, Volume 12, Issue 1, pp 21-36

The movement into soil of P from superphosphate grains and its availability to plants

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access

Abstract

The movement of P applied as grains of triple superphosphate into two soils (laterite and podzol) of differing P sorption capacities was studied in a laboratory experiment. The availability of this P for plant growth was evaluated by measuring the P desorption characteristics of the fertilized soil and also through a plant growth experiment. Four weeks after fertilizer application to the soil 45% and 72% of the fertilizer P had dissolved for the laterite and podzol, respectively. For both soils all the added P was retained within 80 mm of the fertilizer grain and was considered to occur in the soil in three discrete zones. These zones consist of: (1) the residual grain and a small adjacent zone of soil where most P occurs as insoluble fertilizer compounds and possibly as compounds precipitated from fertilizer solution (2) an inner region where both precipitates and P adsorbed on to the soil at about the maximum adsorption value are present and (3) an outer region where all the added P is adsorbed on to the soil at levels less than the maximum adsorption value.

The desorption of fertilizer P from soil in 0.01M CaCl2 solution at different solution:soil ratios as a function of total soil P followed a relationship of the type Y = aXb where Y is desorbed P and X is adsorbed P. For both soils the values of exponent (b) decreased and tended to unity as the solution:soil ratio increased. A much higher proportion of total P (1.5–3 fold) was desorbed from the podzol as compared to the laterite.

The results of the greenhouse trial showed that P from soil reacted at three P concentrations corresponding to the three discrete zones surrounding fertilizer grains was equally available. This result was obtained for two successive wheat crops for both the soils. When the P fertilized soil was banded it was much more effective (about 3 to 5 times for the laterite and 2 to 3 times for the podzol) than when mixed through the soil.