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Development and Evaluation of Subsurface Drip Irrigation for Northwestern New Mexico

Project No. 1-3-42279: Funds provided by the USDA through the Hatch Program, the State of New Mexico through general appropriations, and the US Bureau of Indian Affairs

Subsurface Drip Irrigation for Field Crops

Mick O’Neill, Renae Pablo, and Todd Begay

Introduction

Trickle or drip irrigation has come a long way in the past 20 years with reliable systems used for field crops, row crops, orchards and numerous high-value crops. For comparable yields, water applications can be less than sprinkler systems resulting in greater water use efficiency and net savings. In some cases, yields may even be higher with drip irrigation than with other irrigation systems. Continuous injection of nitrogen and other fertilizers provides available nutrients over the length of the cropping season. By limiting the total amount of water applied, deep percolation and nutrient losses are eliminated. Environmental contamination by leached nutrients and agricultural chemicals is minimized and sizable social savings are thereby realized.
 

The Navajo Agricultural Products Industry (NAPI) is located in the northeast corner of the Navajo Nation, south of Farmington, New Mexico. The project was initiated in 1970 to develop, operate, and manage the agribusiness functions of the Navajo Indian Irrigation Project (NIIP). Soils are predominately sandy loams and presently there are 46,000 cultivated acres with potatoes, corn, alfalfa, and wheat as the principal crops.

 

Initial irrigation was through side roll sprinkler systems, but they have been completely replaced with more than 500 center pivots. This has resulted in a sizable portion of land being removed from production as rectangular fields were changed to circular. Drip irrigation, with its flexible installation characteristics, offers an opportunity to reclaim bordering acreage outside the irrigated circles and abandoned rectangular fields not appropriate for circular systems, although design criteria and operational management are not well understood.

Objectives

The principal objective of this field trial is to evaluate the performance of subsurface drip irrigation on a Wall sandy loam soil (Typic Camborthid, coarse, loamy, mixed, calcareous, mesic family) (Anderson 1970). More specifically, the objectives are to:
·Determine optimum drip tape depth for sandy loam soils, crop selections, and management practices typical of northwestern New Mexico.

·Determine appropriate applications of irrigation to soil with a limited soil water holding capacity (~ 3.4 inches of available water in the top 2 feet).

·Determine appropriate nitrogen application rates in amounts that minimize or eliminate leaching losses.
 
 

Materials and methods

To address these objectives, the NMSU Agricultural Science Center (ASC) at Farmington has begun a three-year project on 8 acres of land for the establishment of an experimental subsurface drip irrigation (SDI) system. Procedures for the SDI trial are presented in Table 1. Installation commenced in April 2001 with the construction of a control facility, which includes 2 sand media filters, back flush mechanisms, chemical control injection systems, and a computer-linked control panel. Drip tape with a 15-mil thickness (Netafim Typhoon 630) was direct buried through a 2-row injector in the center of each 34-inch row at depths of 3, 5, 7, and 9 inches below the bottom of the furrow. Row length was 400 feet to allow for large plots that would approach commercial production practices. Main lines were connected to submains for each 8-row plot through a valve tree, which included a solenoid valve, ball valve connector, pressure release valve, and flow indicator. Flush manifolds were connected at the lower end of each 8-row plot. Soil moisture sensors (GroPoint by Environmental Sensors, Inc.) were buried in the root zone at 3 inches below the soil surface and at 18 inches below the drip tape (2 replicates at each tape depth). All solenoid valves and moisture meters were direct wired to the control panel. The control panel was linked to a computer running irrigation-scheduling software (AquaLink by Intelligent Irrigation Systems). Chemical injection (Injection Systems Incorporated) was provided through acid and fertilizer ports.
 
 
The majority of the system was installed during April, May, and June. Oats (cv. Monida) and single drop chipper potatoes (cv. Atlantic) were planted on June 12, 2001, a date considerable out of their normal cropping cycle. Irrigations were applied through the system on a nearly daily basis to satisfy evapotranspiration (ET) demand as calculated by a locally formulated crop coefficient curve. Urea ammonium nitrate fertilizer (32-0-0) and N-Phuric acid (10-0-0) were injected through the system to provide nitrogen and maintain an acidic pH in the irrigation water. Diquat was applied on June 5, 2001 and a mixture of Banvel and 2, 4-D was applied on July 2, 2001 to control weeds. Potatoes were harvested on November 5 and total weight, jumbo weight, and No 1 weight were determined for each plot. Oats were harvested on November 9, 2001; plot weight, bushel weight and moisture content were determined. Yield data were subjected to ANOVA and Fisher separation tests with the SAS statistical software program.

 

Table 1. Procedure for the subsurface drip irrigation trial; NMSU Agricultural Science Center at Farmington, NM, 2001.
 
Operation
Procedure
Number of crops:
Two: Oats. cv. Monida; Potatoes, cv. Atlantic
Planting Date:
June 12, 2001
Planting Rate:
Oat, 80 lb/acre; Potatoes, 20 bu/acre
Plot Design:
Complete randomized block 
Plot Size:
Oats, 8 rows by 400 ft; Harvested area, 4 rows by 400 ft


Potatoes, 4 rows by 100 ft; Harvested area, 2 rows by 20 ft
Harvest Date:
Oats, November 9, 2001; Potatoes, November 5, 2001
Fertilization:
Urea ammonium nitrate fertilizer (32-0-0), 43.2 lb N/acre


N-Phuric acid (10-0-0), 32.5 lb N/acre
Herbicide:
Diquat was applied on June 5, 2001 and a mixture of Banvel and 2, 4-D was applied on July 2, 2001
Insecticide:
None
Soil Type:
Wall sandy loam
Irrigation:
Subsurface drip irrigation; total applied = 48.4 inches
Results and Discussion:
Yield and other characteristics are presented in (


Table 2 and Table 3)

Results and discussion

Not withstanding the delayed planting date, excellent germination and emergence of both crops occurred, although there was a directly related delay of emergence with tape depth for the oats. The depth of tape placement only slightly affected potato emergence. Development of both crops was rapid and vigorous throughout the season.
 
 
Water application was sufficient to meet ET demand for both crops (Figure 1). The procedure, developed by Smeal (personal communication), calculates daily ET based on cumulative growing degree days since the date of planting. This compensates for different planting dates and locations. Total water applied amounted to 48 inches, which included large applications during the early season while the system was still under construction. The temperature of the irrigation water averaged 48.1°F and the pH averaged 6.8 over the cropping season. Total nitrogen injected as fertilizer and acid was 75.5 lb N per acre.

 
 


Figure 1. Cumulative evapotranspiration demand as calculated by growing degree days and cumulative application to oats and potatoes in the subsurface drip irrigation trial, NMSU Agricultural Science Center, Farmington, NM.
 
 

Oats in the deep tape treatments made late season growth gains. This offset faster development during the early season by shallow tape treatments. Final oat yields were not different among the tape depths (Table 2.) demonstrating that sufficient water was delivered through the drip tape for satisfactory germination, emergence, and crop growth, not withstanding tape depth. Mean oat yield was 90 bu/acre, about 50% of the average oat yield for the past 3 years in the Northwestern States Oats Nursery grown at the ASC, Farmington.
 
 
 

Table 2. Oat grain yield and other characteristics for the subsurface drip irrigation trial; NMSU Agricultural Science Center at Farmington, NM, 2001.
Tape


Depth
Yield
(bu/acre)
Moisture
(%)
Test Wt
(lb/bu)
Height
(in)
3 inch
85.1 a
18.0 a
36.3 a
41.5 a
5 inch
78.9 a
19.0 a
35.0 a
45.3 a
7 inch
101.7 a
16.7 a
37.2 a
45.8 a
9 inch
92.5 a
19.5 a
35.0 a
47.0 a
Mean
89.6
18.3
35.9
44.9
P
0.4602
0.6718
0.4814
0.0298
CV (%)
23.2
16.1
5.9
4.3
LSD (0.05)
N.S.
N.S.
N.S.
N.S.

 
 

Total potato yield and yield of number 1’s were significantly greater at the 3 inch depth than at the other depths (Table 3.). Sufficient moisture may not have subbed up to the potato tuber in the deeper tape treatments for maximum production. Given the late planting date, total yield at the 3-in tape depth of 245 cwt/acre compares favorably with the total yield in the Southern Regional Potato Nursery, which averaged 394 cwt/acre from 1983 to 2000. Reduced oat and potato yields compared to previous years are most likely due to the late planting date of June 12 in this trial.
 

Table 3. Potato yield and other characteristics for the subsurface drip irrigation trial; NMSU Agricultural Science Center at Farmington, NM, 2001.
Tape


Depth
Total
Jumbos
No 1's
Culls
–––––––––––––––(cwt/acre)–––––––––––––––
(%)
3 inch
245 a
12 a
201 a
32 a
5 inch
160 b
8 a
131 b
21 a
7 inch
137 b
14 a
104 b
19 a
9 inch
145 b
17 a
111 b
17 a
Mean
172 b
13 a
137 b
22 a
P
0.0015
0.4895
0.0003
0.1112
CV (%)
16.5
67.2
15.0
37.6
LSD (0.05)
45
N.S.
33
N.S.

Useful Findings

Two inexperienced employees from the Navajo Agricultural Products Industry (NAPI) were transferred to the NMSU Agricultural Science Center at Farmington for a two-year, on-the-job training program in the installation, operation, and management of microirrigation. They initially experienced a steep learning curve but were able to grasp the concepts within a short period. As a technology transfer training tool, a list was developed of advantages and disadvantages of the system installation and operation. Some advantages include ease of connecting and installing the plumbing parts, automation of irrigation, and the reduction of surface water losses through evaporation and runoff. Disadvantages include initial installation costs, difficulty to learn the computer software, and the hazards associated with handling concentrated acid.
 

Although planting was undertaken late in the season, satisfactory germination and emergence occurred with both crops at all tape depths. Visual observations indicate that the crops matured faster in the shallow tape-depth treatments. The potatoes and oats in the deeper treatments seem to have matured at a slower rate but not to an extent to drastically affect yield. Oat yields were not significantly different at any tape depth while total potato yield and the yield of No. 1 potatoes were greater when the drip tape was buried 3 inches below the depth of the furrow bottom.
 

Additionally, no tape from any injection depth appeared to be damaged after potato digging with a mechanical plot harvester.  This is especially encouraging in the sandy loam soils found in the area as an appropriate balance must be made between water conservation, potato production, and the depth of tape placement for potato harvesting without tape damage.

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