Mohamed Ali

Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Plant Science

First Advisor

Paul Fixen


Phosphorus is an important nutrient in crop production, since many soils in their native state do not contain sufficient available phosphorus to maximize crop yield. Now, more than ever, the importance of an adequate supply of plant nutrients to insure [sic] sufficient crop production is being recognized. Soil scientists and agronomists are continually striving to overcome nutrient deficiencies as well as use improved management practices in order that yields may more nearly approach the genetic limit of crop plants. Phosphorous forms sparingly soluble compounds with divalent and trivalent cations in soils. Therefore, the amount of P in the soil solution at any one time is very small. Plants growing in the soil apparently absorb P only from the soil solution. The limiting soil factor in P uptake by plants is likely to be renewal of the P in the soil solution near the plant roots by processes of dissolution, desorption and diffusion. The factors involved in renewal of soil solution P are the amount of P which can be solubilized, solubility, and the rate of P diffusion from the solid surface to the plant root surface. Thus, unless the soil contains adequate P or P is supplied to soil from external sources, plant growth will be restricted. South Dakota soils are frequently low in P due to crop removal and low indigenous levels. A successful and reliable soil testing method is, therefore, essential for predicting P need before crops are seeded. Several Midwest soil testing laboratories base their P fertilizer recommendations on the modified Bray & Kurtz 1 (weak acid) soil test. The Olsen method is also frequently used for P determination for more alkaline soils. These tests have been evaluated in many states and several countries; results of greenhouse studies varied from no difference between tests (2, 53, 106, 109) to significant advantage for the Bray & Kurtz-1 (67) or in other studies significant advantage for the Olsen test (93). Much less work under field conditions has been reported. In such cases, correlations have generally been quite low. Olsen et al. (71) reported correlation coefficients of 0.63 and 0.58 for Bray & Kurtz-1 and Olsen tests respectively with percent yield increase for 40 wheat experiments in Nebraska. Research with calcareous soils shows that widening the soil to solution ratio of the Bray & Kurtz (Bray) extracting reagent results in higher correlations with yield response. In other instances grouping the soils by genetic origin has increased the resulting correlations (57). Consideration of climatic factors has also improved the correlation between these soil tests and yield response (17, 68, 74). Fixen and Carson (28) compared the Bray (soil to solution ratio of 1:7, 1:10, 1:20, and 1:50) and Olsen P. Results of 74 South Dakota small grain field experiments over a 13-year period indicated the modified Bray, 1:50, was the soil test most highly correlated with yield response. The objectives of this study were: (1) To determine the influence of P additions under field conditions on Bray and Kurtz-1 and Olsen test levels for alkaline soils in eastern South Dakota. (2) To determine the effects of various soil factors on P extracted by the two tests. (3) To determine the relationship between P extracted and crop yield response in alkaline soils of eastern South Dakota.

Library of Congress Subject Headings

Soils -- Phosphorus content
Soils -- Testing
Soils -- South Dakota




South Dakota State University