Climate ready rice: Augmenting drought tolerance with best management practices

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Climate ready rice: Augmenting drought tolerance with best management practices Stephan M. Haefele a,∗ , Yoichiro Kato b , Sudhanshu Singh c a b c

Australian Centre for Plant Functional Genomics, University of Adelaide, Adelaide, Australia International Rice Research Institute (IRRI), Los Ba˜ nos, Philippines International Rice Research Institute (IRRI)-India, NASC Complex, New Delhi 110012, India

a r t i c l e

i n f o

Article history: Received 31 August 2015 Received in revised form 31 January 2016 Accepted 2 February 2016 Available online xxx Keywords: Decision support Drought Management Rainfed lowlands Rice Soil fertility

a b s t r a c t Drought stress is one of the most important limitations for rice production in rainfed lowland systems. This is the case in rainfed systems now, and will probably even be more important in the near future given the changing climate. Recent advances in rice breeding provide much improved drought tolerance in modern rice cultivars as has already been shown in farmers’ fields. To accompany these new cultivars, complementary crop management practices and diversified production systems have an important role to help farmers minimize risks and raise productivity and profitability. To evaluate the options we reviewed a wide range of studies investigating management options for rainfed lowland rice with a specific focus on drought-prone environments. To introduce the environment we provide an overview of general characteristics with a more detailed analysis of soil quality in rice-based rainfed lowlands around the world. Reviewed management technologies to mitigate drought stress include water management options, the choice of appropriate germplasm, adjusted cropping systems, improved nutrient management, different crop establishment options, better field management and soil amelioration. Several of these technologies do offer important advantages but their usefulness and applicability is dependent on site and system characteristics. Thus, a combination of germplasm × environment × management is necessary to choose the best management for a given rainfed lowland system. Getting this right can transform rice-based systems in rainfed lowlands, make them more productive, and increase and stabilize farmers’ income. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Because rice is critical for food security in so many of the poorest countries, investments in the rice sector should be designed to alleviate poverty and meet the food demands of still growing populations. In many of these countries and especially in the rural regions, the economies are still essentially agricultural, and the average employment in agriculture is high. Income from agriculture then often depends on the availability and quality of resources, and although rainfed lowlands include favourable environments with conditions similar to irrigated systems, most of the area in this ecosystem faces various bio-physical constraints for rice production. The main climatic factor in most of the region is the monsoon, which deposits >80% of the rainfall within just a few months. This limits the options for crops other than rice in the rainy season because of at least temporary flooding in most years and does not

∗ Corresponding author. E-mail address: [email protected] (S.M. Haefele).

allow a rainfed crop in the dry season. Thus, the absence of water control results in a low and unstable system productivity, a large part of the agriculture is still subsistence-oriented with low productivity, and poverty is widespread in communities largely dependent on rainfed rice. To improve the productivity and the production of droughtprone systems, a combination of improved varieties and crop management is necessary. Improved germplasm can significantly reduce risk and increase productivity in drought-prone rice-based lowlands and considerable progress was made recently (e.g., Kumar et al., 2015; Verulkar et al., 2010). Several varieties with increased drought tolerance have been released in South and Southeast Asia. For example, the variety Sahbhagi Dhan, released and notified in India in 2010, showed a consistently good performance under rainfed direct seeded upland and transplanted low land conditions (Dar et al., 2012). Yamano et al. (2014) has shown a yield advantage of 0.8–1.0 t ha−1 over other varieties under drought conditions. And in an extensive study conducted in drought-prone environments of Bihar, Singh et al. (2014a) reported 108% higher yields with Sahbhagi Dhan compared with popular local varieties. Similarly, Dar

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and Singh (2013) did not observe any yield penalty in Sahbhagi Dhan in a drought spell of 10–12 days in Eastern Uttar Pradesh (UP) and Bihar although other varieties yielded 0.75 t ha−1 less. When the drought spell increased to 16–18 days, Sahbhagi Dhan still yielded 4.4 t ha−1 whereas other varieties averaged 3.6 t ha−1 . In the same region, Sahbhagi Dhan needed 1–2 irrigations only to yield 4.7 t ha−1 while Sarju 52, a popular variety in Eastern UP, needed 3–4 irrigations to yield 3.9 t ha−1 . Optimal use of such new germplasm will require the combination with adequate and, if possible, improved management techniques. The various effects of drought on rainfed lowland rice are shown in Fig. 1. Less available water reduces transpiration of the plants, and transpiration is directly linked with biomass development and growth (Haefele et al., 2009). Drought stress at specific development stages can cause spikelet sterility, thereby reducing the number of filled grains (O’Toole and Moya, 1981). Drought after flowering can reduce grain filling and cause small, shrivelled or chalky grains (Cai et al., 2006). Reduced soil water saturation decreases the soil water–root contact and thereby nutrient uptake; it also changes the soil chemistry which affects the solubility of some nutrients negatively (Witt and Haefele, 2004; Kato and Katsura, 2014). And because a number of rice management activities are depending on flooded fields (transplanting, weeding, fertilizer application), they are often not done at the optimal time and therefore less efficient (Siddiq, 2000). In addition, risk averse input use will affect crop yields even in years with sufficient water supplies. Farmers in drought prone regions will not invest much in e.g., good seed or fertilizer because there is a considerable risk of losing that investment. Limited input use thereby keeps yields and the possible profit low. In a similar way does the preferred use of traditional-type varieties, with often higher drought tolerance but usually lower yield potential, limit achievable yields and profit in all years. New, more stress tolerant modern-type rice varieties could change this situation in many ways. And they will interact with a range of management interventions used in rainfed lowland rice cultivation. Therefore, our objective was to present an overview of important and often limiting characteristics of rice-based rainfed lowlands and to describe important management options to reduce the effect of drought on rice.

2. General characterization of drought-prone lowlands Table 1 gives an overview of the distribution of rice-based rainfed lowlands and their soil quality across the world, based on the world rice area according to FAOSTAT (2013) and their soil quality based on Haefele et al. (2014). According to this data source, total rainfed lowland rice area in 2008/09 was about 48.4 million ha. The data show that India had by far the largest area of rainfed lowlands, followed by Thailand and Bangladesh. Rainfed lowland areas around or below 3 million ha are found in Myanmar, Indonesia, Vietnam, Cambodia, China, Philippines, Nigeria, Nepal, Lao PDR and Tanzania. All other countries have areas below 0.3 million ha in that ecosystem. Rainfed lowland rice environments can be sub-divided into shallow rainfed lowlands (field water depths usually fluctuate between 0 and 0.3 m) and intermediate rainfed lowlands (field water depths fluctuate between 0.3 and 1.0 m) (Huke and Huke, 1997; Garrity et al., 1986). Intermediate rainfed lowlands are located in the lower part of the landscape, usually in the vicinity of larger rivers or lakes, or in the floodplains and deltas. Drought may occur but submergence and/or stagnating flood water is much more common (Tsubo et al., 2006; Singh et al., 2011; Mackill et al., 1996). Regular floods can deposit important quantities of alluvial sediments and thus contribute to soil fertility. Shallow rainfed lowlands are mostly

situated outside the larger floodplains and the typical topomorphology is an undulating landscape with small to medium height differences, creating a toposequence (Limpinuntana, 2001; Homma et al., 2007). Depending on the slope and soil characteristics, this can have considerable effects on plant available water and nutrient resources (Inthavong et al., 2011; Boling et al., 2008; Hayashi et al., 2007; Oberthür and Kam, 2000). On upper terraces, a coarser texture can contribute to lower water- and nutrient-retention capacity of the soil and lower levels of indigenous soil fertility. Water movement down the slope further reduces available water resources and nutrients. The groundwater level is often below the main rooting zone and contributes little to plant-available water resources. On medium terraces, water and nutrient losses to lower positions can be balanced by inputs from upslope. On lower terraces and valley bottoms, water and nutrient losses are usually smaller than inputs from above. The water table is often close to the surface and the main rooting horizon (Inthavong et al., 2011; Hayashi et al., 2007; Boling et al., 2008). Soils generally have a higher level of indigenous soil fertility due to finer texture, nutrient inputs from above, and often higher soil organic matter contents (Oberthür and Kam, 2000; Homma et al., 2007; Haefele and Konboon, 2009). Table 1 is also showing the estimated relative area of four soil fertility groups in rainfed lowland rice soils for each country, based on Haefele et al. (2014). The first two groups are “good” and “poor” soils which do not have major soil chemical constraints but differ in their degree of weathering and, therefore, their indigenous soil fertility. “Very poor soils” are highly weathered with a high probability of soil chemical constraints to crop growth (i.e., acidity, Al/Fe toxicity, low CEC, low inherent fertility) and “Problem soils” include acid-sulphate soils, peat soils, and saline and alkaline soils, which are partly characterized by low fertility and partly by soil chemical constraints. The table clearly indicates the prevalence of very poor rice soils in Thailand, Indonesia, Cambodia, Philippines, Lao PDR and Tanzania, whereas a higher percentage of soils without major constraints are found in Bangladesh, Myanmar and China. Poor soils are common in India and Nigeria, whereas problem soils are most common in Vietnam. The dominance of very poor soils in Southeast Asia, and especially in Lao PDR, northeast Thailand and Cambodia, has been reported by many researchers. Kawaguchi and Kyuma (1977) found that most of the soils tested with very low “inherent potentiality” came from northeast Thailand, and most of the soils with very low “available phosphorus status” came from northeast Thailand and Cambodia. Perhaps slightly unexpected is the widespread occurrence of good and poor soils without major constraints in rainfed lowlands of India and Bangladesh but many of the rainfed lowlands there are located in flood-prone areas with relatively young sediments. Most rainfed rice lies in the humid to sub-humid tropics, where considerable rainfall occurs during the wet season. However, rainfall is rarely evenly distributed, causing regularly stagnating water and flash floods at some time of the season. At the same time, drought remains one of the most limiting factors for rainfed lowlands in the region, for several reasons. One is the strong seasonality of rainfall. In most of the region, 80 to 90% of the total annual rainfall falls within six months (IWMI, 2012) but longer drought spells can occur at any time in the season. Another reason especially in Southeast Asia is the widespread occurrence of sandy soils with a low water-holding capacity and high water conductivity. Together with the often very heavy tropical rainfalls in the wet season and the undulating topomorphology, this causes flash-floods in the lower parts of the landscape while drought appears on upper fields within days after heavy rainfall. The third reason is that most lowland rice is very drought-susceptible as compared with, for example, wheat. Rice is often the only crop that can be grown in the wet season due to extensive water logging, but yield losses occur from soil water tensions >50 kPa (Lafitte et al., 2003). And loss of soil saturation

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Drought effects in rainfed lowland rice Direct drought effects when drought occurs

Indirect drought effects in every season

Reduced Reduced nutrient transpiration availability and uptake limits growth and limit growth and biomass biomass development development

Spikelet sterility and reduced sink size may limit attainable yields

Risk-averse input use is low and limits production also in favourable years

Drought also affects grain size and grain quality

Increased weed pressure: many weeds are more competitive than rice in dry fields

Preferred use of traditional stress tolerant varieties with often low yield potential

Management disruptions: delayed planting, weeding and fertilizer application reduce the attainable yield

Fig. 1. An overview of direct and indirect drought effects in rainfed lowland rice. Water deficiency affects the crop directly by limiting growth and biomass development, it can reduce the sink size or grain quality, and/or it affects crop management negatively. Indirect effects of drought affect system productivity even in good years because farmers’ risk averse crop management limits attainable yields.

Table 1 Distribution of rice soil fertility in rainfed lowlands around the world (2011/2012 data). Country

Total rainfed lowland rice area (ha × 106 )

India Thailand Bangladesh Myanmar Indonesia Vietnam Cambodia China Philippines Nigeria Nepal Lao PDR Tanzania Others Total/mean

15.95 8.49 5.08 3.20 3.08 2.28 1.95 1.73 1.58 1.24 0.76 0.53 0.40 2.70 48.43

Good soils

Poor soils

Very poor soils

Problem soils

41 19 13 8 29 13 12 15 23 45 36 8 18 24 26

14 64 10 27 41 25 51 40 48 25 30 79 54 36 31

7 5 12 12 9 34 9 3 – 3 0 3 3 8 9

(% of country total) 38 12 67 52 27 31 26 42 29 25 33 10 26 29 35

Source: based on Haefele et al. (2014).

frequently harms rice plants on poor and problem soils because soil oxidation lowers the soil pH causing Al toxicity and immobilizing some nutrient elements such as phosphorus (Bell and Seng, 2004). Thus, even relatively short drought-spells during the wet season can affect grain yields. 3. Management options for rice in drought-prone environments 3.1. Water management options The safest way to avoid drought is to irrigate. This approach was practiced in many previously rainfed lowland systems and contributed to large productivity increases as part of the green revolution. Generally, these systems were medium to large surface irrigation schemes, centrally planned and controlled. However, the potential for more such schemes is limited, and in most regions developers and donors concentrate on the maintenance or rehabilitation of existing schemes (FAO, 2007). Important other water resources for rice farming are tube wells and smaller surface water sources. Shallow groundwater tube wells

and pumps have and still are spreading fast in many regions. Older examples are the establishment of large numbers of tube wells in e.g., east India and Bangladesh (Singh et al., 2003); more recently they are spreading fast in Southeast Asia (IWMI, 2012). In rice, these water sources are mostly used for the start of the season or to provide lifesaving irrigation in short drought spells or at the end of the season. Thus, better use of ground water has great potential for drought-prone rice cultivation and diversification into non-rice crops, but more knowledge and regulation for sustainable use is necessary. In some regions with excessive ground water use, ground water levels are dropping fast (e.g., Singh, 2011), and in some regions like e.g., in northeast Thailand and parts of Laos, salinity in the groundwater may be limiting its use (Bell and Seng, 2004). High levels of other elements, like for example arsenic (van Geen et al., 2006), can be a problem in some areas and groundwater quality needs to be carefully evaluated. Another option to create additional water resources is rainwater harvesting. In northeast Thailand, some regions of eastern India, the Philippines, and Indonesia considerable numbers of village and farm ponds were established (Patamatamkul, 2001; Pal and Bhuiyan, 1995; Penning de Vries and Ruaysoongnern, 2010).

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They usually serve multiple purposes including fish production. For rice they usually can only provide crop-saving irrigation in short drought spells due to their limited capacity. Insufficient water resources at the tail-end of irrigation canal systems, high water costs or efforts to reduce methane emission from flooded rice fields have instigated the development of new water management techniques in irrigated systems. Their main objective was water saving but they can help to avoid or reduce drought by making better use of limited water resources. In “alternate wetting and drying” (AWD), the rice field is alternately flooded and non-flooded but the soil water tension is kept low to avoid yield losses (Bouman and Tuong, 2001). A constant water layer is usually maintained in the first days after crop establishment and around flowering. A similar water management is recommended in the “System of Rice Intensification” (SRI) (Stoop et al., 2002). Another option to reduce water use without affecting grain yield negatively is controlled soil drying during grain filling (Yang and Zhang, 2006). 3.2. Cropping system changes If the drought pattern is relatively stable and of the early-season or late-season type, drought avoidance can be achieved by adjusting the cropping season to the time when the rainfall is best or by reducing the length of the cropping season with the help of shorter duration varieties. Although these options seem obvious, farmer’s variety choice often does not appear to be optimal in this respect. Sometimes that can be due to the missing access of farmers to adequate new varieties. However, even in droughtprone environments, drought stress is often only one of several stresses the crop has to cope with during the season and farmer’s variety selection criteria is based on additional characteristics like yield potential, disease resistance and consumer or market preferences. Therefore, varieties preferred often represent a compromise and several varieties widespread in drought-prone rainfed lowlands are of comparatively long duration (e.g., KDML105, Mahsuri, Swarna). In addition, some rainfed lowlands seem to lack adequate short duration material, e.g., rainfed lowland farmers in large parts of Cambodia use traditional-type photoperiod-sensitive varieties with 160–180 days duration (Fukai and Ouk, 2012). Providing germplasm satisfying farmers’ various other demands on varietal characteristics and having shorter duration will therefore continue to reduce the damage of drought in many rainfed lowlands. In some regions, the recent shift from deepwater rice in the rainy season (or no crop at all) to flood recession rice (rice is established right after the flood waters have receded; Nesbitt, 2002) or shallow tube-well irrigated dry season rice increased productivity enormously (e.g., Myanmar, Cambodia, Bangladesh, Thailand), and this production system change still offers opportunities in some deepwater areas. In a similar way can the change from a very drought-prone rice crop to a much more drought tolerant upland crop remove the water limitation. In rainfed areas, this development is considerably influenced by field hydrological conditions (Fig. 2). In lowland areas with poor drainage, rice is often the only choice in the wet season. However, rice on upper terraces is often suffering from drought, and upland crops like maize or sugar cane can be the better option. This change from traditional, subsistence-oriented systems to diversified, market-oriented systems for income generation is now ongoing in many drought-prone rainfed lowlands (e.g., Haefele et al., 2013) and can be an option to reduce drought risk at the cropping system level. Short duration varieties can also open the option for diversification through a post-rice crop as was demonstrated for the recently released drought-tolerant, short-duration rice varieties Sahbhagi Dhan and IR64-Drought1 in eastern India (unpublished data). Using these varieties, farmers can grow three crops – rice followed by early peas and late sown wheat varieties – thus increasing

their annual production and income. The early maturity of Sahbhagi Dhan could also allow farmers of eastern India to establish a rice–pulse system. At harvest of this rice variety, the residual moisture is just appropriate for pulse germination and growth (Dar and Singh, 2013). Moreover, new improved varieties of dry season crops, notably pulses, enable more options for dry season cropping. Singh et al. (2014b) showed that the lentil varieties Pusa Vaibhav and Mallika matched well with Sahbhagi Dhan in drought-prone parts of Bihar. Both lentil varieties are of medium duration and suitable for rice-fallow areas of eastern India. 3.3. Nutrient management Nutrient management is an essential element of rice crop management, contributing to the high average yield level achieved in many rice growing areas (Mueller et al., 2012). The main sources are either local (e.g., farmyard manure, crop residues, sludges, other organic wastes) or external inputs (e.g., inorganic fertilizers, mineral amendments). The general trend in rice cultivation is a decreasing use of local nutrient sources, mainly because of increasing opportunity costs of the labour needed for collection and application (Pandey, 1999), and an increasing use of inorganic fertilizers. Between rice environments, the relative contribution from local nutrient sources increases from irrigated lowlands to rainfed lowlands to uplands, whereas inorganic fertilizer use has the opposite trend. This is of course due to comparatively higher risk and poorer farmers in most rainfed rice environments. But another reason might be the often lower soil fertility in rainfed environments, requiring more organic fertilizer to improve/maintain soil fertility (Haefele et al., 2014). Given their importance for crop growth, nutrients were repeatedly recognized as another major limiting factor in many rainfed lowlands (Wade et al., 1999; Pandey, 1998; Akbar et al., 1986). And although nutrient management is rarely seen as an option to mitigate drought stress, it can alleviate the effects of drought (Biswas et al., 1982; Tanguilig and De Datta, 1988; Otoo et al., 1989; Zaman et al., 1990). Better growth resulting from better nutrition will lead to a better canopy cover which in turn increases transpiration and reduces evaporation. Better aboveground growth is also mirrored by better root growth, thereby enabling better access to available soil water reserves. Bouman et al. (2005) estimated for irrigated rice that about 30% of the seasonal evapo-transpiration is evaporation and 70% transpiration. However, small changes of that distribution may greatly affect yield. Tuong (1999) gave an example where the fertilizer-induced decrease of evaporation from 41 to 29% of total evapo-transpiration (without any change in total ET) increased rice yield from 2.1 to 4.8 t ha−1 . In this case, high evaporation in the unfertilized treatment was caused by a slow and incomplete closure of the crop canopy, a condition which can be regularly observed in many rainfed lowlands. An often repeated explanation for low fertilizer use in droughtprone environments is that drought reduces the fertilizer efficiency. Analysing a data set of field trials in rainfed environments, Haefele and Bouman (2009) reported that with the exception of extreme drought or drought around flowering, water stress does not necessarily reduce fertilizer use efficiency. They found however, that where traditional varieties were used, attainable yields were low, and optimal and efficient N rates were considerably lower than in most irrigated environments. In another study, Haefele et al. (2013) could clearly show that improved plant nutrition reduced yield losses due to drought stress (Fig. 3). That nutrient × water interactions could be an important component for improving crop management for rice-based rainfed systems has been repeatedly hypothesized (e.g., Wade et al., 1998; Lafitte, 1998). Unclear remains if fertilizer use can increase the drought risk in drought-prone rice environments (Prasertsak and

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Lower terraces

Valley booms

5

Upper terraces (a) (a) Uplands (b) (b)

Fig. 2. Drought avoidance on upper terraces in rice-based rainfed lowlands. In valley bottoms and lower terraces with poor drainage, rice is often the only choice in the wet season. However, rice on upper terraces (a) is often suffering from drought and upland crops like maize or sugar cane (b) can be the better option. This reduces drought risk for rice and increases system diversification.

6000

Grain yield (kg ha-1)

5000

4000

3000

2000 0-0-0 NPK 90-0-0 NPK 90-20-0 NPK 90-20-20 NPK 90-30-20 NPK

1000

0 1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

Mean seasonal field water stress Fig. 3. Rice grain yield across several sites and all fertilizer treatments but dependent on the mean seasonal field water stress. Field water stress levels were scored according to 1 = permanently flooded, 2 = permanently wet soil surface, and 3 = permanently dry soil surface. The envelope lines were fitted manually. The figure indicates that normal fertilizer use can contribute considerably to reduce the negative effect of drought stress on grain yield. The envelope lines indicate the trend for the unfertilized and the fully fertilized treatments. The experiments were conducted at three different sites in 2009 and 2010, Pangasinan, Philippines (based on Haefele et al., 2013).

Fukai, 1997). In the case of a mid-season drought spell, total evapotranspiration should not be affected by the crop biomass as long as the soil surface is wet. However, when the soil surface becomes dry and evaporation very small, a larger canopy will result in higher transpiration. This would lead to a faster decline of remaining plant available water and higher drought damage, a phenomenon (“haying-off”) known from upland crops relying mostly on water stored in the soil (Cantero-Martinez et al., 1995). But fertilizer application was also shown to increase access and extraction of soil water, thereby counteracting higher transpiration needs (Viets, 1962). The position of the field in the toposequence, type of drought and the soil type will further modify the possible “risk” of fertilizer applications in water limited environments. In a study conducted in farmers’ fields in northeast Thailand, it was found that organic fertilizer gave a good response on very sandy soils with clay contents below 5%, whereas the response to inorganic fertilizer on such soils was often low; the opposite response to organic and inorganic fertilizers was observed on finer textured soils (Haefele et al.,

2006). In the toposequence, water resources are scarce in upper terraces, relatively good in medium terraces, and submergence can be a bigger danger in lower fields (Boling et al., 2008). Such variable soil conditions, water limitations, and topographic effects do occur across most rainfed lowlands, and traditional-type varieties are still widely used in many rainfed environments. It can be concluded that uniform fertilizer rates across large regions are likely to result in low fertilizer-use efficiency of rainfed lowland rice, and that the only possible option for improved nutrient management for rainfed rice is site- or even fieldspecific nutrient and crop management advice. To address this, site-specific nutrient management (SSNM) recommendations for rainfed as well as irrigated lowland rice have been advocated (Dobermann and White, 1999 Pingali et al., 1998). Obviously, farmers are already using their experience to modify existing recommendations (Wijnhoud et al., 2003; Pandey, 1999) but advanced decision-support tools could help them to improve their management practices further. White et al. (1997) developed recommendations based on soil types but they ignored other

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Variety used

Topography, distance to farmhouse

Soil fertility/ Yield without fertilizer

Establishment method

Residue mgt.

Available inputs

Integrating decision support tools for regions with similar cropping systems Data bases on e.g., regional agronomic trials, crop model outputs, soil maps, etc.

Drought/ flooding risk Field-specific crop management recommendations on e.g., seeding window, fertilizer type, fertilizer rates, application timing, herbicide timing, critical growth stages, etc. Fig. 4. Scheme of a tailored decision support tool to help farmers improve their crop management. Site-specific information on farmers’ field and production characteristics is collected based on farmers’ answers to a few questions. This information together with algorithms derived from many regional agronomic trials and possibly crop models is used to determine a recommendation for the specific field. Based on the variety used by the farmer, the tool can also determine the best timing for split applications and calculate the amounts needed for a variety of fertilizer types (straight or compound fertilizers). Including further management advice leads then to an advisory crop management tools.

important factors affecting yields and fertilizer response in a given field (such as variety used, field hydrology, field specific soil fertility). Haefele and Konboon (2009) developed a simple decisionsupport tool using farmers’ knowledge of their fields and their planned crop to determine the best fertilizer rate for rainfed rice in northeast Thailand. The next step was to develop telephone or tablet based tools (Buresh, 2008; Banayo et al., 2014; Wongboon et al., 2014). Based on farmers’ answers to a few questions on their field and production characteristics, and together with algorithms derived from many regional fertilizer trials, the tools determine fertilizer recommendations for a specific field (Fig. 4). Based on the variety used by the farmer, the tool can also determine the best timing for split applications and calculate the amounts needed for a variety of fertilizer types (straight or compound fertilizers). Including further management advice leads then to advisory crop management tools (Fig. 4), of which an older example is the “Rice Check”, which was successfully adapted in a number of countries (Lacy, 1994). An earlier on-farm study of SSNM in 2002–2003 indicated a mean 7% increase in grain yield with SSNM compared to farmer’s practice across locations in India, the Philippines, and Vietnam (Pampolino et al., 2007). Recently, IRRI and partners developed a prototype of a Crop Manager for Stress Tolerant Rice in Bihar (CMSTR; http://webapps.irri.org/in/br/cmstr/ ), which provides farmers with site and stress specific recommendations for drought and flood tolerant rice varieties. In addition to a printout at the beginning of the season, farmers also receive text messages during the season providing stress-specific fertilizer recommendations based on real-time climatic data. Testing of CMSTR in 20 villages in India during 2014 revealed its high farmer acceptance, with 80% of farmers willing to pay for CMSTR services (unpublished data).

3.4. Crop establishment In lowland ecosystems, three principal methods of rice establishment are used: dry direct seeding (DDS), wet direct seeding (WDS), and transplanting (TP). DDS consists of sowing dry seeds on dry or moist soils, whereas in WDS, pre-germinated seeds are sown on water-saturated soils. TP involves replanting of rice seedlings from nurseries into puddled and saturated soils. “Beushening” or “Biasi”, which is wide-spread in Indian rainfed lowlands, is a mixture where dry rice seed is broadcast on plowed fields after the first rains, followed at 20–35 days after emergence and when there is 5–10 cm of water standing in the fields by wet plowing and some re-planting (Fujisaka et al., 1993). The preferred establishment method largely reflects the degree of water control, the labour available, the accessibility of chemical weed control methods, and the need and opportunities to intensify and/or diversify the production system. A change in any of these factors can convince a farmer to adjust the preferred establishment method. DDS can substantially reduce water requirements for land preparation and crop establishment (Lantican et al., 1999; Haefele and Bouman, 2009; Rathore et al., 2009). It allows earlier establishment as compared with TP (sometimes by a month; Rathore et al., 2009), thus reducing deep percolation and evaporation losses from early-season rains. But reduced water losses at the beginning of the season can be offset by higher water losses later in the season, because DDS does not allow puddling which reduces percolation losses by closing cracks in the soil. The roots of DDS rice tend to be deeper, finer, and more extensive; as a result, these crops consistently perform better under drought conditions (Ingram et al., 1994; Singh et al., 1995; Castillo et al., 1998; Fukai et al., 1998). If photoperiod-insensitive varieties are used, directseeded rice matures earlier than transplanted rice, but not in the case of photoperiod-sensitive varieties. Earlier establishment and

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shorter crop duration can open opportunities for intensification through a post-rice crop (Pandey and Velasco, 2002) and reduces the late season drought risk. DDS is probably the oldest rice-establishment method (Pandey and Velasco, 2002), but has long ago given way to TP and more intensive cropping, especially in favourable lowlands. By the 1950s, TP had become the dominant crop establishment system in most Asian countries because of higher and more stable yields. DDS of rice has remained the preferred establishment practice in areas where labour is in short supply and mechanization is limited, and/or hydrological constraints prevent land intensification (too much or limited and unstable water supply). In more recent times, increasing labour cost has become a major reason for the shift from TP to DS in several Asian countries (Pandey and Velasco, 2002). Labour as well as drought constraints were the two main factors driving the expansion of direct-seeded rice area in northeast Thailand (especially in the drier southwestern part), which increased from 4% in 1989 to about 36% in 2005 (Hayashi et al., 2007). DDS is also common in flood-prone areas, for example in Cambodia, either to establish the crop quickly before the rising water levels or immediately behind the receding floods. Driven by developments in South Asia, increasing research and development on seed drills for DDS, tested with or without minimum tillage, is being conducted in South and Southeast Asia (e.g., Esdaile et al., 2010). Fully developed seed drills are available in India but they are usually made for four-wheel tractors; implements for two-wheel tractors, which dominate in Southeast Asia, were focused on only recently (Hossain et al., 2009). Weeds remain a major constraint in direct-seeded systems with and without full water control, and weedy rice can become a problem quickly (Ho, 1996; IRRI, 2014). The problem with both can be further aggravated by combine harvesters, spreading the seed between fields rapidly (Ho, 1996). Levelling equipment can help to improve crop, water and weed management (Rickman et al., 2001), and such equipment is spreading in some parts of the region, but further adaptation of the technology and feasible business models will be needed. Without puddling, a permanent water layer and the head start of transplanted rice seedlings, the weed pressure increases significantly. In drought-prone environments with often limited nutrient availability, weed competition for water and nutrients may contribute greatly to crop losses. In early-season drought spells, the competitive advantage of weeds rather than actual drought damage often results in crop abandonment. Herbicides are an essential component of direct-seeded rice wherever it is successfully practised but herbicide use is limited in rainfed lowlands. Increased seed rates can help to suppress weeds to some extent but they are not a real solution for weed management (Fukai and Ouk, 2012). Thus, although direct seeding offers substantial advantages and opportunities for drought management, direct-seeded systems are generally less resilient than transplanted systems and good management is more critical for successful crop establishment, effective weed control, and high and stable yields (Chauhan, 2012). Another issue is the selection of varietal characteristics favourable for direct seeding. Current rice breeding is mostly conducted under transplanted conditions, and varietal testing under direct-seeded conditions is rare. Favourable characteristics for direct-seeded systems include seed germination in anaerobic conditions, high early vigour, high tiller numbers, intermediate height, and herbicide-resistance (Majahan and Chauhan, 2013). Field observations indicate that tall, long-duration, traditional-type varieties, such as are widespread in northeast Thailand, are highly weed-competitive as long as the growth conditions are favourable, but even they are outperformed by weeds under water limitation. Efforts to include screening for varieties for direct seeding have increased lately, especially in Cambodia and Thailand (e.g., Fukai et al., 1997; Tong et al., 2007).

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A completely different approach for water limited lowland systems would be “Aerobic Rice” (AR). AR is direct seeded with a drill seeder and grown in well-drained, non-puddled, and nonsaturated soils (Bouman et al., 2005). This new system of rice cultivation is still under development but could provide opportunities in drought-prone rainfed lowlands (Kato and Katsura, 2014). The biggest challenge for AR are suitable varieties with a high yield potential, preferred grain quality and drought tolerance (most traditional upland rice varieties lack all three characteristics (Atlin et al., 2004)). Other issues are soil-borne pests and diseases, making crop rotations a requirement in aerobic systems which is not necessary in flooded systems (Haefele and Bouman, 2009). 3.5. Soil and field management Field and soil preparation can have considerable effects on the use efficiency of available water resources in rainfed lowland systems. Several studies investigated management options to improve water-use efficiency in irrigated and rainfed rice, covering a range of management options. Basic techniques to keep water in the field and reduce percolation in rice farming are bunding, levelling, and puddling. Bunds keep water in the field but cracks developing under bunds can cause substantial water losses to the subsoil (Tuong et al., 1994). Bigger fields with less bunds and sealing cracks at the side of the bunds during puddling can help to reduce such losses. Field levelling helps to distribute available water resources in the field evenly. Thereby, a closed water layer can be maintained longer in the field with the same amount of water, the crop experiences less and more evenly distributed drought stress across the whole field, and the closed flood water layer supresses weeds more efficiently. Field studies in Cambodia showed considerable yield gains from land levelling in rainfed environments (Rickman et al., 2001). Even and less deep water layers in the field can also contribute to reduce water losses under the bunds. Good levelling can be achieved with conventional farm equipment (e.g., animal drawn levelling boards, puddling machines) but tractor-based laser levelling of the dry field is becoming more widespread and affordable in many rice regions. Puddling reduces percolation losses and provides a levelled field for planting but it also requires considerable amounts of water (Ghildyal, 1978). That can be a disadvantage if rainwater is used for puddling because it may delay planting considerably and increase the late season drought risk (Rathore et al., 2009). Other options tested tried to increase the access of roots to groundwater resources, to reduce percolation losses or to improve the soil water holding capacity. In lowland rice fields, most rice roots are restricted to the puddled topsoil and do not penetrate the plow layer. Breaking the plow sole to allow roots to grow deeper and either tap deeper soil water or the groundwater was proposed by Samson and Wade (1998). However, the flipside of this approach is that percolation losses will increase, reducing the available water resources in the top-soil layer where most rice roots are located. Thus, this could be a suitable option for aerobic rice systems and when deeper rooting aerobic rice varieties become available. The opposite approach, using subsoil compaction as a method to reduce percolation, especially in sandy or sandy loam soils, was evaluated by Trébuil et al. (1998). They found that the effect of subsoil compaction was dependent on site-specific conditions and its use needs to be carefully evaluated. In some cases, it helped by increasing the water resources above the compacted layer, in others this was not enough to compensate for the reduced access to sub-soil water resources. More studies would be needed to see if suitable large areas with clear characteristics and mostly positive results could be defined. Targeted for specific fields, soil amendments (e.g., biochar, clayey sediments) can also be used to improve water holding and cation exchange capacity on extremely light textured soils (Haefele et al., 2011; Noble et al., 2004). Such soil amelioration measures are

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generally beneficial but their use depends much on the cost/value ratio.

4. Conclusions Rice breeding for drought tolerance made recently some big advances, which have the potential to considerably change the ricebased rainfed lowland system. More drought tolerant rice varieties will have less stress-induced yield losses and increasingly replace traditional-type varieties with limited response to fertilizers. But a whole range of further interactions with crop management have the potential to bring additional benefits. Increased drought tolerance will reduce the production risk and reward higher input use, in good as well as in bad years. Higher fertilizer use can have a positive feedback on water-use efficiency and increase drought tolerance of the crop further. Labour shortages in many regions increase the incentive for adoption of labour-saving innovations, and especially direct seeding of rice could contribute to reduced yield and crop losses caused by drought. The development of seed drills for direct seeding of rice is advancing rapidly and will also allow to band basal fertilizer applications with the seed, which contributes to increased fertilizer use efficiency. Improvements in infrastructure and the growth in demand for a wider range of agricultural products have increased the returns to diversification. This will enable replacement of rice on drought-prone fields with more suitable upland crops, reducing the drought risk of the whole cropping system. The rapidly increasing mechanization in all rice environments also offers better land preparation which contributes to reduced water losses and weed pressure, especially important in drought environments. And where still possible, the spread of shallow tube wells will continue to transform rainfed systems, supported by water saving irrigation technologies. The task of research and policy makers will be to ensure the sustainable and safe use of existing ground water resources. However, we also outlined the tremendous diversity of rice-based rainfed lowlands, showing that crop management needs to be integrated with the relevant system and even specific field conditions. To achieve this, modern decision support tools tailored to specific regions with similar system characteristics are necessary. We conclude that combining the new varieties with established and new management options and opportunities to address drought stress can transform rice-based systems in rainfed lowlands, make them more productive, and increase and stabilize farmers’ income.

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Please cite this article in press as: Haefele, S.M., et al., Climate ready rice: Augmenting drought tolerance with best management practices. Field Crops Res. (2016), http://dx.doi.org/10.1016/j.fcr.2016.02.001