SOIL SCIENCE AND AGRICULTURAL CHEMISTRY

Abstract

Potassium, an essential plant nutrient, has major role in crop production including legumes crops like soybean. Reviews in the literature on potassium application to soybean suggest that soybean needs potassium, absorb it and response to potash fertilizers in terms of yield and monetary returns. However, the Mahatma Phule Krishi Vidyapeeth, Rahuri has completely ignored potassium in the recommendation of general fertilizer prescription to soybean. Looking to the present status average productivity (10.58 q ha-1) of Maharashtra State and its comparison with the national (10.64 q ha-1) and international average productivity of soybean, there is scope to increase the state productivity of soybean with a application of potassium to soybean. It is, therefore, the present experiment was planed to ascertain the optimum dose of potassium to soybean in Inceptisol for enhancing productivity of soybean in the state and to make concrete suggestions to the University for reconsideration of recommendation of potash and their inclusion in general fertilizer prescription dose to soybean. With the above facts and views, a present field investigation entitled, “Response of potassium on yield and quality of soybean in Inceptisol ” was conducted at Post Graduate Institute, Research Farm of Mahatma Phule Krishi Vidyapeeth, Rahuri during kharif season, 2012-13 so as to find out the optimum dose of potassium for maximum economic yield of soybean. The field experiment was laid out in a randomized block design with the seven treatments and four replications. The applied treatments were : T1 (Absolute control); T2 (RD: 50:75:00 N:P2O5: K2O kg ha-1); T3 (RD + 20 kg K2O ha-1); T4 (RD + 30 kg K2O ha-1); T5 (RD + 40 kg K2O ha-1); T6 (RD + 50 kg K2O ha-1) and T7 (RD + 60 kg K2O ha-1). The experimental soil was slightly alkaline in a reaction (pH 8.01), low in electrical conductivity ( 0.41 dSm-1 ) and medium in calcium carbonate content (6.5%), low in available nitrogen (155 kg ha-1), phosphorus (12.80 kg ha-1) and medium in potassium (232 kg ha-1) content. The results obtained in the present investigation revealed that the growth parameters viz., and plant height, number of branches per plant, chlorophyll content, nodule count were significantly influenced by various levels of potassium application. The significant highest height (47.65 cm), number of branches (12.25), chlorophyll content (53.71), effective nodules (24.16), number of pods per plants (41), test weight(14.94 g) were observed in treatment of application of RD+60 kg K2O ha-1(T7). The highest grain (31.62 q ha-1), straw (40.80 q ha-1), protein (10.36 q ha-1) and oil (6.38 q ha-1) yield were recorded under the same treatment of RD + 60 kg K2O ha-1 (T7). The grain and straw yields were at par with treatments T6 (RD + 50 kg K2O ha-1) and T5 (RD + 40 kg K2O ha-1) while the protein and oil yield were at par with treatments T6, T5 and T4. The total uptake of nitrogen, phosphorus and potassium were significantly influenced by the potassium application and maximum NPK uptake was observed in the treatment T7 (RD+60 kg K2O ha-1) treatment and it was at par with treatments T6 and T5. Increase levels of potash resulted in to increase in soil fertility status after harvest of soybean with respect to all available nutrients. However, treatments plots of available N and P decreased over the initial status from all. The highest soybean yield and quality were recorded in treatment T7 however, the B:C ratio of soybean cultivation under treatments of various levels of potash was found maximum (2.47) in the treatment T6 followed by treatments T5 (2.46) and T7 (2.46). The maximum monetary returns per Rs invested on potash fertilizer (Rs 6.93) was recorded by application RD + 40 kg K2O ha-1 to soybean. Thus, from the above results of present study it can be concluded that application of 40 kg K2O ha-1 along with recommended 50 kg N and 75 kg P2O5 is found most optimum dose of potash to soybean to harvest maximum economical yield and quality of soybean in Inceptisol