A.  Reporting Period:

        Sept. 1997 - Aug. 1999

B.     Summary of Progress: (Address all applicable objectives, data must be included)

Objective 1:   Quantify the spatial and temporal variability of factors that can be addressed by precision agriculture practices.

        In the course of evaluating the spray/tillage tool, measurements were made to quantify resulting cotton yield. Measurements were typically made at each of 40 geo-referenced sites in a 9-acre field irrigated by an 8-span, LEPA irrigation system. Depending on the attribute, measurements were obtained once (soil texture), or multiple times (soil water) over the two year project period. A correlation matrix analysis of 33 measured attributes in 1998 and 42 measured attributes in 1999 is summarized in Table 1.

        The 1998 crop year was hot and dry. Seasonal irrigation quantity was strongly correlated to lint yield in 1998, but was not an experimental variable the following year. In 1999, cotton was replanted in June due to hail with seasonal rainfall near normal. The relationships among factors differed from 1998 to 1999, however, cotton lint yields in both years were most strongly correlated to factors related to seasonal water use - soil texture, slope or elevation, and soil water measurements. We currently plan to continue this experiment for one additional year.

The following preliminary conclusions were reached based on the work conducted through 1999:

• Variability in cotton lint yield is most strongly correlated with factors associated with crop water use (slope, elevation, soil texture, and seasonal irrigation) and with certain plant characteristics (boll count and plant height), and less well correlated with other factors (perennial weed infestations, residual nitrogen, or plant population).
• Spray/tillage equipment using DGPS systems for site-specific control of perennial weeds is useful and should have a long-term positive effect on weed control, but does not yet show an economic advantage over traditional methods.
• Use of a row-guidance system to position tillage devices and spray nozzles for the control of woollyleaf bursage in cotton, for reduced application rates of burn down chemicals on cover crops, and for efficient placement of growth regulators on narrow row cotton irrigated with LEPA has been positive.

Objective 2:  Develop and evaluate instrumentation and software to measure and analyze

This objective was not addressed within this project.

Objective 3:  Determine the economic and physical feasibility of precision agriculture  components as they relate to farming systems.

        Site-specific application of herbicides on perennial weeds.

        Herbicides were applied in a site-specific manner under seven spans of the 9-acre LEPA irrigated cotton field. The area under "span 4" was treated conventionally. Table 2 gives a summary of the differences in yield and chemical costs associated with applications on specific weed pests in site-specific and conventional areas during the 1999 growing season. The data indicate that cotton lint value over chemical cost is greater for the conventional area than for the site-specific area. These results are preliminary and are contrary to results of multiple studies showing decreased lint yield with increased perennial weed infestation. We predict that weed infestations will increase in the conventional areas (reducing yields) and decrease in the site-specific areas (increasing yields) over time.   

Precision tillage with chemical application in woollyleaf bursage invested cotton.