconclusive on the effects of aerobic production on yield, but seems to suggest that there is minimal yield reduction in well-irrigated crops with good management of weeds, pests, diseases and nutrition (Bouman and Tuong, 2001; Farooq et al., 2001; Hobbs et al., 2000; Sridhara et al., 2012). Aerobic rice requires no ponding, although farmers may see benefits from leaving bunds closed from after emergence until fields require draining for harvest. This aspect of the

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Table 8 Summary of research questions, outcomes and key assumptions. Modelling question

Risks/opportunities identified

Assumptions

Why does transplanted rice yield poorly, and often fail on medium-uplands, despite high rainfall?

Lack of adequate ponding (more variable than rainfall). Medium-duration varieties used by farmers are only a partial solution.

Model parameter values are widely applicable. Ponding presently essential for rice. Other management issues are important, but not the primary constraint on yield.

Can WSD eliminate drought risk in transplanted rice?

No – ponds dry seasonally and don’t refill in a lowrainfall monsoon as there is little runoff to capture. Shallow groundwater is available in a dry year, but too late for rice. However, there is potential for WSD to greatly increase post-monsoon crop production.

Large ponds with permanent water are generally unlikely, even with WSD. Deep groundwater is not always available. WSD is not a prerequisite for reducing climate risk and increasing productivity.

Can alternative kharif crops be grown safely on medium-uplands?

Yes – numerous options, but un-puddled, directseeded (aerobic) rice is preferred, as rice is the staple crop. Vegetables are a possible cash crop. Freedom from ponding should allow remediation of soil degraded by rice culture.

New rice technology can be developed for medium-uplands that is safe, high-yielding, economic and adoptable by farmers (rainfed crops may also be grown with low risk of drought in some upland). Opening bunds does not significantly reduce water for a second crop. Effects of new technologies on catchment hydrology need evaluation

Can cropping be intensified without WSD?

Yes, with manageable risk. Diversify crop types in both the kharif and rabi, and intensify cropping either by opportunistically growing a second crop (the usual meaning) or by growing more intensive crops in the kharif and/or rabi (e.g. vegetables)

Without irrigation – short-duration essential for rice and rabi crops. Rice yield may fall but system production should rise. Increased rabi crop area if irrigation is not needed. With limited irrigation – more frequent second crop, longer-duration varieties should increase yield, greater crop choice possible. A ‘5% pit’ in medium upland often provides water for irrigation to Nov.; seepage pits provide more water and for longer. Farmers develop skills for climate-responsive cropping systems.

technology needs local development whilst addressing multiple agronomic issues to ensure successful aerobic rice (Farooq et al., 2001). 4.4. Opportunities for more intensive and diverse cropping systems In addition to securing the rice crop, poor families on the EIP need to increase cash incomes and improve diets through more intensive and diverse cropping systems. The kharif presents opportunities to diversify crops with no risk of drought, including vegetables in well-drained upland fields. Furthermore, the residual water left by rice provides a foundation for second-cropping. It should be possible to grow a second crop of 90 d duration every year with only 1–2 irrigations after medium-duration (125 d) transplanted rice (Table 6). This involves minimal system change for a farmer who has access to some irrigation but is unwilling or unable to change rice production methods and varieties. Strategic use of limited irrigation maximises water productivity. It ensures crop establishment so crops can exploit residual soil water, it wets dry surface soil to allow roots through to subsoil water that would not otherwise be used, and it enhances the uptake of nutrients in otherwise dry surface soil, leading to greater subsoil water use (Cornish, 2010). Growing shorter-duration rice or other kharif crops would reduce the irrigation requirement of rabi crops, potentially increasing the area sown and helping to manage risk. This is because shorterduration rice increases the soil water when the rabi crop is sown, and increases the chance of receiving post-monsoon rainfall (Tables 1 and 4). It is the key to successful second cropping without WSD, whether farmers persist with transplanted rice or make the shift to aerobic rice or other kharif crops. Targeting wetter fields will help to reduce irrigation requirement and manage risk: fields where rice is harvested first, and the least stony deeper soils lower in the landscape. Timely planting of both rice and the rabi crop is also important, especially for the rabi crop because water is lost rapidly from the soil after rice harvest (up to ~7 mm d−1). When choosing the rabi crop to plant, consideration needs to be given to the crop water requirement in relation to the water available, which includes the soil water at planting (observed by digging a hole), any rain expected after sowing, and any irrigation resources. Although few farmers have access to major irrigation infrastructure without WSD, many have access to, or could construct,

inexpensive water harvesting structures that capture local runoff or seepage to provide limited irrigation capacity (e.g. Pangare and Karmakar, 2003; Verma, 2007). There is often runoff and always seepage (Section 3.3.3) that could be used opportunistically to partially irrigate crops. The area irrigated each year would depend on the soil water and the water available for irrigation. Second cropping should be possible for most families, even those with no water resources for irrigation. Although sounding radical, the long-term modelling suggests that farmers using short-duration transplanted rice could grow a successful quick maturing rabi crop almost every year, without irrigation (Table 7). With a shift to nonponded kharif crops there may be less residual water, but the chance of taking a successful second crop remains relatively high. These innovative cropping systems would require forward planning and the flexibility to vary planting decisions based on present and expected water. The approach demands significant management skill. The area of rabi crop planted will inevitably vary from year to year as the farmer responds to opportunities and manages climate-risk. Such a climate-responsive cropping system should allow water-use to balance water supply and present much lower risk to water resources than more intensive irrigation development based on deeper aquifers, but further research on this is needed. In any further research of the rice-fallow versus multiple cropping, system productivity and not just crop production needs to be assessed, because multiple cropping may come at the expense of animal production from weeds that are grazed in a rice-fallow. Research also needs to consider that adopting shorter-duration rice to facilitate second-cropping may reduce rice yield in some years. If second-cropping with little or no irrigation holds such promise, it begs the question of why it is not practiced already. There appear to be two main biophysical reasons for this, apart from uncontrolled grazing. First, most rice in medium-uplands is mediumduration that is harvested from late October (av. 27th Oct. at Pogro, Table 1). By then, evapotranspiration and drainage have depleted soil water following the monsoon that nominally ends on 30th Sept. Even with timely land preparation after rice there is only a modest chance of surface soil being wet enough to germinate a second crop in anticipation of using residual water in the subsoil, and almost no chance of further post-monsoon rainfall on which to plant. Whilst some farmers have ponds that could provide water to establish a crop, the amount of water generally falls far short of what farmers

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believe is needed for irrigation. They appear not to appreciate the value of residual soil water or that limited irrigation could enable plants to tap into it. The second reason has to do with soil fertility on medium-uplands and lowlands. Soil surveys and fertiliser experiments associated with this research show that successful rabi cropping is impossible without significant P inputs because of P-deficiency after rice (Cornish et al., 2010) and surface drying that further reduces P uptake (Cornish, 2010). 4.5. Policy The foregoing conclusions suggest that policies and programmes promoting WSD need to be complemented by others that promote more efficient use of rainfall in the kharif for food security, as well as support the use of existing water resources to intensify and diversity cropping. The agronomic options for second-cropping, and the socioeconomic impacts of system change, are considered in Cornish et al. (2015). Acknowledgements Generous research funding was provided by the Australian Centre for International Agricultural Research (Project number LWR/2002/ 100), whose Program Managers are thanked for their personal support. We thank senior staff of PRADAN for their willing support and commitment of resources, and the entire PRADAN Purulia Team for each of their contributions to the project, and in particular Mr Avijit Choudhury and Mr Arnab Charkraborty as Team Leaders. Buddheswar Mahato, a Tribal farmer and village resource person for PRADAN, contributed much to the success of the farming systems research which provided input to, and verification of, the model. The Indian Council for Agricultural Research also committed resources to this project, and we particularly thank Dr Alok Sikka for posing important questions, Dr Shivendra Kumar for administrative and other support, and Dr Pradip Dey for contributions to the soil science. We also thank Prof. Bill Bellotti for helpful comments on the project and this manuscript and Dr Murray Unkovich for detailed comments on the manuscript. Finally, a great many farmers participated in the research, and without their ideas and hard, dedicated work this project would not have been possible. Appendix: Supplementary material Supplementary data to this article can be found online at doi:10.1016/j.agsy.2015.01.008. References Agarwal, B.K., Kumar, R., Shahi, D.K., 2010. Soil Resource Inventory of Jharkhand, Problem and Solution. Department of Soil Science and Agricultural Chemistry, Birsa Agricultural University, Ranchi. . Allen, R.G., Periera, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration – guidelines for computing crop water requirements. FAO Irrigation and Drainage paper 56, Table 22. Anon, 2010a. World Rice Statistics. International Rice Research Institute, Los Bana¯s, Philippines. Anon, 2010b. NSC distributes seeds in drought-hit east India. The Financial Express, Sept. 16. Basu, S., Leeuwis, C., 2012. Understanding the rapid spread of System of Rice Intensification (SRI) in Andhra Pradesh: exploring the building of support network and media representation. Agric. Syst. 111, 34–44. Bhager, R.M., Bhuiyan, S.I., Moody, L.E., Estorninos, L.E., 1999. Effect of water, tillage and herbicide on ecology of weed communities in intensive wet-seeded rice system. Crop Prot. 18, 293–303. Bonnerjee, A., Koehler, G., 2010. Hunger: the true growth story of India. International Development Economics Associates. .

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Please cite this article in press as: Peter S. Cornish, Dinabandhu Karmakar, Ashok Kumar, Sudipta Das, Barry Croke, Improving crop production for food security and improved livelihoods on the East India Plateau. I. Rainfall-related risks with rice and opportunities for improved cropping systems, Agricultural Systems (2015), doi: 10.1016/ j.agsy.2015.01.008