Assessing effect of time, temperature, moisture and labile P content on phosphate availability in rhizosphere soil of tomato by resin disc technique

摘要

Resin disc has been devised using circular plastic ring, nylon net of 100 mesh and Amberlite IRA 410 resin saturated with hydroxyl ion in diffusion study to assess the effect of time, temperature, moisture and labile-P content on phosphate diffusion.Three different soils were impregnated with solutions of varying labile P content (0.067,0.389 and 0.712 mmol/l) up to 100% and 50% of water holding capacities of the soils. The diffusion assembly was covered with plastic sheets and tied with rubber bandand left in the incubator for desired period of time (48-192h), at two different temperatures 27±1deg C and 37 +- 1 deg C. Resin extracted phosphate was estimated using 0.5 N NaOH as extractant. The phyto-availability of phosphate was correlated by inserting disc in the rhizosphere of tomato cv. Sel-7 crop for a specific time (from 4h to 21 days) by measuring the concentration and diffusion coefficient value and expressed in terms of resin adsorbed quantity (RAQ) with an index COD. The index value, ppm (cm~2s~(-1))~(1/2) was highest in alluvial (Typic Ustochrept) soil (12.2) followed by red and latterite (Ultic Paleustalf) soil (10.6) and black cotton (Calcic Chromusterts) soil (8.9). An increase in index values with increase in temperature and moisture content was observed. Time of contact up to 192 h, do not influence significantly to phyto-availability index of phosphate. The COD value was found to be highest at high 0.712 mmol/l labile-P content with a mean of 15.98 and lowest (3.089) at a low 0.067 mmol/l labile-P content. The total phosphate uptake by tomato plant (wet digestion of plant biomass) was highly correlated (r=0.88) to RAQ as compared to Olsen's extractable (0.5 M NaHCO_3 at pH-8.5) available phosphate in rhizosphere soil of tomatocrop (r=0.43) indicating superiority of resin technique for in-situ management of phosphorus in rhizosphere soil.