TITLE:
Testing of Precision Agriculture Technologies in Irrigated Cotton at AG-CARES, Lamesa, Texas, 2001.
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 Associates 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 16 lb P2O5/ac
Zero-P
Planting date: May
Harvest date: October
Irrigation: LEPA on a 3.5 day schedule at 75% estimated cotton ET
replacement
SUBSTANTIALLY LESS P FERTILIZER WAS APPLIED TO THE VARIABLE-RATE PLOTS (AVERAGE OF 16 LB P2O5/AC) THAN IN THE BLANKET-RATE PLOTS (30 LB P2O5/AC). HOWEVER, LANDSCAPE POSITION/SLOPE AT LAMESA, HAD GREATER IMPACT ON COTTON P ACCUMULATION AND YIELDS THAN P MANAGEMENT.
Cotton [Gossypium hirsutum (L.)] response to P fertilizer is often inconsistent. Variable-rate fertilization can match soil test P and P fertilizer rate on a site-specific basis. Soil properties and landscape positions may affect P fertilizer response and yields. Our main objective was to compare variable-rate P, blanket-rate P, and zero-P applications on a 27-ac site at AG-CARES, Lamesa, TX. Soil samples (0-6 in.) were taken in the spring of 2001 on a 0.5 ac grid, and analyzed for Mehlich-3-P. Phosphorus uptake at early squaring (Fig. 1) and lint yields (Fig. 2) were greater in the bottomslope than in the south-facing sideslope. In 2001, lint yields responded to blanket-rate P in the south-facing sideslope only.
Table 1. Lint yield as affected by phosphorus fertilization and landscape position, AG-CARES, Lamesa, TX, 2001.
|
Phosphorus treatment |
North-facing sideslope |
Bottomslope |
South-facing sideslope |
S.E. of the difference |
Mean |
|||||
|
|
----------------------------------------------- lb/ac------------------------------------------- |
|||||||||
|
Variable rate-P |
892 a† |
1047 a |
866 ab |
50 |
935 a† |
|||||
|
Blanket rate-P |
963 a |
1013 a |
885 a |
50 |
953 a |
|||||
|
Zero-P |
896 a |
1021 a |
769 b |
50 |
896 a |
|||||
|
S.E. of difference |
46 |
51 |
90 |
|
29 |
|||||
|
Mean |
916 b‡ |
1026 a |
840 b |
29 |
|
|||||
† Means in a column followed by the same letter are not significantly different by pairwise t test (P=0.05)
‡ Means in a row followed by the same letter are not significantly different by pairwise t test (P=0.05)
Fig. 1. Phosphorus uptake at early squaring and grid soil/plant sampling locations, AG-CARES, Lamesa, TX 2001
Fig. 2. Lint yields (interpolated between hand sampling points), (V = VRT,
B=blanket-rate, Z=xero-P), AG-CARES, Lamesa, TX 2001