CHAPTER 5 RESULTS AND DISCUSSION
5.1 Season 1 Results and Discussion
5.1.9 Cotton Yield and Quality
process of the cotton. The amount of soil water kept increasing above the drained upper limit which raises the possibility of plant stress. During the period from November 2019 to February 2020 the evapotranspiration demand increased as the growth stages progress towards the flowering stage, but due to the frequent high rainfall events and soil water conditions above DUL, this increase had no real effect as the cotton water needs are rather low. During February 2020 a peak in soil water content is observed and the total amount of soil water is approximately three times the DUL of the soil form. The soil water content decreased drastically from February 2020 to March 2020 as the soil water needs of the cotton increased as the growth progressed to the boll burst growth stage. The soil water conditions above DUL lasted from the period just after emergence in early December 2019 until after harvest where it remained constantly far above the DUL. The soil water content was above DUL during all the growth stages except emergence. The soil profile being high above DUL throughout the season indicated signs of plant stress.
Figure 5-21: Soil water regime on the Oakleaf soil form in Schietfontein.
with 3,65 ton/ha. The third highest producing soil form is the Westleigh soil form with 3,25 ton/ha.
The lowest yield was measured on the Tukulu soil form with 2,93 ton/ha. The average cotton yield for Pretorius Rust was 3,45 ton/ha.
No statistical differences in yield were observed with the four dominant soil forms of Pretorius Rust. From the results it is evident that the sandy clay loam soils, Avalon and Bainsvlei, produced the highest yield in comparison with the sandy clay soils, Westleigh and Tukulu. The average cotton yield in South Africa under dryland conditions is between 1,2-2 ton per hectare (Cotton SA, 2021b). By considering this the Pretorius Rust cotton field produced an above national average cotton yield in the 2019/2020 cotton season.
Figure 5-22: Pretorius Rust seed cotton yield (ton/ha) per soil form.
5.1.9.2 Schietfontein Cotton Yield
Figure 5-23 illustrates the cotton yield data per soil form for the Schietfontein cotton field for the 2019/2020 production season. From Figure 5-23 it is evident that the Oakleaf soil form produced the highest cotton yield at 2,61 ton/ha. The Avalon soil form produced the second highest yield with 2,50 ton/ha. The Glencoe soil form produced the third-highest yield with 2,32 ton/ha. The Tukulu soil form produced the lowest yield with 2,04 ton/ha. The average cotton yield from the four dominant occurring soil forms for Schietfontein for the 2019/2020 cotton season was 2,37 ton/ha. This is significantly lower than the average yield of the four dominant soil forms of the Pretorius Rust cotton field.
No statistical differences in yield were observed with the four dominant soil forms of Schietfontein.
From the data it is evident that the sandy clay loam soils, Oakleaf, Avalon and Glencoe, produced the highest yield in comparison with the sandy clay soil forms such as the Tukulu. The cotton yield in this cotton field is well above the national average of 1.2-2 ton/ha.
Figure 5-23: Schietfontein cotton yield (ton/ha) per soil form.
5.1.9.3 Pretorius Rust Cotton Quality
Table 5-13 was generated by compiling averages of all the cotton quality parameters from the repetitive sampling points for each soil form. The data is discussed per soil property and assigned to a cotton quality class on basis of a classification scheme considering these quality properties and the current value of the specific cotton class. Statistical analysis revealed that there is no distinct significant difference between the cotton quality parameters of Pretorius Rust, but based on the classifications the small differences account for different quality classes and associated price differentials on the cotton lint.
It is evident that the Tukulu soil form has the highest upper half mean length (UHML) with 1,18 inches. The second highest UHML is that of the Avalon and Westleigh soil forms with 1,16 inches.
The cotton fibre with the lowest UHML is that of the Bainsvlei soil form with an average length of 1,15 inches. The higher the UHML, the higher the spinning consistency will be, and a higher price value will be assigned to the cotton fibre batch.
The highest fibre strength is that of the Westleigh soil form with 26,89 g/tex, followed by the Bainsvlei soil form with 26,51 g/tex. The Tukulu soil form has the third strongest fibre strength with 26,44 g/tex. The Avalon soil form has the least strong cotton fibre with a strength of 26,26 g/tex. All the above soil form strength values are categorized as a medium strength. It is evident that the sandy clay soils such as the Westleigh soil forms, produced the higher strength cotton fibres in comparison with the sandy clay loam soils such as the Avalon.
Table 5-13: Pretorius Rust cotton fibre quality per soil form.
Soil form UHML Strength Micronaire Class Price (kg) Price differential (%)
Westleigh 1,16 a 26,89 a 3,73 a AO+ R22,90 14,5
Tukulu 1,18 b 26,44 a 3,52 a AX R23,20 16
Avalon 1,16 a 26,26 a 3,34 a AOM R22,20 11
Bainsvlei 1,15 a 26,51 a 3,37 a AOM R22,20 11
The soil form producing the highest micronaire value is the Westleigh soil form with 3,73. The second highest micronaire produced is that of the Tukulu soil form with 3,52. The third highest micronaire is that of the Bainsvlei soil form with 3,37. The Avalon soil form produced the lowest micronaire value with 3,34. The Avalon, Bainsvlei and Tukulu soil forms micronaire values are classified as fine. The Westleigh soil form micronaire is classified as medium. It is evident that the sandy clay soils (Westleigh and Tukulu) produced higher micronaire cotton fibre in comparison with the sandy clay loam soils (Avalon and Bainsvlei).
By considering Table 5-13 it is evident that the best cotton quality by class was delivered by the sandy clay soils, Westleigh and Tukulu. All the above soil forms fall in the group O which is the second-best quality group. Within the group classes, AO and AOM exist. The sandy clay loam soil forms, Avalon and Bainsvlei, fibre quality falls within the class AOM which is secondary to the AO class in group O. There is a slight price difference between the two classes but considering the yield, these small differences accounts for a large sum of money.
Table 5-14 illustrates the difference in price based on 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 higher rand value than a higher quality to the cost of a lower yield. Both the Westleigh and Avalon soil forms were above DUL during the growth stages where the cotton is most sensitive to soil water stress. The Avalon produced the highest yield, but a lower quality cotton. By considering Table 5-14 the quality of the cotton does not influence the value of the cotton, but the yield. When comparing the Avalon and Westleigh soil forms the limiting layer horizon is different. The yield and quality are
affected by the limiting layer horizon. The Westleigh soil form’s gleyic limiting layer horizon tend to create waterlogged conditions that inhibit the formation of bolls and resulting in a lower yield.
However, it is more profitable to farm the higher yield soils such as the Avalon and Bainsvlei in comparison with the soils that produce higher quality cotton such as the Westleigh and Tukulu.
Table 5-14: Influence of cotton quality on the rand value of cotton lint (ton/ha) in the Pretorius Rust field.
Soil form Yield (ton/ha) Price (R/kg) Rand value per ton/ha
Westleigh 3,25 22,9 R74 425
Tukulu 2,93 23,2 R67 976
Avalon 3,96 22,2 R90 684
Bainsvlei 3,65 22,2 R84 680
5.1.9.4 Schietfontein Cotton Quality
Table 5-15 was generated by compiling averages of all the cotton quality parameters from the repetitive sampling points for each soil form. The data is discussed per soil property and assigned to a cotton quality class on basis of a classification scheme considering these quality properties.
Statistical analysis revealed that there is no distinct significant difference between the cotton quality parameters of Schietfontein, but based on the classifications the small differences account for different quality classes and associated price differentials on the cotton lint.
The UHML varied quite significantly between the different soil forms in the Schietfontein cotton field. The longest UHML was produced by the Glencoe soil form with 30,53 mm, followed by the Avalon soil form with 29,99 mm. The Oakleaf soil form had the third longest UHML with 29,37 mm. The Tukulu soil form produced the shortest UHML with 29,68 mm. A clear trend is observed that the sandy clay loam soils, Glencoe, Avalon and Oakleaf produced the longest fibres in comparison with sandy clay soils such as the Tukulu.
Table 5-15: Schietfontein cotton fibre quality per soil form.
Soil form UHML Strength Micronaire Class Price (R/kg) Price Differential (%)
Tukulu 1,17 27,50 4,32 AO+ R22,90 14,5
Oakleaf 1,16 27,34 4,04 AO+ R22,90 14,5
Glencoe 1,20 27,35 3,78 AX R23,20 16
Avalon 1,18 28,07 4,02 AX R23,20 16
The strength varied between the different soil forms. The Avalon soil form produced the strongest cotton fibres with 28,07 g/tex, followed by the Tukulu soil form with 27,50 g/tex. The third strongest cotton fibre was produced by the Glencoe soil form with 27,35 g/tex. The weakest cotton fibre was produced by the Oakleaf soil form with 27,34 g/tex. There is a significant difference between the strongest and weakest cotton fibres, but not enough to be classified in different strength categories. All the soil forms produced medium strength fibres.
The micronaire values varied quite between the different soil forms. The Tukulu soil form produced the highest micronaire with 4,32, followed by the Oakleaf soil form with 4,04. The Avalon soil form produced the third highest micronaire with 4,02. The lowest micronaire value was produced by the Glencoe soil form with 3,78. All the soil form micronaire values is described as medium. A key finding is that one sandy clay soil, Tukulu, produced the highest micronaire value.
The micronaire values of the Schietfontein cotton field is higher than that of the Pretorius Rust cotton field due to the influence of the cotton variety planting.
By considering Table 5-15 it is evident that two AX class cotton quality was produced by the Glencoe and Avalon soil forms which is the best quality cotton. The Oakleaf and Tukulu soil forms produced AO class cotton. The AO class is considered the best class of the Group O. There is a very small price difference between the cotton produced in the two classes of cotton quality.
Table 5-16 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. The Oakleaf, Glencoe and Tukulu soil forms was above DUL during the growth stages where the cotton is most sensitive to soil water stress. The Oakleaf soil form produced the highest yield, but a lower quality cotton. By considering Table 5- 16 the quality of the cotton does not influence the value of the cotton, but the yield. When comparing the Oakleaf and Tukulu soil forms the limiting layer horizon is different. The yield and quality are affected by the limiting layer horizon. The Tukulu soil form’s gleyic limiting layer horizon tend to create waterlogged conditions that inhibit the formation of bolls and result in a lower yield.
However, it is more profitable to farm the higher yield soils such as the Oakleaf and Avalon.
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