Opportunities for water saving with higher yield from the system of rice intensification

The system of rice intensification (SRI) developed in Madagascar, is showing that by changing the management of rice plants, soil, water and nutrients it can increase the yields of irrigated rice by 25–50% or more while reducing water requirements by an equivalent percent. This gives farmers incentive to reduce their irrigation water use when growing rice, especially since SRI methods can also reduce farmers’ costs of production which increases their net income ha⁻¹ by even more than yield. Even though these results sound fantastic, the validity of SRI concepts and practices has been demonstrated in more than 20 countries to date. This article considers, first, the methods that make these improvements possible and how these are achieved. It then briefly surveys SRI experience in five Asian countries, incentives in addition to yield, water-saving and profitability for adopting SRI, and possible limitations or disadvantages with the methodology. Next, it comments on the debate over SRI in the agronomic literature and then adds to the empirical record by reporting in some detail on SRI evaluations in two of India’s main rice-growing states, Andhra Pradesh and Tamil Nadu, where water availability is becoming more problematic and where SRI use is spreading. Finally, the article briefly discusses some implications of saving irrigation water by changing resource management rather than by using on more or different inputs.

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Productivity impacts of the system of rice intensification (SRI): A case study in West Bengal,India

The system of rice intensification (SRI) has generated considerable debate globally, particularly with regard to its potential to raise rice yields. Proponents of SRI have reported that the average rice yield with SRI is double the current average yield and can be increased to the level of three to four times. Opponents say the reported high yields are due to measurement error and that usual information expected in support of these fantastic yields is missing. The number of SRI adopters has increased in India in recent years. We evaluate the impact of adoption of SRI practices on rice yields, the economics of paddy cultivation and labour inputs based on field research conducted in Purulia, West Bengal, India. Paddy yields with SRI were higher than those under conventional paddy cultivation by 32% and net returns were higher by 67%. Labour input was reduced by 8%. SRI adoption enabled farmers consistently to enhance paddy yields, increase returns and save labour; and enhance productivity with respect to the key inputs in terms of paddy output per unit of seed, fertilizer and labour-day. SRI promises to be a significant alternative for not only raising paddy yields, but also for managing paddy based farming in resource-starved regions.     

Heterogeneity of crop productivity and resource use efficiency within smallholder Kenyan farms: Soil fertility gradients or management intensity gradients?

The decrease in crop yields at increasing distances from the homesteads within smallholder farms of Sub-Saharan Africa (SSA) is normally ascribed to the existence of within-farm soil fertility gradients. Field observations also suggest that a large part of such variability is concomitantly caused by poor agronomy. To understand the interaction between soil fertility (S factors) and management decisions (M factors) affecting crop variability, we combined field research conducted in western Kenya (Vihiga, Kakamega and Teso districts; rainfall: 1600, 1800 and 1200 mm, respectively) with explorations using the simple dynamic crop/soil model for dynamic simulation of nutrient balances, previously tested for the region. Field measurements indicated within-farm differences in average maize grain yields of 48% (2.7 vs. 1.4 t ha⁻¹) in Vihiga and of 60% (1.5 vs. 0.6 t ha⁻¹) in Teso, between fields that were close and far from the homestead, respectively. Extreme values ranged widely, e.g. between 4.9 and 0.3 t ha⁻¹ for all the farms surveyed in Vihiga, where the average farm size was 0.6 ha. Maize grain yields tended to increase with increasing contents of soil C, total N, extractable P and exchangeable bases. However, the negative relationship between S factors and distance from the homestead was not as strong as expected, and yield variability was better explained by multiple regression models considering M factors such as planting date, plant density, resource use and weed infestation (40–60% across sites). Then, we analysed the variation in resource (cash, labour, N) use efficiency within farms of different resource endowments with the aid of the simulation model. N balances at plot scale varied from ca. +20 to −18 kg ha⁻¹, from −9 to −20 kg ha⁻¹ and from −16 to −18 kg ha⁻¹ for the different fields of the high, medium and low resource endowment case-study farms, respectively. Labour productivities ranged between ca. 10 and 38 kg grain man-day⁻¹ across field and farm types. The results indicate the need of considering within farm heterogeneity when designing soil fertility management interventions. Resource use efficiency was strongly affected by soil quality. As farmers invest more effort and resources in the more productive and less risky fields, the interaction between S and M factors leads to farmer-driven resource use efficiency gradients within smallholder farms.     

保护性耕作对土壤理化性质和作物产量的影响

应用定位田间试验的方法，研究了不同耕作方式和秸秆还田方式对作物产量和土壤理化性质的影响。研究结果表明，传统翻耕的土壤容重大于进行保护性耕作的土壤容重；随着免耕年限的增加，土壤团聚体不断增大，进行5年保护性耕作的土壤团聚体比进行2年、3年保护性耕作的土壤团聚体有明显增加：进行免耕秸秆覆盖处理的土壤养分除碱解氮外．有机质、全氮、全钾、全磷及速效磷、速效钾均高于免耕无秸秆覆盖和传统翻耕的土壤：在施肥量相同的情况下。进行保护性耕作处理的小麦和水稻产量均比传统翻耕高，其中以半量秸秆还田免耕增产幅度最高，分别达小麦14．45％，水稻6．47％。     

Water productivity analysis of irrigated crops in Sirsa district,India

Water productivity (WP) expresses the value or benefit derived from the use of water, and includes essential aspects of water management such as production for arid and semi-arid regions. A profound WP analysis was carried out at five selected farmer fields (two for wheat–rice and three for wheat–cotton) in Sirsa district, India during the agricultural year 2001–02. The ecohydrological soil–water–atmosphere–plant (SWAP) model, including detailed crop simulations in combination with field observations, was used to determine the required hydrological variables such as transpiration, evapotranspiration and percolation, and biophysical variables such as dry matter or grain yields. The use of observed soil moisture and salinity profiles was found successful to determine indirectly the soil hydraulic parameters through inverse modelling.Considerable spatial variation in WP values was observed not only for different crops but also for the same crop. For instance, the WP_ET, expressed in terms of crop grain (or seed) yield per unit amount of evapotranspiration, varied from 1.22 to 1.56 kg m⁻³ for wheat among different farmer fields. The corresponding value for cotton varied from 0.09 to 0.31 kg m⁻³. This indicates a considerable variation and scope for improvements in water productivity. The average WP_ET (kg m⁻³) was 1.39 for wheat, 0.94 for rice and 0.23 for cotton, and corresponds to average values for the climatic and growing conditions in Northwest India. Including percolation in the analysis, i.e. crop grain (or seed) yield per unit amount of evapotranspiration plus percolation, resulted in average WP_ETQ (kg m⁻³) values of 1.04 for wheat, 0.84 for rice and 0.21 for cotton. Factors responsible for low WP include the relative high amount of evaporation into evapotranspiration especially for rice, and percolation from field irrigations. Improving agronomic practices such as aerobic rice cultivation and soil mulching will reduce this non-beneficial loss of water through evaporation, and subsequently will improve the WP_ET at field scale. For wheat, the simulated water and salt limited yields were 20–60% higher than measured yields, and suggest substantial nutrition, pest, disease and/or weed stresses. Improved crop management in terms of timely sowing, optimum nutrient supply, and better pest, disease and weed control for wheat will multiply its WP_ET by a factor of 1.5! Moreover, severe water stress was observed on cotton (relative transpiration < 0.65) during the kharif (summer) season, which resulted in 1.4–3.3 times lower water and salt limited yields compared with simulated potential yields. Benefits in terms of increased cotton yields and improved water productivity will be gained by ensuring irrigation supply at cotton fields, especially during the dry years.     

Can soil bunds increase the production of rain-fed lowland rice in south eastern Tanzania?

Rain-fed lowland rice is by far the most common production system in south eastern Tanzania. Rice is typically cultivated in river valleys and plains on diverse soil types although heavy soil types are preferred as they can retain moisture for a longer period. To assess the effects of soil bunds on the production of rain-fed lowland rice, the crop was cultivated in bunded and non-bunded farmers’ plots under the common agronomic practices in the region, in three successive seasons on Grumic Calcic Vertisols (Pellic). For the three seasons and for the two plot types, crop transpiration was simulated with the BUDGET soil water balance model by using the observed weather data, soil and crop parameters. Comparison between the observed yields and the simulated crop transpiration yielded an exponential relationship with a determination factor of 0.87 and an RMSE of 0.15 tonnes ha⁻¹. With the validated soil water balance model crop yields that can be expected in bunded and non-bunded fields were subsequently simulated for wet, normal and dry years and various environmental conditions. Yield comparison shows that soil bunds can appreciably increase the production of rain-fed lowland rice in south eastern Tanzania in three quarters of the years (wet and normal years) when the soil profile is slow draining (K_SAT equal to or less than 10 mm day⁻¹). In normal years a minimum yield increase of 30% may be expected on those soil types. In wet years and when the soil hardly drains (drainage class of 0–5 mm day⁻¹), the yield may even double. In dry years the yield increase will be most of the time less than 10% except for plots with a percolation rate of 0–5 mm day⁻¹.     

Optimizing yield,water requirements,and water productivity of aerobic rice for the North China Plain

Water resources for agriculture are rapidly declining in the North China Plain because of increasing industrial and domestic use and because of decreasing rainfall resulting from climate change. Water-efficient agricultural technologies need to be developed. Aerobic rice is a new crop production system in which rice is grown in nonflooded and nonsaturated aerobic soil, just like wheat and maize. Although an estimated 80,000 ha are cultivated with aerobic rice in the plain, there is little knowledge on obtainable yields and water requirements to assist farmers in improving their management. We present results from field experiments with aerobic rice variety HD297 near Beijing, from 2002 to 2004. The crop growth simulation model ORYZA2000 was used to extrapolate the experimental results to different weather conditions, irrigation management, and soil types. We quantified yields, water inputs, water use, and water productivities. On typical freely draining soils of the North China Plain, aerobic rice yields can reach 6–6.8 t ha⁻¹, with a total water input ranging between 589 and 797 (rainfall = 477 m and water application = 112–320 mm). For efficient water use, the irrigation water can be supplied in 2–4 applications and should aim at keeping the soil water tension in the rootzone below 100–200 kPa. Under those conditions, the amount of water use by evapotranspiration was 458–483 mm. The water productivity with respect to total water input (irrigation plus rainfall) was 0.89–1.05 g grain kg⁻¹ water, and with respect to evapotranspiration, 1.28–1.42 g grain kg⁻¹ water. Drought around flowering should be avoided to minimize the risk of spikelet sterility and low grain yields. The simulations suggest that, theoretically, yields can go up to 7.5 t ha⁻¹ and beyond. Further research is needed to determine whether the panicle (sink) size is large enough to support such yields and/or whether improved management is needed.     

Soybean yields and soil water status in Argentina: Simulation analysis

Recent changes in management of soybean production in Argentina may have large impacts on the soil water balance and on crop yield response. Changes in this system have included widespread adoption of a no-till management leaving crop residue on the soil surface, intensive cropping rotations (e.g. double cropping of wheat and soybean) so that the soil may not be fully recharged with water at the time of soybean sowing, and the occurrence of high water tables in a number of areas. The objective of this analysis was to assess the need to account for these factors in simulating soybean yields in Argentina. The influence of no-till management was simulated by simply decreasing the soil evaporation estimated for a bare soil by 70%. However, this alteration resulted in an over prediction in yield in many cases when it was assumed that the soil water content had been fully recharged at the initiation of the simulations. The difficulty with assuming a full soil water profile was confirmed when simulated yields were found to match well with observed yields when measured soil water content was used as an input to the model at the beginning of the soybean season. Finally, even with decreased soil evaporation there were still a few cases where simulated yield was less than observed yield. In these cases, a hypothetical water table, which relieved any drought stress once roots reached a depth of 1 m, resulted in yields that more closely matched observations. Overall, these results highlighted the need to estimate well both the influence of crop residue on soil evaporation and the soil water profile at sowing in simulating soybean yields in Argentina.     

Modelling soil detachment rates in rainfed agrosystems in the south-central Pyrenees

Distributed erosion models are potential tools for identifying soil sediment sources and guiding efficient Soil and Water Conservation (SWC) planning. However, the uncertainty of model predictions has yet to be resolved. Splash erosion is one of the most important mechanisms in soil loss. In this study, monthly splash detachment rates were predicted using the Morgan, Morgan and Finney (MMF) empirical erosion model and the more complex Revised Morgan, Morgan and Finney (RMMF) erosion model. These two models were used to assess active and abandoned fields in the Spanish Pyrenees. Land uses were barley fields, pasture, recently and old abandoned fields. Input parameters assessed were rainfall characteristics, soil properties, land forms, and land cover. The splash detachment rates predicted by the MMF and the RMMF models were higher for barley fields than for pasture and abandoned fields. However, the more complex RMMF model predicted lower splash detachment rates, especially in pastures. In contrast, runoff detachment was highest in old abandoned fields although rates were much lower than those of splash detachment. Moreover, soil detachment by runoff was low or equal to zero from November to May for the different land uses since the soil remained unsaturated during this period as a consequence of low rainfall intensities and soil surface roughness. Monthly values for total detachment were highest in barley fields, reaching a maximum of 17.2 and 16.9 Mg ha⁻¹ in September and October. The mean annual detachment rates for barley, pastures and recently and old abandoned fields were 81.1, 0.8, 61.8 and 22.3 Mg ha⁻¹, respectively. The splash and runoff detachment rates of the RMMF model appeared to be sensitive to land cover factors, rainfall intensity and soil micro-topography, thus it is a better model for assessing soil detachment for various land uses. The comparison of erosion rates between the ¹³⁷Cs and the MMF and RMMF models shows that the models predict lower erosion rates due to the low estimated rates of the runoff transport capacity. However, the estimated and measured rates are in close agreement and are under the limit of the tolerable soil loss for soils under Mediterranean conditions.     

Increasing crop yield in water scarce environments using locally available materials: An experience from semi-arid areas in Mpwapwa District, central Tanzania

This paper presents experience on working with farmers in water scarce environments in improving crop yield through the application of locally available materials in semi-arid areas of Mpwapwa District, central Tanzania. Findings are presented from the interdisciplinary study that involved documenting farmers perceptions and on-farm field experimentation. In the farmers’ perceptions study, three different traditional tillage practices applied by smallholder farmers in the area were identified. These are traditional no-till (TNT), shallow tillage (ST) and ridging tillage (RT). The impacts of various tillage practices on soil fertility improvement, reduced weed infestation, soil moisture retention and crop yield were the main factors considered by farmers when selecting a particular tillage practice to apply. In two cropping seasons (i.e. 2006/7 and 2007/8) on-farm field experimentations were carried to test the effects of the three traditional tillage practices, manure and mulching practices on soil moisture retention and crop yield. Results from this experiment showed traditional no-till fields to have the lowest soil moisture retention capacity and the lowest infiltration flow rate as well as lowest crop yield compared to other studied practices. It was observed that improving the current tillage practices by the application of manure to both ST and RT, and mulching to ST at rates affordable to smallholder farmers as identified during perception study (i.e. 5 tons/ha for manure and 3 tons/ha for mulching materials) results in increased crop yield. When the grain yield is compared between traditional no-till and shallow tillage with manure and mulching practices, the yield increase is between 50 and 100%. It was concluded that crop yield in water scarce environments such as the semi-arid areas of Mpwapwa District can be increased by applying locally available materials such as cow manure and mulching at rates affordable to smallholder farmers.     

Evaluation on the irrigation and fertilization management practices under the application of treated sewage water in Beijing, China

Irrigation and fertilization management practices play important roles in crop production. In this paper, the Root Zone Water Quality Model (RZWQM) was used to evaluate the irrigation and fertilization management practices for a winter wheat–summer corn double cropping system in Beijing, China under the irrigation with treated sewage water (TSW). A carefully designed experiment was carried out at an experimental station in Beijing area from 2001 to 2003 with four irrigation treatments. The hydrologic, nitrogen and crop growth components of RZWQM were calibrated by using the dataset of one treatment. The datasets of other three treatments were used to validate the model performance. Most predicted soil water contents were within ±1 standard deviation (S.D.) of the measured data. The relative errors (RE) of grain yield predictions were within the range of −26.8% to 18.5%, whereas the REs of biomass predictions were between −38% and 14%. The grain nitrogen (N) uptake and biomass N uptake were predicted with the RE values ranging from −13.9% to 14.7%, and from −11.1% to 29.8%, respectively. These results showed that the model was able to simulate the double cropping system variables under different irrigation and fertilization conditions with reasonable accuracy. Application of RZWQM in the growing season of 2001–2002 indicated that the best irrigation management practice was no irrigation for summer corn, three 83 mm irrigations each for pre-sowing, jointing and heading stages of winter wheat, respectively. And the best nitrogen application management practice was 120 kg N ha⁻¹ for summer corn and 110 kg N ha⁻¹ for winter wheat, respectively, under the irrigation with TSW. We also obtained the alternative irrigation management practices for the hydrologic years of 75%, 50% and 25%, respectively, in Beijing area under the conditions of irrigation with TSW and the optimal nitrogen application.     

Tillage and irrigation effects on crop yields and soil properties under the rice-wheat system in the Indian Himalayas

Conservation tillage systems generally improve soil organic C (SOC), plant available water capacity (PAWC), aggregation and soil water transmission. A field experiment was conducted for 4 years (2001-2002 to 2004-2005) to study tillage (conventional tillage (CT) and zero tillage (ZT)) systems. The selected irrigation treatments were at four levels (I₁: pre-sowing (PS), I₂: PS + active tillering (AT)/crown root initiation (CRI), I₃: PS + AT/CRI + panicle initiation (PI)/flowering (FL), and I₄: PS + AT/CRI + PI/FL + grain filling (GF)), applied at the critical growth stages on rice (Oryza sativa L.) and wheat (Triticum aestivum L.). Their effects on direct seeded rice productivity and soil properties (SOC and selected physical properties) after rice and wheat harvest were investigated. Soil organic C contents after rice and wheat harvest in the 0-15 cm soil depth were higher under ZT than under CT. Soil organic C increased significantly with I₂ over I₁ for both crops and with I₄ over I₂ for the wheat crop. The PAWC was significantly higher with ZT than CT. Zero tilled and frequently irrigated plots showed enhanced infiltration characteristics (infiltration rate, cumulative infiltration and sorptivity) and saturated hydraulic conductivity. Both direct seeded rice and wheat yields were not significantly different in the plots under ZT and CT. There was a significant increase in both rice and wheat yields in the plots under I₂ over I₁. However, water use efficiency between irrigation treatments was not significantly different. Hence, under direct seeded rice-wheat system in a sandy clay loam soil of the sub-temperate Indian Himalayas, farmers may adopt ZT with two irrigations in each crop for optimum resource conservation.     

Effects of winter crop and supplemental irrigation on crop yield,water use efficiency and profitability in rainfed rice based cropping system of eastern India

Soil moisture availability is the main limiting factor for growing second crops in rainfed rice fallows of eastern India. Only rainfed rice is grown with traditional practices during the rainy season (June–October) with large areas (13 m ha⁻¹) remaining fallow during the subsequent dry season (November–March) inspite of annual rainfall of the order 1000–2000 mm. In this study an attempt was made to improve productivity of rainfed rice during rainy season and to grow second crops in rice fallow during dry (winter) season with supplemental irrigation from harvested rainwater. Rice was grown as first crop with improved as well as traditional farmers’ management practices to compare the productivity between these two treatments. Study revealed that 87.1–95.6% higher yield of rice was obtained with improved management over farmers’ practices. Five crops viz., maize, groundnut, sunflower, wheat and potato were grown in rice fallow during dry (winter) season with two, three and four supplemental irrigations and improved management. Sufficient amount of excess rainwater (runoff) was available (381 mm at 75% probability level) to store and recycle for supplementary irrigation to second crops grown after rice. Study revealed that supplemental irrigation had significant effect (P < 0.001) on grain yield of dry season crops and with two irrigation mean yields of 1845, 785, 905, 1420, 8050 kg ha⁻¹ were obtained with maize (grain), groundnut, sunflower, wheat and potato (tuber), respectively. With four irrigations 214, 89, 78, 81, 54% yield was enhanced over two irrigations in respective five crops. Water use efficiency (WUE) of 13.8, 3.35, 3.39, 5.85 and 28.7 kg ha⁻¹ was obtained in maize, groundnut, sunflower, wheat, potato (tuber), respectively with four irrigations. The different plant growth parameters like maximum above ground biomass, leaf area index and root length were also recorded with different levels of supplemental irrigation. The study amply revealed that there was scope to improve productivity of rainfed rice during rainy season and to grow another profitable crops during winter/dry season in rice fallow with supplemental irrigation from harvested rainwater of rainy season.     

Modelling of water and nitrogen balances in the ponded water and soil profile of rice fields in Northern Greece

This paper presents a water and nitrogen balance model for the surface ponded water and soil profile system of rice (Oryza sativa L.) fields. The model estimates the daily water balance components, as well as, the daily losses and transformations of nitrogen. Data from two neighbouring rice fields during the growing season of 2005 in the Thessaloniki plain of Northern Greece were used for the application of the model. The data set of field A was used for the calibration of the model, while the data set from the field B for validation of model. Simulation results of total inorganic nitrogen in the soil and runoff water exhibited reasonable agreement with the measured data during calibration and verification of the model. Significant amounts of applied irrigation water were lost through surface runoff and deep percolation into the groundwater. The sum of nitrogen inputs from fertilization, mineralization and irrigation water were 292.7 and 280.4 kg ha⁻¹ for field A and B, respectively. Nitrogen uptake by algae in ponding water and plants was one of the main processes of nitrogen reduction in the rice field systems with an amount of 125.7 and 131.8 kg ha⁻¹ for field A and B, respectively. Leaching through percolated water was the other significant process with 118.3 and 120.8 kg ha⁻¹, respectively. Gaseous losses of nitrogen (via volatilization and denitrification) were also substantial processes of nitrogen reduction in the flooded compartment. The study showed that the simple model presents important results for the water and nitrogen management in rice fields. This information can be used for irrigation water saving and prevention of water resources contamination in rice-based agroecosystems.     

Characterising rice-based farming systems to identify opportunities for adopting water efficient cultivation methods in Tamil Nadu, India

Efficient water use in rice cultivation is a prerequisite for sustaining food security for the rice consuming population of India. Novel rice production practices, including water-saving techniques, modifications in transplanting, spacing, weeding and nutrient management, have been developed and shown to be effective on farm, but adoption of these techniques by farmers has remained restricted. Potential constraints include technical difficulties with new practices, and labour and gender issues which differ between farms. On the basis of a rapid survey of 100 rice-based farms, four farm types were identified based on their socio-economic and biophysical characteristics. Detailed farm surveys were conducted on three representative farms of each farm type to evaluate land use patterns, use of inputs such as water, labour, nutrient, capital and machinery, income from crop and animal production and off-farm activities. Opportunities exist for one or more new rice cultivation techniques to be adopted in all the four farm types. For all farm types, however, the opportunities for use of water-saving irrigation were the least promising. In general, adoption of water-saving irrigation will not improve farmers’ livelihoods despite its importance in reducing water scarcity problems at regional scale. At farm scale, the potential for adoption of water-saving irrigation depends on the season, location of fields and the irrigation source. Changes in government policies such as rules and regulations, pricing, institution building and infrastructure development, as well as training and education of farmers are needed to improve the adoption of modified methods for rice cultivation.     

Soil matric potential-based irrigation scheduling to rice (Oryza sativa)

About half of the total fresh water used for irrigation in Asia is used for rice production. Decreasing water resources and increasing water costs necessitates increasing water use efficiency for rice. The most common method of irrigation in northwestern India is through alternate wetting and drying with a fixed irrigation interval, irrespective of soil type and climatic demand resulting in over-irrigation or under-irrigation under different soil and weather situations. Soil matric potential may be an ideal criterion for irrigation, since variable atmospheric evaporativity, soil texture, cultural practices and water management affect rice irrigation water requirements. A 4-year field study was conducted to assess the feasibility of rice irrigation scheduling on the basis of soil matric potential and to determine the optimum matric potential so as to optimize irrigation water without any adverse effect on the yield. The treatments included scheduling irrigation to rice with tensiometers installed at 15–20 cm soil depth at five levels of soil matric suction viz. 80, 120, 160, 200 and 240±20 cm, in addition to the recommended practice of alternate wetting and drying with an interval of 2 days after complete infiltration of ponded water. The grain yield of rice remained unaffected up to soil moisture suction of 160±20 cm each year. Increasing soil matric suction to 200 and 240±20 cm decreased rice grain yield non-significantly by 0–7% and 2–15%, respectively, over different years compared to the recommended practice of the 2-day interval for scheduling irrigation. Irrigation at 160±20 cm soil matric suction helped save 30–35% irrigation water compared to that used with the 2-day interval irrigation. With a soil matric potential irrigation criterion the total amount of irrigation water used was a function of the number of rainy days and evaporation during the rice season.     

Communicating complexity: Integrated assessment of trade-offs concerning soil fertility management within African farming systems to support innovation and development

African farming systems are highly heterogeneous: between agroecological and socioeconomic environments, in the wide variability in farmers’ resource endowments and in farm management. This means that single solutions (or ‘silver bullets’) for improving farm productivity do not exist. Yet to date few approaches to understand constraints and explore options for change have tackled the bewildering complexity of African farming systems. In this paper we describe the Nutrient Use in Animal and Cropping systems - Efficiencies and Scales (NUANCES) framework. NUANCES offers a structured approach to unravel and understand the complexity of African farming to identify what we term ‘best-fit’ technologies - technologies targeted to specific types of farmers and to specific niches within their farms. The NUANCES framework is not ‘just another computer model’! We combine the tools of systems analysis and experimentation, detailed field observations and surveys, incorporate expert knowledge (local knowledge and results of research), generate databases, and apply simulation models to analyse performance of farms, and the impacts of introducing new technologies. We have analysed and described complexity of farming systems, their external drivers and some of the mechanisms that result in (in)efficient use of scarce resources. Studying sites across sub-Saharan Africa has provided insights in the trajectories of change in farming systems in response to population growth, economic conditions and climate variability (cycles of drier and wetter years) and climate change. In regions where human population is dense and land scarce, farm typologies have proven useful to target technologies between farmers of different production objectives and resource endowment (notably in terms of land, labour and capacity for investment). In such regions we could categorise types of fields on the basis of their responsiveness to soil improving technologies along soil fertility gradients, relying on local indicators to differentiate those that may be managed through ‘maintenance fertilization’ from fields that are highly-responsive to fertilizers and fields that require rehabilitation before yields can improved. Where human population pressure on the land is less intense, farm and field types are harder to discern, without clear patterns. Nutrient cycling through livestock is in principle not efficient for increasing food production due to increased nutrient losses, but is attractive for farmers due to the multiple functions of livestock. We identified trade-offs between income generation, soil conservation and community agreements through optimising concurrent objectives at farm and village levels. These examples show that future analyses must focus at farm and farming system level and not at the level of individual fields to achieve appropriate targeting of technologies - both between locations and between farms at any given location. The approach for integrated assessment described here can be used ex ante to explore the potential of best-fit technologies and the ways they can be best combined at farm level. The dynamic and integrated nature of the framework allows the impact of changes in external drivers such as climate change or development policy to be analysed. Fundamental questions for integrated analysis relate to the site-specific knowledge and the simplification of processes required to integrate and move from one level to the next.     

Modified rice cultivation in Tamil Nadu,India: Yield gains and farmers’ (lack of) acceptance

The looming water crisis and water-intensive nature of rice cultivation are driving the search for alternative management methods to increase water productivity in rice cultivation. Experiments were conducted under on-station and on-farm conditions to compare rice production using modified methods of irrigation, planting, weeding and nutrient management with conventional methods of cultivation. Farm surveys were used to evaluate adoption of modified rice cultivation method. On-station experiments showed that, a combination of water-saving irrigation, young seedling or direct seeding, mechanical weeding and green manure application increased the rice water productivity though the largest yields were obtained for a combination of conventional irrigation, young seedling or direct seeding, mechanical weeding and green manure application. On-farm experiments demonstrated a yield advantage of 1.5 t ha⁻¹ for the modified method over conventional method. We found, however, that yield advantages were not the sole factor driving adoption. Associated changes required in management, including the increased labour demand for modified planting, unwillingness of agricultural labourers to change practices, difficulties with modified nursery preparation and the need to replace cheaper women’s labour for hand weeding with more costly men’s labour for mechanical weeding, all reduced the chance of adopting the modified rice cultivation method. Risks associated with water-saving irrigation, such as uncertainty about the timing and amount of water release for irrigation affect adoption adversely as well. There was no incentive for farmers to adopt water-saving irrigation as water from reservoirs and electricity for pumping well-water are both free of charge. To date farmers continue to experiment with the modified cultivation method on a small part of their farms, but are unlikely to adopt the modified method on a large-scale unless policies governing water management are changed.     

Factors affecting soil quality changes in the North China Plain: A case study of Quzhou County

At the end of the 1970s there were 3,300,000 ha of salt-affected land in the North China Plain. After the successful removal of the salt in the 1980s, the land has gradually been used for increasing intensive forms of agriculture. The Household Responsibility System (HRS) was adopted in Chinese rural areas at the time of the economic reform of the early 1980s. Farm households became the basic decision-making units that could directly control soil quality. This paper describes the change in soil fertility after 20 years of intensive agriculture and the driving factors of soil fertility change. Quzhou County was selected as it is representative for the North China Plain. The soil fertility status and nutrient flows of the salt-affected land for 1980–1981 and 1999 in Quzhou County were evaluated. Over 20 years, the total nitrogen (N), the extractable phosphorus (P) and the soil organic matter (SOM) in salt-affected land increased by 127%, 601% and 51% respectively; but exchangeable potassium decreased by 31%. The N, P, K and SOM balance in 1980–1981 was −15, −2, −29 and −24 kg ha⁻¹ y⁻¹, but in 1999 the N and P balance had changed to 24 kg ha⁻¹ y⁻¹ and 25 kg ha⁻¹ y⁻¹ as a result of the widespread use of N and P fertilizer. With the rapid increase in crop production and the sparse use of K fertilizer, the K balance continues to be negative. Straw production increased along with crop yields and there was a development of stock breeding. Together with better straw restitution practices, the SOM balance increased to a positive 613 kg ha⁻¹ y⁻¹. The analysis of farm household land-use and inputs indicated that there were significant differences in behaviour between almost totally off-farm households and other household types. These differences were in the choice of land-use type, the use of fertilizers and crop residue management. However, there was no significant relationship between socio-economic factors and fertilizer inputs. Current nutrient management is not optimal. Therefore, it is important to establish a better system for bottom-up knowledge collection and transfer of scientific information to farmers.     

Using remote sensing to evaluate the spatial variability of evapotranspiration and crop coefficient in the lower Rio Grande Valley,New Mexico

Pecan is a major crop in the lower Rio Grande Valley (LRGV), New Mexico. Currently, about 11,000 ha of pecan orchards at various stages of growth are consuming about 40% of irrigation water in the area. Pecan evapotranspiration (ET) varies with age, canopy cover, soil type and method of water management. There is a need for better quantification of pecan ET for the purpose of water rights adjudication, watershed management and agronomical practices. This paper describes a process where remote sensing information from Landsat-5 and Landsat-7 were combined with ground level measurements to estimate pecan ET and field scale actual crop coefficient (K _c) for the LRGV. The results showed that annual pecan water use for 279 fields ranged from 498 to 1,259 mm with an average water use of 1,054 mm. For fields with NDVI > 0.6 (normalized difference vegetation index), which represented mature orchards (total of 232 fields), the annual water use ranged from 771 to 1,259 mm with an average water use of 1,077 mm. The results from remote sensing model compared reasonably well with ground level ET values determined by an eddy covariance system in a mature pecan orchard with an average error of 4% and the standard error of estimate (SEE) ranging from 0.91 to 1.06 mm/day. A small fraction (5%) of the pecan fields were within the range of maximum ET and K _c.