Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Effect of soil forms on soil moisture and dryland cotton production

Auteur : Gagiano, Ruan

Université de soutenance : North-West University

Grade : MSc (Environmental Sciences) 2022

Résumé partiel
Cotton (Gossypium hirsutum) production in South Africa relies on rainfed cultivation, and as such the availability of water is a key factor in the production of the crop. Cotton production in South Africa is declining gradual annually. The decline is marked by the competition with traditional crops, high input costs, international market prices and a lack of technical production information. The cotton produced in the 2019/2020 season consisted of 27 850 hectares in total from which 15 966 hectares is produced under dryland conditions, and 11 884 hectares under irrigated conditions. Dryland cotton production has been becoming more prominent, which establishes the need for technical information in the production under these conditions. Technical knowledge regarding soil moisture regimes is unknown in the industry and this uncertainty prevents the continued cultivation of the crop. This study aims to quantify the effect of the different soil forms and their associated water regimes on the rainfed cotton seed yield and quantity. The effect of the water table was duly visible as bedrock interflow soils exhibited a higher amount of soil water throughout the production season in comparison with sandy clay soils. It was expected that the sandy clay soils would indicate higher soil water contents throughout the production season, but certain interflow soils had a substantial amount of soil water more during the both the productions seasons. To determine the soil water regime the relationship between the soil water and the soil matric potential was established. The soil matric potential was determined by means of undisturbed core sampling and suction under pressure by using a pressure plate apparatus. By determining the soil water capacity at 33 and 1500 kPa, the drained upper limit (DUL) and lower limit (LL) was established for each of the various soil forms. Through the utilization of these parameters, the amount of planting-available water was determined which is critical in the production of cotton. Considering the DUL and LL the state of the soil water content throughout the production season was assessed for each of the soil forms. It was evident that sandy clay loam soils tend to be above DUL during a high rainfall period, but due to the drainage capacity of the soils, the period above DUL does not occur over a long period.

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