Maize and sorghum yields under tied ridges of fertilised sandy soils in semi-arid south-east lowveld of Zimbabwe

Growing maize and sorghum in furrows of 1.0 m and 1.5 m wide tied ridges with either 100 kg or 200 kg compound D ha-1(8:14:7 NPK, basal fertilizer) + 50 kg N ha-1 top dressing were compared to the traditional farmers' practice of growing these crops on flat land without fertilizer. The crops were grown under rainfed conditions on sandy soils of Matibi 1 and Chivi communal areas in semi-arid agro-ecological regions IV and V in the south-east lowveld of Zimbabwe, from 1987/88 to 1989/90. Grain yield of maize in 1.0 m wide tied ridges was increased significantly by 22 to 85% over sowing on flat land and sorghum grain yield was increased by 18%. Application of inorganic fertilizer resulted in significant yield increases of 35 to 115% in maize grain, 59 to 200% in sorghum grain, 27 to 96% in maize stover and 63 to 161% in sorghum stover, compared to no fertilizer application. The benefits of growing crops in tied ridges and the incremental gross margins in Z$ha-1 of fertilizer application were more associated with monthly rainfall distribution than with the total summer rainfall.La culture de maos et de sorgho en sillons espaces de 1.0 et 1.5 m avec des billons lies et une fertilisation de 100 kg ou 200 kg par ha du compose D (8:14:7 NPK, engrais de fond) avec 50 kg N/ha d'engrais de couverture a ete comparee avec la culture traditionelle des fermiers i.e une culture sur terre plate sans engrais. La culture etait etablie de 1987/1988 jusque 1989/1990 dans de conditions de precipitation naturelle et sur des sols sableux de Matibil et des aires de la commune Chivi dans des regions agro-ecologiques semi arides IV et V dans les plaines du sud est de Zimbabwe. Le rendement des grains de maos sur des billons de 1,0 m augmentait significativement de 22 jusque 85rapport la culture sur terre plate, alors que le rendement de grains de sorgho augmentait de 18une augmentation significative du rendement de grains de maos de 35 jusque 115de 27 jusque 96rapport e la culture sans engrais. L'avantage des cultures en billons lies et les marges beneficaires en Z$ pour l'engrais etaient plutot associes a la distribution de la precipitation mensuelle qu'a la precipitation totale en saison pluvieuse

Year-round poultry litter decomposition and N, P, K and Ca release

Poultry litter is an important nutrient source in agriculture, although little information is available regarding its decomposition rate and nutrient release. To evaluate these processes, poultry litter (PL) was applied to the soil to supply 100, 200 and 300 kg ha-1 N contained in 4,953, 9,907 and 14,860 kg ha-1 PL, respectively. The litter bag technique was used to monitor the process of decomposition and nutrient release from the litter. These bags were left on the soil surface and collected periodically (after 15, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330, and 365 days). The dry matter (DM) loss was highest (35 %) after the first 30 days of field incubation. The highest nutrient release occurred in the first 60 days on the field, when 40, 34, 91, and 39 %, respectively, of N, P, K, and Ca of the initial PL dry matter (4,860 kg ha-1) was already released to the soil. In absolute terms, these percentages represent 40, 23, 134, and 69 kg ha-1 of N, P, K, and Ca and these values doubled and tripled as the PL fertilization rates increased to 9,907 and 14,860 kg ha-1, respectively. After one year of field incubation, the residual contents in the litter were 27, 15, 18 and 30 % of the initial DM , and N, P and Ca, respectively. The release rate of K was the fastest and 91 % of the K had been released from the PL after 30 days of field incubation