Absorption and translocation of 32P by root (wilt) affected coconut palms

Abstract

An investigation entitled “Absorption and translocation of 32P by root (wilt) affected coconut palms” was conducted in the Department of Soil Science and Agricultural Chemistry, College of Horticulture, Vellanikkara. Two separate experiments were conducted in farmers’ fields at Mannarkkad, Chittur, Chavakkad, Kayamkulam and RARS, Pattambi. Three types of palms namely healthy, apparently healthy and diseased palms were identified from three soil types of Kerala (laterite, sandy and black cotton soil), where root (wilt) disease was prevalent. Four morphologically uniform palms of same age were selected from each group of palms and soil samples were collected from two depths; 0-20 cm and 20-40 cm from the basin. Index leaf samples (14th leaf) were also collected from the experimental palms. Soil samples were characterized for different physico-chemical properties and plant samples for N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B, Cl and Na. Absorption and translocation of nutrients in coconut palm were studied using radioactive phosphorus in laterite soil. Before 32P application, in order to make homogeneous soil conditions, soil and plant samples were analysed and soil test based fertilizer combinations including organic manures and micronutrients were applied. Three months after fertilizer application, soil and plant samples were again collected and analysed. Three different methods (cotton pad technique, root feeding and soil injection) were employed for 32P application. The index leaf samples were collected at 24 hours, 15 and 30 days after application and radioassayed. The result of basic characterisation of soil showed that all the physico-chemical properties varied significantly among different soil types. Laterite soil recorded the highest value for available P, K, Fe, Mn, Cu and B. High values of EC, Cl, Na and AEC were obtained for sandy soil. Black cotton soil registered the highest values for pH, organic carbon, Ca, Mg, S, Zn and CEC. Among soils under different palms within same soil type, there was significant variation in the content of Mg, B, Zn and Cu. Among different palms K accumulated more in the foliage of diseased palms, while the concentrations of N, Ca, Mg, Fe, Mn, Zn, Cu and B were more in the foliage of healthy palms, indicating nutritional imbalance in the root (wilt) affected palms. Before application of fertilizer in laterite soil, the contents of nutrients were not homogeneous among soils under different palms. After fertilizer application, the soil became more or less similar with respect to the nutrient content. The contents of N, Ca, Mg, Fe, Mn, Zn and Cu were significantly more in the foliage of healthy palms and K was more in the foliage of diseased palms before fertilization. Even after application of fertilizer same trend was observed. Though there was a slight increase in nutrient status of diseased palms after fertilizer application, the rate of increase was comparatively less with respect to healthy palms. This showed that integrated nutrient management targeting soil application cannot fully manage the root (wilt) disease. In absorption and translocation studies using 32P, it was observed that the absorption of radioactive phosphorus was more for healthy palms compared to diseased palms, after 24 hours, 15 days and 30 days of application. For healthy palms, the count rate was more for root feeding method, while in diseased palms highest count rate was obtained by using cotton pad technique. The count rate in the foliage after 15 days was more when compared to 24 hours after application and it tended to decrease 30 days after application. Nutrient imbalance was one of the major problems noticed in root (wilt) affected palms, so it should be corrected first by proper method of application. Among the different methods tested, cotton pad technique can be a promising technique of delivery of nutrient into root wilt affected palms especially for micro nutrients, which needs less quantity compared to major nutrients.