Spatial variatbility [sic] of selected soil properties in and between map units

[摘要] English: Soils vary at all levels of observation. When describing soil physical or chemical properties we initially think in terms of homogeneous material. However, for characterizing the land use ability it is necessary to consider variability within and between soil map units as soils vary significantly over a land and within a homogeneous soil. The combinations of knowledge about soil interrelationships and the representation of the soil variability will be useful in the process of characterizing the variability of soil properties for different land use abilities, for example precision agriculture. The objectives of this study were therefore to (i) characterize the spatial variation of selected soil properties in and between map units (ii) describe the relationship between physical properties of selected soil forms and the root density of maize (iii) characterize the hydrology of the Tukulu, Sepane and Bloemdal soil forms at Paradys. A field experiment was conducted on a 55 ha cultivated field on the experimental farm of the University of the Free State, Paradys (S -32°35'21'', E -77°43'6''). The experimental site was subdivided into 75 experimental plots. For objective 1 all 75 plots were analysed for pH, Ca, K, Mg, Na and 7 texture classes . For objective 2, 13 plots were sel ected from the 75 experimental plots to cover a range of relative dry biomass yield plots. Root samples and soil samples were taken per master horizon. They were analysed for silt + clay content , water stable aggregates, modulus of rupture, bulk density and organic carbon content. For objective 3 , three modal profiles were selected and the instantaneous profile method was used to describe the volumetric wetness �?time relationship, the hydraulic head �?depth relationships and the hydraulic conductivity. It was clear that most of the soil physical and chemical properties had a strong relationship with clay. It was found that there was a higher variation between map units than within map units . Despite any variation Inverse Distance Weighting (IDW) fairly accurately predicted the variation within map units varying from 97% to 99% irrespective of horizon or soil. It also accurately predicted thevariation between map units varying from 91% to 94%. It was found that the A and C horizon has varying interrelationship due to varying silt + clay contents. The B horizon is the main factor that distinguishes the three soils. The silt + clay content of the B horizon for Tukulu varied between 31% and 34%, the Sepane between 49% and 55%, and the Bloemdal between 28% and 34%. The Bloemdal had the highest root length index (RLI) followed by the Sepane and Tukulu. It was clear that in the case of the Bloemdaland Tukulu , the C horizon controls the hydrology, while in the case of the Sepane it is the B horizon. It may be concluded that the variation in soil properties is higher between than within map units. Soil physical properties have a close interrelationship and varying effects on the RLI. The hydrology of the Bloemdal and Tukulu is influenced by the C horizon, while the Sepane is influenced by the B horizon.

[发布机构] University of the Free State