Exante assessment of dual-purpose sweet potato in the crop–livestock system of western Kenya: A minimum-data approach

Mixed crop–livestock systems have a crucial role to play in meeting the agricultural production challenges of smallholder farmers in sub-Saharan Africa. Sweet potato is seen as a potential remedial crop for these farmers because of its high productivity and low input requirements, while its usefulness for both food and feed (dual-purpose) make it attractive in areas where land availability is declining. In this paper, we develop and apply a ‘minimum-data’ methodology to assess exante the economic viability of adopting dual-purpose sweet potato in Vihiga district, western Kenya. The methodology uses and integrates available socio-economic and bio-physical data on farmers’ land use allocation, production, and input and output use. Spatially heterogeneous characteristics of the current system regarding resources and productivity are analyzed to assess the profitability of substituting dual-purpose sweet potato for other crops currently grown for food and feed. Results indicate that a substantial number of farmers in the study area could benefit economically from adopting dual-purpose sweet potato. Depending on assumptions made, the adoption rate, expressed as the percentage of the total land under adopting farms, is between 55% and 80%. The analysis shows that the adoption rate is likely to vary positively with the average total yield of dual-purpose sweet potato, the harvest index (the ratio between tuber and fodder yields), the price of milk, and the nutritional value of available fodder. This study demonstrates the usefulness of the minimum-data methodology and provides evidence to support the hypothesis that dissemination of the dual-purpose sweet potato could help improve the livelihoods of smallholder farmers operating in mixed crop–livestock systems in east Africa.     

Biophysical and economic tradeoffs of intercropping timber with food crops in the Philippine uplands

Steadily rising prices for timber on Mindanao in the Philippines have given an incentive to farmers to devote some of their land to fast-growing tree species. The costs and benefits of intercropping young timber trees with food crops was studied in a 1000 stem ha⁻¹ stand of Paraserianthes falcataria. At 2 years of age, diameter at breast height and height of intercropped trees were 33 and 21% greater, respectively, than sole trees. Management costs of intercropped trees were less than half of sole trees. Allometric equations for Mindanao falcataria were used to project future tree growth and system returns. In the base scenario (1000 trees ha⁻¹, 5-year rotation), the sum of biophysical and economic benefits of intercropping trees with a maize/vegetable rotation for two years were less than the costs of reduced intercrop yield, compared to sole cropping of each component. A linear relationship of crop decline to the increase in basal area of the stand was used to predict returns to intercropping under alternative tree densities and intercropping periods. Intercropping becomes more attractive as labor becomes scarcer relative to land, the need to minimize cash inputs becomes more important to farmers, and trees increase in value relative to annual crops.     

Design of microirrigation subunit of minimum cost with proper operation

Matlab software named PRESUD (Pressurized Subunit Design) was developed to identify the optimum microirrigation subunit design using the annual water application cost per unit of irrigated area (C _T). This is defined as the cost per cubic meter of water applied to the soil for crop use, calculated as the sum of investment, maintenance, energy, and water (C _w) costs. In this study, only rectangular subunits are considered, using an iterative method for calculating the lateral and manifold pipelines. The infrastructure necessary for water delivery to the subunit inlet was taken into account in the price of water. The results indicate that C _w is the most important factor in C _T, which includes the investment and energy costs for moving water from the source to the subunit inlet. Other important factors, in order of importance, are the emission exponent (x), coefficient of variation of emitter manufacturer (CV_qmf), and emitter spacing (s _e). The minimum water application cost for a typical subunit to irrigate vegetable crops such as pepper is obtained with a subunit of 0.3–0.5 ha, with 80 m of paired lateral pipe length of 16 (13.6 mm) PE 0.25 MPa diameter, and 50 (44 mm) PE 0.4 MPa of manifold pipe diameter. The cost of a typical drip irrigation subunit design for a crop, such as grapevines on trellises, is equivalent to 25 % of the C _T of a typical subunit to irrigate vegetable crops, such as pepper.     

‘More crop per drop’: how to make it acceptable for farmers?

In countries facing water scarcity, governmental water agencies try to transfer this constraint to farmers, e.g. by encouraging them to shift from traditional to localized irrigation methods to save water. However, water shortage is often much less a problem for farmers than soil limitations, their objective being mostly to maximize their income per cultivated area (US$ per hectare rather than per cubic meter of water). This discrepancy can only be solved if governments find ways to ‘transfer’ water scarcity, e.g. through economic incentives such as water pricing and/or subsidies. The aim of this study was to address the question of how to match the interest of both water managers and farmers. We aimed particularly at evaluating whether shifting to drip irrigation is a relevant way to save water and increase farmer's income.Our analysis was based on the interactive impacts among economic, environmental, technical and methodological parameters on the net productivity of two crops. We focused on the case study of Turkey considering two crops with contrasted gross productivity, tomato and cotton, characterized by partial vegetation cover during a large part of crop cycle. A 3D crop energy balance model was applied showing that crop transpiration is increased by up to 10% when shifting from furrow to drip irrigation. These results were used to correct the maximal evapotranspiration (ET_m), estimated with the simple “crop coefficient” (K_c) method, and then used to enhance net productivity estimation both for furrow and drip irrigation.The results suggest that water managers and farmers share a common interest in adopting drip irrigation of tomato. Inversely, interests divergence may increase with low/medium value crops as cotton; the combination between water pricing and subsidies could be a way of agreement, but it would require subsidies for irrigation equipment of at least 40%, for low water tariffs, to 60%, for high water tariffs, to make the transfer from furrow to drip irrigation acceptable. This approach appeared generic enough to be applied for other economic, technical or environmental conditions, to modernize irrigation by harmonizing constraints faced by water managers and farmers.     

Oxyfertigation of a greenhouse tomato crop grown on rockwool slabs and irrigated with treated wastewater: Oxygen content dynamics and crop response

This work assesses the seasonal dynamics of the substrate oxygen content and the response to nutrient solution oxygen enrichment (oxyfertigation) of an autumn-spring tomato crop grown on rockwool slabs and irrigated with treated wastewater of very low dissolved oxygen (DO) content under Mediterranean greenhouse conditions. DO values in the nutrient solution were clearly higher for the oxygen-enriched (14.6 mg L⁻¹) tomato crop than for the non-enriched one (4.5 mg L⁻¹). However, DO values in the substrate solution were similar for both oxygen treatments (mean seasonal values of 5.1 and 4.8 mg L⁻¹ for the enriched and the non-enriched one, respectively), except for a short crop period at the end of the cycle when they were significantly higher for the oxygen-enriched crop. For both treatments, substrate DO values were highest for the winter period and decreased progressively during the spring period, reaching minimum values of around or below 3 mg L⁻¹ at the end of the spring. The oxygen enrichment of the nutrient solution did not affect any of the irrigation and fertigation parameters evaluated in the tomato crop: water uptake, volumetric water content of the substrate, electrical conductivity (EC) or nutrient concentration in the leached nutrient solution. Moreover, the oxygen enrichment of the nutrient solution did not affect the aboveground biomass and the biomass partitioning, the fresh weight of total and marketable tomato fruits or the tomato fruit quality parameters. Overall, it appears that oxygen deficiency conditions did not occur as the substrate DO values were higher than, or about, 3 mg L⁻¹ throughout most of the tomato crop cycle for both treatments and the rockwool slabs maintained good aeration conditions throughout the whole cycle.     

Prototype decision support system based on the VegSyst simulation model to calculate crop N and water requirements for tomato under plastic cover

The simulation model VegSyst was calibrated and validated for tomato grown under plastic cover. Calibration was conducted with an autumn–winter soil-grown crop, and validation with five crops with differences in season, cropping media, and site. VegSyst accurately simulated daily dry matter production (DMP), N uptake, and ET_c. Comparing simulated and measured values by linear regression, slope and intercept values were not statistically significantly different (P < 0.05) from 1 and 0, respectively. Slopes between simulated and measured values indicated average differences of 4, 2, and ?1 % for DMP, N uptake, and ET_c, respectively. Model performance was good with autumn–winter and spring cropping cycles, and in soil and substrate. A prototype decision support system (VegSyst-DSS) based on VegSyst was developed to calculate daily irrigation and N fertilizer requirements and nutrient solution [N] for fertigated tomato. N fertilizer requirements are based on crop N uptake and consider soil mineral N, and N mineralized from manure and soil OM and the N efficiency of each N source. Irrigation requirements are based on ET_c and consider application efficiency and salinity. VegSyst-DSS requires very few inputs which are all readily available to farmers and advisors. Scenario analysis compared a scenario representative of local farming practice, where N supplied from soil is not considered, with scenarios with different amounts of N supplied from soil mineral N at planting and mineralization of soil OM and of manure. Relative to the scenario representative of farmer practice, VegSyst recommendations resulted in reductions of 34–65 % in fertilizer N.     

Water requirement of drip irrigated tomatoes grown in greenhouse in tropical environment

Four different levels of drip fertigated irrigation equivalent to 100, 75, 50 and 25% of crop evapotranspiration (ET_c), based on Penman–Monteith (PM) method, were tested for their effect on crop growth, crop yield, and water productivity. Tomato (Lycopersicon esculentum, Troy 489 variety) plants were grown in a poly-net greenhouse. Results were compared with the open cultivation system as a control. Two modes of irrigation application namely continuous and intermittent were used. The distribution uniformity, emitter flow rate and pressure head were used to evaluate the performance of drip irrigation system with emitters of 2, 4, 6, and 8 l/h discharge. The results revealed that the optimum water requirement for the Troy 489 variety of tomato is around 75% of the ET_c. Based on this, the actual irrigation water for tomato crop in tropical greenhouse could be recommended between 4.1 and 5.6 mm day⁻¹ or equivalent to 0.3–0.4 l plant⁻¹ day⁻¹. Statistically, the effect of depth of water application on the crop growth, yield and irrigation water productivity was significant, while the irrigation mode did not show any effect on the crop performance. Drip irrigation at 75% of ET_c provided the maximum crop yields and irrigation water productivity. Based on the observed climatic data inside the greenhouse, the calculated ET_c matched the 75–80% of the ET_c computed with the climatic parameters observed in the open environment. The distribution uniformity dropped from 93.4 to 90.6%. The emitter flow rate was also dropped by about 5–10% over the experimental period. This is due to clogging caused by minerals of fertilizer and algae in the emitters. It was recommended that the cleaning of irrigation equipments (pipe and emitter) should be done at least once during the entire cultivation period.     

Urban agriculture, using sustainable practices that involve the reuse of wastewater and solid waste

This study proposes a safe method for the disinfection of wastewater destined for reuse in urban agriculture. It also discusses the year-round production of fresh vegetables in confined urban spaces, using sustainable practices that involve the recycling and reuse of waste while at the same time saving water. To address the aforementioned problems, this study aimed to determine the efficiency of applying organoponic techniques to urban crops, using selected organic compounds and recyclable solid waste products, plus home-made organic fertilizers and treated wastewater. The results obtained demonstrate that in addition to disinfecting the wastewater, ozone contributes oxygen and nutrients to the soil, thereby reducing the need for chemical fertilizers. Ozone also reduces the risk of infection by eliminating highly pathogenic micro-organisms, and increases the rate of plant growth such as: radishes (Raphanus sativus L.), tomatoes (Lycopersicum esculentum), spearmint (Mentha piperita), camomile (Matricaria recutita), Romaine lettuce (Lactuca sativa) and Chinese cabbage (Brassica rapa). Great benefits can therefore be derived from employing these urban agriculture techniques because, in addition to putting to good use waste products that are generated by the ton, these techniques also produce quality food plants that are 100% organic.     

Simulation of transpiration, drainage, N uptake, nitrate leaching, and N uptake concentration in tomato grown in open substrate

Free-drainage or “open” substrate system used for vegetable production in greenhouses is associated with appreciable NO₃⁻ leaching losses and drainage volumes. Simulation models of crop N uptake, N leaching, water use and drainage of crops in these systems will be useful for crop and water resource management, and environmental assessment. This work (i) modified the TOMGRO model to simulate N uptake for tomato grown in greenhouses in SE Spain, (ii) modified the PrHo model to simulate transpiration of tomato grown in substrate and (iii) developed an aggregated model combining TOMGRO and PrHo to calculate N uptake concentrations and drainage NO₃⁻ concentration. The component models simulate NO₃⁻-N leached by subtracting simulated N uptake from measured applied N, and drainage by subtracting simulated transpiration from measured irrigation. Three tomato crops grown sequentially in free-draining rock wool in a plastic greenhouse were used for calibration and validation. Measured daily transpiration was determined by the water balance method from daily measurements of irrigation and drainage. Measured N uptake was determined by N balance, using data of volumes and of concentrations of NO₃⁻ and NH₄⁺ in applied nutrient solution and drainage. Accuracy of the two modified component models and aggregated model was assessed by comparing simulated to measured values using linear regression analysis, comparison of slope and intercept values of regression equations, and root mean squared error (RMSE) values. For the three crops, the modified TOMGRO provided accurate simulations of cumulative crop N uptake, (RMSE = 6.4, 1.9 and 2.6% of total N uptake) and NO₃⁻-N leached (RMSE = 11.0, 10.3, and 6.1% of total NO₃⁻-N leached). The modified PrHo provided accurate simulation of cumulative transpiration (RMSE = 4.3, 1.7 and 2.4% of total transpiration) and cumulative drainage (RMSE = 13.8, 6.9, 7.4% of total drainage). For the four cumulative parameters, slopes and intercepts of the linear regressions were mostly not statistically significant (P < 0.05) from one and zero, respectively, and coefficient of determination (r²) values were 0.96-0.98. Simulated values of total drainage volumes for the three crops were +21, +1 and −13% of measured total drainage volumes. The aggregated TOMGRO-PrHo model generally provided accurate simulation of crop N uptake concentration after 30-40 days of transplanting, with an average RMSE of approximately 2 mmol L⁻¹. Simulated values of average NO₃⁻ concentration in drainage, obtained with the aggregated model, were −7, +18 and +31% of measured values.     

Improving agricultural water management in the semi-arid region of Brazil: experimental and modelling study

Agricultural practice in the semi-arid region of Brazil is highly dependant on irrigation. As access to water is limited in the region, there is a need to guarantee its efficient use, especially in small-scale farming schemes. Models adequately calibrated for semi-arid conditions and for typical crops are useful tools for analysis of on-farm strategies to improve water use efficiency. A physically based agrohydrological model, SALTMED, is calibrated and validated for carrots (Daucus carota L., Brasília variety) and cabbage (Brassica oleracea var. capitata), two of the main crops in small-scale irrigated agriculture in the northeast of Brazil. SALTMED is also calibrated for castor beans (Ricinus communis L.) under rainfed conditions. The results demonstrated the suitability of the SALTMED model for simulating soil water dynamics and crop yield in the area. Predicted time series of soil water content and matric potential of root zone showed good agreement with observed values, as shown graphically and statistically. Using the calibrated and validated model, management scenarios were analysed in terms of applied irrigation water, irrigation frequency, soil and crop types. Impact of climate change on the irrigation water requirements was also briefly analysed for possible changes in annual temperature using two different emission scenarios. Analysis of possible impact of climate change on temperature related to two emission scenarios on the area showed an increase around 11% of the crop water requirement for carrots and cabbage, for the low emission scenario, and around 17% for the high emission scenario. The analysis of management scenarios indicated possible over-irrigation in the area. The simulation showed that the deficit irrigation was a useful water-saving strategy for the region. The simulations also indicated that irrigation frequency affected crop water use and differed according to the soil type.     

Developing crop coefficients for field-grown tomato (Lycopersicon esculentum Mill.) under drip irrigation with black plastic mulch

A 2 years field study was conducted to develop crop coefficients for field-grown tomato (Lycopersicon esculentum Mill.), a major irrigated crop in the Jordan Valley, under drip irrigation system with black plastic mulch. The area of the study field was 1.5 ha surrounded by many similar tomato fields. Actual crop evapotranspiration (ET_C) was measured using eddy covariance technique which distinguishes this study from other previous studies conducted in the Jordan Valley that relied on the old indirect approach for ET_C estimation based on the soil water balance.Grass reference evapotranspiration (ET_O) was determined by using the FAO Penman–Monteith method utilizing the agrometeorological parameters measured at the study site. The crop coefficient (K_C) was determined as the ratio of ET_C to ET_O. The tomato crop coefficients were determined following the FAO crop coefficient model. The average crop coefficient during the midseason growth stage (K_C mid) was 0.82 which is far below the adjusted FAO crop coefficient of 1.19 by about 31%. Also, the late season crop coefficient (K_C end) was much lower than the adjusted FAO crop coefficient of 0.76 by about 40%. Moreover, the weighted average crop coefficient over the entire growing season (K_C GS) was 0.69, which is about 36% lower than the FAO corresponding value. In fact, the low K_C values obtained reflect the effect of practicing both localized drip irrigation and plastic mulch covering. This study showed that there is a big difference between the reported FAO crop coefficients and the one measured in the filed using a precise approach. These exact updated values of crop coefficients will enhance future estimation of crop water requirements and hence irrigation management of tomato crop which is the major irrigated crop in the Jordan Valley.     

Plant viruses in irrigation water: reduced dispersal of viruses using sensor-based disinfection

The increasing use of recirculating nutrient solutions and drainage water for irrigation purposes requires effective sanitation methods to minimise the dispersal of plant pathogens. Among these, plant viruses are of particular interest because they cannot be cured. A new disinfection system was tested in regard to its ability to inactivate plant viruses in nutrient solution in greenhouses. Potassium hypochlorite produced onsite by an electrolytic disinfector and injected once weekly into the nutrient solution by a sensor, prevented the dispersal of Pepino mosaic virus in the tomato crop. The management program assures that virus particles released from infected plants do not accumulate, forming an infectious virus reservoir which represents an inoculum potential in the hydroponic system. Both tested applications at 0.2 or 0.5 mg free chlorine/l nutrient solution for 60 or 30 min ensured virus inactivation and did not cause phytotoxicity. The yield of tomato plants grown in KCIO-treated nutrient solution was even significantly higher than that of control plants. PepMV-infected source plants solely bore unmarketable tomatoes showing discoloration. By inhibiting the dispersal of PepMV and the infection of test plants, the amount of unmarketable tomato fruits was reduced rigorously in treated variants.     

Water-use efficiency of wheat-based rotation systems in a Mediterranean environment

Crop production in Mediterranean-type environments is invariably limited by low and erratic rainfall (200-600 mm year⁻¹), and thus soil moisture, and by high evapotranspiration resulting from high temperature. Consequently, a major research challenge is to devise cropping systems that maximize water-use efficiency (WUE). In a long-term trial in northern Syria (1986-1998) we compared the effects of seven wheat-based rotations on soil water dynamics and WUE in both the wheat and non-wheat phase. The cropping systems were durum wheat (Triticum turgidum L.) in rotation with fallow, watermelon (Citrullus vulgaris), lentil (Lens culinaris), chickpea (Cicer arietinum), vetch (Vicia sativa), medic pasture (Medicago spp.), and wheat. Seasonal recharge/discharge were identified using the neutron probe. Depth of wetting varied with seasonal rainfall (233-503 mm). Based on crop yields, WUE was calculated for each cropping option in relation to the durum wheat crop.The greatest limitation to growth was the supply of water and not the soil moisture storage potential. Wheat grain yield was dictated by the extent to which the alternative crops in the rotation dried out the soil profile, in addition to seasonal rainfall and its distribution. Chickpea and medic extracted as much water as continuous wheat. Wheat after these crops was solely dependent on current seasonal rainfall, but fallow, lentil, watermelon, and vetch did not deplete soil moisture to the same extent, leaving some residual soil moisture for the succeeding wheat crop. This difference in soil water resulted in a significant difference in wheat yield and hence WUE, which decreased in the following crop rotation sequence: fallow, medic, lentil, chickpea, and continuous wheat. However, on the system basis, the wheat/lentil or wheat/vetch systems were most efficient at using rainfall, producing 27% more grain than the wheat/fallow, while the wheat/chickpea system was as efficient as wheat/fallow system, with continuous wheat being least efficient. With N added to the cereal phase, system WUE of the system increased, being least for continuous wheat and greatest for wheat/lentil. Wheat-legume rotation systems with additional N input in the wheat phase not only can maintain sustainable production system, but also are more efficient in utilizing limited rainfall.     

Leaching requirement for salinity control. II. Oat,tomato, and cauliflower

Leaching requirement, defined as the minimum leaching fraction that maintains full crop production, was determined in field plots at the U.S. Salinity Laboratory for three crops; oat, tomato, and cauliflower. Six replicated leaching-fraction treatments were pulse-irrigated daily with water having an electrical conductivity of 2.1 dS/m. All three crops were grown in rotation during 1977 and 1978 with a third tomato crop in 1979.The leaching requirement (L_r) was 0.10 for oat grain, 0.21 for tomato fruit, and 0.17 for cauliflower heads. For oat forage, the L_r was more than 0.17. These values agree closely with those predicted by a leaching-requirement model based on an exponential crop water-uptake pattern. Evapotranspiration during each crop's growing season coincident with the leaching requirement was 390, 850, and 230 mm for oat, tomato, and cauliflower, respectively.     

The economics of low pressure drip irrigation and hand watering for vegetable production in the Sahel

Low pressure drip irrigation is being promoted in Sub Saharan Africa as an alternative to traditional methods of small scale irrigation of vegetables. The African Market Garden (AMG) is a horticultural production system for smallholders based on low-pressure drip irrigation combined with an improved crop management package. The agronomic and economic performance of the AMG is compared to two gardens irrigated manually with watering cans. One of these gardens is managed according to the same improved crop management package as in the AMG, this treatment is called Improved Management (IM). The other garden is managed according to common practices of vegetable producers in the area, this treatment is called the Farmer Practice (FP). Crop productivity, labor and water use were monitored for two vegetable species (okra and eggplants). The experiment was performed on-station in Niger on three adjacent 500 m² plots in a sandy acid soil. It was found that improved crop management practices greatly enhance crop productivity over traditional methods at comparable production costs. The AMG gave higher crop yields and higher returns to investment than the treatments irrigated with watering cans. Labor accounts for up to 45% of the production cost in vegetable gardens irrigated by hand, where 80% of the producer time is spent on irrigation. The total labor requirement for the drip irrigated AMG was on average 1.1 man hours per day against 4.7 man hours per day for the Farmers Practice on a 500 m² garden. Returns on labor are at least double for the AMG against the other treatments. The returns on land from eggplant were found to be US$ 1.7, 0.8 and 0.1 per m² for the AMG, IM and FP respectively. The returns on water for the cultivation of eggplant are around US$ 2 per m³ in the AMG, against US$ 0.1 in the Farmers Practice. This experiment showed the strong positive impact of drip irrigation and improved crop management practices on profits at minimal environmental costs, indicating that transformation of existing practices poses a considerable potential towards sustainable agricultural development.     

Modeling nitrogen cycling in tomato–safflower and tomato–wheat rotations

The use of crop models to simulate the nitrogen (N) cycle in crop rotations is of major interest because of the complexity of processes that simultaneously interact. We studied the performance of the Erosion Productivity Impact Calculator (EPIC) model in simulating the N cycle in two different rotations under irrigation: tomato (Lycopersicon esculentum Mill.)–safflower (Carthamus tinctorius L.) and tomato–wheat (Triticum aestivum L.). Processing tomatoes were grown on raised beds and furrow irrigated in 1994 in the Sacramento Valley of California, USA. Safflower and wheat were grown in 1995 and 1994–95, respectively, after the previous tomato crop. A data set from safflower grown on different plots in 1994 was used to calibrate the model for this crop. The model accurately predicted the yield, biomass and N uptake of the crops in the rotation. Soil inorganic N was also accurately simulated in the two rotations. The model predicted important amounts of N leached during the winter period of 1994–95 due to the heavy rainfall. The model was used to explore the influence of rotation type (tomato–safflower or tomato–wheat) and irrigation type (fixed amounts and dates or flexible automatic irrigation). Simulation results of the two rotations during 10 years (1986–95) predicted average losses by leaching higher than 200 kg N ha⁻¹ for each rotation period, irrespective of the rotation type. Losses were more important during the fall–winter and increased as rainfall increased above a threshold rainfall of 300 mm. The flexible automatic irrigation resulted in lower N leached during the tomato crop season. Simulation results indicated that a fallow period during the fall–winter following processing tomatoes should be avoided because of the high risk of N leaching losses. The introduction in the rotation of a deep-rooted crop, such as safflower, grown with low irrigation, drastically reduced the risk of N leaching during the following fall–winter period, without substantial yield reductions.     

A method for exploring sustainable development options at farm scale: a case study for vegetable farms in South Uruguay

The methodology presented in this paper aims at analysing whether there is room for improvement of vegetable farmers’ income in Canelón Grande (Uruguay), while reducing soil erosion and improving physical and biological soil fertility, and to gain insight in the influence of farmers’ resource availability on the opportunities for sustainable development. The (generic) approach we developed to support re-design of farming systems in this region is unique in dealing with complex temporal interactions in crop rotations and spatial heterogeneity on farms in one integrated method, while revealing trade-off between economic and environmental objectives. Rather than an arbitrary sub-set, all feasible crop rotations were generated, using a tool named ROTAT. The crop rotations were combined with a range of production techniques according to pre-defined design criteria to create a wide variety of alternative production activities at the field scale. We used process-based simulation models supplemented with empirical data and expert knowledge to quantify inputs and outputs of production activities. We developed a mixed integer linear programming model (MILP), named Farm Images, to allocate production activities to a farm with land units differing in soil quality, while maximising or minimising socio-economic and environmental objectives, subject to constraints at the farm level. Production activities comprised current practices as well as activities new to the area. We used Farm Images to design farm systems for seven existing farms in Canelón Grande with different resource availability. The farm systems designed by the model had higher family income than current systems for six of the seven farms studied. The estimated average soil erosion per ha decreased by a factor of 2–4 in the farm systems proposed compared to the current systems, while the rate of change of soil organic matter increased from negative in the current systems to +130 to +280 kg ha⁻¹ yr⁻¹ in the proposed farm systems. The degree to which the objectives could be achieved was strongly affected by farm resource endowment, i.e., particularly by the fraction of the area irrigated, soil quality and labour availability per ha. The study suggests that decreasing the area of vegetable crops by introducing long crop rotations with pastures and green manure during the inter-crop periods and integrating beef cattle production into the farm systems would often be a better strategy than the actual farmers’ practice.     

Constraints to farmers’ adoption of direct-seeding mulch-based cropping systems: A farm scale modeling approach applied to the mountainous slopes of Vietnam

Substantial initiatives are under way in the tropical world to develop and promote direct-seeding mulch-based cropping systems (DMC) in order to reduce soil erosion and improve crop nutrient and water balances. DMC have been adopted by large-scale mechanized farmers, especially in America and Australia, but seldom by resource-poor farmers in the developing world. This study was conducted in Vietnam with the aim of evaluating the feasibility of farmers’ implementing DMC in a mountainous area. The method involved simulation of rational households maximizing their income subject to food security constraints and availability of resources. It generated insight into why farmers of a small region were reluctant to adopt DMC due to the extra labor and input required to implement these techniques during the first years, which hampers their economic performance. In another region, under different biophysical and economic environmental conditions, the study showed that DMC were more likely to be adopted provided that possible constraints at the community level are overcome. The method also allowed us to discuss the types of technical improvements that would make DMC more attractive to farmers. For most farm types, labor required by mulch establishment would have to be reduced by more than 30%. This would mean spreading much less biomass than the 7 t ha⁻¹ currently necessary, compromising the weed-control function of mulch. This would be technically feasible only by using herbicides but this would not be economically sound since it would increase cash requirements. The study showed that subsidies of 50 to more than 200 USD ha⁻¹ were necessary to enable the conversion of all conventionally managed sloping land into DMC in the simulations. These amounts are high relatively to gross margins (250-750 USD ha⁻¹) under conventional management.     

The agronomic and economic benefits of fertilizer and mulch use in highland banana systems in Uganda

Banana is the most important food crop in Uganda. However, there has been a decline in productivity, attributed to declining soil fertility, drought, pests and diseases and crop management factors. This study aimed to explore the possibility of increasing yields through the use of fertilizer and mulch, and to evaluate the benefits of these inputs across the major banana producing regions in Uganda. This study was carried out in 179 smallholder plots in Central, South, Southwest and East Uganda in 2006/7. Half of the plots were ‘demonstration plots’ of an agricultural development project, while the other half were neighboring farmer plots that acted as ‘control’. Demonstration plots received mineral fertilizer (100% of plots), averaging 71 N, 8 P, 32 K kg ha⁻¹ yr⁻¹ and external mulch from grass and crop residues (64% of plots), whereas control plots received no mineral fertilizer and little external mulch (26% of plots). Demonstration plots had significantly (P ? 0.05) higher yields than control plot in Central, South and Southwest, but average yield increases varied from 4.8 t ha⁻¹ yr⁻¹ (Southwest) to 8.0 (Central), and 10.0 (South). Average weevil corm damage (3%) and nematode-induced root necrosis (7%) was low and similar for both plot types, so yield increases could only be explained by the use of fertilizer and mulch. The highest demonstration plot yield increases were observed where fertilizer addressed key nutrient deficiencies identified using the compositional nutrient diagnosis approach. Farm gate bunch prices declined from 0.17 (Central Uganda) to 0.07 USD kg⁻¹ (Southwest Uganda). Consequently, average marginal rate of return (MRR) of fertilizer and mulch use ranged from 0.1 (Southwest) to 5.8 (Central). The technologies were likely to be acceptable to farmers (MRR ? 1.00) up to 160 km away from the capital. Fertilizer use is likely to be acceptable in all regions (MRR = 0.7-9.4) if local fertilizer prices of 2006/7 (average USD 0.56 kg⁻¹ of fertilizer) declined by 50%. Doubling of fertilizer prices is likely to make fertilizer use unacceptable beyond 100 km away from the capital. The study concludes that there is scope for increased input use in banana systems in Uganda, but that regional variations in crop response, input/output prices, and price fluctuations have to be taken into account.     

Water use and distribution profile under pulse and oilseed crops in semiarid northern high latitude areas

Oilseed and pulse crops have been increasingly used to replace conventional summer fallow and diversify cropping systems in northern high latitude areas. The knowledge of water use (WU) and its distribution profile in the soil is essential for optimizing cropping systems aimed at improving water use efficiency (WUE). This study characterized water use and distribution profile for pulse and oilseed crops compared to spring wheat (Triticum aestivum L.) in a semiarid environment. Three oilseeds [canola (Brassica napus L.), mustard (Brassica juncea L.) and flax (Linum usitatissimum L.)], three pulses [chickpea (Cicer arietinum L.), dry pea (Pisum sativum L.) and lentil (Lens culinaris Medik.)], and spring wheat were seeded in removable 100 cm deep × 15 cm diameter lysimeters placed in an Aridic Haploboroll soil, in southwest Saskatchewan in 2006 and 2007. Crops were studied under rainfed and irrigated conditions where lysimeters were removed and sampled for plant biomass and WU at various soil depths. Wheat yields were greater than pulse crop yields which were greater than oilseed yields, and WUE averaged 4.08 kg ha⁻¹ mm⁻¹ for pulse crops, 3.64 kg ha⁻¹ mm⁻¹ for oilseeds, and ranged between 5.5 and 7.0 kg ha⁻¹ mm⁻¹ for wheat. Wheat used water faster than pulse and oilseed crops with crop growth. Pulse crops extracted water mostly from the upper 60 cm soil depths, and left more water unused in the profile at maturity compared to oilseeds or wheat. Among the three pulses, lentil used the least amount of water and appeared to have a shallower rooting depth than chickpea and dry pea. Soil WU and distribution profile under canola and mustard were generally similar; both using more water than flax. Differences in WU and distribution profile were similar for crops grown under rainfall and irrigation conditions. A deep rooting crop grown after pulses may receive more benefits from water conservation in the soil profile than when grown after oilseed or wheat. Alternating pulse crops with oilseeds or wheat in a well-planned crop sequence may improve WUE for the entire cropping systems in semiarid environments.