M.Sc.

Supply of nutrients in a balanced manner is one of the most important factors determining crop yield. Sometimes due to interaction between nutrients in soil, the applied nutrients may not be available for plant use. When the supply of one nutrient element affects the absorption and utilization of other nutrient element, the elements are said to be in interaction and interactions may be negative or positive. In Kerala, black cotton soils are seen in Chittur taluk of Palakkad district occupying an area of approximately 2000 ha. These soils are sandy clay loam, dark, calcareous, neutral to alkaline (pH 7.0 to 8.5), high in clay content and CEC. These soils are deficient in phosphorus (P) and sulphur (S). Finding the interaction between P and S in these soils will help to understand the factors determining the availability of these nutrients to crops.
The present study was carried out at Nellimed in Chittur taluk of Palakkad district during 2017-19. The objectives of the study were to find out the interaction of P and S in black cotton soils of Palakkad and to assess the treatment level of phosphorus and sulphur for maximizing the yield. The study consisted of a field experiment with groundnut variety, K-6 in black cotton soils of Chittur, Palakkad followed by analysis of soil, plant and pod samples taken from the experimental field. Soil samples were collected from different locations of Chittur and analyzed for available P and S. Field experiment was carried out in the field deficient in both P and S.
Experiment was laid out in factorial RBD with 17 treatments and 3 replications. Soil test based recommendation was taken as T1 and treatment combinations were made with four levels of P and four levels of S. The levels of N and K applications are kept same (based on POP recommendations of KAU) for all treatments, except for the first treatment where soil test based recommendation was given. P0 - 0 kg ha-1, P1 - 60 kg ha-1, P2 -75 kg ha-1 and P3 -90 kg ha-1 were the four levels of P and S0 - 0 kg ha-1, S1 - 10 kg ha-1, S2 - 20 kg ha-1 and S3 - 30 kg ha-1 were the four levels of sulphur.
Physical characteristics of soil viz., texture and bulk density were analyzed before experiment and chemical characteristics viz., pH, EC, organic carbon, N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu and B were analyzed before and after the experiment. Growth parameters such as plant height and number of leaves per plant were recorded at flowering, pegging, pod formation and




harvesting stages and yield parameters like number of pods per plant and yield were recorded at harvesting stage. The nutrient contents in plant were analyzed and uptake was computed in critical growth stages. The nutrient content, protein and oil content in pod were analyzed.
Soil nutrient status, plant nutrient content and uptake of nutrients were influenced by main effect and interaction effect of P and S. Application of P at 90 kg ha-1 and S at 30 kg ha-1 resulted in highest plant height and number of leaves per plant. Application of P at 90 kg ha-1 and S at 30 kg ha-1 resulted in highest number of pods per plant and yield. Highest protein and oil content were recorded by application of P at 90 kg ha-1 and S at 30 kg ha-1.
Application of increased dose of P increased the availability of S. Application of P reduced the availability of Fe, Mn and Zn in soil due to the formation of insoluble compounds like Fe-P, Mn-P and Zn-P. Application of P enhanced the availability of N. The K content in soil was reduced with increased dose of P application. Ca content in soil was reduced due to P fertilizer application.
Plant nutrient content showed a decreasing trend from flowering to harvest stage. Application of P and S enhanced content of P in plant and pod. Content of N, P, Mg and S was increased with increased levels of P and content of Fe, Mn, Zn, Cu and B was reduced with increased dose of P. The uptake of nutrients followed an increasing trend from flowering to harvest due to increased dry matter production. Uptake of S, Fe, Zn and Cu by kernel is higher compared to plant.
P and S showed a positive interaction and P at 90 kg ha-1 and S at 30 kg ha-1 was found to be the best treatment in black cotton soils of Palakkad for high yield, protein and oil content in groundnut.