Threshold values and sufficiency levels for potassium in maize producing sandy soils of South Africa
Year: 2008
Type: article
Abstract: South African maize farmers apply only two thirds of the potassium (K) which is annually removed in the grain, causing a deficit of more than 13 000 tons K per season. It is expected that these maize fields will gradually become depleted and more K will be required to maintain or improve yields. Research goals were set for sandy soils in the main maize producing areas of South Africa to determine the lower & upper threshold values and sufficiency levels for soil K, the K status of these soils and to evaluate the sufficiency level concept for K at the various localities in the Free State Province. Field experiments were conducted at nine localities during four consecutive seasons. The experimental data included the soil K extracted with NH4OAc and the relative maize yields (RY) of the treatments, +K which received macro, secondary and micro nutrients and 0K which received the same nutrients but K was omitted. The results indicated a lower threshold value of 125 mg K kg−1 below which maize is expected to respond positively and an upper threshold value of 190 mg K kg−1 above which maize is expected not respond to additional K. The extractable K from 25 000 sandy soil samples received from maize farmers indicated that approximately 50% of these samples contained less K than the lower threshold value, approximately 30% was between the lower and upper threshold values and the remaining 20% was above the upper threshold value. The sufficiency levels obtained with the Mitscherlich model at 98% RY, ranged from 109–340 mg K kg−1. The difference between the sufficiency values and the extractable soil K at any of these localities, gives an unbiased measurement of the K fertilizer to be recommended.
Authors: J.J. van Biljon, D.S. Fouche, A.D.P. Botha
Institution: Omnia (South Africa)
Language: English
Subfield: Soil Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: bronze
OpenAlex ID: W2126409690