USO PECUARIO INTENSIVO, PROPIEDADES QUÍMICAS DEL SUELO Y SOSTENIBILIDAD EN LOS ANDES AL NORTE DEL ECUADOR

The study was carried out in 35 farms in the Ecuadorian Sierra, Tupigachi parish, Pichincha, at 3000 masl under Semi-humid Mesothermal climate. The grassland, of kikuyo (Pennisetum clandestinum), ryegrass (Lolium perenne, Lolium multiflorum) and clover (Trifolium repens), grows on Mollisols of long term agricultural use (pre-Inca), derived from volcanic ash, without mineral fertilization, depending on the recycling of nutrients from animal excretion. The impact of intensive livestock between 2008-2017 on the chemical properties of the soil was analyzed, repeating soil analyzes in both years following standard laboratory procedures, and based on the diagnosis, recommendations are made to improve the agricultural system. The pH from 6.1 to 6.5), K and Na (250%) and S (420%) increased significantly (p≤0.01), while Ca, Mg and micronutrients did not present significant differences in the evaluated period, and MOS, N, P and S contents were kept very low for local edaphoclimatic conditions. Total N and extractable P reserves in the soil was calculated at 5.2 Mg.ha^-1 and 8,3 kg.ha^1-, respectively, equivalent to about 11 times the estimated annual contribution of 413,2N and10% of the contribution of 83,7P kg.ha^1- in excreta + urine. To improve the sustainability of the production system, and reducing risks of environmental impact, we suggest establishing a silvopastoral system (SSP), semi-stabulate the cattle and compost the excreta, increase the cultivation of oats, maiz and forage barley to optimize the diet of the cattle and apply biofertilizers to the pasture based on mycorrhizal fungi and nitrifying bacteria.