Horizontal matter fluxes and leaching losses in urban and peri-urban agriculture of Kabul, Afghanistan

Little is known about nutrient fluxes and nutrient-use efficiencies in urban and peri-urban agriculture (UPA) of rapidly expanding cities in developing countries. Therefore, horizontal flows of carbon (C), nitrogen (N), phosphorus (P), and potassium (K) as well as leaching losses of mineral N and P were measured over 2 years in three representative agricultural production systems of Kabul. These comprised 21 gardens and 18 fields dedicated to vegetable farming, cereal farming, and table-grape production (vineyards). Across sites (fields and gardens) biennial inputs averaged 375 kg N ha(-1), 155 kg P ha(-1), 145 kg K ha(-1), and 15 kg C ha(-1) while with harvests 305 kg N ha(-1), 40 kg P ha(-1), 330 kg K ha(-1), and 7 kg C ha(-1) were removed. In vegetable gardens, biennial net balances were 80 kg N ha(-1), 75 kg P ha(-1), 205 kg K ha(-1), and 4 kg C ha(-1), whereas in cereal farming biennial horizontal balances amounted to 155 kg N ha(-1), 20 kg P ha(-1), 355 kg K ha(-1), and 5 kg C ha(-1). In vineyards, corresponding values were 295 kg N ha(-1), 235 kg P ha(-1), 5 kg K ha(-1), and 3 kg C ha(-1). Annual leaching losses in two selected vegetable gardens varied from 70 to 205 kg N ha(-1) and from 5 to 10 kg P ha(-1). Night soil and irrigation water were the major sources among the applied nutrient inputs in all studied farming systems, contributing on average 12% and 25% to total N, 22% and 12% to total P, 41% and 53% to total K, and 79% and 10% to total C, respectively. The results suggest that soils in extensive cereal fields are at risk of N and K depletion and in vegetable gardens of K depletion, while vineyards may be oversupplied with nutrients possibly contributing to groundwater contamination. This merits verification.