Mulching is important in protecting the surface structure and reducing erosion of poorly structured degraded soils. The high intensity short duration erosive rain storms experienced at the onset of the wet cropping season in Zimbabwe makes soil cover especially important. Conservation Agriculture (CA), comprising minimal soil movement, surface mulch and crop rotation, is being researched and promoted to increase land and labour productivity while enhancing the natural resource base dedicated to agriculture. Maintaining soil cover under CA systems also contributes to soil biota biomass build-up. Given competing uses of crop residues on the farm, knowledge of mulch losses through decomposition is important in maintaining and managing the mulch over the winter and spring seasons to maintain sufficient soil cover at the onset of the rainy season. Coarse-meshed polyester litter bags were used to study the rate of maize litter loss from the soil surface. The aim of the experiment was to assess the rate of fauna-driven mulch decomposition on CA and conventionally ploughed plots. A total of 256 litter bags, mesh size 5 mm, were used to measure loss of litter mass during winter and spring in one on-station trial (Henderson Research Station) and four on-farm sites (two each from Shamva and Zimuto). The sites represented agro-ecological zones II and IV of Zimbabwe, some with heavy clay and others with sandy soils. At Henderson litter bags were applied on the soil surface of four treatments with different levels of soil movement: conventionally ploughed (CP), direct seeded (DS), manually-dug basins (BA) and manual sowing into rip lines (MR). The on-farm sites included conventional ploughing, ripper (RR) and direct seeder treatments were used. A negative exponential decay model y = yoe-kt described surface litter loss data adequately. At Henderson, daily k rates were in the order BA>DS=CP>MR whereas at Chinyanga and Kajengo (Shamva) and Zhinya (Zimuto) DS>SS>CP. The influence of soil mulch on the microclimate explained the variation in decomposition between CA treatments and conventional ploughing. The measurements suggest low decompositions rates of surface applied maize litter during winter and spring. Losses can be managed by mulch supplementation to achieve adequate soil cover at the start of the rainy season. Further, the results show that decomposition during winter allows carryover of mulch on CA plots into the next season

Conservation Agriculture Program

English

Lucia Segura

INT2939