Irrigation economics of drip-irrigated cotton under deficit-irrigation

In a case study spanning 16 years, the adoption of sub-surface drip irrigation (SDI) on cotton was found to be highly beneficial when compared against traditional furrow method of irrigation for a 486-acre farm in the St. Lawrence, TX area. The study, broken into two eight-year periods, consisted of a Pre-SDI period (1980-1988) characterized by the use of normal irrigation methods typical to the area (furrow irrigation with short [700 foot] runs) and a Post-SDI period (1989-1996) in which SDI was slowly introduced to the farm, starting with a 40-acre block in 1989. Over time the SDI acreage increased to its current level of 345 acres. The average annual return to investment since installation was 444%. Increased net income ($66,454 per year) came from increased on-farm production (stemming from increasing both average yield levels and planted acreage) and from decreases in irrigation labor and cultivation costs. The additional costs resulting from installation of the SDI system (-$20,607 per year on average) came from the system cost itself (including installation, this amounted to about $500 per acre) and increased water/fertilizer costs. Total revenues to date from the venture are $673,423 (based on interest on farm profit at 9%). The system and all associated costs were, in effect, recovered within the first several months of use. Two models were developed to estimate the yield increase that could be attributed to the introduction of SDI on this farm. Annual rainfall amounts continue to influence final yields and production levels for the study farm even after SDI was installed. The second model employed to estimate yield impact incorporated both SDI acreage and precipitation. Yield levels for the county were stagnant between the sixteen years of the study; however, the SDI farm increased yield levels by 17.6%. The increase in yields, coupled with the increased cotton acreage, resulted in a 43.7% increase in total, on-farm cotton production for the farm as it changed from furrow irrigation to sub-surface drip irrigation.