On-farm assessment of physico-chemical properties of an Arenosol under application of mineral fertilizers and their impact on the yield of millet in the Sahelian Zone of Niger

Poor soil fertility is a major threat to crop production and rural livelihoods in Niger where resource-poor farmers mostly rely for their subsistence. Field investigations were carried out over 2012 and 2013 seasons to assess changes in selected soil physico-chemical properties of a Sahelian sandy soil (Arenosol) and their impacts on water and phosphorus bioavailability and yield of pearl millet. Treatments were selected from an on-going 14 year-old on-farm experiment on soil fertility restoration technologies carried out at Karabédji, Niger. The treatments consisted of four rates of fertilizer application viz. (i) control or farmer practice, (ii) Di-ammonium Phosphate (DAP) and (iii) NPK 15-15-15 both at 4 kg P per ha and (iv) NPK 15-15-15 + Tahoua Rock Phosphate (TRP) and two farmer management levels (top and bottom farm types). Results showed no significant (P > 0.05) influence of fertilizer rates and farm type on most of the soil physical properties measured. However, the difference in farm by farm type accounted for most of the variability observed in air capacity, structural stability and plant available water whereas no such effect was observed with macro-porosity. Fertilizer application rates and farm type interacted significantly (P < 0.05) to affect soil structural stability and this was higher in top farm than in bottom farm type. Soil physical quality index (S) varied with depth and the critical values set for sandy soils by Dexter matched the Sahelian Arenosol. Moreover, significant positive relationship (R2 = 0.24, P < 0.05) was found between stability of aggregate under water drop effects and soil physical quality index. Plant available water changed with fertilizer application rates, farm type and depth. Higher plant available water was recorded in the fertilizer-treated soils than the control and on top farm than in the bottom farm by farm type and soil depth. Total N, available phosphorus and exchangeable potassium were generally low and were not influenced iii much by the treatments on both farm types. However, higher exchangeable K values were recorded at the beginning than at the end of the season and higher values were recorded on top farms than on bottom farm types. Farm by farm type influenced the observed variability in exchangeable potassium. Millet leaf P concentration was more influenced by growth stage and farm type whereas variation in leaf K concentration was much more related to fertilizer application rates x growth stages interaction. Millet grain yield was influenced by fertilizer application rates but depended heavily on farm type. Significant positive relationships were obtained between pearl millet yield and stability of aggregate and plant available water thereby showing the importance of soil physical properties in explaining the variability in millet yield. APSIM model simulated grain and biomass yields with relatively good precision using both measured and generated climatic data, even though biomass yield was underestimated under the control treatment in both years. A socio-economic survey conducted confirmed the subsistence nature of the production system in Karabedji to be mainly characterized by low input-output and highly variable soil properties. Moreover, low purchasing power was viewed by most farmers as the main reason for inadequate use of mineral fertilizers. Some opportunities to overcome these constraints were revealed, including membership to farmers’ associations, project interventions, presence of input shops and warrantage warehouses, which improved access to farm inputs and resilience capacity for non-resource endowed farmers. Average quantity of mineral fertilizer used varied from 3 to 14 kg ha-1 among farmers. The results could serve as policy guide for promoting more resource-efficient technologies for small-scale farmers use and required focus towards farmers’ needs.

Source: KNUST