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ThesisItem Open Access Feasibility of phosphogypsum as an ameliorant for soil acidity in laterite soil(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 2003) Jeena Mathew, KAU; Manorama Thampatti K C, K CAn investigation was carried out at College of Agriculture. Vellayani, to study the feasibility of using phosphogypsum as an ameliorant for correcting soil acidity in laterite soil with cowpea as the test crop. The experiment comprises of an incubation study and a micro plot field experiment. The incubat{on study was carried out to understand the kinetics of dissolution of phosphogypsum and the nutrient release pattern in laterite soils after its application with the following seven treatments T I (absolute control) T2 (Lime @ full LR), T3 (PG @ full LR) T4 (Lime @ half LR), r, (PG @ half LR) T6 (Lime and PG each @ half LR) T7 (Lime as per POP). The study was conducted for a period of 60 days and the chemical parameters were analysed at an interval of 12 days as per standard procedures. The results revealed the enhanced solubility of phosphogypsum which was evident from the higher EC values in the treatments with phosphogypsum through out the study period. Most of the plant available nutrients were solubilised by the 24 th day of incubation. A reduction in exchangeable acidity was noticed by the application of phosphogypsum after a peri,od of 24 days, which is mainly due to reduction in exchangeable aluminium. But this was not efficient as lime in decreasing the exchangeable H+ and hence the pH, remained unaltered. The micro plot field experiment was laid in RBD with a main crop and a residue crop of cowpea var. Kanakamoni. The treatments include TI (POP), T2 (Lime @ full LR), T 3 (PG @ full LR), T 4 (Lime @ half LR), T s (PG @ half LR), T 6 (Lime and PG each @ half LR), T 7 (Lime and PG each @ 14 LR) and T 8 (absolute control). Fertilizers and amendments were applied on the basis of soil test data except in T I where, they were applied on the basis of POP of Kerala Agricultural University. In the residue crop, the amendments were not added and was taken immediately after the main crop. The available nutrients in soil like, P, Ca and S were increased by the application of phosphogypsum. However, considerable leaching was noticed in the case of Mg and K. The growth characteristics of cowpea were improved by the application of phosphogypsum. The highest grain yield was recorded with phosphogypsum applied at full LR and was on par with the combination treatment which received the amendments at one fourth LR. But considering the cost factor treatment with phosphogypsum at full LR is the best. Its B: C ratio was also the highest among other treatments. The yield attributes were also improved by the treatment with phosphogypsum at full LR. The concentration and uptake of N, P, K, Ca, and S in bhusa were favourably influenced by the application of phosphogypsum either at full LR or at halfLR. The residual effect of phosphogypsum was visualized in the crop, taken after the main crop. The application of phosphogypsum increased the organic carbon content, P, and S. The leaching of calcium, Mg and K beyond the root zone was much pronounced in the residue crop. The yield attributes of cowpea were also positively related with phosphogypsum treatment. But by the time of residue crop, the bhusa yield was more for lime treated plots'. The concentration of N, Ca and Mg were more in lime treated plots, but the uptake of nutrients was more for treatment with phosphogypsum. This also emphasizes the mobility and downward leaching property of phosphogypsum. The micronutrient content and uptake were also influenced by the application of phosphogypsum. Phosphogypsum is hence highly beneficial in increasing the yield and yield attributes of cowpea, by mitigating the adverse effects of soil acidity, such as aluminium toxicity, which in effect is the major reason for acidity in laterite soils. Further, utilization of an industrial by product, which otherwise remain unutilized is also facilitated.ThesisItem Open Access Soil test crop response studies on ginger in laterite soils of Kerala(Department of Soil Science and Agricultural Chemistry, College of Horticulture,Vellanikkara, 2001) Jayalakshmi, M; KAU; Hassan M ATo establish soil test based balanced fertilizer prescription for ginger variety Maran in laterite soils of Kerala, an investigation was undertaken at the College of Horticulture, Vellanikkara. The field study consisted of fertility gradient experiment and STCR experiment. The fertility gradient experiment was conducted during March-April 2000 in the farm attached ,to the College. The desired gradient in soil fertility was created in "<; - .t one and the same field by applying graded doses of N, P and K fertilizers and raising fodder maize var. Co. I. The STCR experiment was conducted in the same field during May-Nov 2000 using the test crop, ginger variety Maran. The treatments consisted of fractional factorial combinations of four levels of N (0, 50, 100 and 200 kg ha-I), three levels of P (0,37.5, 75kg P205 ha-I) and five levels of K (0, 37.5, 75, 150 and 300kg K20 ha-I) along with three levels of farmyard manure (0, 15 and 30 t / ha) fitted in a response surface desi~n. Using multiple regression model, the fertilizer adjustment equation for N at varying soil test values for available N for maximum rhizome yield (t ha-I) of ginger in laterite soil was derived as FN = 153 - O.28SN where FN is fertilizer N (kg hal) and SN is soil available N (kg ha-l ). At varying soil test values for organic carbon % (OC) and Phosphorous kg / ha the above equations become FN = 312.94 - 518.4 OC and FP = 79.8 - O.94SP for maximum rhizome yield. The behaviour of fertilizer K was found to produce responses other than 'normal' and hence optimization could not be done for fertilizer K for maximum rhizome tuber yield at varying soil test values. The nutrient requirements of ginger variety Maran were estimated to be 2.1, 0.3, S.6kg N, P20S and K20 respectively to produce one kg of rhizome. In the laterite soil, the efficiencies of contribution of nutrients from the soil for ginger were calculated as 10.1,6.9 and 44% N, P20S and K20 respectively. The fertilizer efficiencies were worked out as 27.3, 10.9 and S3.2% N, P20S and K20 respectively. The efficiencies of contribution of nutrients from farmyard manure were calculated as 30, 7 and 60% N, P20S and K20 respectively. From the above basic data, fertilizer prescription equations for specific yield targets of ginger var. Maran in the laterite soil were derived as given below. Without FYM FN =7.8T - 0.37 SN FP =2 .. 8T - 0.64 SP FK = 10.6T - 0.833 K With FYM FN = 7.8T - 0.37SN - 1.11 ON FP = 2.8T - 0.64 SP - 0.7 OP FK = 10.6T - 0.835 SK - 1.13 OK. Where, FN, FP, FK - Fertilizer N, P20S, and K20 respectively in Kglha. T - Target of fresh rhizome yield in t/ha. SN, SP, SK - Soil available N, P and K in kg/ha respectively. ON,OPOK - quantities of N, P and K supplied through organic manure in kg/ha. Based on the fertilizer prescription equations ready reckoners were developed for different yield targets. The study has revealed the superiority of fertilizer application over the semi quantitative approach followed in the soil testing laboratories and the generalized package of practices recommendation followed in the state for the crop. The fertilizer dose can be adjusted based or. the specific objective and available resources of the farmer. To know the influence of native elements on yield soil and plant samples were analyzed for micronutrient contents. In soil Ca, Mg and Mn showed positive correlations and Zn, Fe showed negative correlations with yield. In plant leaf magnesium and rhizome manganese showed positive correlation and rhizome iron showed negative correlation. Further path analysis was carried out to know the nutrient interactions.
