RESUMO
Soil degradation in semi-arid West Africa can be reversed through an intensified application of organic matter, especially on coarse soils. Woody perennials have been promoted in the region to secure organic matter sources and improve soil productive capacity, yet the mechanisms by which perennials provide benefits to soils and crops remain poorly understood, and no effective, generalizable agronomic recommendations exist. Here, we reviewed the effects of trees and shrubs on soil properties and on crop yields in semi-arid West Africa (< 1000 mm year-1). Specific objectives of this meta-analysis were to (i) describe and (ii) quantify the effects of the presence of woody perennials and of ramial wood amendments on crop productivity and soil characteristics, and (iii) identify general recommendations on the integration of perennials with crops. An iterative keyword search was conducted to gather relevant literature. The search string consisted of four parts: source, practice, responses, and countries of interest. In total, 26 references on agroforestry parklands and 21 on woody amendments were included in the meta-database (314 entries, 155 for parklands, and 159 for ramial wood). We show that (1) the presence of shrubs and trees on agricultural fields had an overall positive but variable effect on soil total C (i.e. + 20 to 75%); (2) millet and sorghum yields were often higher in the presence of shrubs (- 25 to + 120%); (3) more variability was observed in the presence of trees (- 100 to + 200%); and (4) the use of shrub- and tree-based ramial wood resulted in equal or higher cereal yields as compared to the control (- 30 to + 100%). Upscaling the use of biodiversity-driven processes in farming systems of West Africa may provide benefits to overall ecosystems, but species' choice and trade-offs perceived at the farm level, including labour management and low ramial wood availability, should be addressed through future research.
RESUMO
Proper N fertilizer and irrigation management can reduce nitrate leaching while maintaining crop yield, which is critical to enhance the sustainability of vegetable production on soils with poor water and nutrient-holding capacities. This study evaluated different methods to measure nitrate leaching in mulched drip-irrigated zucchini, pepper, and tomato production systems. Fertigation rates were 145 and 217 kg N ha(-1) for zucchini; 192 and 288 kg N ha(-1) for pepper; and 208 and 312 kg N ha(-1) for tomato. Irrigation was either applied at a fixed daily rate or based on threshold values of soil moisture sensors placed in production beds. Ceramic suction cup lysimeters, subsurface drainage lysimeters and soil cores were used to access the interactive effects of N rate and irrigation management on N leaching. Irrigation treatments and N rate interaction effects on N leaching were significant for all crops. Applying N rates in excess of standard recommendations increased N leaching by 64, 59, and 32%, respectively, for pepper, tomato, and zucchini crops. Independent of the irrigation treatment or nitrogen rate, N leaching values measured from the ceramic cup lysimeter-based N leaching values were lower than the values from the drainage lysimeter and soil coring methods. However, overall nitrate concentration patterns were similar for all methods when the nitrate concentration and leached volume were relatively low.
