SOIL TEST BASED FERTILIZER CALIBRATIONS IN PRESS MUD AMENDED RICE-WHEAT SEQUENCE IN ALLUVIAL SOILS OF INDIAD.K. Benbi and B.S. Sekhon
A field experiment with a range of soil fertility and fertilizer regimes was conducted for two years on an alluvial soil of Punjab state of India to develop fertilizer calibration relationships based on soil test for rice wheat sequence amended with pressmud (PM), a sugarcane industry waste.. The nitrogen (N), phosphorus (P), and potassium (K) nutrient requirements and fractional contribution of these nutrients from soil (CS), fertilizer (CF), and pressmud (CPM) for meeting the nutrient needs of rice and wheat were worked out empirically by using appropriate sets of fertilizer N, P, K and PM combinations. These parameters were used to develop soil test and yield goal based fertilizer calibration linear relationships, which in turn were used to develop quick-reference guides for ascertaining optimum fertilizer doses. These fertilizer recommendations had higher site-specific character than the conventional soil test category based approach which recommended the same dose for a range of soils. The calibration relationships allowed dynamic adjustment for changes in soil test status and organic amendment rates. The ready reckoners suggested that over a wide soil fertility range using the PM @ 5 t ha-1 before transplanting rice for attaining respective yield targets 7.0 t ha-1 and 5.0 t ha-1 of rice and wheat helped cut down fertilizer N, P, and K dose in rice by 66-93%, 9-17%, and 30-40% and in wheat by 0-10%, 12-20%, and 7-13% respectively. These savings not only have the monetary significance but also imply concomitant environmental, food security, and sustainability benefits.
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