Evaluation of Subsurface Drip Irrigation

Transcription

1 Evaluation of Subsurface Drip Irrigation William C. Robertson, Frank E. Groves, Robert Hogan, Jr., Leo Espinoza, and Matt Cordell 1 RESEARCH PROBLEM Drip irrigation of cotton is increasing throughout the United States, particularly in the West. A major benefit of drip irrigation is the ability to apply small amounts of water at high frequency intervals. This provides the opportunity to maintain the soil moisture at a specified moisture deficit. This is particularly beneficial in areas of the mid-south with soils that have shallow rooting potentials. However, significant rainfall and cloudy days experienced in the mid-south present challenges for cotton production using drip irrigation that are not normally present in the West. Limited information is available concerning drip irrigation in the mid-south. BACKGROUND INFORMATION Drip systems provide not only the potential to irrigate more frequently, but also the ability to more readily maintain specific moisture deficits at levels below field capacity either for part or all of the irrigation season. Irrigating to maintain a specified root-zone soil-moisture deficit provides the opportunity for increased soil-moisture storage from rainfall during the irrigation season. Timely delivery of nutrients through the system is another benefit. Drip-irrigation systems are more plentiful in the western United States. Low rainfall and the occurrence of few cloudy days contribute to the success of drip systems in the West. Significant rainfall and cloudy days experienced in the mid-south present challenges for cotton production using drip irrigation that are not normally present in the West. The objective of this study was to evaluate the growth and development of cotton grown under dryland, furrow-irrigated, and low-pressure drip-irrigation systems 1 Extension entomologist - cotton, Crop, Soil, and Environmental Sciences Department, Little Rock; cotton research verification program coordinator, Southeast Research and Extension Center, Monticello, extension entomologist, Northeast Research and Extension Center, Keiser; extension agronomist - soils, Cooperative Extension Service, Little Rock; and cotton program associate, Cooperative Extension Service, Little Rock, respectively. 179

2 AAES Research Series 543 in Arkansas and to compare revenue and expenses associated with each system, using partial budget analysis. RESEARCH DESCRIPTION A thirteen-acre field located on the Cotton Branch Experiment Station located near Marianna, Ark., was utilized for this study. NetaFim USA sponsored this study by installing a low-pressure system on approximately five acres of this field. The dripirrigation, furrow-irrigation, and dryland plots were arranged in a complete randomized block design with four replications. The drip tape was installed to the side of each row. Poor water-infiltration rates dictated installation on every row as opposed to every other row, as commonly installed for cotton in the Western United States. The cotton (Gossypium hirsutum L.) cultivar DP444BG/RR was planted 12 May 2005 into the silt-loam study area utilizing no-till best management practices. The University of Arkansas irrigation scheduling program was used to trigger furrow irrigations. Daily potential evapotranspiration and crop coefficients were used to trigger drip timings and rates. Recommended cultural practices were tracked throughout the season. Partial budget analysis was utilized to compare differences in expenses for plots receiving both irrigated methods compared to the dryland plots. RESULTS AND DISCUSSION Plant Growth and Development Although COTMAN growth curves differed during the season (Fig. 1), plantmapping data collected prior to harvest revealed no significant differences (Table 1). Days from planting to cutout also did not differ. Irrigation rates and timings varied. A total of 9.72 in. of water was applied to the furrow-irrigated plots in 8 events. The drip received a total of 5.25 in. in 24 irrigation events. Fertilizer applications for the dryland plots totaled in two knife applications. An additional 30 units N were applied to the furrow plots for a total of in two knife applications. The fertility program for the drip consisted of a knife application of and through the tape for a total of A liquid blend of was the fertilizer source used for the drip. Mepiquat chloride (MC) needs differed for the irrigation treatments. The dryland plots received 8.0 oz/acre in a single application. The furrow-irrigated plots received an additional 24 oz with one additional application. An additional 40 oz of MC and two applications beyond that of the dryland plots were used in the drip plots. Yield and Fiber Quality Significant differences were observed for turnout and lint yield (Table 2). More lint was produced in the irrigated plots. The drip plots out-yielded the furrow plots. Turnout did not differ between any of the irrigated plots and was less than the dryland plots. Fiber-quality parameters did not differ statistically in the study. 180

3 Summaries of Arkansas Cotton Research 2005 Partial Budget Analysis Revenues and expenses are included in Table 3 to reflect differences in yield for the irrigation system and additional inputs beyond those used for the dryland system, which serves as the basis for this analysis. Fixed costs are also included which basically reflect ownership costs associated with each of the irrigation systems. Although the fixed costs for the drip exceeds those of the furrow-irrigation system, land-leveling costs often associated with furrow irrigation are not included. Fixed costs of a centerpivot are $ A cost of $400/acre was used for the low-pressure drip irrigation system with a life of six years. Costs for the system and labor involved in its use and system life vary by location and according to water quality. An expected cost of this system can range from $400 to $600/acre with an expected system life of three to eight years. PRACTICAL APPLICATION Although this system was small, challenges were encountered similar to those that could be expected in a real-time production situation. Learning curves such as dealing with the calculation of effective rainfall accumulation as well as having a good understanding of dealing with water quality issues are the most noted differences in the low-pressure drip system compared to the furrow-irrigation system. Perhaps the greatest challenge to system adoption is related to fertility. Costs and availability of product will improve with increasing demand. Although lint yield and revenue were greatest with drip, the fertility program costs pulled the net of partial total expenses lower than that of the dryland plots. Holding all values from this study constant, with the exception of fertility, a change in direct costs for the fertility program in the drip system from $257 down to $80/acre or less would move the drip system from last to first in terms of net partial total expenses. No value for the 54% reduction of total irrigation amounts observed with the low-pressure drip system was factored into this study. Lint-yield expectations of the drip system will likely increase over time compared to the furrow-irrigated plots as management and knowledge of the drip system improve. However, costs of production, particularly fertility, must be addressed in order for the drip system to be profitable. 181

4 AAES Research Series 543 Table 1. Plant-mapping data at harvest. Irrigation system Retention Height Nodes H:N ratio Cutout (% first position) (in.) (no.) (DAP) Dryland Furrow Drip LSD (0.05) NS z NS NS NS NS z NS = not significant. Table 2. Yield and fiber parameters. Irrigation system Turnout Lint Mic Length Strength (%) (lb/acre) (in.) (g/tex) Dryland Furrow Drip LSD (0.05) NS z NS NS z NS = not significant. Table 3. Partial budget analysis utilizing the dryland system as the basis for comparison. Item Dryland Furrow Drip Yield (lb/acre) Loan ($) Lint revenue ($) Change in direct (irr) (irr) costs ($) (fert) (fert) (MC) (MC) Net of partial direct expenses ($) Change in fixed costs ($) (irr) (irr) Net of partial total expenses ($)

5 Summaries of Arkansas Cotton Research 2005 Fig. 1. COTMAN growth curves for dryland, furrow-, and drip-irrigated plots. 183