Influence of soil fertility variability and nutrient source on maize productivity and nitrogen use efficiency on smallholder farms in Zimbabwe

Shamie Zingore1

1 International Plant Nutrition Institute, Box 30772, Nairobi, Kenya, 00100,,


Poor soil fertility is a major constraint to crop productivity on smallholder farms in sub-Saharan Africa. This study evaluated the effects of soil type, soil fertility status and nutrient source on maize productivity and partial factor productivity (PFPN) of fertilizer N in north-east Zimbabwe. Four on-farm sites representative of major soil fertility categories in the region were selected for the study: (i) depleted sandy soil (DSS); (ii) sandy soil (SS); (iii) depleted clay soil (DCS); and clay soil (CS). Fertilizer and manure treatments were applied over nine cropping seasons as follows: (i) no fertilizer; (ii) 100 kg N/ha; (iii) 100 kg N/ha + cattle manure (15 t/ha); (iv) 100 kg N/ha + 30 kg P/ha in combination with 20 kg Ca/ha, 5 kg Zn/ha and 10 kg Mn/ha. Initial maize yields were in the order DSS<DCS<SS<CS. Across all trials, maize grain yield response and PFPN values in the sole N-fertilizer (100 kgN/ha) treatment were low, indicating multiple constraints to crop productivity. Yields on the sandy soils were marginally increased with balanced fertilizer application. Across all fields, the highest yields and PFPN after nine seasons were achieved with application on N in combination with manure, indicating the importance of manure in maintaining soil fertility, maize productivity and optimum PFPN levels in smallholder farming systems where crop residues are removed to use as livestock feed.

Benefits, costs and risks of nutrient use in cropping in the high-rainfall zone of southern Australia

Kerry Stott1, Brendan Christy2, Penny Riffkin3, Malcolm McCaskill3

1 Agriculture Victoria, Parkville Centre, Department of Economic Development, Jobs, Transport and Resources, Carlton, Victoria, 3053.

2 Agriculture Victoria, Rutherglen Centre, Department of Economic Development, Jobs, Transport and Resources, Rutherglen, Victoria, 3685.

3 Agriculture Victoria, Hamilton Centre, Department of Economic Development, Jobs, Transport and Resources, Hamilton, Victoria, 3300.


We describe how crop modelling, production economics and Monte Carlo simulation can be used to aid decision-making regarding the profitability and risks of nutrient usage in wheat production in the high-rainfall zone (HRZ) of southern Australia. Given good seasonal conditions, a case-study paddock deficient in P (10 mg/kg soil Colwell P) was shown to have high yield potential, estimated at 9.0 t/ha with profit maximising applications of N (95 kg N/ha) and P (51 kg P/ha). Profit maximising nutrient applications and yields are lower in average seasons and more so in poor seasons. The grower could respond tactically to evolving seasonal conditions by applying N in split applications.  P-fertiliser application is best at or before seeding; however growers still have flexibility when considering the uncertain season ahead thanks to the flat response function at the economic optimum.  The results suggest that the unrealised potential of crops in the HRZ can, in part, be explained by the cost of nutrient inputs and the risks associated with variable seasons.  The analysis optimises one variable input at a time (e.g. N or P, other inputs held constant). The method is being extended to a more realistic analysis that simultaneously examines multi-variable input response processes (such as N and P or S or K) on wheat and canola yields. The purpose of this work is to equip growers and their advisors to confidently assess crop nutrient demands and limitations, predict yield potential and pay-offs associated with high input use in the HRZ environment.