Phosphorus and zinc nutritional problems and their remedial measures in calcareous soils grown to corn

Results showed that Bolinao sandy loam which contained montmorillonite, vermiculite and illite had an initial P content of 0 and 1.6 ppm Zn while Faraon clay which contained primarily montmorillonite and kaolinite had 37 ppm P and 2.67 ppm Zn. The application of high rates of either P or Zn had depressive effects on the soil test values and tissue concentrations of the other element. Phosphorus deficiency symptoms were observed in treatments that received 0-120 kg P205/2 x 10 to the sixth power. Deficiency symptoms were corrected when P application were increased to 180-300 kg P205/2 x 10 to the sixth power. On the other hand, application of Zn at 90 kg/ 2 x 10 to the sixth power maintained soluble zinc above the critical level of 1.5 ppm. In Bolinao sandy loam, dry matter yield of corn was significantly affected by the application of P. The highest yield increase was 111 percent, obtained from 300 kg P2O5 and 30 kg Zn. With this treatment available P was 26.0 ppm while Zn soil test value was 0.52 ppm. Phosphorus and zinc concentrations were 0.17 percent and 45.0 ppm, respectively. Zinc fertilization had much smaller effect on the relative dry matter yield. The highest increase of 23 percent was obtained at 90 kg Zn over all P levels. With this treatment, available Zn was 1.8 ppm, which was higher than the critical level of 1.5 ppm. Available P however, was 9.7 ppm overall P levels. The concentrations of P and Zn in the tissues were 0.16 percent, and 60.8 ppm, respectively. The dry matter yield in Faraon clay was slightly affected by P and Zn application. Similarly, a high rate of P205 (300 kg) was needed to induce a significant yield increment over the control. Dry matter yield increment was also greatest at 23 percent in 300 kg P205 and 60 kg Zn. Corresponding zinc test values were 0.8 ppm in soil and 54.0 ppm in tissue. On the other hand, phosphorus test values were 48.6 ppm in the soil and 0.20 percent in the tissue