The South Burnett region of Queensland is Australia's most important rainfed peanut (Arachis hypogea L.) production area. It also produces a considerable amount of cereal and grain legume crops. The cropping soils of the region are red, acid to neutral, clay loams that are classified as Ferrosols (Australian Soil Classification). Over 50 years of cropping on these soils has resulted in severe depletion of nutrient reserves, particularly potassium (K). In addition, the remaining K is predominantly confined to the surface 10 or 15cm of the soil profile, a feature commonly refered to as nutrient stratification. Dry periods during the summer cropping season are common due to the highly variable, summer-dominant rainfall pattern of the South Burnett. As topsoil dries out, crops forage for moisture and nutrients from lower in the soil profile where K reserves are smaller. It is therefore suspected that the combination of dry periods and stratified K reserves have resulted in an increasing incidence of K deficiency symptoms in summer crops. To investigate these issues, K relations of Ferrosols of the South Burnett were studied using soils from two representative sites. The pools of soil K that are important to crop growth in Ferrosols, and their interaction was examined through fractionation of soil K pools, and determination of quantity/intensity relationships, charge characteristics and clay mineralogy, and a leaching column study. A rapid K uptake period was identified for peanut and the effect of profile distribution and soil moisture during this period on K accessibility was studied in a divided column experiment. Finally, on-farm trials were used to evaluate commercial-scale options for improving K distribution in field profiles. It was found that the immediately available exchangeable K pool in these soils was the most important source of soil K, and was poorly buffered by slowly available non-exchangeable K. However the leaching column study revealed that K was preferentially adsorbed onto soil cation exchange sites, displacing calcium (Ca) and magnesium (Mg) ions, and therefore was not susceptible to vertical movement within the soil profile. These observations helped to explain the development of stratified K profiles in these soil types. Peanut (cv. Streeton) was found to take up most of its K requirement between 25-70 days after planting. The divided column study showed that profile distribution, and topsoil iv moisture content during this rapid K uptake period, were able to affect the ability of peanut plants to access K. Plants that grew in low K soil, or where soil was dry at the site of K supply, had reduced access to K. However, improving access to K did not result in improved growth, but rather in a significant reduction in dry matter (DM) production, apparently due to interference in the availability of other nutrients, possibly phosphorus (P), magnesium (Mg) or boron (B). Field studies showed that application of K and profile inversion improved K uptake and DM production of various crop species. However, in most instances improved K uptake and DM production was not reflected in increased yield. It was suggested that a combination of agronomic factors, seasonal conditions and crop type prevented the expression of yield responses to improved K nutrition and these influences need to be understood. The findings of this project have important consequences for nutrition of crops grown on Ferrosols in the South Burnett region. Surface applied K cannot be expected to increase exchangeable K in the subsoil unless it is incorporated to depth. Similarly, band applied K will remain close to the site of application as a result of only limited vertical or lateral movement. This may affect the ability of roots to access band applied K. The ability of surface applied K to displace Ca and Mg from soil exchange sites may have negative implications for the Ca nutrition of developing peanut pods. On the other hand, it could present an opportunity for the movement of Ca into deeper soil layers to address the amelioration of acid subsoils. The unexplained negative responses to potassium chloride application and apparent effect on P, Mg or B nutrition need to be investigated.
| Identifer | oai:union.ndltd.org:ADTP/253730 |
| Creators | White, Jonnie Rachelle |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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