Author: Brad Watkins

Arkansas has experienced a significant expansion in irrigated cropland since the beginning of the 1980s. From Census year 1982 to Census year 2017, irrigated harvested cropland acres grew from 2.022 million acres to 4.848 million acres, respectively, representing an increase of +2.826 million acres (USDA, NASS, 2023a). The majority of this increase in irrigated cropland acres (approximately 75% of the increase) was due to the expansion of irrigated soybean area. 

Figure 1 presents Arkansas soybean harvested acres split into all acres, non-irrigated acres, and irrigated acres for the years 1979 – 2018. All soybean harvested acres (non-irrigated + irrigated) dropped from a record level of 5.15 million acres in 1979 to 3.20 million acres in 1988 and thereafter remained relatively level for the state at 3.21 million acres. Non-irrigated acres dropped steeply from 4.80 million acres in 1979 to 0.51 million acres in 2018, while irrigated acres expanded from 0.35 million acres in 1979 to 2.71 million acres in 2018. It is obvious that most expansion in irrigated soybean acres was the result of converting non-irrigated acres to irrigated acres. Every county in eastern Arkansas experienced an increase in irrigated soybean area during this time, but counties experiencing the greatest expansion were those bordering the Mississippi River, where ample water from lateral river recharge of the underground aquifer allowed for greater transition of non-irrigated area to irrigated area (Gautam and Watkins, 2021). 

A major factor for the upward trend in irrigated soybean acres in Arkansas is the increased world demand for soybeans, particularly in China. Increased world demand for soybeans has increased the value of soybeans relative to other crops grown in the state, such as rice and cotton. However, a more fundamental and straightforward reason for expanded irrigated acres is more consistent yields under irrigation relative to non-irrigation. Figure 2 presents detrended soybean yields for Arkansas non-irrigated soybeans versus irrigated soybeans from 1979–2018. Yields have been detrended to remove the influence of technological advancement over time. Yields were 12.6 bushels per acre greater on average under irrigation compared to non-irrigation. Also, variation around the irrigated soybean mean, which represents yield variation due to weather, is considerably narrower relative to variation around the non-irrigated soybean mean. Thus irrigation makes soybean yields more stable relative to yields under non-irrigation. 

The phenomenon of expanded irrigated soybean area was not isolated to Arkansas alone. Other locations in the Mid-South also experienced significant irrigated soybean area expansion during the same timeframe. Changes in both irrigated acres and irrigated soybean acres from Census year 1982 to Census year 2017 are presented for locations in the Mid-South. All Mid-South locations in Table 1 receive most irrigation water from the Mississippi River Valley alluvial aquifer. Irrigated soybeans account for approximately 69% of increased irrigated area expansion in this region. Arkansas experienced the largest expansion in soybean area (75% of increased irrigated area) but all locations experienced significant expansion as well.

Preliminary evidence indicates that irrigated soybean acres may be leveling off in many parts of Arkansas, particularly in counties farther removed from the Mississippi River, where groundwater is more limiting. However, expansion in irrigated acres appears to continue in counties bordering the Mississippi River. A closer evaluation needs to be conducted to verify these preliminary findings.

Table 1. Change in Irrigated Acres and Irrigated Soybean Acres (Census Years 1982 to 2017) for Mid-South Locations.
Change Category	Arkansas	Mississippi	Northeast Louisiana	Southeast Missouri	Total Change
Change in Irrigated Acres	2,826,397	1,381,386	490,458	957,188	5,655,429
Change in Irrigated Soybean Acres	2,108,158	952,742	293,230	538,836	3,892,966
Irrigated Soybean Expansion (%)	74.6%	69.0%	59.8%	56.3%	68.8%
Source: Derived from USDA-NASS Census of Agriculture data.

References and Resources

Gautam, T.K. and K. B. Watkins. 2021. Irrigated Acreage Change and Groundwater Status in Eastern Arkansas. Journal of the American Society of Farm Managers and Rural Appraisers 2021. https://higherlogicdownload.s3.amazonaws.com/ASFMRA/aeb240ec-5d8f-447f-80ff-3c90f13db621/UploadedImages/Journal/2021Journal_ASFMRA_HR.pdf

USDA-NASS (2023a). United States Department of Agriculture, National Agricultural Statistics Service, Census of Agriculture. https://www.nass.usda.gov/Publications/AgCensus/2017/Full_Report/Census_by_State/Arkansas/index.php

USDA-NASS (2023b). United States Department of Agriculture, Quick-Stats. https://quickstats.nass.usda.gov/

Watkins, Brad. “The Rise of Irrigated Soybeans in Arkansas.” Southern Ag Today 3(32.3). August 9, 2023. Permalink

Irrigation water can be one of the largest expenses associated with rice production, particularly when energy prices are high as in the current production season. Multiple inlet rice irrigation (MIRI) has potential to reduce the cost of applying irrigation water to rice. MIRI uses poly pipe to distribute irrigation water to all rice paddies simultaneously. This differs from conventional cascade flood in which water is applied to the first paddy at the top of the field and then flows over spills to lower paddies until the entire field is flooded. Fields are flooded much faster with MIRI. Based on examples in Arkansas, applied water savings of up to 25 percent are achievable with MIRI relative to cascade flood. Other potential benefits of MIRI relative to cascade flood include reduced irrigation labor and higher rice grain yields. Labor is reduced with MIRI due to less adjustment of levee gates and better management of water depth during the growing season. Yields can be 3 to 5 percent higher under MIRI due to a reduced “cold water” effect at the top of the field (more cold water concentrated at top of field with cascade flood) and improved nitrogen efficiency due to faster flooding of the field. 

Figure 1 presents rice irrigation variable costs per acre for both cascade flood and MIRI. Irrigation variable costs include energy, repairs and maintenance, irrigation labor, and for MIRI, the additional cost of poly pipe pick-up and removal. Rice irrigation variable costs are presented for three total dynamic head (TDH) levels (80 ft, 100 ft; 120 ft), and assume 32 acre-inches of water are applied under cascade flood and 24 acre-inches of water are applied under MIRI during the growing season. Both applied water amounts are typical water amounts for cascade flood and MIRI as reported in the Arkansas Rice Production Handbook. 

Irrigation variable costs are presented for both diesel and electric power. Irrigation energy costs were calculated based on diesel and electric energy consumption data from McDougal (2015). A diesel price of $3.94/gallon and an electric price of $0.138/kWh were used in the energy cost calculations. The diesel price comes from 2022 Arkansas field crop enterprise budgets, while the electric price represents a median price estimated from electric rate schedules for irrigation from various electric cooperatives located throughout eastern Arkansas. Irrigation labor is charged at $11.33/hour, also from 2022 Arkansas field crop enterprise budgets. 

Irrigation variable costs are much lower for electric power than for diesel power (Figure 1). Farmers have switched many of their diesel irrigation motors to electric motors because the cost of electricity has been lower and less variable over time relative to the cost of diesel. Irrigation variable costs are lower for MIRI than for cascade flood at all TDH levels. Lower costs are associated with less applied water and lower irrigation labor under MIRI. Monetary savings from MIRI are greater for diesel power than for electric power because applied water costs are much greater under diesel power than under electric power. Applied water cost for diesel power ranged from $5.35/acre-inch at 80 ft TDH to $8.02/acre-inch at 120 ft TDH. In contrast, applied water cost for electric power ranged from $2.10/acre-inch at 80 ft TDH to $3.15/acre-inch at 120 TDH. Diesel irrigation motors could potentially receive larger monetary payoffs from MIRI than electric irrigation motors on farms. Nonetheless, rice fields supplied with irrigation water by both diesel and electric motors could potentially benefit monetarily from MIRI relative to conventional cascade flood irrigation.

References and Resources

McDougall, W. M. (2015). A Pump Monitoring Approach to Irrigation Pumping Plant Performance Testing. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/1146

University of Arkansas System Division of Agriculture, Cooperative Extension Service. 2022. Arkansas Field Crop Enterprise Budgets. https://www.uaex.uada.edu/farm-ranch/economics-marketing/farm-planning/budgets/crop-budgets.aspx

University of Arkansas System Division of Agriculture, Cooperative Extension Service. 2021. Arkansas Rice Production Handbook. https://www.uaex.uada.edu/farm-ranch/crops-commercial-horticulture/rice/

Wilkins, Brad. “Potential Cost Savings of Multiple Inlet Rice Irrigation“. Southern Ag Today 2(21.3). May 18, 2022. Permalink