Soil variability and related crop productivity within a sample area of the Templeton soil mapping unit : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Agricultural Science in the University of Canterbury

Abstract

The soils of the study area have been formed on texturally layered alluvial deposits. This textural layering brought about by fluvial processes has resulted in highly variable morphological parameters of the soils of the study area. This study has indicated that the existing classification scheme for the Templeton age-group soils (Cox,1978) is unsatisfactory for the description of the soils of the study area. An attempt was made to quantify this classification scheme by producing a modified Cox's classification scheme but it was also unsatisfactory. A new classification scheme was devised, based on texture/depth criteria, described as the present classification scheme. A 30 m x 30 m grid map of soil profile class distribution under the present classification scheme relates the soil pattern to fluvial sedimentation in the study area. This classification scheme is clearly superior to the modified Cox's classification scheme in associating soil variation with Manapou barley (Hordeum vulgare) crop height and productivity variations in the study area. However, both classification schemes were unable to relate Kopara wheat (Triticum aestivum) productivity variations to soil variation. The dichotomy of the results regarding the productivity of barley and wheat in relation to the soil pattern can be explained by the difference in the sowing time of the two crops. The winter sown wheat had enough time to develop its root system to a depth where soil moisture content was not limiting crop performance. In the case of the spring sown barley there was not enough time to develop its root system to such a depth. The results indicate that the observed variations in "barley height" and barley production were affected by plant available soil moisture, the rate of soil moisture depletion, and by differences in Nitrogen uptake in a manner determined in part by the soil textural pattern. The results of this study indicate the need to investigate alternative management of the barley crop in order to reduce variation in yield and increase its production per unit area.