Robert B. Zougmoré

Runoff and sorghum performance as affected by the spacing of stone lines in the semiarid Sahelian zone.

Crop yields are primarily water-limited in dryland production systems in semiarid regions. This study was conducted in a catchment located in the ‘‘plateau central’’ of Burkina Faso to assess the impact of the space between stone lines on runoff and crop performance. The experimental design consisted of four plots in which stone lines were installed. The spacing between the lines was 100 m in the first plot, 50 m in the second, 33 m in the third, and 25 m in the last plot. The soil was a Ferric lixisol and the slope, which is characteristic of the area, was about 1‐3%. Subplots placed at regular and fixed distances from the lines were used to monitor soil water content and crop yield. Runoff from all plots was measured using a water discharge recorder. It was found that 31% of rainfall was lost through runoff in plots without stone lines. The efficiency of stone lines in checking runoff and in improving soil water storage increased with reduced stone line spacing (runoff was reduced by an average of 5% on plots where the space between the lines was 33 m, but was reduced by 23% when the stone line spacing was 25 m). Soil water content decreased with increasing distance from the stone line. Sorghum (Sorghum bicolor (L.) Moench) performance was greatly affected by stone line and plant straw and grain yield were doubled in plots with stone lines compared with those of plots without stone lines. At an area of about 6 m from the stone lines (upslope), where organomineral sediments were collected, sorghum grain yields were 60% greater than that obtained at 19 m from stone lines. The stone line technique seems to be a sound option to mitigate water stress during dry spells. # 2000 Published by Elsevier Science B.V.

Decomposition of organic amendment and nutrient release under the zai technique in the Sahel

In the West African Sahel, farmers use the zai technique to reclaim degraded cropland. Although the nutrients released by the decomposition of the amendments are central to the success of the technique, little is known regarding the impact of the zai pits on the decomposition process and whether the nutrient release is synchronized with plant requirements. The decomposition of millet stalks and cattle manure applied in zai pits or at the soil surface was studied in Niger using litterbags, under controlled irrigation on-station in 1999 and on-farm in 1999 and 2000 at two locations (Damari and Kakassi) with contrasting soils. In addition, a satellite trial was conducted in 2000 on-farm at the same locations to study the relative contribution of termites to manure decomposition. Only at Damari did termite presence enhance manure decomposition, by a factor three for surface placement compared to the zai pits. At Damari, zai pits enhanced the decomposition when termite activity was suppressed. Whereas manure decomposition proceeded two to three times faster than that of millet stalks at Damari, the type of amendment had no effect on decomposition rate at Kakassi. Nutrient release followed the trend of organic amendment decomposition except for K. When applied prior to the rainy season, nutrient release rate of organic amendments strongly exceeded plant nutrient uptake, which could lead to important leaching losses during the first 4–6xa0weeks after sowing, especially for N and to a lesser extent for K. However, at harvest, total nutrient absorption by plants was generally higher than the total amount released. The results indicate a highly site-specific response of amendment decomposition to zai and the need for a better timing of amendment application to reduce potential leaching losses, possibly through a split application.

Soil nutrient and sediment loss as affected by erosion barriers and nutrient source in semi-arid Burkina Faso

In semi-arid Sahel, soil erosion by water is one major factor accounting for negative nutrient balances in agricultural systems. A field experiment was conducted on a Ferric Lixisol in Burkina Faso to assess the effects of soil and water conservation barriers (stone rows or grass strips of Andropogon gayanus), the sole use of organic (compost) or mineral (urea) source of nitrogen (N), and the combined use of barriers and compost or urea nitrogen on soil nutrient and sediment erosion. The run-off barriers were put along contours. Organic carbon (OC) and nutrients losses through run-off and sediments were monitored during 2001 and 2002. Carbon and nutrient concentrations of generated sediments were very high, of 14–29 g kg−1 OC, 1.0–3.7 g kg−1 N and 0.32–0.71 g kg−1 total P. concentration in run-off water reached 0.023 g L−1 in stone rows treatments compared to only 0.002 g L−1 with treatments without barriers. Annual losses of organic C, N, P, and K were high and greatly dependant on soil loss magnitude. Compared to the control plots, soil losses were reduced on average by 84% during the 2 years with stone rows treatments, while by 71% with grass strips treatments. Compost application reduced soil loss by 75% in plots without barriers and by 89% in plots with stone rows as compared to control plots. With urea application, soil loss was on average 13% lower than in plots with compost. Integrated water and nutrient management can effectively alleviate soil, carbon, and nutrients losses by water erosion, therefore may contribute to intensifying crop production in Sahelian smallholder farming.

Economic benefits of combining soil and water conservation measures with nutrient management in semiarid Burkina Faso

Nutrient limitation is the main cause of per capita decline in crop production in the Sahel, where water shortage also limits an efficient use of available nutrients. Combining soil and water conservation measures with locally available nutrient inputs may optimize crop production and economic benefit in cereal-based farming systems. A study conducted in 2001 and 2002 at Saria, Burkina Faso (annual rainfall 800 mm, PET of 2000 mm yr−1) assessed the combined effects of two types of semi-permeable barriers (stone rows and grass strips of Andropogon gayanus Kunth cv. Bisquamulatus (Hochst.) Hack.) and the application of compost or urea on sorghum performance and economic benefits. The field experiment was carried out on a Ferric Lixisol, 1.5% slope and comprised 9 treatments in which the barriers were put along contours and combined with compost-N or urea-N. Installation of stone rows or grass strips without addition of nutrient inputs was not cost effective, although it induced sorghum yield increase (12–58%) particularly under poor rainfall conditions. Combining compost with stone rows or grass strips significantly increased sorghum yield that induced positive interaction effects (mean added effects of 185 kg ha−1 for stone rows combined with compost-N and 300 kg ha−1 for grass strips combined with compost-N). Economic benefits were substantial (109 480 to 138 180 FCFA ha−1) when compost-N was added to both stone rows and grass strips, whereas limited economic benefits were observed with the application of urea-N (1120 to 22 120 FCFA ha−1). This may provide farmers with capital to invest in soil management and may also contribute to poverty alleviation in sub-Saharan Africa.

Agroecological analysis and economic benefit of organic resources and fertiliser in till and no-till sorghum production after a 6-year fallow in semi-arid West Africa

A field experiment was conducted in Gampela (Burkina Faso) in 2000 and 2001 to assess the impact of organic and mineral sources of nutrients and combinations thereof in optimising crop production in till and no-till systems and to assess the economic benefit of these options. The study showed that under conditions of rainfall deficiency, the use of a single organic resource at an equivalent dose of 40xa0kgxa0Nxa0ha−1 better secured crop yield than the application of an equivalent amount as urea-N, while a combination of organic resources and fertiliser was better in increasing crop yield than the application of the same N amount in the form of urea. In a year of rainfall deficiency, a mix of organic resources and fertiliser in both till and no-till systems increased crop water use efficiency, with the result that the farmer was able to purchase only half of the normal quantity of N fertiliser to obtain a higher yield that he would have done when all of the N was supplied in the form of urea. Under conditions where soil N is deficient, an economic benefit was achieved when urea was combined with easily decomposable organic material (e.g. sheep dung); mixing the urea at a dose of 40xa0kgxa0Nxa0ha−1 with maize straw was not sufficient in alleviating the negative interaction due to the enhanced N immobilisation. The results demonstrate that the use of N fertiliser alone was risky and that a higher yield, with the accompanying economic benefit, was scarcely achieved under the prevailing rainfall conditions. The application of soil and water conservation measures can contribute greatly to increasing the economic benefit of mineral, organic or combined organic and mineral-derived nutrient application under semi-arid conditions.

Effect of stone lines on soil chemical characteristics under continuous sorghum cropping in semiarid Burkina Faso

In the semiarid Sahel, farmers commonly lay stone lines in fields to disperse runoff. This study was conducted in northern Burkina Faso to assess the chemical fertility of soil under a permanent, non-fertilised sorghum crop, which is the main production system in this area, 5 years after laying stone lines. The experimental design consisted of four plots in which stone lines had been laid. The spacing between the lines was 100 m in the first plot, 50 m in the second, 33 m in the third, and 25 m in the fourth. To determine soil chemical characteristics in relation to the stone line spacing patterns studied, soil samples were taken from subplots at regular and fixed distances from the lines at the start of the trial and then 5 years later. Under the continuous non-fertilised sorghum cropping system, the beneficial effect of stone lines on soil fertility was limited. Five years after installing stone lines, soil organic C, total N, available P and Na concentrations and soil pH had decreased. Within the plots, these same variables were higher upslope than downslope of stone lines, probably because of water storage and sediment accumulation in front of the stone lines. In plots where stone lines were relatively close together (<33 m) the decrease in soil fertility was less. It is concluded that in Sahelian zones, stone lines alone are not sufficient to insure the conservation of soil fertility. Combining soil and water conservation techniques with soil fertility management practices are needed to sustain soil productivity.

Benefits of Integrated Soil Fertility and Water Management in Semi-arid West Africa: An Example Study in Burkina Faso

The synergistic effect of soil and water conservation (SWC) measures (stone rows or grass strips) and nutrient inputs (organic or mineral nutrient sources) was studied at Saria station, Burkina Faso. The reduction in runoff was 59% in plots with barriers alone, but reached 67% in plots with barriersxa0+xa0mineral N and 84% in plots with barriersxa0+xa0organic N, as compared with the control plots. Plots with no SWC measure lost huge amounts of soil (3xa0txa0ha−1) and nutrients. Annual losses from eroded sediments and runoff reached 84xa0kgxa0OCxa0ha−1, 16.5xa0kgxa0Nxa0ha−1, 2xa0kgxa0Pxa0ha−1, and 1.5xa0kgxa0K ha−1 in the control plots. The application of compost led to the reduction of total soil loss by 52% in plots without barriers and 79% in plots with stone rows as compared to the losses in control plots. SWC measures without N input did not significantly increase sorghum yield. Application of compost or manure in combination with SWC measures increased sorghum grain yield by about 142% compared to a 65% increase due to mineral fertilizers. Yields increase did not cover annual costs of single SWC measures while application of single compost or urea was cost effective. The combination of SWC measures with application of compost resulted in financial gains of 145,000 to 180,000 FCFA ha−1xa0year−1 under adequate rainfall condition. Without nutrient inputs, SWC measures hardly affected sorghum yields, and without SWC, fertilizer inputs also had little effect. However, combining SWC and nutrient management caused an increase in sorghum yield.