Zai Pit Soil Fertility Improved with Cattle Manure on Sandy Soil in Southern Africa.

“Zai” refers to a method developed in West Africa for rehabilitating degraded land. Seeds of grain crops are sown into planting pits that, though labor intensive to dig, enable farmers in sub-Saharan Africa to produce food on soils too encrusted to plow. To optimize the zai pit system, an understanding is necessary of soil-related impacts of fertility sources available to smallholder farmers. This two-season study in South Africa focused on cattle manure as the nutrient source for sorghum (Sorghum bicolor) sown in 30-cm wide pits dug 15 cm deep, with hole centers spaced 75 (in-row) X 75 (between-row) cm. Treatments, arranged in a randomized complete block design and replicated four times, included 1) non-amended flat ground, 2) non-amended pits, 3) pits that received 400 g of cattle manure prior to planting sorghum seeds and 4) pits that received 200 g of cattle manure before and another 200 g two months after planting sorghum. In non-amended soil, pits failed to increase soil mineral concentrations in comparison to flat ground. Manure-amended pits had substantially higher macro (nitrate, phosphorus and potassium), secondary (calcium, magnesium and sulfur), and micro (iron, manganese, and zinc) nutrient concentrations than non-treated pits. For instance, at nine weeks after planting the first season, the soil in pits with preplant-applied manure contained 49 mg·kg-1 phosphorus, more than double that (22 mg·kg-1) in non-amended pits. Active carbon (at the end of each season) and nitrogen mineralization (at the end of season 2) were also higher with than without manure. There were no consistent advantages of splitting the manure into two applications. Results showed that soil health and sorghum grain production were improved with cattle manure as the only amendment to zai pits.