Selection of the proper irrigation method will be advantageous to manage limited water supplies and increase crop profitability. The overall objective of this study was to evaluate the effect of subsurface drip irrigation (SDI) and furrow irrigation on onion yield and irrigation use efficiency. This study was conducted in two locations, a commercial field and a field located at the Texas A&M AgriLife Research Center in Weslaco, TX. This study was conducted as a split-plot design for both sites with two treatments (SDI and furrow irrigation) and three replications per treatment. The total onion yield obtained with the SDI systems was more than 93% higher than the yield obtained with furrow irrigation systems. The large onion size was 181% higher for the SDI system than the furrow system in both sites. The colossal size yield was also higher. At one site colossal yield was 206% higher than furrow, while at another site furrow yielded no colossal onions and SDI had some production. It was concluded that drip irrigation systems more than double yields and increased onion size while using almost half of the water. This was due to SDI allowing for more frequent and smaller irrigation depths with higher irrigation efficiency than furrow irrigation systems.
Texas is frequently affected by periods of drought, including the drought that started in 2011 and continued in 2012 and 2013, with 2012 being one of the driest years on record. These drought periods commonly cause water shortages and impose additional restrictions which reduce irrigated acreage, impacting the farming productivity and profitability. Under these circumstances, farmers often seek alternatives to increase their productivity and net return per unit of water applied by converting from furrow to drip irrigation systems and implementing irrigation scheduling strategies. Federal and state governments have implemented several programs that support this irrigation system conversion. However, many producers feel that the costs of employing these water saving technologies far exceed the benefit of increased vegetable yields and water savings. To reduce the economic risk of farming operations it is important to make sound decisions when selecting an irrigation method for a particular crop. Farmers that continue to use traditional furrow irrigation methods may benefit by using deficit irrigation [
In Texas, where deficit irrigation is widely practiced and where many irrigated areas obtain their water supply from aquifers, it has been observed that SDI systems have been increasingly adopted especially for irrigating cotton. Presently, there are more than 170,972 acres of SDI and 81,569 of surface drip irrigation [
In Colorado, Halvorson et al. [
This study was conducted during the 2012-2013 fall-spring onion growing seasons in a commercial field located in Los Ebanos close to Rio Grande City, TX (longitude 26°15′9.62′′N, latitude 98°33′W), and during 2013-2014 at the Texas A&M AgriLife Research Center located in Weslaco, TX (longitude 26′′9′N, latitude 97′′57′W). The soil at the commercial field was a Reynosa silty clay loam (35% clay, 45% silt, and 20% sand: fine-silty, mixed, active, hyperthermic Torrifluventic Haplustepts) and the soil at the research site was a Hidalgo sandy clay loam (22% clay, 18% silt, and 60% sand: fine-loamy, mixed, hyperthermic Typic Calciustolls). This region has a semiarid climate and the average annual rainfall is 558 mm of which only about 226 mm is received during the onion growing season, of which more than 60% is received during the first three months when the onion crop germinates and grows very slowly. Onions (
Production operations and crop growth parameters for the two seasons this study was conducted.
Operation | 2012-2013 | 2013-2014 | ||
---|---|---|---|---|
Los Ebanos |
Los Ebanos |
Weslaco |
Weslaco | |
Planting | November 8 | November 8 | October 24 | October 24 |
First in-season irrigation | November 4 | November 4 | October 28 | October 28 |
Preplant fertilization | October 1 | October 1 | None | None |
1st fertilizer application | November 22 | November 22 | October 26 | October 26 |
2nd fertilizer application | December 22 | December 22 | January 17 | January 17 |
3rd fertilizer | January 28 | January 2 | February 5 | January 28 |
4th fertilizer | February 15 | February 15 | February 10 | February 10 |
5th fertilizer | March 8 | None | February 21 | None |
Last irrigation | April 5 | April 5 | April 7 | April 7 |
Harvest | April 22 | April 22 | April 25 | April 25 |
Rainfall growing season | 140 | 140 | 294 | 294 |
Length of growing season (days)a | 158 | 158 | 156 | 156 |
Plot length was 97.5 m, and there were four beds per plot for a total area per plot of 397 m2 at the Weslaco site. Two rows were left unplanted between each plot as a buffer. Standard commercial practices for spring onion production were followed [
Fertilizer was applied through the drip system in four or five split applications each year (Table
This study was conducted as a split-plot design for both sites with two treatments (SDI and furrow irrigation) and three replications per treatment. The Rio Grande River was the source of irrigation water and had an average electrical conductivity of 0.13 S m−1 and was filtered using sand media filters at both locations for the SDI systems. There is no risk of salinization considering that the soils are well drained and there is enough leaching in the fall season due to heavy rains produced during the hurricane season. The drip tubes at the commercial field had nominal discharge ratings of 1.02 L h−1 per emitter and 30 cm emitter spacing (T-Systems International, Inc., San Diego, CA) and 0.93 L h−1 per emitter with 30 cm emitter spacing at the Weslaco site (Netafim USA, Fresno, Cal.). One drip-line was buried at approximately 0.05 m depth and placed beneath each planted row.
Irrigation at the commercial field site was done by a cooperating commercial grower and was based on empirical methods such as the feel and appearance method when soil moisture reached 25% depletion within the top foot depth. A water balance approach was used for irrigation scheduling at the Weslaco site (
The amount of water applied to each plot through irrigation was recorded with totalizing water meters connected to the irrigation system. One flow meter of 15 mm was installed per replication for the SDI irrigation system, and one flow meter of 200 mm was used for all the furrow irrigated plots in both locations. Approximately the same amount of water was applied to the different SDI replications during each irrigation event at both sites.
Crop single coefficient was estimated using the crop coefficients for seed onions (0.7 for initial, 1.05 for mid, and 0.8 for end) as suggested by Allen et al. [
Total rainfall amounts for the two growing seasons were 140 mm in 2012-2013 and 294 mm in 2013-2014. In the 2012-2013 growing season, more than 65% of the rainfall was received within the first 12 weeks between October and December, and around 72% was received in 2013-2014 in the same period. The rainfall was insufficient to meet the water demands of the crop in both years which were 409 and 411 mm, for 2012-2013 and 2013-2014, respectively (Table
The average furrow length for this region is approximately 365 m, but vegetables producers have reduced the furrow length to 200 m to conserve water and improve irrigation efficiencies. The experiment conducted in the commercial field had a furrow length of 178 m and the average irrigation depth applied with furrow systems was 112 mm with a total of six irrigation applications. The average irrigation depth of 112 mm is excessive for shallow root systems and this may explain the low irrigation efficiencies for furrow systems (67.1%). A common problem is the need to decide whether to reduce the number of irrigations or to reduce the irrigated area when water is limited in order to concentrate the available water for vegetable irrigation. Farmers that have a SDI system can apply small and frequent irrigations but they have to pump the water directly from the river, have a reservoir on their farm, or be located near a canal where water can be pumped continuously. At the commercial field that was located close to the Rio Grande River, more frequent irrigations with smaller irrigation depths were possible with the SDI system in which an average irrigation depth of 21.1 mm per irrigation was applied resulting in a high irrigation efficiency of 88.5% (Table
In the Weslaco field site, the furrow length was 100 m long. A total of 14 irrigations were applied with SDI and 5 irrigations with the furrow system at the Weslaco field site (Table
Total onion yields were significantly different for SDI and furrow irrigation in both locations (Table
Effect of irrigation method on average yield parameters (Mg ha−1) as classified by size classes, onion quality, and gross return at the Los Ebanos and at the Weslaco research station field sites (2012–2014).
Spacing (cm) | Size class (Mg ha−1) | Pyruvic acid ( |
Soluble solid concentration (%) | Gross return $ ha−1 | ||||
---|---|---|---|---|---|---|---|---|
Small | Medium | Large | Colossal | Total | ||||
Los Ebanos (2012-2013) | ||||||||
SDI | 0.6 | 14.0 | 44.1 | 4.3 | 62.9 | 4.3 | 8.3 | 25,042 |
Furrow | 0.6 | 12.1 | 14.4 | 1.6 | 28.7 | 4.4 | 8.8 | 11,372 |
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NS | NS | * | * | * | NS | * | * |
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Weslaco research station (2013-2014) | ||||||||
SDI | 3.7 | 24.4 | 10.7 | 0.6 | 39.3 | 4.4 | 6.0 | 15,994 |
Furrow | 4.1 | 12.3 | 3.8 | 0 | 20.2 | 4.3 | 6.2 | 7,855 |
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NS | * | * | * | * | NS | NS | * |
Number of irrigations, irrigation applied, onion evapotranspiration, and irrigation use efficiency for SDI and furrow irrigation systems (2012–2014), Weslaco, TX.
Irrigation system | Number of irrigations | Irrigation applied (mm) | Onion ET (cm) | Rainfall (mm) | Irrigation efficiency (%) | Irrigation use efficiency (kg m−3) |
---|---|---|---|---|---|---|
Los Ebanos (2012-2013) | ||||||
SDI | 17 | 359 | 442 | 140 | 88.5 | 17.5 |
Furrow | 6 | 677 | 442 | 140 | 54.1 | 4.2 |
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Weslaco research station (2013-2014) | ||||||
SDI | 14 | 211 | 411 | 294 | 81.4 | 25.2 |
Furrow | 5 | 318 | 411 | 294 | 67.1 | 6.5 |
Onion bulb pungency (pyruvic acid content), an indicator of the hotness of the onion, had an average range from 4.3 to 4.4
The irrigation use efficiency is calculated by dividing the total onion yield by the irrigation water applied. At the commercial field site for the 2012-2013 season irrigation use efficiency was 17.5 kg m−3 for the SDI system and 4.2 kg m−3 for the furrow system. At the Weslaco field site, irrigation was scheduled with a water balance method and this may be the reason why higher irrigation efficiencies were observed at the Weslaco field site than at the commercial field site. The irrigation use efficiency was higher for the SDI system with 25.2 kg m−3 and only 6.5 kg m−3 for the furrow system. In previous studies, Enciso et al. [
The SDI system allowed more frequent application at smaller irrigation depths than the furrow irrigation system. The irrigation efficiencies were also higher for the SDI system (81–88%) than the furrow system (54–67%). The irrigation use efficiency obtained with the SDI system ranged from 17.5 to 25.2 kg m−3 and from 4.2 kg m−3 to 6.2 for the furrow system in both locations. It was concluded that drip irrigation systems more than double yields and increased onion size while using at least 44% less water. This was due to SDI system allowing for more frequent application and smaller irrigation depths with higher irrigation efficiency than furrow irrigation systems. Additionally, we can point out that heavy rains during the fall season reduce the potential for salinization.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This research was funded by USDA-NRCS as part of the Conservation Innovation Grants no. 69-3A75-1382 and the financial support of the Texas Water Development Board for funding this project as part of the Agricultural Water Conservation Demonstration Initiative (ADI), also known as the Texas Project for Ag Water Efficiency (AWE). The authors are also grateful for the assistance of Corina Fuentes who helped with the onion quality analysis and Dr. Ashely Gregory, who helped with the editing.