Short-Term Effects of Soil Fertility, Tillage and Residue Management on Soil Organic Carbon, Aggregate Stability and Water Infiltration on a Sandy Soil in Urban Agriculture, Harare

Manure is a key nutrient resource to urban farmers due to its multiple benefits, especially on inherently infertile sandy soils. Research on cattle manure in sub-Saharan Africa has mainly focused on its role in supplying N required by crops with little attention given to its multiple benefits such as its effects on other soil properties. The objective of this study was to determine short-term integration of soil fertility and water management practices on soil organic carbon (SOC), aggregate stability and water infiltration in urban agriculture (UA). An experiment was carried out on sandy soils fertilized with organic and inorganic fertilizers under conventional (CT) and zero tillage (ZT) systems with (5 t ha-1 ) and without maize stover mulch. Cattle manure (1.26 % N) and Compound D (N:P:K = 7:6.1:5.8) were applied as basal fertilizers and NH4 NO3 was applied at top dressing. Soil organic carbon and aggregate stability significantly (p<0.01) decreased with depth in all treatments. Fertilization and mulching significantly improved SOC and aggregate stability by at least 30% and 7% in surface layersand 41% and 8% in the 5-15 cm depth respectively. However, ZT had the highest SOC and Ima in surface layers than the subsurface layers while CT had a more uniform SOC distribution within the 0-30 cm soil profile and had significantly higher SOC than ZT in the 5-15 cm depth. Steady state infiltration rate varied significantly with tillage and fertilizer at p<0.01 and mulch at p<0.05. Mulching (p<0.05) and ZT (p<0.01) significantly improved steady state infiltration rates by at least 14% and 39% respectively. Only the fertilizer x tillage interaction significantly (p<0.01) affected steady state infiltration rates. The steady sate infiltration rate was highest in ZT plots which received cattle manure and inorganic fertilizer (39.6 cmh-1 ). Conventionally tilled plots had significantly (p<0.01) lower steady state infiltration rates compared to ZTplots except for the unfertilized plots. It was concluded that integration of organic and inorganic fertilizers, mulching using crop residues and ZT over two seasons improved soil health through increase in SOC, aggregate stability and steady state infiltration rate.