ABSTRACT
A multilocation field experiment was conducted on major agricultural soils with different degrees of past erosion in three ecoregions in Tanzania to assess the effect of topsoil depth (TSD) and soil management on grain and stover yield of maize (Zea mays). Soil management treatments were farmyard manure, N and P fertilizers, tie-ridging and farmer’s practice. Experiments were conducted on eight soils in humid, sub-humid and semi-arid ecoregions. There were two soils in humid (Kirima Boro and Xero Helena), two in sub-humid (Mlingano-1 and 2), and four in semi-arid ecoregions (Misufini 1-3 and Mindų). Compared to least and slightly eroded soil classes, maize grain and stover yields declined with increasing severity of erosion at six out of the eight study sites. Productivity decline on severely eroded soils ranged from 8 and 7% for grain and stover yields, respectively at Mlingano 1 to 50% and 16% for grain and stover yields respectively at Misufini 1. Earleaf N concentration decreased with decreasing TSD from 1.94% on slightly eroded soil class to 1.91% on moderately eroded soil class in Kirima Boro soil. Maize grain and stover yields increased significantly with farm yard manure (FYM) application at all sites. Applications of N and P fertilizers were effective for Kilimanjaro sites only. Grain and stover yields increased for more than 150% for both maize and cowpeas at both sites in Kilimanjaro while average increase in crop yields for all sites in Morogoro and Tanga ecoregions ranged from 50 to 100%. Both FYM and fertilizer application treatments had significant effects on earleaf N and P concentrations. Earleaf nitrogen increased by 0.15 and 0.91% at Mlingano 1 and Kirima Boro sites respectively, while earleaf P content increased by 0.03% at Mlingano 1. In comparison with the farmer’s practice, the combined effect of FYM and N and P fertilizers was associated with maize grain yield increase by 1.7 mg/ha or equivalent to 63% yield increase across all sites.
