Fertilising techniques and nutrient balances in the agriculture industrialization transition: The case of sugarcane in the Cauca river valley (Colombia), 1943-2010

Population size and per capita food consumption are assumed to be the two greatest drivers of global environmental change. The intensification of agriculture for food and fiber production, and specially, for energy crops, affects ecosystems due to the use of limited soil resources (e.g. nitrogen, phosphorus, potassium and other macronutrients and micronutrients) which are necessary for their functioning, the release of pesticides, and the conversion of natural ecosystems. However, the location and extent of intensive agriculture and its associated ecological impacts within tropical countries is often well unknown. The purpose of this study is to provide an understanding of the fertilisation practices associated to the phase of sugarcane industrialization in an inter-Andean valley in Colombia. Changes in the nitrogen (N), phosphorus (P) and potassium (K) fluxes were calculated over time (1943, 1984, 1998 and 2010) by using the concept of social metabolism. We applied a nutrient balance model, which was especially created for past agroecosystems (historical studies). The N balances were positive and oscillated between 108 and 98kg N ha^-1 year^-1, with a relatively low N use efficiency (about 63% and 42% for 1943 and 2010, respectively). The main inputs were chemical fertilisation and irrigation, and the main outputs of N included harvested N and leaching due to low N use efficiency and high irrigation flows. By 2010, values of atmospheric deposition rose up to 35.6kg N ha^-1 year^-1, mainly because the nitrate concentrations in rain water were very high in comparison to previous decades. The K and P balances were positive and near zero, which represents an adequate management according to local conditions.The positive N balance in the four analysed years suggests that this element has been historically over applied. This has caused not only high production costs, but also, water and atmospheric pollution. The study of fertilisation systems is, therefore, essential to understand agrarian growth and the process of agricultural intensification. Calculations of N, P and K budgets can be helpful for understanding agroecosystem functioning and proposing more sustainable management strategies.