TITLE:

Testing of Precision Agriculture Technologies in Irrigated Cotton at AG-CARES, Lamesa, Texas, 2000.

AUTHORS:

            K.F. Bronson, J.W. Keeling, T. Wheeler, R.J. Lascano, R. K. Boman, E. Segarra, J.

Booker, J.D. Booker, J. Mabry, Assistant Professor, Professor, Associate Professor, Professor, Extension Specialist, Professor, Research Assistants and Technician.

METHODS AND PROCEDURES:

            Experimental Design: Randomized complete block with 3 replications

            Plot size:              53 ft wide (16 40-inch rows) and > 500 ft long.

            Experimental area:  27 ac

            Soil type:                   Amarillo sandy loam to sandy clay loam

            Variety:                      Paymaster Roundup® Ready 2326

            Soil sampling:           Half-ac grid (Fig.1 and 2)

            P fertilizer rate:        Blanket-rate of 30 lb P₂O₅/ac,

                                                Average Variable-rate of 38 lb P₂O₅/ac

Planting date:           May 10, 2000

            Harvest date:            October 4, 2000

            Irrigation:                  LEPA on a 3.5 day schedule at 75% estimated cotton ET

replacement

RESULTS

Cotton responded to P fertilizer in all three landscape positions of the precision agriculture site at AGCARES (Table 1 and 2). Historically, the greatest yields have been observed in the bottomslope where re-distribution of water and nutrients occurs. Variable-rate (VRT) and blanket-rate resulted in lint yields greater than zero-P in both sideslopes. In the bottomslope, only the variable-rate treatment affected lint yields. The south-facing sideslope had the lowest lint yields in 2000. This may be due to the greater amount of blowing observed there and to faster soil water evaporation. The Micro-Trak® yield data was less variable than the hand-picked lint data and only the machine data showed the P fertilizer response (Table 1 and 2).

Temik® was applied at planting at a rate of 5 lb/ac to the entire 27-ac area. Greater nematode numbers were observed in the bottomslope, and for this reason, the VRT strips of this area received an additional 5 lb/ac sidedress of Temik. However, yields in this area were not affected by Temik®.

Preliminary cost and returns economic analysis of the VRT technology is shown in Table 3. This analysis does not consider the greater cost of grid-soil sampling or of VRT equipment. The

average P fertilizer rate applied in the VRT plots was 38 lb P₂O₅/ac, compared to 30 lb P₂O₅/ac in the blanket-rate plots. Although statistically there was no difference between the VRT-P and blanket-P treatments we did this analysis by calculating a “return to P fertilizer” for each. This preliminary analysis indicates that up to $24/ac return of VRT-P is possible. Extra or variable-rate Temik was not economical.

Table 1. Micro-Trak® cotton lint yields (lb/ac) for variable-rate, blanket-rate and zero-rate P

  fertilizer application, Lamesa, TX, 2000.

1 Means in a column followed by similar letter are not different by pairwise comparisons, p>0.05

Table 2. Hand-picked cotton lint yields (lb/ac) for variable-rate, blanket-rate and zero-rate P fertilizer application, Lamesa, TX, 2000.

1 Means in a column followed by similar letter are not different by pairwise comparisons, p>0.05

Table 3. Input application rates and cost and returns of input applications, Lamesa, TX, 2000

^a Assumes no gain in yield

^b Does not consider capital costs of variable-rate application equipment or the greater cost of 0.5-ac grid soil sampling and laboratory analysis for the VRT treatments.

Fig. 1. Half-acre grid soil sampling locations and Mehlich-3 P, AGCARES, Lamesa, TX 2000

Fig. 2. Variable-rate inputs experimental layout and P fertilizer rates applied (V = VRT,

B=blanket-rate, Z=xero-P), AGCARES, Lamesa, TX 2000