Optimizing Maize Planting Date, Plant Population, and Fertilizer Application Rates for Lesotho Subsistence Farmers

Due to perpetually low yields, smallholder farmers throughout Southern Africa plow increasingly large plots of land in an attempt to increase their household food security. However, extensive agriculture further depresses yields because expensive inputs are spread over a larger area, provides little soil cover, and results in high soil erosion rates. To address these challenges, farmers in the Kingdom of Lesotho are beginning to adopt conservation agriculture (CA) systems. Under CA and conventional tillage systems the optimum plant population, planting date, and fertilizer rates are unknown. The effects of field preparation, planting date, weed control strategies, plant populations, and nitrogen (N), phosphorus (P), and potassium (K) fertilizer application rates on maize yields at Maphutseng and Roma, Lesotho were investigated. During the 2009-2010 growing season two factorial experiments were conducted at Maphutseng: the first to determine the effects of tillage type, weed control methods, and planting date; the second to determine the effects of plant population density, N fertilizer application rate, and P fertilizer application rate on maize yield. During the 2010-2011 growing season, the effects of plant population, N, P, and K fertilizer application rates were studied using separate studies conducted on no-till fields at both study locations.

The planting date, tillage type, and weed control study found that planting in October attained the highest yields in both the tilled (7.32 Mg/ha) and no-till (10.25 Mg/ha) plots, and that in the tilled plots the glyphosate and hand hoeing weed control treatment resulted in the highest yields (7.79 Mg/ha). The plant population density study found that the 1 seeds/basin and 126 basins/plot treatment attained the highest yield (11.57 Mg/ha). The fertilizer application rate study concluded that there was no significant yield gain above 50 kg N/ha (8.9 Mg/ha), 30 kg P₂O₅ [phosphorous pentoxide]/ha (2.16 Mg/ha), and 60 kg K₂O [potassium oxide]/ha (4.01 Mg/ha). These results illustrate that intensifying agriculture through the use of higher fertilizer rates and denser plant populations can result in household food security on less than 0.5 ha of land area, depending on household size.