Developing and Testing a Trafficability Index for Planting Cotton in the Texas Blackland Prairie

The Texas Blackland Prairie is one of the most productive agricultural regions in Texas. This region provides a long growing season coupled with soils that have a high water holding capacity. However, the soils also provide significant challenges to producers because the high water holding capacity is a product of a high clay percentage. This research was aimed to develop and test an expert-based trafficabililty index, based upon soil moisture, for planting cotton (Gossypium hirsutum L.) in the Texas Blackland Prairie. Testing the index focused on quantifying the potential effect of high soil moisture at planting on seed furrow sidewall compaction and associated plant growth response. Once the trafficability index was developed, three workable soil moisture regimes were recreated in no-tillage and conventional tillage plots at the Stiles Farm Foundation in Thrall, Texas. The index nomenclature included: “Dry-Workable”, “Optimal” and “Wet-Workable”. After planting cotton into the plots, 0.45 x 0.20 x 0.15 m intact soil blocks were removed from each plot and kept in a controlled environment. After 28 days, each block was destructively harvested to quantify plant root and shoot growth responses. The trafficability index was created using experienced producers by collecting qualitative and quantitative soil moisture measurements. From “Dry Workable” to “Wet Workable”, the gravimetric soil moistures were 0.17, 0.22, and 0.26 g g-1. No evidence of a detrimental plant response because of seed furrow, sidewall compaction from planting at too high a soil moisture content could be quantified in the controlled study. Because the results showed a definite advantage to plant growth by planting the “Wet Workable” index, the tillage practice that allows the producer to enter the field with a planter at higher moisture contents has an advantage.