Integrated soil fertility, residue and tillage management for improved soil quality and maize (Zea mays, L.) production in urban agriculture in Harare and Chitungwiza

Crop production has been affected by poor soil fertility and persistant droughts in urban agriculture (UA) in Zimbabwe. This gave rise to the use of livestock manure and organic municipal wastes as basal fertilizers despite their nutrient relesease patterns and health risks associated with their use being largely unknown. This study was carried out to determine the interactive effects of soil fertility, tillage and residue management on soil quality and maize yield under UA farming conditions. Additionally, nutrient mineralization patterns of sewage sludge (SS), cattle manure (CM), pig manure (PG) and poultry manure (PM) and their potential use as basal fertilizers in maize production were determined. Mineralization patterns of organic soil fertility amendments were determined in a 56-day incubation experiment. Maize biomass production, nutrient- and heavy metal (Cd, Cu, Ni and Zn) uptake were determined in a glasshouse pot experiment. Mineral fertilizer (N:P2O5:K2O = 7:14:7), PG, PM, SS and CM were applied at 40 kg N ha-1. After harvesting, a second maize crop was grown without adding fertility amendments. Each time, aboveground biomass was harvested at 4 weeks after emergence. A 2-year field experiment was also carried out in sandy (Chitungwiza) and red clay soils (Harare) to determine short term effects of integrated soil fertility, residue and tillage management on soil quality, maize nutrient uptake and yield. Treatment combinations that included mineral fertilizer, CM or PG + mineral N, 0 or 5 t ha-1 maize stover mulching and reduced (RT) or conventional tillage (CT) were imposed on sandy and red clay soils. Soil fertility amendments were applied at 0 and 120 kg N ha-1. After two cropping seasons, soil samples were taken from the top 30 cm depth profile for determination of selected soil chemical and physical properties. Results showed significant (p PM>CM>SS and PM≈PG>CM>SS for nitrogen (N) and phosphorus (P). In the glasshouse, maize grown in PM and PG amended soil significantly (p CM + mineral N > sole mineral fertilizer > no fertilizer and PG + mineral N ≈ CM + mineral N ≈ sole mineral fertilizer > no fertilizer, respectively in red clay soils. In sandy soils, both maize grain and stover yields iii followed the order; CM + mineral N > sole mineral fertilizer > no fertilizer. Manure + mineral N, maize stover mulching and RT significantly improved soil chemical and physical properties which ultimately improved maize nutrient uptake and yields. However, when the different soil quality parameters were classified, they remained low to medium. It was concluded that CM, PM and PG can substitute mineral fertilizers as basal fertilizers and that, nickel toxicity is likely when SS is used as a soil fertility amendment in maize production. It was also concluded that manure + mineral N, maize stover mulching and RT improved soil quality and ultimately maize nutrient uptake and yield in UA. It was however, recommended that urban farmers should lime their soils to reduce soil acidity. Long term effects of integrated soil fertility, residue management and tillage are recommended under urban farmer conditions since the practice has shown potential in improving soil quality and maize yield in the short term.,1. RUFORUM (grant no. RU/2009/GRG03) 2. FAR