Potato (Solanum tuberosum L.) is an important cash crop in the semi-arid region of Paraíba, Brazil. However, potato productivity is limited by low soil fertility and the limited and highly variable precipitation pattern of this region. Animal manure is the main nutrient source for soil fertility amelioration, but farm manure available is usually not enough to fertilize crops. A cover crop could decrease the demand for animal manure. The characteristics of Crotalaria (Crotalaria juncea L.) recommend it as green manure. A field experiment was conducted from 1996 to 2002 to quantify the effects of annual organic fertilization with animal manure and/or crotalaria on potato productivity and soil nutrient stocks. Treatments consisted of: crotalaria incorporation (C), goat manure, 15 t ha-1 (E), crotalaria incorporation + goat manure, 7.5 t ha-1 (CE), and control plots (T). At the end of the study period, treatment E increased soil total N, total P and available P and K by 73, 45, 221 and 43 %, compared to the control plots. Treatments C and CE increased soil total N by 76 and 63%, but had no effect on other soil nutrients. Overall 5-year averages of crotalaria aboveground accumulation of dry matter, N, P and K were 3550, 69, 6 and 55 kg ha-1, respectively. Average potato productivities for the 5-year period were 15204, 12053, 11085, and 7926 kg ha-1, for treatments CE, C, E and T, respectively. Despite the significant increases in soil nutrient stocks as a result of the annual manure addition of 15 t ha-1, potato productivity was consistently higher in the combination of crotalaria plus 7.5 t ha-1 manure treatment.
Entisol; semi-arid region; Solanum tuberosum; nitrogen; phosphorus; potassium
