A farm-level evaluation of nitrogen and phosphorus fertilizer use and planting density for pearl millet production in Niger

Abstract

Mineral fertilizer use is increasing in West Africa though little information is available on yield response in farmers' fields. Farmers in this region plant at low density (average 5,000 pockets ha⁻¹, 3 plants pocket⁻¹), which can affect fertilizer use efficiency. A study was conducted with 20 farmers in Niger to assess the response of pearl millet [Pennisetum glaucum (L.) R. Br.] to phosphorus and nitrogen fertilizers under farm conditions. In each field, treatments included control, single superphosphate (SSP) only, SSP plus N (point placed near plant), and either SSP or partially acidulated phosphate rock (PAPR) plus N broadcast. N and P were applied at 30 kg N ha⁻¹ and 30 kg P₂O₅ ha⁻¹. Farmers were allowed to plant, weed, etc., as they wished and they planted at densities ranging from 2,000 to 12,000 pockets ha⁻¹. In the absence of fertilizer, increasing density from 2,000 to 7,000 pockets ha⁻¹ increased yield by 400%. A strong interaction was found between fertilizer use and density. Farmers planting at densities less than 3,500 pockets ha⁻¹ had average yields of 317 kg grain ha⁻¹ while those planting at densities higher than 6,500 pockets ha⁻¹ showed average yields of 977 grain ha⁻¹. Though phosphate alone increased yields significantly at all densities, little response to fertilizer N was found at densities below 6,000 pockets ha⁻¹. Significant residual responses in 1987 and 1988 were found to P applied in high-density plots in 1986. Depending on fertilizer and grain prices, analysis showed that fertilizer use must be be combined with high plant density (10,000 pockets ha⁻¹) or no economic benefit from fertilizer use will be realized.