Upland rice production under conservation agriculture cropping systems in cold conditions of tropical highlands

Field Crops Research 138 (2012) 33–41

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Upland rice production under conservation agriculture cropping systems in cold conditions of tropical highlands Julie Dusserre a,∗ , Jean-Louis Chopart a , Jean-Marie Douzet a , Jacqueline Rakotoarisoa b , Eric Scopel a a b

CIRAD, UPR SCA, F-34398 Montpellier, France FOFIFA, Ampandrianomby, B.P. 1690, 101 Antananarivo, Madagascar

a r t i c l e

i n f o

Article history: Received 26 July 2012 Received in revised form 6 September 2012 Accepted 8 September 2012 Keywords: Upland rice Yield components Nitrogen uptake Root length density No tillage Madagascar

a b s t r a c t In response to the extensive development of upland rice on the hillsides of the Malagasy highlands, alternative cropping systems based on conservation agriculture have been recommended to halt loss of soil fertility. To assess the yield performances of these cropping systems, an experiment was set up in 2003 at Andranomanelatra (1640 m asl) in the Malagasy highlands. Grain yield, yield components, biomass accumulation and nitrogen uptake of upland rice were analyzed in the 2004–2005, 2006–2006, and 2006–2007 seasons, and root length density was measured in the 2007–2008 season. The rice crop was planted every second year following two different crops: maize intercropped with soybean (M + S, with both conventional tillage and no tillage) and maize intercropped with Brachiaria ruziziensis (M + B only with no tillage). For each cropping system, two levels of fertilization were used: no fertilizer or application of organic inputs and mineral fertilizer. The season, cropping system, and fertilization treatment had significant effects on rice grain yields. Higher yields were associated with a greater number of plants per m2 , which decreased significantly over the three seasons, probably due to the highly variable beginning of the rains, and in the final season, with attacks by soil insects. The rice yield with conventional tillage was the highest and differed significantly from rice yield when maize was intercropped with Brachiaria under the no-till system, but not when the maize was intercropped with soybean with no tillage. In all three seasons, grain yields were closely linked to crop N at harvest. Differences in N uptake between treatments appeared very early in the crop cycle. Under conventional tillage, root length density at 68 days after sowing was higher between 0 and 30 cm depth than with no tillage. In these cold highlands conditions, plant establishment appeared to be more difficult with no tillage and resulted in reduced plant development and plant N uptake, particularly when rice was planted after maize intercropped with Brachiaria. © 2012 Elsevier B.V. All rights reserved.

1. Introduction In the Malagasy highlands (region of Vakinankaratra), the increasing demand for rice combined with increasing land pressure in lowland areas has led to the extensive cultivation of upland rice on the hillsides. In the mid 1990s, new upland rice varieties suitable for cultivation at high altitudes (from 1200 to 1800 m asl) were developed by FOFIFA (Malagasy Research for Rural Development) and CIRAD (French Agricultural Research for Development) meaning that rice could be cultivated on hillsides where farmers had formerly grown corn, beans or cassava (Dzido et al., 2004; Raboin et al., 2011). The cultivation of upland rice by local farmers has expanded very rapidly in the last 15 years,

∗ Corresponding author at: SRR FOFIFA, B.P. 230 Antsirabe 110, Madagascar. Tel.: +261 32 07 235 11. E-mail address: [email protected] (J. Dusserre). 0378-4290/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fcr.2012.09.011

especially in the Vakinankaratra region, where most research and extension actions have been undertaken (Raboin et al., 2011). Upland rice is typically grown as a rainfed crop during the wet season on marginal land. It is usually cultivated for subsistence under a low-input production system by resource-poor farmers, mainly using family labor. Yields are often low due to moisture stress, weed infestation, and infertile soil (George et al., 2001; Fageria, 2001). The poor infrastructure and lack of markets in these fragile environments do not offer much economic incentive for farmers to purchase fertilizers. Use of mineral fertilizer is uniformly low in rural Madagascar, because of its excessive cost (Minten et al., 2007). Moreover, in the fragile ecosystem of the Malagasy highlands, which are characterized by steep slopes, upland crop production systems based on conventional tillage are not sustainable, mainly because erosion threatens crop productivity through rapid loss of soil fertility. Conservation agriculture offers new opportunities to improve the sustainability of rainfed crops. The term ‘conservation agriculture’ covers a wide range of techniques, all based on three

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J. Dusserre et al. / Field Crops Research 138 (2012) 33–41

Table 1 Selected physicochemical properties of 0–10 and 30–60 cm soil layers at Andranomanelatra (adapted from Rakotoarisoa et al., 2010). Standard deviations are in parentheses. Item

Unit

Depth (cm) 0–10

pH (KCl) CEC Available P (Olsen) Available K Bulk density Total C Total N Organic matter C:N ratio Particle size distribution Clay Silt Sand

30–60

cmol kg−1 mg kg−1 cmol kg−1 g cm−3 g kg−1 g kg−1 g kg−1

4.19 (0.07) 3.71 (0.45) 13.9 (2.33) 0.20 (0.06) 0.85 4.45 (0.16) 0.35 (0.01) 7.65 12.71

4.55 (0.14) 2.63 (0.17) 0.06 (0.01) 1.04 2.42 (0.30) 0.17 (0.03) 4.16 14.24

% % %

59.4 (4.70) 27.5 (3.11) 13.1 (1.90)

72.0 (7.31) 15.2 (3.65) 12.1 (4.24)

principles defined by the FAO (Food and Agriculture Organization, 2010): minimal soil disturbance, permanent soil cover with crop residues or growing plants, and crop rotations. Conservation agriculture has been successfully adopted by large-scale mechanized farmers, especially in America, Australia, and central Brazil, because of its ability to interfere with water erosion and improve the soil water balance (Scopel et al., 2005; Bolliger et al., 2006; Triplett and Dick, 2008). However the system is seldom used by resource-poor farmers in the developing world (Erenstein, 2003; Bolliger et al., 2006; Affholder et al., 2010). As there is still some controversy surrounding the promotion of conservation agriculture in smallholder farming systems in sub-Saharan Africa (Giller et al., 2009), the potential benefits for African smallholder farmers require further investigation. In addition to protecting the soil from erosion, cover crops or crop residues from the preceding crop play an important role in nitrogen (N) cycling and in increasing soil N content. The effect of a cover crop on the supply of N for the succeeding main crop is the combined effect of N uptake by the cover crop and N released by mineralization when the cover crop has been left to dry out or harvested (Tonitto et al., 2006; Cherr et al., 2006). As upland rice is mainly cultivated by smallholder farmers without the use of fertilizers, N is often the main limiting nutrient (Fageria, 2010). Rice plants require N during the vegetative stage for growth and tillering, which determines the potential number of panicles, and N contributes to spikelet production during the early panicle formation stage (Mae, 1997). Root length density is a key factor for water and nutrient uptake, especially under rainfed conditions, and ˜ can be significantly modified by soil management (Munoz-Romero et al., 2010). A 3-year experimental study was conducted in the highlands of Madagascar at an altitude of 1640 m asl to assess the yield performances of no-till cropping systems in the cold conditions of this region. In this paper, we highlight the effects of the management system (with or without tillage, and using two different rotation crops) and of fertilization on root growth, crop biomass accumulation and N uptake, and yield. 2. Materials and methods 2.1. Experimental site The experiment was conducted at Andranomanelatra (19◦ 47 S, 47◦ 06 E, 1640 m asl) in the Vakinankaratra region of the Malagasy highlands. The area has a tropical altitude climate, characterized by a hot rainy season from November to April and a cold dry

season from May to October. Mean temperatures range from 18 ◦ C in October at the beginning of the rice sowing period, to close to 20 ◦ C during the reproductive stage. Minimum temperatures can fall below 10 ◦ C in the early vegetative stage and are usually below 15 ◦ C during the reproductive and grain filling stages. The night–day thermal amplitude is high (10–12◦ ) throughout the rice-growing season. Low temperatures slow down rice growth at almost all stages: panicle initiation is delayed and the grain filling and maturation stages are lengthened. Cold during the reproductive stage may lead to a high sterility rate (Chabanne and Razakamiaramanana, 1997). For the present study, data on daily temperatures and rainfall came from an on-site automatic meteorological station (ENERCO 404 Series, Cimel, France). According to the World Reference Basis (FAO, 2006), the soil in the study area is classified as Ferralsol (Razafimbelo et al., 2006) and is acid, with a high clay content (Table 1). 2.2. Experimental design The upland rice (Oryza sativa L.) cultivar FOFIFA 161 was grown in a rainfed experiment. The study took place over a 3-year period (2004–2005, 2005–2006 and 2006–2007 growing seasons) as part of a long-term experiment that started in 2003. Three cropping systems were compared: rotation of rice followed by maize (Zea mays L.) associated with soybean (Glycine max (L.) Merr.) with conventional tillage (M + S CT) or no tillage (M + S NT), and rotation of rice followed by maize associated with Brachiaria ruziziensis only with no tillage (M + B NT). The rice crop was sown every second year after maize. Each season the two crops of the rotation were present in the experimentation (Table 2). Under each management system, two levels of fertilization were used: no fertilizer (NF) and application of organic inputs and mineral fertilizer (MF) comprising NPK (11% N, 22% P2 O5 , 16% K2 O) at 300 kg ha−1 , dolomite (CaMg(CO3 )2 ) at 500 kg ha−1 , cattle manure at 5 t ha−1 , and two top dressings of urea (46% N) at 50 kg ha−1 applied at the beginning of tillering and at the mid-tillering stage (i.e. total MF of 79 kg N ha−1 ). The experimental design comprised a split plot with four replications to compare the three management systems (main plots) and two levels of fertilization (subplots). With conventional tillage, most of the residues of the preceding rotation crop were removed, whereas in the no-till system, a mulch made of the crop residues was left on the surface of the soil. Six to eight rice seeds were sown by hand in hills spaced 20 cm × 20 cm apart (25 hills per m2 ). Weeds were controlled by hand weeding, and rice plants were protected from insect attacks by treating the seeds with an insecticide (Gaucho® , 35% imidacloprid + 10% thirame at 2.5 g per kg of seeds). An additional study was conducted on root growth in the 2007–2008 growing season that only concerned rice grown after the rotation with maize intercropped with soybean under conventional and no till systems with organic mineral fertilizer. But high cyclonic winds during flowering in the 2007–2008 season led to high grain sterility (only 25–50% grain filling) and data on yield for this season were consequently not used. 2.3. Measurements 2.3.1. Plant biomass and nitrogen uptake In the three growing seasons, above-ground dry matter and N concentration were measured four times in each plot, at 55 days after sowing (DAS) in 2004–2005 and at 34 DAS in 2005–2006 and 2006–2007 (P1); at 75 DAS in 2004–2005 and at 65 DAS in 2005–2006 and 2006–2007 (P2); at the beginning of stem elongation (P3) and at flowering (P4), on rice plants in a subplot consisting of a 0.6 m long section in two adjacent rows, i.e. 0.24 m2 . At harvest, sub-samples of grain and straw from the 4 m2 harvest area were used for analysis of tissue N. The plant samples were dried at

J. Dusserre et al. / Field Crops Research 138 (2012) 33–41

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Table 2 Description of experimental treatments showing crop sequences and soil management methods. Plot Month

Crops in year n November–May

Crops in year n + 1 November–May

Conventional tillage (CT)

Rice Maize + soybean (M + S)

Maize + soybean (M + S) Rice

Tillage, residues removed

No tillage (NT)

Rice Maize + soybean (M + S) Rice Maize + brachiaria (M + B)

Maize + soybean (M + S) Rice Maize + brachiaria (M + B) Rice

No tillage, residues left on the soil

60 ◦ C for 72 h and weighed to estimate aerial biomass production. The amount of nitrogen absorbed (kg ha−1 ) was obtained for each biomass sample by measuring the total nitrogen content of a subsample by dry combustion in an elemental analyzer (FP528-LECO). Total N uptake at harvest was calculated from N concentration and biomass production. 2.3.2. Grain yield and yield components Each yield component was determined for a specific period of the cropping cycle and was consequently an indicator of growth conditions during the period concerned. Analyzing the yield components made it possible to identify the periods of the rice cycle during which growth differences between management systems appeared. In all three seasons, grain yield (using unhulled seeds, after drying at 60 ◦ C for 3 days), yield components, and straw dry weight were measured at maturity. Grain and straw yield were measured at harvest in a 4 m2 area located in the center of each plot. The number of plants, panicles, and spikelets per panicle, the number of filled and unfilled spikelets, and 1000-grain weight were determined on a subplot of eight hills located at the edges of the 4 m2 area. All plant samples were separated into straw and panicles. Panicles were counted and hand threshed, and filled spikelets were separated from unfilled spikelets. Dry weights of filled spikelets and unfilled spikelets were determined after oven drying. Two subsamples of 200 filled spikelets and 200 unfilled spikelets were weighed to calculate the total number of filled and unfilled spikelets and 1000-grain weight. The number of spikelets per panicle and the grain filling percentage (100 × number of filled spikelets/total number of spikelets) were calculated. 2.3.3. Root length density Root intersections were counted along a soil trench profile following the method of Chopart et al. (2009a) and Azevedo et al. (2011). This method only requires freeing the roots from the surface of the trench profile for a few millimeters in such a way that all the root intersections visible on the side of the soil profile can be counted. The intersections were counted on a 5 cm × 5 cm section of a 40 cm × 20 cm grid. Ramifications located outside the counting plane were not taken into account. Data obtained using this 2-D mapping method (points on a plane) were transformed into root lengths per volume (root length density = RLD), with a 3-D geometry, using a model designed specifically for upland rice (RLD = RID CO CE, where RID is root intersection density, CO is geometrical coefficient – based on the direction of the roots in the soil – and CE is the experimental coefficient – which depends on the root intersection densities) by Dusserre et al. (2009). RACINE software (Chopart et al., 2009b) was used to store spatial data on root intersections and to calculate root length density (cm cm−3 ) from root intersection density. The trench profiles were dug at three dates in 2007–2008 (68, 87 and 128 days after sowing) under the system comprising maize intercropped with soybean with conventional tillage and no tillage with organic mineral fertilizer. The trench profiles were replicated three times per treatment on two hills (40 cm) dug to a depth of 1 m.

Soil management

2.3.4. Data analysis Statistical analyses were performed with SAS 9.2 (SAS Institute Inc., Cary, NC, USA). The GLM procedure (with Random statement) was used for analysis of variance of the mixed model. Means were compared according to the least significant difference (LSD) with Fisher’s LSD test with a probability level of 0.05. Combined analysis across seasons was performed for yield, yield components, biomass accumulation and N uptake. For biomass accumulation and N uptake, combined analysis across seasons was performed only across the two last seasons for the two first samples (P1 and P2), and across the three seasons for the last samples. 3. Results 3.1. Weather conditions Climatic conditions (monthly temperatures and rainfall) in the three study years are presented in Table 3. Minimum and mean temperatures before the rice was sown (in September and October) were highest in the 2004–2005 season (minimum temperature of 12.2 ◦ C in October in the 2004–2005 season, 8.9 ◦ C in 2005–2006 and 9.8 ◦ C in 2006–2007). In the 2004–2005 season, most rain fell during the month of October (222.5 mm, compared with 53 mm in 2005–2006, and 40 mm in 2006–2007). The average annual rainfall over the three study years was 1486 mm (1207 mm in 2005–2006, 1587 mm in 2006–2007 and 1665 mm in 2004–2005). December and January were the rainiest months. Despite some variability in rainfall patterns (short periods of drought in December in 2004–2005 and 2006–2007, and in January and February in 2005–2006, or very rainy periods during cyclones like in January 2007), the rainfall ensured an adequate water supply for rainfed crops during the growing cycle (November-April) in each of the three study years. However, the erratic beginning of the rainy season in 2005 obliged us to sow in dry soil. The best climatic conditions for crop establishment occurred in 2004 (higher minimum temperatures, more abundant rainfall). 3.2. Yield and yield components The season, the cropping system, and fertilization had significant effects on rice grain yields (Table 4). The grain yield of upland rice was much higher in the first year (mean of 3.7 t ha−1 in 2004–2005), than in the second season (1.8 t ha−1 in 2005–2006) and in the third (1.2 t ha−1 in 2006–2007). Higher yields were associated with more plants per m2 (linear regression, R2 = 0.74, data not shown), which decreased significantly over the three seasons (193.5 plants per m2 in 2004–2005, 131.8 in 2005–2006 and 108.5 in 2006–2007). Conditions that affect this component occurred mainly between sowing and early tillering. There was a significant effect of the season on the number of spikelets per panicle. The percentage of filled grain (grain fertility) decreased significantly over the three seasons, but was not a limiting factor (88.8% of fertility in 2004–2005, 85.2% in 2005–2006 and 81.4% in 2006–2007).

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J. Dusserre et al. / Field Crops Research 138 (2012) 33–41

Table 3 Min, mean, max monthly temperature (◦ C) and cumulated monthly rainfall (mm) for the tree growing seasons at Andranomanelatra, Madagascar. Season

August

2004–2005 Min temp. Mean temp. Max temp. Rainfall

8.0 13.1 21.5 26.5

2005–2006 Min temp. Mean temp. Max temp. Rainfall 2006–2007 Min temp. Mean temp. Max temp. Rainfall

September

October

November

December

January

February

March

April

May

9.8 15.4 23.2 33.5

12.2 17.0 24.8 222.5

11.8 17.0 24.5 143.5

14.4 18.2 24.8 430

14.3 18.7 25.0 219

13.9 18.7 26.0 287.5

13.3 18.1 25.3 202.5

10.7 16.7 24.8 50

10.0 14.9 22.1 56.5

5.9 12.3 20.8 1.5

7.6 13.9 22.6 4

8.9 16.4 25.7 53

10.9 17.6 26.1 108

14.5 18.2 25.2 462

13.9 18.4 25.1 117.5

14.0 18.4 25.2 106.5

13.3 18.5 26.1 208.5

11.7 17.0 24.7 68

8.4 14.9 23.4 10

6.4 13.0 21.1 5

7.2 14.5 23.9 3

9.8 16.6 25.9 40

12.0 18.1 26.4 154.5

14.1 18.3 24.8 305.5

15.2 18.1 23.5 699

15.1 18.7 24.9 205.5

12.6 18.0 25.2 83

12.1 16.9 24.1 52,5

10.6 15.5 22.9 33

Season 2004–2005: rice sowing date November 12, seedling emergence November 22, harvest April 26; Season 2005–2006: sowing date November 5, seedling emergence November 28, harvest May 10; Season 2006–2007: sowing date November 15, seedling emergence November 26, harvest May 8.

Rice yield was highest under conventional tillage (2.73 t ha−1 ) and differed significantly from the rice yield after maize intercropped with Brachiaria under the no-till system (1.79 t ha−1 ), but not from the rice yield after maize intercropped with soybean with

no tillage (2.20 t ha−1 ). Among yield components, only the number of spikelets per panicle differed significantly between cropping systems, despite an interaction between the season and cropping system (for the component ‘number of panicles per plant’

Table 4 Rice grain yields (t ha−1 ) and yield components of upland rice in Andranomanelatra, under the different seasons, management systems: conventional tillage (CT) and no tillage (NT), maize intercropped with soybean (M + S) and maize intercropped with Brachiaria ruziziensis (M + B), and two levels of fertilization: no fertilizer (NF) and with application of organic inputs and mineral fertilizer (MF). Panicles plant−1

Spikelets panicle−1

Grain filling (%)

1000-grain weight (g)

Combined analysis across three seasons Season 193.5 a* 2004–2005 2005–2006 131.8 b 108.5 c 2006–2007

1.44 b 1.58 a 1.36 b

73.2 a 67.8 b 60.8 c

88.8 a 85.2 b 81.4 c

26.3 26.7 26.5

3.71 a 1.83 b 1.18 c

Cropping system M + S CT M + S NT M + B NT

151.1 140.2 142.4

1.55 1.47 1.36

74.7 a 67.9 b 59.1 c

85.8 85.5 84.2

26.3 27.1 26.2

2.73 a 2.20 ab 1.79 b

Fertilization MF NF

144.7 144.4

1.60 a 1.32 b

74.6 a 59.9 b

84.5 85.8

26.2 26.8

2.63 a 1.85 b

Source of variation Season (S) Cropping system (C) S×C Fertilization (F) C×F F×S C×F×S

<0.0001 0.0912 0.3002 0.9567 0.1305 0.7429 0.3417

0.0016 0.0093 0.0006 <0.0001 0.3113 0.4969 0.8328

0.0001 <0.0001 0.0002 <0.0001 0.3100 0.8214 0.6206

<0.0001 0.4120 0.3826 0.0809 0.0246 0.9023 0.1572

1.38 b 1.49 a 1.44 ab 1.89 a 1.58 ab 1.29 b 1.37 1.34 1.36

74.7 73.2 71.9 85.7 a 67.0 b 50.6 c 63.9 a 63.5 a 54.9 b

Treatment

Plants (m−2 )

Analysis of cropping systems by season 2004–2005 M + S CT 2004–2005 M + S NT 2004–2005 M + B NT 2005–2006 M + S CT 2005–2006 M + S NT 2005–2006 M + B NT 2006–2007 M + S CT 2006–2007 M + S NT 2006–2007 M + B NT Analysis of fertilization treatment by season 2004–2005 MF 2004–2005 NF 2005–2006 MF 2005–2006 NF 2006–2007 MF 2006–2007 NF *

Within treatments, means followed by different letters are significantly different according to LSD (P < 0.05).

0.7495 0.2799 0.0864 0.3239 0.3220 0.8086 0.3427

Rice grain yield (t ha−1 )

<0.0001 0.0007 0.3732 <0.0001 0.2598 0.0009 0.4235

4.38 a 3.04 b 2.11 a 1.54 b 1.40 a 0.96 b

J. Dusserre et al. / Field Crops Research 138 (2012) 33–41

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Table 5 Biomass accumulation (t ha−1 ) at different growth stages of upland rice in Andranomanelatra under the different seasons, management systems: conventional tillage (CT) and no tillage (NT), maize intercropped with soybean (M + S) and maize intercropped with Brachiaria ruziziensis (M + B), and two levels of fertilization: no fertilization (NF) and with organic inputs and mineral fertilizer (MF). Treatment

P2

Beginning of stem elongation

Flowering stage

Harvest

Combined analysis across three seasons Season (0.94) 2004–2005 2005–2006 0.09 a 2006–2007 0.07 b

P1

(2.38) 0.60 a 0.48 a

3.42 a 2.53 b 1.18 c

6.86 a 4.49 b 2.56 c

7.91 a 4.64 b 2.67 c

Cropping system M + S CT M + S NT M + B NT

0.10 a 0.07 b 0.06 b

0.82 a 0.47 b 0.33 b

3.05 a 2.35 b 1.73 c

5.70 a 4.49 b 3.72 b

6.29 a 4.84 b 4.08 c

Fertilization MF NF

0.09 a 0.06 b

0.74 a 0.33 b

3.08 a 1.67 b

5.87 a 3.40 b

6.15 a 3.99 b

Source of variation Season (S) Cropping system (C) S×C Fertilization (F) C×F F×S C×F×S

0.0101 0.0012 0.2759 <0.0001 <0.0001 <0.0001 0.2360

0.0007 0.0012 0.2824 <0.0001 0.0008 0.0004 0.6201

<0.0001 <0.0001 0.3950 <0.0001 0.0158 0.0295 0.1342

<0.0001 0.0001 0.4992 <0.0001 0.1957 0.1346 0.3663

<0.0001 <0.0001 0.0235 <0.0001 0.0041 0.0004 0.8767

Comparison of cropping systems by fertilization 0.14 a M + S CT MF M + S NT MF 0.09 b 0.06 c M + B NT MF M + S CT NF 0.07 0.06 M + S NT NF 0.06 M + B NT NF

1.17 a 0.66 b 0.41 b 0.47 a 0.27 b 0.25 b

4.06 a 3.02 b 2.15 c 2.04 a 1.66 ab 1.30 b

7.84 a 5.72 b 4.88 c 4.74 a 3.96 b 3.28 c

Comparison of fertilization by season 1.23 a 2004–2005 MF 2004–2005 NF 0.65 b 2005–2006 MF 0.12 a 0.06 b 2005–2006 NF 2006–2007 MF 0.07 2006–2007 NF 0.06

3.22 a 1.54 b 0.86 a 0.34 b 0.63 a 0.32 b

4.32 a 2.52 b 3.33 a 1.72 b 1.59 a 0.78 b

9.54 a 6.27 b 5.62 a 3.65 b 3.27 a 2.06 b

P1 at 34 days after sowing (DAS) in 2005–2006 and 2006–2007, and at 55 DAS in 2004–2005. P2 at 65 DAS in 2005–2006 and 2006–2007, and at 75 DAS in 2004–2005. Combined analysis and comparison of cropping systems by fertilization were performed only across the two last seasons for P1 and P2, across the three seasons for the last samples. * Within treatments, means followed by different letters are significantly different according to LSD (P < 0.05).

the interaction between the season and the cropping system was higher (P < 0.0006) than the cropping system effect (P < 0.0093), see Table 4). Significantly higher rice yields were obtained with organic inputs and mineral fertilizer (MF) than with no fertilization (NF), although the difference in yield between fertilization treatments varied with the year (source of the interaction fertilization × season). Among yield components, the number of panicles per plant and the number of spikelets per panicle differed significantly between cropping systems. Conditions that affect these components occurred mainly between early tillering and heading. The percentage of filled grain was not affected by the management system or fertilization. No difference was observed in 1000-grain weight between seasons, management systems, and fertilization treatments.

3.3. Aboveground plant biomass and N accumulation, relationship with yield The season, the cropping system, and fertilization had significant effects on the accumulation of plant biomass (Table 5). Combined analysis across seasons was performed only across the two last seasons for the two first samples, and across the three seasons for the last samples. At the first sampling date, biomass

accumulation was higher in the second season than in the third, but the difference was not significant at the second sampling date. From the beginning of stem elongation until the final sampling at harvest, biomass accumulation decreased significantly over the three seasons. In all three seasons and at all growth stages, fertilization (MF) resulted in significantly higher biomass accumulation than no fertilization (NF). Conventional tillage produced significantly more biomass than the two no-till systems at any stage of growth; and at the beginning of stem elongation and at harvest, biomass accumulation also differed significantly between the two no-till systems (4.84 t ha−1 at harvest for maize intercropped with soybean with no tillage and 4.08 t ha−1 for maize intercropped with Brachiaria with no tillage). However, with fertilization there were significant differences between the three cropping systems from the first sampling to the final sampling at harvest (except for the second and the fourth samplings between the two no tillage systems), while without fertilization, there were significant differences between the three cropping systems only at harvest. The season, the cropping system, and fertilization also had significant effects on plant N accumulation (Table 6). At the two first sampling dates, N uptake was higher in the second season than in the third. At the stage of beginning of stem elongation, N uptakes was higher in 2004–2005 and 2005–2006 than in 2006–2007. From the flowering stage on, N uptake decreased significantly over the three seasons. Like biomass accumulation, in all three

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J. Dusserre et al. / Field Crops Research 138 (2012) 33–41

Table 6 N crop uptake (kg N ha−1 ) at different growth stages of upland rice in Andranomanelatra, under the different seasons, management systems: conventional tillage (CT) and no tillage (NT), maize intercropped with soybean (M + S) and maize intercropped with Brachiaria ruziziensis (M + B), and two levels of fertilization: no fertilization (NF) and with organic inputs and mineral fertilizer (MF). Treatment

P2

Beginning of stem elongation

Flowering stage

Harvest

Combined analysis across three seasons Season (26.4) 2004–2005 2.8 a 2005–2006 1.7 b 2006–2007

P1

(52.1) 17.9 a 9.8 b

63.8 a 59.1 a 23.5 b

99.7 a 69.2 b 29.1 c

105.3 a 55.6 b 32.5 c

Cropping system M + S CT M + S NT M + B NT

3.1 a 1.9 b 1.7 b

21.2 a 12.3 b 8.1 c

65.3 a 45.5 b 35.6 b

77.6 a 67.6 b 52.8 b

79.4 a 62.3 b 51.6 c

Fertilization MF NF

2.8 a 1.7 b

20.0 a 7.7 b

63.5 a 34.1 b

84.6 a 47.4 b

79.3 a 49.6 b

Source of variation Season (S) Cropping system (C) S×C Fertilization (F) C×F F×S C×F×S

0.0007 0.0012 0.2824 <0.0001 0.0008 0.0004 0.6201

0.0001 <0.0001 0.0539 <0.0001 0.0003 0.0003 0.2753

<0.0001 <0.0001 0.0835 <0.0001 0.0055 0.0161 0.2428

<0.0001 0.0035 0.2822 <0.0001 0.6969 0.0411 0.4951

<0.0001 <0.0001 0.0540 <0.0001 0.0007 <0.0001 0.7315

Comparison of cropping systems by fertilization 4.3 a M + S CT MF M + S NT MF 2.2 b 1.9 b M + B NT MF

31.0 a 18.1 b 10.8 c

87.3 a 58.4 b 44.8 c

101.9 a 73.9 b 62.0 c

M + S CT NF M + S NT NF M + B NT NF

11.4 a 6.4 b 5.4 b

43.4 a 32.6 b 26.4 b

57.0 a 50.7 a 41.1 b

68.6 a 35.7 b 26.6 a 9.3 b 13.4 a 6.2 b

78.5 a 49.1 b 79.4 a 38.8 b 32.5 a 14.5 b

1.9 1.6 1.5

Comparison of fertilization by season 35.6 a 2004–2005 MF 2004–2005 NF 17.1 b 3.8 a 2005–2006 MF 2005–2006 NF 1.8 b 2006–2007 MF 1.8 2006–2007 NF 1.5

126.3 a 73.1 b 87.9 a 50.6 b 39.7 a 18.5 b

128.7 a 81.9 b 69.2 a 42.0 b 40.0 a 25.0 b

P1 at 34 days after sowing (DAS) in 2005–2006 and 2006–2007, and at 55 DAS in 2004–2005. P2 at 65 DAS in 2005–2006 and 2006–2007, and at 75 DAS in 2004–2005. Combined analysis and comparison of cropping systems by fertilization were done only across the two last seasons for P1 and P2, across the tree seasons for the last samples. * Within treatments, means followed by different letters are significantly different according to LSD (P < 0.05).

seasons and at all growth stages, fertilization resulted in significantly higher N uptake than no fertilization. N uptake differed significantly between cropping systems, although the difference between cropping systems varied with the fertilization treatment. With fertilization, conventional tillage enabled significantly higher N uptake at all growth stages than the two no-till systems, while between the two no-till systems (with higher N uptake for maize intercropped with soybean than maize intercropped with Brachiaria) differences were observed from the second sampling date to the final sampling at harvest. Without fertilization, conventional tillage resulted in significantly higher N uptake than the two no-till systems starting at the first sampling date, and between the two no-till systems differences were observed only at harvest. Differences in N uptake appeared very early in the crop cycle. In all three seasons, grain yields were closely associated with total crop N at maturity, but did not approach a ceiling corresponding to the yield potential (Fig. 1).

3.4. Root length density In the 2007–2008 season, with conventional tillage, root length density at 68 DAS was significantly higher at depths of 7.5 cm and 27.5 cm than with no tillage (Fig. 2A). At 87 DAS, root length density with no tillage was significantly higher at depths of 17.5,

Fig. 1. Grain yield versus crop N at harvest in upland rice grown in Andranomanelatra in the 2004–2005, 2005–2006 and the 2006–2007 growing seasons using different management systems: conventional tillage (CT) and no tillage (NT), maize intercropped with soybean (M + S) and maize intercropped with Brachiaria ruziziensis (M + B), and two levels of fertilization: no fertilizer (NF) and application of organic inputs and mineral fertilizer (MF). Solid line: hyperbola, single rectangular, (A) y = 33.3x/(855.8 + x), R2 = 0.98.

J. Dusserre et al. / Field Crops Research 138 (2012) 33–41

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72.5, 77.5 and 82.5 cm than with conventional tillage (Fig. 2B). At 128 DAS, there was no longer any significant difference in root length density between cropping systems although the root length density curve representing no tillage is located above the conventional tillage curve for the part of the soil profile extending from 20 cm to 100 cm in depth (Fig. 2C). 4. Discussion 4.1. Upland rice yield In these cold highlands conditions, the no-till system presented no advantage over conventional tillage with respect to yield (Table 4). The agronomic performance of no-till systems varies greatly across studies, and highly contrasting soil and climate types exert a strong influence on the success of no-till systems (Kirkegaard, 1995; Triplett and Dick, 2008; Soane et al., 2012). Rice grain yield decreased significantly over the three seasons. The differences in yields between seasons were mainly explained by problems of crop establishment that resulted in lower plant densities. The predominant climatic (seasonal) effect was probably linked to the highly variable beginning of the rains in the three years. But in the last season, there was also a reduction in the number of plants due to attacks by soil insects like white grubs and black beetles. As reported in other studies, such attacks are frequent in the region (Ratnadass et al., 2008, Randriamanantsoa et al., 2010) and can seriously affect crop establishment. In all three seasons, grain yields were closely correlated with crop N at harvest (Fig. 1). Differences in N uptake between treatments appeared very early in the crop cycle (Table 6). In irrigated rice systems, it is recognized that the supply of nitrogen during vegetative growth is the most critical limitation to achieving yield potential in the field (Cassman et al., 1998; Sheehy et al., 1998). 4.2. Crop establishment in the no-till system In these cold highlands conditions, crop establishment appeared to be more difficult with no tillage than with conventional tillage and resulted in reduced plant growth (Table 5) and plant N uptake (Table 6). At the beginning of the cycle, tilling the soil may provide better conditions for the young rice plants by temporarily increasing soil porosity and thus improving growth conditions for the roots (Whiteley and Dexter, 1982; Passioura, 2002). Our data indicate possible greater and faster root development at the beginning of the crop cycle after the soil was plowed (Fig. 2A), probably explaining some of the differences in N uptake between soil management treatments. The reduced soil disturbance and increased resistance in the no-till system in our study may have restricted root growth and caused the early growth lag. Some authors reported differences in crop growth with different tillage practices. In wheat, conventional tillage resulted in faster growth at the beginning of the season than no tillage (Kirkegaard, 1995; Verhulst et al., 2011). However, McMaster et al. (2002) found faster, more uniform and greater seedling emergence with no tillage than with conventional tillage due to more favorable soil water levels in the seeding zone under no-till systems. But in the conditions that prevail in the highlands of Madagascar (abundant rainfall, low temperatures and evapotranspiration), upland crops do not necessarily benefit from the additional water that infiltrates the soil thanks to the mulch (Muller et al., 2005). Riley (1998) reported that growth of spring cereals was delayed with reduced tillage, but this was compensated for later in the season. Our data indicated greater vertical root development before the heading stage with no tillage (Fig. 2B) but no direct impact was observed on final growth and yields. Under the no-till

Fig. 2. Root length density (in cm cm−3 ) of upland rice 68 days after sowing (A), 87 days after sowing (B) and 128 days after sowing (C) grown in Andranomanelatra, Madagascar, in the 2007–2008 growing season, under the different management systems: conventional tillage (CT) and no tillage (NT) with maize intercropped with soybean (M + S), and with application of organic inputs and mineral fertilizer (MF). *Indicates significant differences between cropping systems at P < 0.05.

system, the crop was unable to compensate for the early growth lag despite the improved deep root system in the latter part of the cycle. Another possible explanation for the early growth lag under the no-till system is that keeping the residues of the previous crop may lead to N immobilization. Crop residues with a high C to N ratio, such as straw from cereal crops, immobilize N during the early stages of their decomposition, and consequently compete with the following main crop for available N in the soil (Recous et al., 1995; Mary et al., 1996). This may be particularly limiting under low input management systems when there are no minerals available to balance N immobilization and when large quantities of residues remain on the soil surface (Balde et al., 2011). Conversely, tillage

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results in a flush of soil organic matter mineralization through the physical destruction of soil aggregates (Reicosky et al., 1997). A better understanding of N mineralization–immobilization processes in these soils is needed to predict soil N supply, especially under cold highland conditions. The effect of the presence of a mulch on the topsoil should also be investigated because, in temperate climates, it has been shown that surface residues can cool the topsoil (Azooz et al., 1995), which could delay crop emergence and nutrient uptake in nutrient-poor soils (Chassot and Richner, 2002). Based on their results, Andraski and Bundy (2008) reported that soil temperature rather than N immobilization was the main factor responsible for the reduction in yield at higher residue levels observed in no-till corn systems. 4.3. Types of crops used in rotation with rice Maize associated with soybean in a no-till rotation resulted in significantly higher rice biomass and N accumulation than maize associated with B. ruziziensis in a no-till rotation (Tables 5 and 6), with no significant effect on rice grain yield (Table 4). While the effect of non-leguminous cover crops on soil N supply for the succeeding crop is variable, leguminous cover crops normally increase the supply of soil N since they provide an additional source of N thanks to biological fixation during their growth (ThorupKristensen, 1994; Patil et al., 2001; Cherr et al., 2006). The amounts of external nitrogen needed to meet crop demand are larger when only grass species are included in the rotation. For that reason, cereals (such as corn) and forage (such as brachiaria) intercropped in no-till systems may increase the amount of N required for the satisfactory growth and production of both maize and B. ruziziensis. 5. Conclusion Conservation agriculture systems have been widely implemented under tropical conditions to protect the soil from erosion and to improve management of soil fertility. However, for upland rice grown in cold conditions, changing from conventional to conservation agriculture cropping systems may have a major impact both on N dynamics in the soil and on N uptake by rice. In the present study, no tillage combined with residue retention led to an initial crop growth lag that was not compensated for in later stages of growth. Thus no-till systems currently provide no additional benefits and need to be improved by determining the respective role of soil compaction, soil N immobilization and perhaps soil temperature in this initial growth lag. New conservation agriculture cropping systems (crop sequences, residue management, N management) should be created in order to solve this problem of initial growth lag under these particular soil-climatic conditions. Acknowledgements This research was conducted at the SCRiD unit based on the FOFIFA research station in Antsirabe, Madagascar. We thank all those who helped us with this study. Special thanks to L.M. Raboin for his advice on the manuscript. Thanks are also extended to the reviewers who helped us improve the manuscript. This work was supported by funds from the Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD) and the Groupement Semis Direct de Madagascar (GSDM). References Affholder, F., Jourdain, D., Quang, D.D., Tuong, T.P., Morize, M., Ricome, A., 2010. Constraints to farmers’ adoption of direct-seeding mulch-based cropping systems: a farm scale modeling approach applied to the mountainous slopes of Vietnam. Agric. Syst. 103, 51–62.

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