Fertilizers help Zimbabwean farmers to increase crop yields

Ncube studied smallholder farms in the southwest of Zimbabwe. She mapped resource flows and carried out field experiments. The Zimbabwean semi-arid regions are dry and farmers face food shortages every season. Yet not water management but the supply of fertilizer, especially nitrogen, was found to be the most important factor in increasing cereal yields. Zimbabwean farmers in the semi-arid regions hardly use fertilizer and manure at present. Chemical fertilizer is expensive and manure is not readily available. Moreover, little is known about the correct use of these nutrient sources in dry climates.

Nitrogen

The main issue when cultivating soil is the nitrogen balance. Continually cultivating the same crop disrupts this balance. With field experiments, Ncube demonstrated that a little bit of basal manure, and nitrogen fertilizer added as top dressing improved the maize yield by about one-hundred percent in a good rainy season and by up to fifty percent in drier seasons.

Crop rotation

Crop rotation is another option that could provide a lot of benefit according to Ncube. This is the cultivation of different crops alternately in successive years. Leguminous crops, for example, fix nitrogen. This nitrogen remains in the soil and is taken up during the next season by sorghum, a type of grain that grows well in dry areas. Ncube proved that grain legumes can be grown successfully under the semi-arid conditions in Zimbabwe. These legumes were able to leave enough nitrogen in the ground, which doubled yields of sorghum the following season compared to sorghum-sorghum rotations. With a simulation model Ncube was once again able to show that nitrogen availability was more important in the rotation. These types of treatments often have a negative impact on water availability, yet here nitrogen was shown to be more important.

Bongani Ncube’s research was funded by NWO.