CHAPTER 5 RESULTS AND DISCUSSION
5.2 Season 1 Conclusions
Table 5-16: Influence of cotton quality on the rand value of cotton lint (ton/ha) in the Schietfontein field.
Soil form Yield (ton/ha) Price (R/kg) Rand value per ton/ha
Tukulu 2,04 22,90 R45 891,60
Oakleaf 2,61 22,90 R59 769
Glencoe 2,32 23,20 R53 824
Avalon 2,50 23,20 R58 000
5.2 Season 1 Conclusions
known to be anoxic, but the waterlogged period is much shorter than that of the gleyic horizon due to the apedal horizon on top of the plinthic horizon which has red and yellow colour indicating the shorter periodical saturated conditions. When comparing the two soils that were above DUL during flowering and boll formation when the cotton is most sensitive to water stress it is inevitable that the cotton prefers the more oxidated environment in the subsoil in the form of apedal horizons on the plinthic horizons. A higher yield to the cost of lower quality cotton accounts for much more than a better quality to the cost of lower yield thus, it is more profitable to manage the land in such a manner to focus on the areas with higher yield potential.
5.2.2 Schietfontein
The Schietfontein soil forms are physically uniform with not much variation in the physical properties of the different soils and their associated horizons. All the soil forms identified in the Schietfontein field are texturally classified as sandy clay loam soils. The Oakleaf and Tukulu soil forms had the highest clay percentage in the topsoil and subsoil horizons. As a result, the Oakleaf and Tukulu soil forms had the highest amount of soil water throughout the season. In all the soil profiles the soil water content decreased from harvest to post-season which is characteristic of interflow soils. All the soil forms in Schietfontein have red colour in the subsoil horizon which indicates water flow from the soil profile with the only exception in the Tukulu soil form. When considering the depth profiles the effect of grey colours in the gleyic horizon is inevitable. Less soil water was lost from harvest to post-season throughout the soil profile. In the bottom section of the soil profile the amount of soil water remained the same. The other soil forms decreased in soil water content throughout the soil profile due to deep internal drainage. The Oakleaf, Glencoe and Tukulu soil forms soil water content was above DUL throughout the entire season from the period just before flowering to post-season. The Avalon soil form was below lower limit by planting time and increased in soil water content being above DUL only during flowering and boll formation.
The Oakleaf produced the highest yield of cotton with the Avalon producing the second highest yield. The Tukulu soil form produced the lowest yield which is considerably less than the Oakleaf and Avalon soil forms yield. However, the Glencoe and Avalon soil forms produced the best quality cotton in comparison with the Tukulu and Oakleaf soil forms. The soils with a higher clay content, Oakleaf and Tukulu produced the highest micronaire cotton fibres. A higher yield to the cost of lower quality cotton accounts for much more than a better quality to the cost of lower yield.
The Tukulu soil form has a gleyic limiting horizon which is not favorable 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 where the yield is determined. During the flowering and boll formation growth stages the Tukulu was above DUL contributing to the anoxic conditions. This may be the cause of a lower yield in comparison with the plinthic limiting layer horizons of the Avalon and Glencoe.
The plinthic horizons are also known to be anoxic, but the waterlogged period is much shorter than that of the gleyic horizon due to the apedal horizon on top of the plinthic horizon which has red and yellow colours indicating the shorter periodical saturated conditions. When comparing the soils that were above DUL during flowering and boll formation when the cotton is most sensitive to waterlogged conditions it is inevitable that the cotton prefers the more oxidated environment in the subsoil in the form of apedal horizons on the plinthic horizons. A higher yield to the cost of lower quality cotton accounts for much more than a better quality to the cost of lower yield thus, it is more profitable to manage the land in such a manner to focus on the areas with higher yield potential.
5.2.3 Combined Conclusion
In conclusion the soils with a higher clay content results in a higher soil water content throughout the production season. Soils having a gleyic soil horizon with grey colours in the matrix tend to not decrease in soil water content post-season in comparison with plinthic limiting layer horizons.
It is evident that in the soils with a soil horizon that is anoxic such as the gleyic soil horizon, that the periods above DUL have an effect on the yield of the cotton of the specific soil form, but crop management factors may be the real cause. No statistical differences occurred in the soil horizons clay percentage. However, variation occurred in the amount of soil water that a soil can hold against gravity (DUL), which then explains the variation in soil water content throughout the production season. The soil water content was observed to be above the drained upper limit during critical growth stages (flowering and boll formation), which may have caused water stress in the cotton through the anoxic conditions. These anoxic conditions suppress the development of the above ground biomass (cotton bolls), resulting in a lowered yield. However, crop management practices such as the application rates of fertilizers might have had an effect. Soil forms with a higher clay content tend to form cotton with a higher micronaire fibre and cotton of a better quality. Although the cotton quality is better the yield remain the deciding factor as a higher yield to the cost of lower quality cotton could prove more valuable than a lower yield to the cost of higher quality cotton.
5.3 Season 2 Results and Discussion