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Cotton was grown in a densely infested woollyleaf bursage area in 1998 and 1999 to determine lint yields as a result of combinations of treatments with the herbicides RoundupÔ and MSMA and tillage with conventional and position-sensitive (using row-guidance) tillage. The treatment area had not been use for crop production for several years prior to 1998 due to this perennial weed. The results are summarized in Table 3. Results show precision tillage with no chemical application produced yields (533 lb./A) approaching those of multiple RoundupÔ applications on transgenic cotton varieties with cultivation (596 lb./A) and far exceeded yields of treatments with MSMA and traditional cultivation (254 lb./A). Precision tillage with Roundup (624 lb./A) or with MSMA (606 lb./A) improved yield over precision tillage alone (533 lb./A). The combination of precision tillage and site-specific herbicide application (using DGPS controlled devices) provides opportunities of reducing weed infested areas without spreading this pest to non-infested areas.
Objective 4:Develop and evaluate variable rate application technology.
A variable-rate spot sprayer/tillage tool was assembled and field evaluations of this tool initiated in the first year of this project. The operation of the tool was refined and its evaluation continued in the second year. The spray/tillage tool is composed of the following elements:
Hamby 4-row tool carrier with gauge wheels to accommodate alternate row LEPA
Accu-TrakÒrow guidance system
SatlocÒL-band DGPS
FujitsuÒ 1200 tablet field computer
Field RoverÒ v1.0 (SSToolboxÒ) - field data acquisition software
ArcviewÒ/ SSToolboxÒ - data analysis software
AgViewÒ by GIS Solutions - field software required for operation of variable rate controller
RavenÒ SCS700 variable rate controller w/valves, meters, radar, etc.
Two "positioning" elements are contained in this tool. The first provides relative location "down the row" using DGPS signals. This allows changes in chemical application rates as the tool moves along established traffic paths. The second element provides location "within the row" using a row-guidance system which mechanically tracks a pre-established plant row or trench. This system allows precise positioning of spray nozzles and tillage devices within a crop canopy. This basic control system could be modified for site-specific applications of nutrients, pesticides, seed, etc. as research and demonstration needs dictate. The following figure shows the assembled spray/tillage tool containing the two positioning elements.
Figure 1. Spray/tillage tool constructed and used in field experiments at TAES, Halfway, TX, 1998-99.
Several field experiments were initiated at the TAES, Halfway using the precision spray/tillage tool. These experiments included:
Perennial weed control by site-specific techniques in irrigated cotton. The objective was to evaluate the use of site-specific applications for the long term control of perennial weed species in cotton and to document yield variability due to weed infestation, soil parameters, slope and irrigation treatments.
Comparison of methods to control woollyleaf bursage in cotton production. The objective was to evaluate the use of row-guidance for placement of chemicals and tillage devices to control the growth and spread of this noxious weed in West Texas cotton fields.
Non-uniform application of agricultural chemicals to improve production efficiencies. The objective was to use the row-guidance elements of this tool in alternative cotton production schemes irrigated by LEPA systems. The tool was used to efficiently terminate narrow strips of cover crops and to apply growth regulators on cotton plants that were physically closer to available irrigation water than other plants.
Much of the equipment development and evaluation was described in previous sections of this summary. Additional work on equipment in 1999 included the laboratory and field evaluation of a revised solution control system for the variable-rate spray applicator and the construction of a "micro-hooded" sprayer for non-uniform solution application "across the bed" without crop foliage damage.
Perennial weed areas were more clearly defined in 1999 by rating infestations at 360 referenced points in the 9-acre field instead of attempting to define weed boundaries. Visual ratings were taken on three dates in 1999. Figure 2 shows the areas infested with blueweed and woollyleaf bursage did not change greatly from 1998 through September 1999. This figure also shows reductions of silverleaf nightshade from 1998 to May 1999 in areas treated by site-specific applications (all spans except Span 4). Although nightshade reappeared in previously infested areas by September 1999, young cotton plants had less competition from this pest early in the growing season and nightshade density remained highest in the conventional area (Span 4).