Selection of an Extraction Method Suitable for Estimating Potentially Available Phosphorus Under the Organic Production System of New Alluvial Zone of the Lower Gangetic Plain of India

The reliability of the methods used in conventional farming for determining immediately available phosphorus (P) might not be suitable for organic farming, where mineralization of labile organic pools is the prime P source for plant availability. A conventional procedure that involves P extraction downplays the significance of organic pools. This necessitates the development of a suitable soil testing procedure for P availability under organic farming. A field experiment was conducted following a 3-year rotation of scented rice-French bean-okra cultivation with farmyard manure (FYM), vermicompost (VC), mustard oil cake (MOC), and poultry manure (PM) along with their combinations. Chemically fertilized plots were appointed as a check. P was evaluated using four extractants, viz, BEDTA (Basic EDTA/0.5 M NaOH+0.5 M EDTA), K2CO3 (1% potassium carbonate), CA (1% citric acid), and 2-KGA (0.5 M 2-ketogluconic acid). In addition, Olsen (0.5 M NaHCO3) method was used to compare these methods. CA extracted P (CA-P) showed the strongest association with mineralized P (R-2=0.854**), followed by Olsen P (R-2=0.789**). Furthermore, the CA-P demonstrated a significant correlation with P% in pod (r=0.732**), pod yield (r=0.742**), dry matter yield (DMY, r=0.754**), and P uptake (r=0.765**). Likewise, the Olsen method was strongly related to those plant factors (r=0.713**, r=0.634**, r=0.666**, and r=0.693*). Additionally, CA and Olsen methods are significantly related to soil characteristics (pH and organic carbon). However, the principal component analysis demonstrated that the CA was the most reliable. Based on CA method, organic certifying agencies, soil scientists, and laboratory personnel will able to give better advice to the organic farmers on P management.