Evaluation of three phosphate fertilizer sources for sweet corn production

Phosphate rocks (PRs) originating from China (CPR) and North Carolina (NCPR), United States of America, were evaluated for their agronomic effectiveness and compared with the standard water soluble P fertilizer source used for annual crop production, triple superphosphate (TSP), on a Serdang series soil (typic Paleudult) using the 32P dilution technique. Sweet corn seedlings in pot studies grown for 1 month have shown that NCPR was just as good as TSP, while CPR was inferior as a P fertilizer source for the corn seedlings. A field study was then conducted to evaluate the effect of these three P fertilizer sources on fresh cob yields of sweet corn. Four rates (25, 50, 100 and 200 kg P/ha) and one control were used for each P fertilizer source. Two sweet corn crops were grown over a period of 1 year, with the same P rates used for the second crop. TSP yielded the highest grade A cobs, which can attain the highest market price. All three sources were suitable for producing grade A and B cobs. The ear leaf P concentration in TSP treated plants averaged 0.34% and was not significantly different from the NCPR treated plants (0.32%). The CPR treated plants had only 0.28% P in the ear leaf. However, in the second crop no differences in the ear leaf P concentration were observed from the three P fertilizer sources tested. The highest gross income for both crops was obtained from TSP treatment at 200 kg P/ha. Using this rate, an isotope aided experiment was conducted with three corn crops grown consecutively over a period of 18 months. It was found that TSP was the most efficient P source, followed by NCPR and CPR. The P rates at 200 kg/ha can support sweet corn production for up to three consecutive crops. (author). 10 refs, 1 fig., 8 tabs