CHAPTER 5 RESULTS AND DISCUSSION
5.3 Season 2 Results and Discussion
5.3.8 Soil water
5.3.8.7 Teerpadblok Soil Water Regime
5.3.8.7 Teerpadblok Soil Water Regime
5.3.8.7.2 Tukulu
Figure 5-42 illustrates the soil water fluctuation throughout the cotton production season of the Tukulu soil form. During November 2020 the total amount of soil water was well above the drained upper limit. During the beginning of November 2020, the first rain was observed which assured that planting can commence. The cotton was planted on the 2nd of November 2020. Frequent rainfall events followed after planting which ensured that soil water was available for uptake during the emergence of the cotton. Between the emergence and flowering growth stages the soil water was readily available for plant uptake and soil water conditions above DUL is observed towards the end of March 2021 just before boll formation commenced. During the period from November 2020 to January 2021 the evapotranspiration demand increased as the growth stages progress towards the flowering stage, but due to the frequent high rainfall events this increase had no real effect as the cotton water needs are rather low. During January 2021 a peak in soil water content is observed during the flowering growth stage. The soil water content decreased drastically from January 2021 to March 2021 as the soil water needs of the cotton increased as the growth progressed to the boll formation growth stage. In the period from boll formation commencement to boll burst the soil water decreased slightly to below DUL. From boll burst to harvest the soil water increased to above DUL once again. From harvest the soil water content decreased once more to below DUL. The soil water content was above DUL throughout the season during critical growth stages and as such crop water stress could affect the yield and quality of the cotton.
Figure 5-42: Soil water regime on the Tukulu soil form in the Teerpadblok.
5.3.8.7.3 Oakleaf
Figure 5-43 illustrates the soil water fluctuation throughout the cotton production season of the Oakleaf soil form. During November 2020 the total amount of soil water was well above the lower limit. During the beginning of November 2020, the first rain was observed which assured that planting can commence. The cotton was planted on the 2nd November 2020. Frequent rainfall events followed the planting which ensured that soil water was available for uptake during the emergence of the cotton. Between the emergence and flowering growth stages the soil water was readily available for plant uptake. During the period from November 2020 to January 2021 the evapotranspiration demand increased as the growth stages progress towards the flowering stage, but due to the frequent high rainfall events this increase had no real effect as the cotton water needs are rather low. During January 2021 a peak in soil water content is observed during the flowering growth stage. The soil water content decreased drastically from January 2021 to March 2021 as the soil water needs of the cotton increased as the growth progressed to the boll formation growth stage. In the period from boll formation commencement to boll burst the soil water decreased slightly. From boll burst to harvest the soil water increased slightly but is still below DUL and water is readily available for planting uptake. From harvest the soil water content decreased slightly. The soil profile was never waterlogged throughout the season and as such crop water stress does not affect the yield and quality of the cotton.
Figure 5-43: Soil water regime on the Oakleaf soil form in the Teerpadblok.
5.3.8.7.4 Westleigh
Figure 5-44 illustrates the soil water fluctuation throughout the cotton production season of the Westleigh soil form. Throughout the season the total amount of soil water was extremely high above the DUL. During the beginning of November 2020, the first rain was observed which assured that planting can commence. The cotton was planted on the 2nd November 2020 during which the soil form was well above drained upper limit. Frequent rainfall events followed the planting which ensured that the soil water content was above DUL which makes crop stress a real effect factor. Between the emergence and flowering growth stages the soil water was readily available for plant uptake and above DUL. The amount of soil water kept increasing well above the drained upper limit which raises the possibility of plant stress. During the period from November 2020 to January 2021 the evapotranspiration demand increased as the growth stages progress towards the flowering stage, but due to the frequent high rainfall events this increase had no real effect as the cotton water needs are rather low. During January 2021 a peak in soil water content is observed during the flowering stage. The soil water content decreased significant from January 2021 to March 2021 as the soil water needs of the cotton increased as the growth progressed to the boll formation and boll burst growth stages. In the period between boll formation and boll burst the soil water content decreased still, but in the period directly before boll burst the soil water content remained constant. In the period from boll burst commencement to harvest the soil water content increased slightly, but after harvest decreased once more.
Figure 5-44: Soil water regime on the Westleigh soil form in the Teerpadblok.
5.3.9 Cotton Yield and Quality