CHAPTER 5 RESULTS AND DISCUSSION
5.4 Season 2 Conclusions
By considering Table 5-30 it is evident that the best cotton quality by class (AO+) was delivered by the sandy clay soil, the Westleigh. All the other soil forms fall in the group O which is the second-best quality group. There is a slight price difference between the two classes but considering the yield these small differences accounts to a big sum of money.
Table 5-32 illustrates the difference in price based off the yield and quality classes. It is evident that the yield’s influence in cotton production considering the rand value of the cotton lint a hectare is highly significant. A higher yield to the cost of slightly lower quality results in a bigger rand value than a higher quality to the cost of a lower yield. In the Teerpadblok the highest yield and cotton quality was produced by the Oakleaf soil form, concluding a much higher amount per hectare. By considering Table 5-29 the quality of the cotton does not influence the value of the cotton, but the yield. It is more profitable to farm the higher yield soils in comparison with the soils that produce higher quality.
Table 5-32: Teerpadblok influence of cotton classes on the rand value of cotton lint (ton/ha).
Soil form Yield (ton/ha) Price (R/kg) Rand value per ton/ha
Avalon 2,70 R22,70 R61 290,00
Tukulu 3,20 R22,70 R72 640,00
Oakleaf 3,60 R22,70 R81 720,00
Westleigh 3,50+ R22,90 R80 150,00
5.4 Season 2 Conclusions
Bloemdal, Sepane and Westleigh soil with accumulation in the bottom 200–300 mm of the soil profiles since all the soil forms in the Hoekblok characteristic water table soil characteristics exhibit. Increases in soil water between harvest and post-season is visible in the sandy clay loam soils Bainsvlei and Bloemdal but decreases in soil water was visible in the sandy clay soils Westleigh and Sepane. All the soil forms were above DUL during the emergence, flowering, boll formation and boll burst stages during which the cotton is most sensitive to soil water stress. The Westleigh and Sepane soil forms were just higher above DUL during these periods than the Bloemdal soil form due to the higher clay percentages. The Bainsvlei is discussed separately as the soil profile depth is not comparable to the other soil forms. The sandy clay soils produced the highest yield in comparison with the sandy clay loam soils. The sandy clay loam soils delivered better quality cotton and higher micronaire cotton fibres than the sandy clay soils. Both the Westleigh and Sepane soil forms has a gleyic limiting horizon which is not favourable for plant roots due to waterlogged or anoxic conditions, and the cotton roots is situated in this section of the soil profile during boll formation. During the flowering and boll formation growth stages the Westleigh and Sepane was above DUL contributing to the anoxic conditions. However, the soil water content being above DUL was much lower than in the previous season sandy clay soils. A different cotton cultivar is planting in the Hoekblok which could have an effect as the rooting system is different in the different cultivars. This cultivar could possibly prefer a higher clay content soil profile. A higher yield to the cost of lower quality cotton accounts for much more than a better quality to the cost of lower yield. It is more profitable to farm the higher yield soils in comparison with the soils that produce higher quality.
5.4.2 Teerpadblok
The Teerpadblok dominant soil forms are physically uniform in terms of texture and as a result the soil water behaviour is mostly the same. Sandy clay soils dominate the Teerpadblok field. The Tukulu and Avalon soil forms had the highest clay percentage in the horizons. The Westleigh soil form has the lowest clay content of all the soil forms but has the highest soil water content throughout the production season. The Avalon which has the second highest clay percentage has the lowest soil water content throughout the production season. Both the Avalon and Tukulu soil forms soil water content increased from harvest to post-season due to the interflow characteristics, but the amount of soil water is less than what was available during planting. Both the Oakleaf and Westleigh soil forms increased in soil water content from harvest to post-season, and more soil water is available post-season than what was available during planting. Interflow was visible post-season on the limiting layer horizon in the Avalon, Tukulu, Oakleaf and Westleigh soil forms with accumulation of soil water in the bottom 200–300 mm of the soil profiles since all the soil forms in the Teerpadblok are characteristic water table soils as they exhibit water table
characteristics which is associated with internal drainage. The Avalon and Oakleaf soil forms soil water content was not below the LL during the season or above DUL which indicates that no planting stress would have occurred due to the good drainage capabilities. Both the Avalon and Oakleaf soil forms soil water content was just below DUL during the flowering and boll formation growth stages which indicates that the soil profile was waterlogged during these stages. The Tukulu soil form was above DUL during emergence, flowering, and boll formation growth stages during which the cotton is most sensitive to water stress. From boll burst to harvest the soil water content was just below DUL, but during these stages the soil water needs are low, and the soil water content remains constant. The Westleigh soil form soil water content was well above DUL throughout the season which might lead to soil water conditions above DUL that may cause water stress in the cotton. The Westleigh soil form produced the highest yield and the Avalon soil form the lowest yield. The Westleigh soil form also produced the best quality cotton in comparison with the other soil forms. The Westleigh produced the highest micronaire fibres in comparison with the other soil forms. A different cotton cultivar is planting in the Teerpadblok which could have an effect as the rooting system is different in the different cultivars. This cultivar could possibly prefer a higher clay content soil profile. A higher yield to the cost of lower quality cotton accounts for much more than a better quality to the cost of lower yield. It is more profitable to farm the higher yield soils in comparison with the soils that produce higher quality.
5.4.3 Combined Conclusions
The soil water content had significant differences depending on the physical characteristics of the soil forms. It was evident that in a field where similar soil properties occur in the various soil forms that the soil water content remained the same. Differences in the textural properties results in different soil water contents throughout the production season. The soils that contain a higher clay content has a higher soil water content, and in the case where a plinthic soil horizon occur the higher soil water content does not seem to be permanent as interflow occur in these horizons throughout the season. Water accumulation occurred in the bottom 200-300 mm of the soil profile post-season which indicates the occurrence of a water table in the fields. The most soil water is extracted from the topsoil to the section just above where water accumulates on the limiting layer because the accumulation zone due to the lack of oxygen in the accumulation zone. The highest yield was produced by the soils with more readily available plant water, characterized by good drainage and oxidized root zones. Different cotton cultivars were planted in the second season fields which may have caused differences in the response of the soil to the cultivar. A better cotton quality and higher micronaire was observed in the Hoekblok of the sandy clay loam soils in comparison with the Teerpadblok where a lower cotton quality and lower micronaire was observed