Plant available potassium in New Zealand steep-land pasture soils

In order to examine the effect of the long-term animal transfer of nutrients, soil K fertility patterns were investigated in two established steep-land pastures in the southern North Island of New Zealand. Spatially randomized and transect style surveys were made of NH4-exchangeable K and plant available nonexchangeable K (Step K) values. Wide-ranging and highly skewed distributions of values were found. The large short-range spatial variability could only form nugget variograms, so that mapping was not possible, however correspondence analysis was useful to examine the distribution of values obtained at different landscape positions. The range of NH4-exchangeable K values increased markedly on ridge-tops in association with well-drained animal campsites. Plant available Olsen P values had a similar pattern. Step K values were affected by a mixture of soil parent material and soil moisture effects, including an interaction between soil moisture and animal camping patterns. Although the animal transfer effects were extensive on the campsite areas, no accompanying reduction of the K fertility on areas of the steeper slopes was found. Analysis of the total K and P content of the topsoils indicated a relatively low rate of transfer of K from the slopes to the ridge-tops. Consequently, the development of significant K deficiencies in the soil on the slopes is not expected. Current soil sampling methods in steep-land usually make estimates from soil samples that are collected over large areas and then combined (composited/bulked). In this study, the wide ranges of values and skewed distributions indicated that more meaningful estimates of K status could be made if a population distribution of K fertility values was described using individual samples.