Effects of cattle manure on selected soil physical properties of smallholder farms on two soils of Murewa, Zimbabwe

The effects of cattle manure and inorganic N-fertilizer application on soil organic carbon (SOC), bulk density, macro-aggregate stability and aggregate protected carbon were determined on clay and sandy soils of the Murewa smallholder farming area, Zimbabwe. Maize was grown in four fields termed homefields (HFs) and outfields (OFs) because of spatial variability induced by management practices and with the following fertility treatments: control (no fertility amelioration), 5, 15 and 25 t/ha cattle manure + 100 kg/ha N applied annually for seven consecutive years. The addition of cattle manure resulted in significant (P 0.05) different on the clay soils. A significant and positive linear relationship (r2 = 0.85) was found between SOC and macro-aggregate stability, while an r2 value of 0.82 was obtained between SOC and aggregate protected carbon on the clay soils. However, no regressions were performed on data from the sandy soils because of the lack of significant changes in soil physical properties. Application of cattle manure and inorganic N-fertilizer significantly increased (P < 0.05) maize grain yield on both soil types. Results show that inorganic N-fertilizer combined with cattle manure at 5–15 t/ha per yr is necessary to increase maize yields and SOC on sandy soils in Murewa, while at least 15 t/ha per yr cattle manure is required on the clay soils to improve physical properties in addition to maize yields and SOC