STUDIES ON POTASSIUM DYNAMICS IN VEGETABLE GROWING SOILS AND RESPONSE OF BRINJAL – CABBAGE SYSTEM TO APPLIED POTASSIUM

CHAITANYA, T

STUDIES ON POTASSIUM DYNAMICS IN VEGETABLE GROWING SOILS AND RESPONSE OF BRINJAL – CABBAGE SYSTEM TO APPLIED POTASSIUM

Date

2016

Authors

CHAITANYA, T

Publisher

PROFESSOR JAYASHANKAR TELANGANA STATE AGRICULTURAL UNIVERSITY RAJENDRANAGAR, HYDERABAD

Abstract

Potassium (K), the third major and most dynamic nutrient with diverse roles to play in plant metabolism, is required in large amount by crops. In most soils, the total K reserves are generally large, but only a small portion of them are immediately or slowly available to plants. Potassium supply to crop is a complex phenomenon involving relationships among various K fractions in soil. In view of the importance of potassium in vegetable crops an investigation was carried out on “Studies on potassium dynamics in vegetable growing soils and response of brinjal – cabbage system to applied potassium” to study extensively various aspects of K in vegetable growing soils of Ranga Reddy and Mahaboobnagar districts. Surface soils in bulk were collected from thirty two locations of Ranga Reddy and forty locations of Mahaboobnagar district. The soils were analysed for their salient characteristics. In the selected soils different chemical extractants viz., NN NH4OAc, 0.03M NaBPh4, 1.38N H2SO4 and 1N HNO3 were used to assess the suitability of these extractants to know the available K status. The soils were analyzed for different forms of K, K-fixing capacity of soils, step K and constant rate K, Q/I parameters and parameters of saturation extract. A field experiment was also conducted to study the response of brinjal-cabbage cropping system to different levels of potassium. The experiment was conducted in randomized block design with seven treatments, replicated thrice. The treatments were decided considering the recommended dose of brinjal + K-fixing capacity of soils (0, 0.5X, 1X, 2X and 2.5X). The K-fixing capacity (X) of experimental soil was 27 kg K2O ha-1. After harvest of brinjal, cabbage was grown by adding recommended dose of potassium to all treatments except control. The soil samples collected at different growth stages of brinjal and cabbage were analyzed for available nutrients and different forms of K. The plant samples were analyzed for N, P, K contents, nutrient uptake. Fruit and curd yields were recorded and analyzed for ascorbic acid content. The soils of Ranga Reddy and Mahaboobnagar districts were light textured, moderately acidic to alkaline and non saline. The organic carbon content of the soils ranged from 0.3 to 1.3 per cent. The mean available nitrogen content of the soils of Ranga Reddy district was 190 kg ha-1 and Mahaboobnagar district was 202 kg ha-1, indicating that the soils were low in available nitrogen. The available phosphorus content of soils of Ranga Reddy district was in the range of 10 to 64.9 kg P2O5 ha-1 and Mahaboobnagar district were in the range of 10 to 65.1 kg P2O5 ha-1, indicating that the soils were low to high in available phosphorus. The available potassium content of the soils of Ranga Reddy district was in the range of 182.8 to 1856.1 kg K2O ha-1 and Mahaboobnagar district was in the range of 71.2 to 1022.8 kg K2O ha-1. Most of the samples were falling under medium to high available K status. The cation exchange capacity of the of soils of Ranga Reddy district varied from 4.2 to 34.8 cmol (p+) kg-1, with the mean value of 18.0 cmol (p+) kg-1 while that of the soils of Mahaboobnagar ranged from 3.9 to 29.8 cmol (p+) kg-1, with the mean value of 15.5 cmol (p+) kg-1. The different forms of potassium viz., water soluble, exchangeable, non exchangeable and mineral K constituted to 0.07, 0.93, 5.5 and 93.7 per cent of total K, respectively, in soils of Ranga Reddy district. In soils of Mahaboobnagar district these forms of potassium constituted to 0.05, 0.63, 0.68, 5.79 and 93.52 per cent of total K, respectively. The level of extraction of K by different extractants followed the order of 1N HNO3 > 1.38N H2SO4 > NN NH4OAc> 0.03M NaBPh4 >Distilled water. Among all the inorganic K-fractions, boiling 1N HNO3 extracted higher amounts of K ranged from 850 mg kg-1 to 2340 mg kg-1. The potassium fixing capacity of soils varied from 11.2 to 67.2 kg ha-1. Almost all the soils were low in potassium fixing capacity. The constant rate K varied from 0.6 to 1.02 me 100g-1. The step K, which is supposed to be plant utilizable nonexchangeable K varied from 0.24 to 2.58 me 100g-1. The results revealed that the release of non-exchangeable K in general was poor in these soils due to less clay and silt contents. Different parameters of the saturation extract i.e., CRK values varied from 0.067 to 0.378 (me l-1)0.5. BCK values varied from 0.30 to 12.36 (me 100g-1)/ (me l-1)0.5. The values of Kam varied from 0.068 to 1.14 (me 100g-1). USQI factor varied from 0.232 to 1.104 (me 100g-1)0.5 × (me l-1)0.5. The parameters derived from the saturation extract namely Kam, BCK and USQI factor were positively and significantly correlated with all soil properties except sand which was negatively correlated. Exchangeable and nonexchangeable K showed positive and significant correlation with BCK , Kam and USQI factor, indicating that these are important parameters governing the release of K and availability of K to plants. The results on quantity-intensity relationships of the soils of Ranga Reddy and Mahaboobnagar showed that the ARK values ranged from 1.10 to 18.75 (ML-1)1/2 ×10-3. The PBCK values were low in all the soils falling in the range of 0.018 to 0.818 (c mol (p+) kg-1)/ (ML-1)1/2 x 10-3. Since K supplying power of soils belonging to Ranga Reddy and Mahaboobnagar district, as indicated by PBCK values, was found to be low, the soils of the district require judicious and frequent application of potassic fertilizers for better crop production. In field experiment of brinjal – cabbage cropping system, the highest fresh fruit yield of 11.2 t ha-1 (brinjal) and fresh curd yield of 31.5 t ha-1 (cabbage) were recorded in T7 (Rec. dose of K2O + 2.5 X kg K2O ha-1 i.e., 127.5 kg K2O ha-1) and the lowest was recorded at T1 (control, No K). With increase in levels of potassium drymatter yield, nutrient content, uptake and yield was increased in both brinjal and cabbage crops, this could be attributed to enhanced crop growth with increased nutrient translocation and utilization by plants resulting in higher yield. In both the crops the quality parameter ascorbic acid content also increased with increase in the level of K. In Brinjal – cabbage cropping system with increase in potassium levels the net returns increased as the yield was increased. The highest net returns of Rs 150517 per Se Se Se Se e hactare recorded in treatment T7 (Rec. dose of K2O + 2.5 X kg K2O ha-1 i.e., 127.5 kg K2O ha-1) followed by T6 (131084 Rs ha-1) with a benefit cost ratio of 1.72 and 1.50 respectively. All the forms of potassium increased with increase in the level of potassium at harvesting stage of both brinjal and cabbage and the highest values were recorded in T7 (127.5 kg K2O ha-1). The available and 1N HNO3 K status in soil after brinjal - cabbage cropping system was compared with the initial status to know the changes in these forms of K and these forms of K and their contribution to crops. It was observed the available K decreased in all the treatments to an extent of 20 (T1), 14 (T2), 11 (T3), 10 (T4), 4 (T5), 2 (T6) per cent, respectively. Whereas, the available K increased to extent of 7 per cent in T7. Similarly 1N HNO3 extractable K showed a decrease to an extent of 29 (T1), 23 (T2), 20 (T3), 17 (T4), 13 (T5), 11 (T6) and 6 (T7) per cent. As the available potassium was taken up by the crops at early stages, the potassium from fixed form was replenished at later stages, which was indicated by its decrease. Application of K fertilizer @ 127.5 kg K2O ha-1 considering the K fixing capacity helps in maintaining the available K status and also prevents the depletion of non - exchangeable K reserve in soil. Based on the yields, net returns, B:C ratio and maintenance of soil available K-status, T7 treatment found to be the best (127.5 kg K2O ha-1) for brinjal-cabbage cropping system when grown on light textured soils of Ranga Reddy and Mahaboobnagar districts of Telangana state.