Initial and residual effects of organic and inorganic amendments on soil properties in a potato-based cropping system in the Bolivian Andean Highlands.

The objective of this study was to determine the effects of applications of organic and inorganic soil amendments on initial and residual soil chemical, physical and biological properties that may affect both shortand long-term soil fertility in a potato (Solanum tuberosum L.)-based cropping system of indigenous rural communities in the Bolivian Andean Highlands (Altiplano). Field experiments were conducted in four representative low and high elevation communities in the semi-arid Central Andean Region of Bolivia from 2006 to 2009. Treatments included a control, and applications of sheep and cow manure, a commercial household/urban compost product, a commercial biofertilizer soil amendment, urea and diammonium phosphate and combinations of these different treatments. Soil samples were taken from all the sites prior to application of treatments and planting of potatoes as well as during the growing season and prior to planting of a Research Article American Journal of Experimental Agriculture, 2(4): 641-666, 2012 642 subsequent crop of quinoa (Chenopodium quinoa, Willd). Soil pH, soil total organic C, and total N increased due to application of organic fertilizers with or without inorganic fertilizers. Soil inorganic N and Bray-1 P were increased by inorganic fertilizers alone or when combined with organic fertilizers. The residual effect of most of the analyzed soil nutrients was detected in the subsequent growing season. In addition, lower soil bulk density was observed after organic fertilizers were applied with or without inorganic fertilizers and this residual effect persisted for the quinoa crop. In a controlled laboratory incubation experiment, soil potentially mineralizable C and N increased as organic fertilizers application rates rose from 0 to 30 Mg ha. These results highlight the importance of a balanced soil fertilization program in this region with use of optimum rates of both inorganic and organic soil amendments to increase shortand long-term soil fertility.