Objectives:

1.   Develop color-enhanced field maps using GIS graphics to display variations in soil characteristics such as topsoil depth and nitrate-nitrogen (NO₃-N) levels, and yields using field data provided by the precision agriculture team at TAES-Amarillo/Etter;

2.  Upon availability of data, compare annual profits and investment payback as nitrogen (N) fertilizer, seeding rates, and irrigation frequencies are varied in accordance with data outputs of the TAES-Amarillo/Etter precision agriculture team;

3.  Help design an appropriate experimental protocol and validate APEX with experimental NO₃-N, P, and sediment losses and simulate probabilities of losses exceeding safe drinking water standards using site-specific vs. uniform fertilization rates on selected treatments at Etter.

A.      Reporting Period:

        Sept. 1997-Aug. 1999

B.     Summary of Progress

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

        Spatial factors quantified in this research included the depth of topsoil and nitrogen variability in a 20-acre field (1100'x1800') at the North Plains Research Field, Etter, Texas. Soil depths were sampled and determined on 100-ft.spacings and geo-referenced. A color map was generated with GIS of the field site to display the topsoil variations that ranged from 12 in. to 72 in. over a short distance of 1000 feet. These data was utilized to determine three selected depth intervals or management zones of less than 30 in., 31 to 48 in., and over 48 in. topsoil depth Subsequently, nitrogen analyses of the soil samples were mapped in a similar fashion to indicate the initial variability in soil fertility. The average nitrate-N concentrations ranged widely and non-uniformly in the topsoil; from approximately 20 to 50 ppm/ft (approximately 80 to 200 lbs/ac for 4 feet of topsoil). Additionally, N nutrient availability was not correlated with topsoil depth.

Objective 2:   Develop and evaluate instrumentation and software to measure and analyze variability in crop production and plant response to that variability.

        The GIS software, GRASS, used in the mapping of soil depths and nitrate-N concentrations was available. 

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

        The physical feasibility of applying precision agriculture technology would be satisfactory in this field due to its high degree of variability in both topsoil depth (water holding capacity) and its initial fertility (nitrate-N concentrations). For irrigated corn, three rates of N fertility were correlated with the three soil depths for precision agriculture technology evaluation and environmental impacts (water quality of irrigation runoff). The N rates included 120 lb/ac N applied to the shallow soil area of the field, 180 lb/ac N to the medium depth soil area, and 240 lb/ac N to the deep soil area. Table 1 indicates that the very dry season of 1998 resulted in a maximum yield of irrigated corn of 198 bu/ac with the high rate of N on the deep soil. The yields on medium and shallow soils using 180 lb and 120 lb/ac N were about the same, 180 and 185 bu/ac, respectively. In the wetter 1999 season, again the high rate of N on the deep soil resulted in the maximum corn yield of 187 bu/ac with the other options following closely at 180 and 173 bu/ac.

        The economic impact of precision agriculture application averaged over the two seasons indicated that reducing N to 120 lb/ac on the shallow soil resulted in equivalent profitability to using the high N rate on deep soils, Table 2. However, this analysis does not account for the costs of VRT fertilizer applicators, GPS equipment, computers, or soil depth and nutrient sampling. In either case, the medium N rate on medium depth soils was not as profitable as the high N rate, a likely result of sharp yield losses with an insufficient reduction in N fertilizer to reduce costs by the amount of grain sales foregone.

        The runoff water quality from irrigating corn with a low energy sprinkler system was not well correlated with the rates of N fertilizer applied, Table 3. In 1998, runoff did not occur until mid-season due to the dry conditions resulting in no early season observations. Mid- and late-season runoff analyses indicated that the medium rate of N resulted in the highest loss of nitrate-N (1.2 lb/ac), the high rate second most (0.6 lb/ac) and the low rate, the least loss of N (.2 lb/ac). In 1999, the rain-supplemented soil water facilitated runoff with each irrigation application and increasing the amounts of N lost to .9 to 1.4 lb/ac, with some relation to the rate of N applied. In this case the high N application on the deep soil resulted in the highest loss of N with the shallow and medium rates of N, respectively, following closely. For the two years, there was no consistent indication that the reduced rates of applied N using low energy sprinkler irrigation resulted in improved water quality although the 2-year average loss was lower for the low rate versus the other two rates. More research is definitely needed in this area of environmental concern.

        The 1998-99 average percentage losses of nitrate-N were below 1% of the amounts applied, ranging from 0.43% to 0.61% for the high and medium rates, respectively. The low rate lost an intermediate percentage of 0.49%.

Objective 4:   Develop and evaluate variable rate application technology.

        This research project involved only two years of field research; one very dry season and one very wet season. Economic implications of VRT nitrogen fertilizer applications were marginal to negative for reducing the N rate on shallow and medium soils respectively. VRT nitrogen reduction on shallow soils resulted in equivalent profits over N costs to that of the high rate of N applied on deep soils but did not pay for any VRT equipment or sampling expenses. Reducing the rate of N with the medium soil depth was not as profitable as the other two options due to lower yields and insufficient reduction in N fertilizer costs.

        Environmental implications regarding the potential degradation of irrigation runoff water quality with increasing rates of N were not found in these two years of research. There was no consistent relation of the rate of N applied to the loss of N with the low energy sprinkler irrigation system. There was an indication that the lowest rate of N had an impact on reducing the runoff loss of nitrate-N but further research is needed.

Objective 5:   Establish an effective network for technology transfer through the AgriPartners program.

        This research project provides valuable information with respect to the VRT applications of nitrogen using sprinkler irrigation. It also provides economic and environ-mental information in an attempt to assess the tradeoffs of water quality with profitability. Though it would appear in the early stages of research that irrigation runoff water quality may not be consistently related to N rates of application, maintaining profitability is a marginal situation and has more potential with sharply reduced rates of N on shallow soil situations.

C.    Education/technology transfer:

        This economic/environmental data and results were presented to farmers at local agricultural conferences and field days.

D.    Milestones achieved:

        The above objectives were met within the timeframe set forth. Recently obtained irrigated corn yields and nitrogen loss runoff data will be statistically analyzed. These results will then be used to validate the APEX simulation model in the near future.

E.    Publications:

        None at this time other than annual reports to the southern regional research committee on precision farming S-283.

F.    Precision agriculture proposals submitted or funded:

• Gerik and Harman. 1999. Precision agriculture technology in Texas: Productivity and profitability versus water quality. THECB-ARP/ATP
• USDA-NRI: Harman and Gerik. 1999. Precision farming: New technology to protect water quality and enhance efficiency.

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

• October, 1997- Regional research organizational meeting of S-283- Precision Farming
• November, 1998- Presented initial 1998 irrigated corn yield and runoff quality of NPRF research and summarized economic implications of VRT nitrogen technology.
• November 1999- Presented 2-year summaries of VRT nitrogen technology research implications on corn yields, economics and environmental implications for runoff water quality.

H. Other developments:

• In relation to the S-283 southern regional research committee, Dr. Allan Jones, Assistant Director of TAES is the newly appointed administrative advisor.
• As part of the economic/environmental objective of the S-283 project, a survey format is being tested on select individual producers to assess barriers to adoption of precision farming technology.
• Another research project at the Amarillo Center has been recently funded in cooperation with the Amarillo National Resources Center for Plutonium to purchase 6 high quality runoff samplers. These will be used to determine background levels of nutrient losses by rainfall under native range conditions facilitating an ecological assessment of water quality of the Texas High Plains. These natural losses of nutrients can then be compared to all other production practices in the region including the option of new cropping technologies such as precision farming.

Table 1. 1998-99 Irrigated Corn Yields With VRT Nitrogen Applications by Soil Depth,Northern Plains Research Field, Etter, Texas.

Table 2. 1998-99 Economic Impact of VRT Nitrogen by Soil Depth in Irrigated Corn, Northern High Plains Research Field, Etter, TX.

*Does not include the cost of VRT fertilizer applicator, GPS equipment, computer, or soil coring and nutrient analyses costs.

Table 3. 1998-99 Nitrogen Runoff Losses from Irrigated Corn, North Plains Research Field, Etter, Texas.