The P fertilizer requirements of subterranean clover, and the soil P status, sorption and buffering capacities from two P analyses

Abstract

The phosphorus fertilizer requirement of subterranean clover (Trifolium subterraneum) was determined on a number of soils in field and glasshouse experiments. The solution phosphorus concentration in a 0.01 M CaCl2 extract (SPC0) determined from a phosphorus sorption curve was found to be closely related (R2 = 0.80 to 0.84) to relative yield. The critical SPC required to achieve 90% of relative yield (SPCc) was 0-128 �g P mL-1 in the field and 0.106 �g P mL-1 in the glasshouse experiments. Phosphorus sorbed at an SPC of 0.10 �g P mL- l (Ps0.1 at SPC0.1) was highly correlated with the phosphorus requirement of subterranean clover in both the field and glasshouse, accounting for 89% and 73% respectively of the variation in phosphorus requirement. A modified two-point sorption curve was found to give a good estimate of phosphorus sorbed at both SPC0.1 (Ps0.1) and SPC0.3(Ps0.3), and greatly increased the number of soil samples that can be processed, compared with a five-point sorption curve. The two-point test involved the addition of solutions containing 0 and 8 �g P mL-1 at a soil: solution ratio of 1:10. The sorption curve constructed using this method was suitable for assessing soils with Ps0.1 levels up to 90 �g P g-1. The soil phosphate buffering capacity at SPC0.1 (PBC0.1) was also accurately estimated using calculations from the two data points, but PBC0.3 values were poorly estimated. It was concluded that the two-point sorption curve is a sensitive and efficient method of predicting the present phosphorus status of clover pastures, their phosphorus fertilizer requirements, and of calculating PBC0.1, a useful soil characteristic.

Phosphorus sorption capacity of low activity clay soils of South Western Nigeria and its usefulness in evaluating P requirement of rice

“…The highly buffered Ofada I, an oxic Tropudalf showed only a small increase SPC with P addition, while the weakly buffered soils responded with large increases (Table 4). This is in agreement with the findings of Dear et al (1992). This Figure 3.…”

Influence of rates of reactive phosphate rock and sulphur on potentially available phosphorous in organically managed soils in the south-eastern near-Mediterranean cropping region of Australia

“…However, for some soil samples, extractable phosphate was also determined in a 1:10, soil 0.01 M CaCl 2 , extract, (SPC 0 ; Dear et al 1992). Plant production was not quantified because, without herbicides (disallowed on organic farms) the botanical composition of herbage could not be controlled between treatments.…”

“…Plant production was not quantified because, without herbicides (disallowed on organic farms) the botanical composition of herbage could not be controlled between treatments. In lieu of actual herbage data, the SPC 0 data were used to estimate the potential herbage yield (of subterranean clover; Trifolium subterraneum) relative to the potential yield with non-limiting P, according to RY ¼ 0:982 À 0:919 Á e Àð18:9ÁSPC 0 Þ (Dear et al 1992). In this determination it is assumed that herbage yield is unaffected by other soil conditions.…”

“…Basing this prediction on subterranean clover is appropriate because this legume underpins much of the restoration of soil N fertility in the southern cropping regions of Australia. The two-point method of Dear et al (1992) was used also to estimate a P sorption index (PSI), based on P sorption from a soil treatment with a solution containing 8 lg P ml -1 , and a phosphate buffering capacity at 0.1 lg P ml -1 (PBC 0.1 ).…”

Estimating the Phosphate Fertilizer Need of Soybean (Glycine Max (L) Merr.) In Some Ultisols In Benue State, Nigeria From Their Solution Phosphate Concentration

“…Volumes of 40cm 3 of 0.01 M CaCl 2 solution containing 0, 15, 25, 40, 100, 200, 400 and 800 mg l -1 P as KH 2 PO 4 were distributed to the tubes as described by Dear et al, (1992). The samples were then shaken for 24 hrs and then centrifuged for ten minutes at 1200 rpm at 4 o C in a refrigerated centrifuge.…”