![[ International Annual Meetings - Home Page ]](images/banner.jpg "[ International Annual Meetings - Home Page ]")
See more from this Session: Symposium--Applying Soil Chemistry to Solve Soil Problems in the "Milky Way": Honoring the Impact of Malcolm Edward Sumner: I
Monday, November 1, 2010: 8:45 AM
Long Beach Convention Center, Room 201A, Second Floor
Poor soil fertility was, and still is, a major constraint in agriculture in KwaZulu-Natal ; a large proportion of the land surfaces are extremely old and the soils highly weathered. They are characterised by acute deficiencies of P and associated P fixation, insufficiencies of other nutrients such as Ca, Mg, K, Zn and Mo, and toxicities of Al and Mn. This presentation outlines research undertaken to address these constraints over the last 40 years.
Prior to this period, many of these problems were recognised, but quantities of lime and fertilizers needed for their remediation could not be determined.
Field trials involving N, P, K and lime have been used to establish soil-test based calibrations. Highlights of this work include the following: A reliable plant-available N test has not been established, but N recommendations are based on an estimate of mineralizable N derived from organic carbon content; this was adopted initially by the sugar industry and subsequently by grain producers. Phosphorus calibration initially involved optimising soil test methodology, and threshold values were shown to be related to soil texture, which can be easily predicted in a routine laboratory using sample density. Potassium calibration work underlined the usefulness of exchangeable K as an index of K requirement. Soil acidity research has demonstrated the relevance of Al-based indices as a criterion for determining lime requirements. Interactions of economic significance between acidity and nutrient availability have been demonstrated. Marked yield responses to several micronutrients (Zn, Mo, B, Cu) have also been recorded.
As a result of this research soil samples submitted by farmers have increased by 100-fold since 1975. This has been accompanied by dramatic increases in fertilizer use and yields. However, the increasing adoption of no-till cropping practices has created a need for established norms to be re-examined, and additional areas of concern include a requirement for S calibrations and the expansion of the work to horticultural crops.
See more from this Division: S02 Soil ChemistryPrior to this period, many of these problems were recognised, but quantities of lime and fertilizers needed for their remediation could not be determined.
Field trials involving N, P, K and lime have been used to establish soil-test based calibrations. Highlights of this work include the following: A reliable plant-available N test has not been established, but N recommendations are based on an estimate of mineralizable N derived from organic carbon content; this was adopted initially by the sugar industry and subsequently by grain producers. Phosphorus calibration initially involved optimising soil test methodology, and threshold values were shown to be related to soil texture, which can be easily predicted in a routine laboratory using sample density. Potassium calibration work underlined the usefulness of exchangeable K as an index of K requirement. Soil acidity research has demonstrated the relevance of Al-based indices as a criterion for determining lime requirements. Interactions of economic significance between acidity and nutrient availability have been demonstrated. Marked yield responses to several micronutrients (Zn, Mo, B, Cu) have also been recorded.
As a result of this research soil samples submitted by farmers have increased by 100-fold since 1975. This has been accompanied by dramatic increases in fertilizer use and yields. However, the increasing adoption of no-till cropping practices has created a need for established norms to be re-examined, and additional areas of concern include a requirement for S calibrations and the expansion of the work to horticultural crops.
See more from this Session: Symposium--Applying Soil Chemistry to Solve Soil Problems in the "Milky Way": Honoring the Impact of Malcolm Edward Sumner: I