Annual Report of Cooperative Regional Project, W-128, for California (UCD, Ken Shackel, Larry Schwankl, Jan Hoppmans, Patrick Brown).
January 1, 2000 to December 31, 2000.
Progress of Work and Principal Accomplishments.
Objective 1: To evaluate and refine microirrigation management strategies to promote natural resource protection and optimal crop production.
Plant-based measurements of midday stem water potential were used to improve the effectiveness of both micro- and other types of irrigation systems in tree crops (almonds, prunes and walnuts). In almonds we found that deficit irrigation during the hull split period caused improved hull split, nut drying and harvestability, and for the second year reduced the incidence of hull rot disease. In prunes a number of demonstration plots were continued in which plant-based RDI strategies allowed a substantial savings (around 40%) in applied water. In one case this savings was related to a 38% savings in the electric energy used for water pumping.
Six commercial orchards / vineyards were evaluated for chemigation uniformity. Evaluations included determining water / chemical travel times through drip irrigation system mainlines/submains and through drip lateral lines. Chemical application uniformity was also determined. Drip irrigation systems travel times were measured by injecting chlorine (calcium hypochlorite) and monitoring its passage through the drip irrigation system using a pool / spa chlorine test kit. Chemical application uniformity was determined by injecting potassium chloride and collecting all the discharge from drip emitters at key locations in the drip irrigation system. The collected samples were then analyzed for potassium content at the UC DANR Analytical Laboratory.
Table 1 shows the travel times through the drip irrigation systems for the commercial vineyards and orchards evaluated. Note that there is a wide range of water / chemical travel times in both the mainline / submain and in the drip lateral line portions of the irrigation system. As the drip irrigation system designs vary from site to site, so do the water / chemical travel times through the irrigation system. No general recommendations on injection time periods to achieve high chemical application uniformity is appropriate for all drip irrigation systems. A one-time, field determination of water / chemical travel times is necessary for each drip irrigation system.
Table 1. Water / chemical travel times through the pipelines and drip lateral lines for the vineyard and orchard field sites evaluated.
Mainline and Submain Mainline / Submain Lateral Line Lateral Line
Site Travel Time (min.) Length (ft) Travel Time (min.) Length (ft)
1 22 1000 10 175
2 30 1500 10 340
3 65 5000 10 340
4 15 1400 23 630
5 8 700 23 625
6 17 820 28 600
Additional work was done on a single drip lateral line to evaluate the impact of chemical application uniformity of varying the injection times and the post-injection irrigation times. The results of some of these evaluations are shown in Table 2. The lateral line evaluated was a 500-foot drip lateral (16 mm polyethylene tubing) with a 1 gallon per hour (gph), pressure-compensating, drip emitters installed every 5 feet. It was determined through field evaluation that the travel time for water / chemicals passing through the lateral line was 25 minutes.
Table 2. Chemigation uniformity in a drip lateral (500-feet long with 1-gallon per hour drip emitters installed at 5-foot intervals) for various injection time periods and various post-injection clean water irrigations. The water / chemical travel time to reach the end of the drip lateral was 25 minutes.
Injection Time Post-Injection Irrigation
Relative Uniformity
(min)
Time (min)
50
50
100
50
25
98
50
0
25
25
50
90
25
25
95
25
0
11
13
25
81
13
0
7
Note that excellent chemical application uniformity was achieved when: (1) the injection period was equal to or greater than the water / chemical travel time to the end of the drip lateral (25 minutes in this case), and (2) the post-injection irrigation time was equal to or greater than the lateral line's water / chemical travel time. The results in Table 2 also show that there are two injection strategies to avoid. First, avoid injection periods which are less than the drip system's water / chemical travel times to the end (hydraulically) of the system. Secondly, an injection should always be followed by a period of "clean" water irrigation. This post-injection irrigation period should be at least as long as the water / chemical travel time to the end of the drip irrigation system. The worst chemigation uniformities would result from a too short (less than the end-of-system travel time) injection period followed by drip system shutdown.
To aid in visually observing what was occurring during an injection, an experimental setup simulating the last two drip emitter intervals at the tail end of a drip lateral was developed. Clear tubing of the same diameter as drip tubing was used with 2, 1-gph drip emitters installed - one 5 feet from the inlet and the other 10 feet from the inlet. With the system operating, colored dye was injected into the water and the time since injection began recorded along with the dye movement along the tube. Once the dye reached the end of the tube, the dye injection was stopped and a record was kept of time vs. dye clearing from the tube. Professional photographs of this event were taken and have been digitized. They are available upon request from the authors.
Objective 2: To improve, modify, and evaluate microirrigation system design and components for natural resource protection and optimal production
Experiments were conducted in Pistachio and in Corn to determine the impact of irrigation regime on pottassium (K) uptake and efficiency of K use and the dynamics of K fixation in soils.
In Pistachio a three year experiment was conducted to examine the effects of K fertilization through the irrigation system on leaf K, nut yield and quality in Pistachio. Treatments included three rates of K application and four K sources, K applications were timed to coincide with the periods of greatest tree K demand with the aim to optimize K use efficiency and tree responsiveness. Results demonstrate that in-season K application through the irrigation system results in significant and economically important yield response. The effectiveness of 'chemigation' as a means of K application was clearly demonstrated. and the exhibited responsiveness was superior to that exhibited with traditional soil K applications (Zeng et al. 2000a)
We hypothesized that the effectiveness of 'chemigation' as a means to supply K in K fixing soils was a consequence of an interaction between soil moisture regime and the propensity of K to become fixed (and hence unavailable) onto clay minerals. To verify this hypothesis a subsequent pot trial utilizing Corn was conducted. In this trial pot grown corn was exposed to differential wetting and drying cycles under a variety of soil K regimes. The dynamics of soil K fixation, the availability and diffusion of K in the soil profile and the relative availability of K to the plants was assessed.. Plants grown under conditions of continuous soil moisture exhibited improved growth as a result of increased K uptake. K availability in the soil was increased under constant soil moisture regime as a result of a minimization of soil K fixation that is induced by sequential wetting and drying cycles.(Zeng et al. 2000b).
Objective 3: To assess and develop decision criteria for adoption of microirrigation technologies
Objective 4: To promote appropriate microirrigation technologies through formal and informal educational activities.
Presentations were made to industry groups in almonds, prunes, walnuts and pears about the value of plant-based measurements for optimal management of irrigation water. A website was developed describing the pressure chamber method (http://fruitsandnuts.ucdavis.edu/pressure-chamber.html) and its specific use in prune RDI (http://fruitsandnuts.ucdavis.edu/prune-pressure.html).
A University of California DANR leaflet – "Uniform Chemigation in Tree and Vine Microirrigation Systems" – is in production and should be available by the end of 2000.
Usefulness of findings.
Objective 1: By using reliable plant-based measurements, site-specific irrigation decisions can be made to achieve a substantial savings in water, in addition to probable savings in labor and reductions in adverse environmental impacts.
The results of the chemigation uniformity work have already come to the attention of a number of chemical companies and the CA Pest Control Advisors who have requested slide shows and presentations of the information. A CD-ROM PowerPoint presentation of the results of the work have been provided to Beyer Chemical, Inc. for distribution to their field representatives.
Objective 2: A commercially available hand-pump pressure chamber will be more likely to be used by growers to obtain site-specific information on the performance of their irrigation system and the effectiveness of their irrigation strategy.
Our experiments in Corn and Pistachio demonstrate the relative improvement in K use efficiency of chemigation in comparison to standard fertilization practices and provide a mechanistic explanation for this effect. Development of chemigation protocols will help improve resource use efficiency in many crops.
Work Planned
Objective 1: Demonstration projects in almond and prune will be continued to evaluate the long term effects of deficit irrigation on tree productivity and to establish the overall economic impact of this practice.
Objective 4: Presentations will be made to industry groups informing them of the benefits of site-specific management of deficit irrigation, and a web site will be developed describing the operation of the pressure chamber.
A number of presentations for extending the results of the chemigation work are planned for this winter and the UC DANR publication will be completed to further extend the results of this work.
Publications
Lampinen, B.D. K. A. Shackel, S.M.. Southwick. 2000. Responses of French Prune (Prunus domestica L. cv. French) to Deficit Irrigation Strategies Based on Midday Stem Water Potential. Irrig. Sci. (in press)
Zeng, Q.m P. Brown, 2000. Soil potassium mobility and uptake by corn under differential soil moisture regimes. Plant and Soil 221: 121-134
Zeng, Q., P. Brown, B. Holtz. 2000. Effects of potassium (K) fertilization on soil K, leaf K concentration, nut yield and quality in mature pistachio trees. Hort Sci. (in press).