The contribution of economic analysis in developing promising research agendas: a maize nitrogen x phosphorus trial in Zimbabwe

Abstract

Maize accounts for 70% of Zimbabwe's cereal growing area. Its productivity, particularly in the communal areas, is limited by both soil and moisture constraints. Most soils in communal areas are coarse-textured sands derived from granite. They are inherently deficient in nitrogen and phosphorus (Grant 1981; Mashiringwani 1983), and have a poor water retention capacity. The majority of these areas are situated in marginal rainfall zones and do not have irrigation facilities, making the application of large quantities of fertilizer risky and uneconomical. A maize fertilizer x plant population on-farm trial conducted by the Agronomy Institute at 19 sites showed that applying more than 50% of the recommended fertilizer--in most cases 350 kg Compound Z 8:14:7/ha and 400 kg ammonium nitrate/ha-was uneconomical (Whingwiri 8t af. 1987; Mataruka 8t af. 1987). However, maize response to nitrogen and phosphorus separately could not be assessed by using compound fertilizers. To establish economically optimum levels for both nitrogen and phosphorus, researchers should use trials with straight fertilizers. This paper discusses results from two seasons of an on-farm trial being conducted by the Agronomy Institute to determine the effects of nitrogen x phosphorous on maize.