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Some Limiting Factors in Estimating the Fertilizer Requirements of a Soil
Author(s) -
McGeorge W. T.,
Breazeale J. F.
Publication year - 1937
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1937.03615995000100000017x
Subject(s) - limiting , biochemist , citation , chemist , fertilizer , agriculture , library science , table (database) , computer science , agricultural science , mathematics , operations research , environmental science , chemistry , history , engineering , database , archaeology , ecology , biology , classics , mechanical engineering , organic chemistry
In attempting to evaluate the productivity of alkaline-calcareous soils many sources of error are met which are entirely foreign to those encountered in the cropping of most types of soil. This applies especially to the estimation of phosphate availability. In Arizona these alkaline-calcareous soils vary from heavy clays to sandy desert types and all contain from two to ten per cent or more calcium carbonate. They are alkaline in reaction with pH values of 8.5 or higher. The heavier soils are often in a puddled or dispersed state, do not drain readily and when wet, dry out very slowly. While they all contain an adequate supply of total phosphorus it is usually of low availability as measured by plant tests and by its solubility in carbon-dioxidefree and carbon-dioxide-saturated water. The most suitable chemical method for measuring the availability of the phosphate in these soils is extraction with carbon-dioxide-saturated water. To illustrate this, data obtained from a series of lettuce experiments are submitted in Table I. In these experiments a direct relation between the increase in solidity, or weight, of lettuce heads from phosphate fertilization and the available phosphate in the soils before fertilization, was found. The advantage of carbon dioxide as an extractant lies in its production of an extracting solution of pH 6.0 to 6.5. With the introduction of acetatebuffered extractants it was anticipated that rapid field tests could be developed for these soils. However, the greater solubility of the phosphorus in acetate buffers necessitated more accurate weights of soil than can usually be obtained in the field. For this reason laboratory tests are being continued at the Arizona Experiment Station until the method can be made more adaptable. Plant tests possess certain advantages over chemical tests as a means of estimating phosphate availability in soils. Of the plants which are adaptable, the tomato possesses certain characteristics which make it particularly suited.