N Rapid Assessment in Relation to Crop Production in Zimbabwe.
Justice Nyamangara, Univ of Zimbabwe, Dept of Soil Science & Agricultural Engineering, Mount Pleasant Drive, Harare, Zimbabwe
An efficient and almost complete recycling of nutrients will have to characterise our future agriculture in order to prevent environmental degradation, either from excess nutrients causing water and air pollution or inadequate nutrients causing nutrient mining and soil erosion. In Zimbabwe, and most of Sub Saharan Africa (SSA), sustainable crop production is constrained by inadequate nutrients and this has resulted in extensive nutrient mining and soil erosion. A study, based on 1997-98 data, was conducted to assess the major sources of N and opportunities for recycling the N. Beef cattle excreta accounted for most of the organic N (84%) and was equivalent to 63.4 kg ha-1 yr-1 (assuming 2.225 million ha cultivated land), and goats contributed the least amount (<1 kg ha-1 yr-1). Nitrogen from harvested crops averaged 28 kg ha-1yr-1 with maize contributing the largest proportion (10.1 kg ha-1 yr-1). N input from human excreta was 21.3 kg ha-1 yr-1. Input from mineral N fertilizer was very limited (ca. 16 kg ha-1 yr-1). The potential for recycling N exists in animal excreta. Most crop residues are fed to domestic animals. However, recycling of N in human excreta is limited because 80% of the Zimbabwean population resides in rural areas where facilities for nutrient recycling are non-existent.