Determination of critical limit of zinc in soil and plant for predicting response of rice to zinc application in calcareous soils

Summary

The DTPA-extractable Zn in 23 calcareous soils ranged from 0.34 to 3.42 ppm and the total Zn in rice leaves of control pots ranged from 15 to 50 ppm. The soil available Zn was negatively correlated with pH (r=−0.41^*) and positively correlated with organic carbon (r=0.71^**)_and rice tissue Zn concentration (r=0.98^**). The Bray's per cent yield ranged from 29.12 to 126.36 and was positively correlated with available Zn (r=0.93^**) and plant tissue Zn (r=0.91^**). The critical Zn concentration in soil and plant below which plant response to Zn application to the soil may be expected, was 0.78 and 19 ppm respectively. In all the soils testing below 0.78 ppm Zn plants responded to Zn application and the per cent mean response at 5 and 10 ppm added Zn levels was 101.21 and 111.38 respectively. A negative response to applied Zn was recorded in soils of the high Zn group where the per cent mean response at 5 and 10 ppm added Zn was −14.90 and −33.78 respectively.