Potassium relationships in selected eutrophic hutton soils of irrigation areas

[摘要] The relationship between red leaf disease and soil fertilitystatus was studied in the glasshouse. For red leaf diseaseaffected plants grown on Mangano soils, no effective fertilizertreatment could be found. However, yield could bepredicted more accurately by soil parameters other than thetraditional ammonium acetate extractable potassium or exchangeable potassium. These parameters were the ratio (Ca+Mg)/K in the soil and exchangeable potassium percentage.These initial findings were tested in fifteen field trialson Mangano soils with variable clay contents and exchangeablepotassium contents at Vaalharts.A large matrix of data resulted from the field investigation.However, only statistical procedures relating soiland leaf-K parameters to yield and leaf-K were investigated.The data were statistically analised by means of analysis ofvariance, correlation and multiple regression on an IBM 900computer. For each soil and leaf potassium parameter relationshipswere established with yield and leaf-K content forindividual trials, pooled data and grouped data.Attention is drawn to the fact that ammonium acetate extractable potassium and exchangeable potassium are not reliablepredictors of cotton yield for this soil/crop relationship.These two parameters should rather be consideredtogether with the ratio (Ca + Mg)/K in the soil, exchangeablepotassium percentage and leaf-K content when cotton yield isto be predicted on Mangano soils at Vaalharts.The initial results from one pot experiment and fifteenfield trials were largely substantiated by two additionalpot experiments. In order to find an explanation for the lackof response to applied potassium, potassium fixation and Kfractionation were also investigated. All the soils testedfixed appreciable quantities of K. Total K amounted toapproximately one percent.Recommendations are made to clarify the complex nature ofpotassium reactions in the soil/crop relationship.

[发布机构] University of the Free State