Principal Investigator: Kevin F. Bronson^a

^aTexas Agric Exp Stn, RR 3, Box 219, Lubbock, TX 79403

Email: k-bronson@tamu.edu

Cooperators: J.W. Keeling^a, T. Wheeler^a, S. Searcy^abc, A. Brashears^d, R.J. Lascano^a, 

C. Trostle^b,  T. Chua^a, R. Boman^b, P. Dotray^abce, and E. Segarra^ae

^bTexas Agric. Extn Serv, Lubbock and College Station, TX

^cTexas A&M University, College Station, TX

^dUSDA-ARS, Lubbock, TX

^eTexas Tech University, Lubbock, TX

Primary Research Location: Lamesa and Ropesville, TX

Project Title: On-farm testing of precision agriculture technologies for Texas High Plains Cotton

Project Objectives:

1. To evaluate at two sites precision agriculture (PA) practices in cotton of grid soil sampling/analysis, and variable-rate technologies (VRT) compared to conventional, blanket applications of fertilizer.

2.   Conduct economic analysis of PA/VRT vs. conventional, blanket farming practices.

3.  Demonstrate PA field practices through extension outreach in conjunction with TAEX and Agripartners

Reporting Period:  January 1 2001 – December 31  2001

A.           Summary of Progress:  

Objective 1. To evaluate at two sites precision agriculture (PA) practices in cotton of grid

soil sampling/analysis, and variable-rate technologies (VRT) compared to conventional, blanket applications of fertilizer.

Introduction:

Phosphorus fertilizer response in cotton is unpredictable, even with soil tests (Funderburg et al., 1996; Bronson et al., 2001).  Nitrogen and water are the main limitations in the Southern High Plains (Morrow and Krieg, 1990), with P probably being the third limiting factor. There have not been many studies on cotton P fertilizer response at the landscape scale (Bronson et al., 2001).  Landscape position has been widely reported to affect productivity and N response of crops like wheat, due to redistribution of water to lowerlying landscape positions  (Pennock et al., 1994; Fiez et al., 1995). 

Objectives:

 (i) compare variable-rate-P, blanket-rate-P,  and zero-P applications on P accumulation and lint yields at two 27-ac irrigated cotton sites in the Southern High Plains, the secondary objective was to (ii) determine the effect of landscape position and soil properties on P fertilizer response, and lint yields.

Materials and Methods:

Experimental design

Studies were conducted at two sites in a randomized complete block design with three replicates, each replicate within a center-pivot irrigation span.  Phosphorus treatments were zero-P, blanket-rate-P and variable-rate-P.  Plots were sixteen, 40-in. rows wide, and ranged up to 1000 yards in length.   Phosphorus fertilizer was applied as H₃PO₄ (0-34-0) near the time of planting with a placement of 4 in. from the seed row and 4 in. deep.  The blanket rate of P was 45 and 30 lb P₂O₅ ac^-1 in both years at Lamesa, and Ropeville, respectively (Table 1) This was based on Mehlich-3-P in the 0-6-in. soil (Zhang et al., 1998).  Variable-rate-P was applied with the same fertilizer rig, fitted with Agchem/Soil-Teq^® variable-rate valves, computer, ground-speed radar and Satloc^® GPS. 

Lamesa

The soil here is Amarillo sandy/sandy clay loam (Aridic Paleustalf).  In March 2000, soil samples were taken at 63 GPS-referenced points in the 27-ac. experimental area.  Ten subsamples were taken, by hand soil probe, of the 0-6-in. depth and analyzed for Mehlich-3-P and NO₃.  Two subsamples were taken of the 6 to 24-in. depth for NO₃ analysis.  A blanket N fertilizer application was based on an N requirement of 120 lb N ac^-1 for a 2 bale ac^-1 (1000 lb lint ac^-1) yield goal and considering the 0-24-in. soil NO₃ (Zhang et al., 1998). On 10 May 2000, Paymaster ® Round-up Ready 2326 cotton was planted into 40-in. rows.

Hand harvesting of lint was done on 22 ft. of row at each GPS referenced point.  Seedcotton was ginned and lint weighed for each sample.  In spring, 2001, the same soil sampling practices and soil analyses were done as in 2000. Paymaster ® Round-up Ready 2326 cotton was planted on 28 May, at which time P fertilizer was applied, similar to 2000.

Ropesville

The two soil series here are Amarillo sandy/sandy clay loam (Aridic Paleustalf), and Portales sandy clay/sandy clay loam (Aridic Calciustolls). In March 2000, soil samples were taken at 60 GPS-referenced points in the 27-ac study area, in the same manner as in Lamesa and analyzed for NO₃ and Mehlich-3-P.  On 6 May 2000, Paymaster ® Round-up Ready 2326 cotton was planted in 40-in. rows.  A blanket N application was based on 0-24 in. soil NO₃ (Zhang et al., 1998).  Hand harvesting of 22 row ft. per GPS point was on 29 September.

On 2 May, 2001, Paymaster ® Round-up Ready 2326 cotton was planted, but a hail storm with 6 in. rain on 25 May destroyed the crop.

Results and discussion:

 

Lamesa

Relative elevation and slope with the row were negatively correlated with biomass, and P accumulation at early squaring, and with lint yield (data not shown).  Soil properties did not have much affect on cotton in 2000 or 2001.  Greater yields on the lowerlying bottomslope at this site were reported by Li et al. (2001) and Bronson et al. (2001).  Li et al. (2001) measured greater soil water content in the bottomslopes, presumably due to runoff of rain and irrigation.  Therefore, we delineated bottomslope from sideslope using slope with the row data (derived from elevation data). The bottomslope had the lowest slope with the row (< 0.4%).  Landscape position and landscape x P treatment was incorporated into the ANOVA. 

Cotton biomass and P accumulation at early squaring were not affected by P fertilizer, but were greater in the bottomslope than in the sideslopes (P accumulation in 2001 shown in Fig. 1).  In 2000, more P was applied to the variable-rate plots (average of 38 lb P₂O₅ ac^-1) than to the blanket plots.  Less P was applied in 2001 to the variable-rate plots (average of 16 lb P₂O₅ ac^-1), despite similar soil P levels.   Lint yield in the bottomslope was greatest in both years of the study (Table 1).  In 2000, lint yield in the north-facing sideslope was less than in the south-facing sideslope.   As mentioned above, water is apparently redistributed to the bottomslope in this location, resulting in greater plant growth.  Response to P fertilizer was less consistent than landscape position.  Lint yields responded to variable-rate-P in 2000, averaged across landscape position. In any particular landscape however, P did not affect lint yields.   In 2001, Lamesa lint yields responded to blanket-rate-P in the south-facing sideslope only (Table 1). 

Ropesville

Strong negative correlations were observed between P accumulation, biomass at early squaring and soil Ca (data not shown).  High soil Ca levels were associated with the calcareous Portales soil, on the west half of the Ropesville study site.  Unlike the Lamesa site, there was no correlation between elevation or slope with the row and plant measurements. We therefore delineated the two soil types in our data sets, and incorporated soil type, and soil type x P management into the ANOVA.

Phosphorus accumulation and biomass at early squaring were both lower in the Portales soil then in the Amarillo soil (Table 2).  In both blanket- and variable-rate-P treatments, responses in P accumulation and biomass were observed, relative to the zero-P plots, but only in the Amarillo soil.  Apparently soil and added P was less available on the calcareous Portales soil.  A lint yield response to both blanket-rate and variable-rate-P was observed in the Amarillo soil only.  Averaged across P management, lint yield was similar between soil types (Table 2).  Less P was applied with variable-rate (on average) than with blanket-rate-P, despite similar soil test P levels. 

Fig. 1.  Phosphorus accumulation at early squaring of cotton, Lamesa, TX, 2001

Table 1. Lint yield as affected by phosphorus fertilization and landscape position, Lamesa, TX, 2000 and 2001.

Phosphorus treatment	North-facing sideslope	Bottomslope	South-facing sideslope	S.E. of the difference	Mean
	------------------------------------- lb ac-1 ------------------------------------
	2000
Variable-rate-P	687 a†	762 a	575 a	50	675 a†
Blanket-rate-P	602 a	690 a	564 a	47	619 ab
Zero-P	604 a	671 a	521 a	49	598 b
S.E. of  diff.	44	51	47		28
Mean	631 b‡	707 a	553 c	27
	2001
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  diff.	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)

Table 2.  Cotton phosphorus accumulation at early squaring, and lint yield as affected by phosphorus fertilization and soil type, Ropesville, TX, 2000.

Phosphorus treatment	Amarillo sandy loam	Portales clay loam	S.E. of difference	Mean
	Phosphorus accumulation
	-------------------------- lb P ac-1 ---------------------------
Variable-rate-P	2.3 a†	1.5 a	0.2	1.9 a†
Blanket-rate-P	2.2 a	1.2 a	0.2	1.7 ab
Zero-P	1.5 b	1.4 a	0.2	1.4 b
S.E. of diff.	0.2	0.2		0.2
Mean	2.0 a‡	1.4 b	0.1
	Lint yield
	--------------------------------- lb  ac-1 ------------------------------
Variable-rate-P	663 a†	622 a	39	643 a†
Blanket-rate-P	646 a	600 a	39	623 a
Zero-P	538 b	606 a	39	572 a
S.E. of diff.	38	39		28
Mean	616 a‡	609 a	23

† 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).

Objective 2.  Conduct economic analysis of PA/VRT vs. conventional, blanket-rate farming practices.

Cost and returns analysis for both blanket-rate and variable-rate-P fertilization is shown in Table 3.  This analysis does not consider the extra costs incurred with variable-rate compared to blanket-rate-P fertilization.   These include cost of grid soil sampling, additional laboratory analyses costs of the larger number of soil samples, and the cost of retro-fitting a liquid fertilizer rig with variable-rate equipment, GPS and ground speed radar.

            Compared to zero-P, blanket-rate-P returned positive cash in Ropesville, 2000 and Lamesa, 2001, but gave a negative return at Lamesa in 2000 (Table 3).  Variable-rate-P applications gave positive cash returns in all three site-years.  However, in Lamesa, 2001, the cash return to P fertilization was greater for blanket-rate-P ($18.00/ac) than for variable-rate-P ($13.93/ac).

Table 3. Cost and returns of phosphorus fertilizer applications, Ropesville, 2000 and Lamesa, TX, 2000-2001

	Lint yield (lb/ac)				Lint income† ($/ac)				Lint income above zero-P				Ave rate of P2O5  (lb/ac)				Cost of P2O5 ‡ ($/ac)			Net return to P fertilizer ($/ac)
			Ropesville, 2000
Variable-rate-P			643				321.50				35.50				41.9			14.66		20.84
Blanket-rate-P			623				311.50				25.50				45.0			15.72		9.78
Zero-P			572				286.00								0			0
			Lamesa, 2000
Variable-rate-P			675	337.50				38.50				38.4				13.44			25.06
Blanket-rate-P			618	309.00				10.0				30.0				10.50			-0.50
Zero-P			598	299.00								0				0
			Lamesa, 2001
Variable-rate-P		935				467.50				19.50				15.9			5.57			13.93
Blanket-rate-P		953				476.50				28.50				30.0			10.50			18.00
Zero-P		896				448.00								0			0

† $ 0.50/lb lint

‡ $ 0.35/lb P₂O₅

B.          Education/technology transfer:

Objective 3.  Demonstrate PA field practices through extension outreach in conjunction with

TAEX and Agripartners.

Bronson, K.F.  Site-specific nutrient management in cotton. Southern Mesa Agricultural Conference. 17 Janaury, 2000, Lamesa, Texas.

Bronson, K.F.  Soil Fertility Management in Cotton. Caprock Cotton Conference. 18 Janaury, 2000, Floydada, Texas.

Bronson, K.F.  Precision Agriculture and Soil Testing.  Texas Ag Industries Association 2^nd Annual Member Conference.  24-25 January, 2000, San Antonio, TX.

Bronson, K.F.  Soil testing site-specific nutrient management.  Precision Agriculture and Soil Testing.  Precision Agriculture Training.  1 August, Ropesville, TX.

Bronson, K.F.  On-farm testing of site-specific nutrient management.  Southern Mesa Agricultural Conference. 15 Janaury, 2001, Lamesa, Texas.

Bronson, K.F.  On-farm testing of site-specific nutrient management.  South Plains Agricultural Conference. 23 Janaury, 2001, Brownfield, Texas.

Bronson, K.F.   Research update on site-specific nutrient management in cotton.  Nutrient, Soil,

and Water Management Worksop^TM, 7 January, 2002, Amarillo, TX.

C.          Milestones achieved: 

Successfully tested PA/variable-rate technologies in cotton on large, field-scale plots.  Additionally, preliminary cost and return economic analysis were executed.  In two of three site-years studied, less fertilizer was applied with PA/VRT approaches than with conventional.                   

D.          Publications:

Published Abstracts

Bronson, K.F., J.D. Booker, J.W. Keeling, and J.L. Mabry.  2000.  Remote sensing of in-season nitrogen requirements for irrigated cotton in the Southern High Plains. 2000 Proceedings Beltwide Cotton Conferences vol. 2. p. 1407. National Cotton Council of  America, Memphis, TN.

Bronson, K.F., J.W. Keeling, T. Wheeler, R.J. Lascano, P. Dotray, A. Brashears, S. Searcy, K. Siders, J.D.   Booker, J. Booker, R. Boman, H. Li, and T. Chua. 2001.  On-farm testing of site-specific management for irrigated cotton.  2001 Proceedings Beltwide Cotton Conferences vol. 1 p. 567. National Cotton Council of  America, Memphis, TN.

Booker, J.D., K.F. Bronson, T. Chua, J.W. Keeling, R.J. Lascano, and R.K. Boman.  2001.  Multi-variate analysis of multi-spectral reflectance to identify nutrient deficiencies in cotton.  Agronomy Abstracts.  2001. Annual Meetings.  [CD-ROM computer file] American Society of Agronomy, Madison, WI.

Booker, J.D., K.F. Bronson, J.W. Keeling, T. Chua, R.J. Lascano, R.K. Boman, S. Searcy, and A. Brashears.  2001.  Grid vs. landscape position or soil type based soil sampling strategies for the High Plains.  Agronomy Abstracts.  2001. Annual Meetings.  [CD-ROM computer file]   American Society of Agronomy, Madison, WI.

Bronson, K.F., J.W. Keeling, T. Wheeler, R.J. Lascano,  J.D. Booker, R.K. Boman, S. Searcy, and T. Chua.  2001.  Response of cotton to variable-rate phosphorus, landscape position and soil type. Agronomy Abstracts.  2001. Annual Meetings.  [CD-ROM computer file] American Society of Agronomy, Madison, WI.

Bronson, K.F., J.D. Booker, T.T. Chua, J.W. Keeling, R.K. Boman, and T. L. Provin. 2002.  Soil test phosphorus extract comparisons for cotton using grid soil data.  2001 Proceedings Beltwide Cotton Conferences vol. _ p. __. National Cotton Council of  America, Memphis, TN (Submitted).

Journal articles

K.F. Bronson, J.W. Keeling, J.D. Booker, T.T. Chua, T. A. Wheeler, R.K. Boman, and R.J. Lascano.  2002.  Cotton and soybean yields and phosphorus accumulation: Influence of variable-rate phosphorus fertilizer, landscape position and soil properties.  Agron J.  (To be submitted 03/02).

K.F. Bronson, J.W. Keeling, J.D. Booker, T.T. Chua, T. A. Wheeler, R.K. Boman, and R.J. Lascano.  2002. Multi-spectral reflectance predicts in-season nutrient content, biomass and lint yields of irrigated cotton.  Agron J.  (To be submitted 03/02).

Experiment Station publications and web page bulletins

Bronson, K.F. 2001. From Grid Soil Sampling to Management Zones in the Southern High Plains.  Texas A&M University, Texas Agric. Exp. Stn Publication. http://lubbock.tamu.edu/soilfertility/pdfs/GridSoilSampling.pdf

Bronson, K.F. , J.W. Keeling, T. Wheeler, R.J. Lascano, R.K. Boman, E. Segarra, J. Booker, J.D. Booker, and J. Marbry. 2001. Testing of Precision Agriculture Technologies in Irrigated Cotton at AG-CARES, Lamesa, Texas, 2000.  Dawson County 2000 Annual Report -  Agricultural Complex for Advanced Research and Extension Systems.  p. 1-9. Texas Agric. Extn. Serv. and Texas Agric. Exp. Stn. http://lubbock.tamu.edu/soilfertility/pdfs/agcarepacot.pdf

Bronson, Kevin, Calvin Trostle, Wayne Keeling, and J.D. Booker.  2001.  Correcting iron deficiencies in soybean. Texas A&M University, Agricultural Program Publication. http://lubbock.tamu.edu/soilfertility/pdfs/IronDeficiencySoybean.pdf

 

Proceedings of Meetings

McFarland, M.L., R.G. Lemon, F.M. Hons, K.F. Bronson, J.J. Sloan, E.L. Clawson, J.T. Cothren, and J.E. Matchoca.  2001.  Soil Fertility Reasearch in Texas.  Proceedings of the 2001 Southern Soil Fertility Conference.  P. 49-59. The Samuel Roberts Nobel Foundation, Ardmore, OK.

Bronson, K.F., J.W. Keeling, J.D. Booker, T.T. Chua, and R.K. Boman.   Variable-Rate

Phosphorus Fertilization of Cotton And Soybean in The Southern High Plains.  (To be presented at 2002 Great Plains Soil Fertility Conference, 5-6 March, 2002, Denver, CO.).

E.          Precision agriculture proposals:

Variable rate phosphorus fertilizer applications for irrigated cotton in the Southern High Plains, $3,000/year, 1999-2001, Phosphate and Potash Institute, Foundation for Agronomic Research, Norcross, GA (Principle investigator)

Improving nitrogen fertilizer use-efficiency in deficit-irrigation systems for cotton in the Southern High Plains, $318,500, 1999-2002, USDA/CSREES National Research Initiative (Principle investigator)

Updating Cotton Soil Test Calibrations and Fertilizer Recommendations for Nutrient Management Plans and Increased Profit in the High Plains, $20,000, 2001-2002, Cotton Incorporated, Texas State Support Committee (Principle investigator)

F.           Precision Agriculture meetings attended/papers (posters) presented:

Bronson, K.F*., R.J. Lascano, J.D. Booker, J. Booker, S. Machado, E. D. Bynum, Jr. T.L. Archer,

H. Li, and J.W. Keeling. 2000.  Grid soil sampling: Comparisons of grid size with landscape and soil texture-based sampling strategies [CD-ROM computer file] . In: P.C. Robert et al. (eds.) Proceedings of the 5^th International Conference on Precision Agriculture, Minneapolis, MN, Jul. 16-19, 2000, ASA, CSSA, and SSSA, Madison, WI.

Bronson, K.F., J.D. Booker, J.W. Keeling, T.T. Chua, T.A. Wheeler, and R.J. Lascano.  2002.  Partial canonical correlation analysis of leaf nutrient concentrations to explain chlorosis in cotton and soybean.  In: P.C. Robert et al. (eds.) Proceedings of the 6^th International Conference on Precision Agriculture, Minneapolis, MN, Jul. 14-17, 2002, ASA, CSSA, and SSSA, Madison, WI (Submitted).