Soil test crop response studies in cluster bean (Cyamopsis tetragonoloba L.) in lateritic soils of Kerala

Abstract

Cluster bean, commonly known as guar, is a legume crop cultivated as a vegetable, green manure and forage crop. India is the leading producer of cluster bean in the world and accounts for around 80 per cent of global production. The generalised application of fertilizers by farmers result in under or over fertilization, lowering production and profitability while also polluting the environment. So the emphasis on soil test based balanced fertilizer recommendation has become more pertinent in the current scenario of high fertilizer costs and yield maximisation programmes. Hence, the investigation entitled “Soil test crop response studies in cluster bean (Cyamopsis tetragonoloba L.) in lateritic soils of Kerala” was undertaken. The study was conducted at College of Agriculture, Vellanikkara in lateritic soils (Ultisol) in the STCR field during 2020-2021 with the objective of developing soil test based fertilizer prescription equation for cluster bean using inorganic fertilizers alone and with the combined use of organic manures. A fertility gradient experiment was conducted to create soil fertility gradient in the field by applying graded doses of N, P and K fertilizers and raising fodder maize var. CO1. After the development of fertility gradient, the main STCR experiment was conducted in the same field with the test crop, cluster bean var. Pusa naubahar. The treatment structure consisted of four levels of nitrogen (0, 10, 20 and 40 kg ha-1 ), four levels of phosphorous (0, 30, 60 and 120 kg ha-1 ) and four levels of potassium (0, 40, 80 and 120 kg ha-1 ) along with three levels of FYM (0, 15 and 25 t ha-1 ). The basic parameters such as nutrient requirement (NR) and contributions of nutrients from soil (CS), fertilizer (CF) and FYM (COM) were computed from the field experimental data. The nutrient requirements (NR) for cluster bean were worked out as 0.68, 0.05 and 0.22 kg N, P2O5 and K2O to produce one quintal yield. The contributions from soil (CS) were estimated as 9.84, 2.29 and 1.99 per cent of N, P2O5 and K2O respectively. The contributions from fertilizer (CF) were calculated as 90.90, 3.29 and 10.82 per cent and that from FYM (COM) were 7.17, 1.92 and 2.96 per cent for N, P2O5 and K2O respectively. From the above basic data, fertilizer prescription equation for specific yield targets of cluster bean in the lateritic soils were derived as follows, NPK alone: FN = 0.74*T - 0.11*SN FP2O5 = 1.47*T – 1.59*SP FK2O = 2.05*T- 0.22*SK NPK + FYM (IPNS) FN = 0.74*T - 0.11*SN – 0.08*ON FP2O5 = 1.47*T – 1.59*SP – 1.34*OP FK2O = 2.05*T - 0.22*SK – 0.33*OK Where, FN, FP2O5 and FK2O = Fertilizer N, P2O5 and K2O in kg ha-1 T = Yield target in q ha-1 SN, SP and SK = STV for available N, P and K in kg ha-1 . ON, OP and OK = Amount of N, P and K supplied through FYM in kg ha-1 . The multiple regression model calibrated with yield as dependent variable and soil test results and inorganic fertilizer doses as independent variables had 62.5 per cent predictability. The yield of cluster bean increased with the application of NPK alone and IPNS viz. NPK plus FYM treatment and the magnitude of increase was higher under IPNS over NPK alone. The study is useful to adjust fertilizer doses based on yield target and available resources of organic manure with the farmers. The equations developed for cluster bean should be tested in places with similar agro climate and soil situations for validation.