No abstract

The relation of ion uptake to soil solution composition is discussed. Uptake of a given ion depends not only on its activity in solution, but also on the activity of other ions and the relation that exists between solution ions and exchangeable or solid‐phase ions. Methods of combining all these factors are reviewed and evaluated. A dimensionless plot, suggested by Howard and Adams, which related relative plant growth to the ratio of the ion activity to the sum of ion activities in solution, ai/Σn1ai, seems to have a wide range of applicability that extends from uptake from a nutrient solution in a beaker to uptake from soil solution in situ.

No abstract

A combination of finely ground phosphate rock (PR) and triple superphosphate (TSP) represents a method that can improve the agronomic value of PR at a lower cost than would be required to manufacture the conventional, fully acidulated fertilizers from that same rock. A reactive PR from North Carolina was evaluated for its effectiveness as a P source when used in conjunction with TSP at P rates up to 266 mg P kg−1 in a short‐term (6‐week) greenhouse experiment. The soil used was a limed Mountview silt loam (Typic Paleudult) with pH 6.2. As measured by dry‐matter yield and P uptake, P availability from PR appeared to increase with increases in the proportions of TSP to PR in the TSP‐PR mixtures. Although PR alone was less effective than TSP, PR was just as effective as TSP when mixed with TSP at a P ratio of at least 1:1. Because plants responded to both TSP and PR, and because there was an interaction between TSP and PR in the soil, neither water solubility nor total citrate solubility could be used to predict the effectiveness of TSP‐PR mixtures with different P ratios.

Cotton (Gossypium hirsutum var. ‘Stoneville 213’) was grown in greenhouse pots containing Hartsells fine sandy loam. Four rates of P were employed and the crop was harvested on three different dates. Dry matter yield of tops and uptake of P were measured. Roots were recovered and their length determined. These data were used to calculate a rate of P uptake per meter of roots which in turn was related to quantity and intensity of soil P. A parameter that combines the effects of quantity, intensity, and P buffering capacity was derived, and rate of P uptake was found to be related to this parameter. Rate of P uptake increased with rate of root growth.