Exploring the effect of graded nitrogen, phosphorus and potassium (NPK) levels on soybean (Glycine max L.) growth, yield and soil fertility responses

A field experiment was conducted during the kharif seasons of 2023 and 2024 at the Soil Test Crop Response (STCR) farm, Department of Soil Science, Mahatma Phule Krishi Vidyapeeth (MPKV), Rahuri, India, to evaluate the effect of graded nitrogen, phosphorus and potassium (NPK) levels on the growth, yield, nutrient uptake and soil fertility status of soybean (Glycine max L.). The experiment involved 12 treatments comprising the application of NPK in various combinations and a control, arranged in a randomised block design (RBD) with three replications. The soil of the experimental site was silty clay loam in texture, low in available N and P, but very high in available K. Results revealed that application of 50:75:45 N:P2O5:K2O kg ha-1 + 10 t ha-1 farmyard manure (FYM) (T12) significantly improved chlorophyll content at 30 (36.28), 45 (37.89), 60 (40.01) and 90 (37.80) days after sowing (DAS), as well as grain (33.07 q ha-1) and straw yield (41.67 q ha-1) of soybean on a pooled basis. It also enhanced the number of pods plant-1 (88.17), number of seeds plant-1 (184.00) and weight of seeds plant-1 (35.92 g) of soybean on a pooled basis. The T12 recorded the highest N, P and K uptake in the grain and straw of soybean, while improving soil organic carbon (SOC) (0.72 %) and the available nutrient status after the harvest of soybean compared with nutrient omission and unfertilised treatments. In contrast, nutrient omission treatments markedly reduced crop performance and nutrient uptake, indicating the importance of a balanced nutrient supply. The principal component analysis (PCA) clearly demonstrated the differential response of soybean treatments to graded NPK levels. The study concluded that the integrated application of inorganic fertilisers with FYM (50:75:45 N:P2O5:K2O kg ha-1 + 10 t ha-1 FYM) enhances soybean productivity, nutrient use efficiency and soil fertility sustainability.