Progress Report on Microirrigation in Arizona, 2003.
The University of Arizona
W-128 Annual Report
November 2003
PROJECT TITLE: Microirrigation Technologies
for Protection of Natural Resources and Optimum Production
PRINCIPAL INVESTIGATORS: Muluneh
Yitayew
PROGRESS OF WORK AND PRINCIPAL ACCOMPLISHMENTS:
Objective 1 To evaluate and refine
microirrigation management strategies to promote natural resource protection
and optimal crop production
Crop Water Production Function for Corn Under Microirrigation and Furrow Systems
A three year comparative water-yield study was done for field corn in Southeast Arizona, using both drip and furrow irrigation methods, and four different levels of irrigation within each irrigation method. The Arizona Irrigation Scheduling (AZSCHED) software determined irrigation frequencies and amounts. The four levels of irrigation treatments were 125%, 100%, 75% and 50% of the AZSCHED prescribed irrigation amounts. Analysis of the data showed that there was no significant difference between yields for furrow and drip irrigation plots at a 95% confidence level. The analysis also showed that level of irrigation was significant. The highest level of irrigation produced significantly higher yields than the other treatments. There was no significant difference between the two middle treatments. The lowest treatment produced significantly lower yields than the other treatments. The average maximum yield was 11.1 Mg/ha, with an average crop-water use, or seasonal evapotranspiration, of 886 mm. The water use efficiency, based on the yield production function, was determined to be 0.0195 Mg/ha for each mm of water used above a threshold of 312 mm.
Figure 1: Total Applied Water versus Yield
Figure 2: Seasonal Evapotranspiration
versus Yield
Conclusions
Three important observations were made
during the course of this study.
1. The average seasonal crop water requirement
(ET) for an average maximum yield of 11.1 Mg/ha was 886 mm.
2. Yields from drip-irrigated plots were
not significantly different from the yields of furrow-irrigated plots.
3. The production function for field corn
in SE Arizona was defined as:
Yield (Mg/ha) = 0.0195(Seasonal ET(mm))
– 6.0821.
The crop water requirement given above
is associated with the highest irrigation level used in this study.
Therefore, there is the potential that higher yields could be realized
with a greater seasonal water application. The yield comparison between
drip- and furrow-irrigated plots was determined to be non-significant.
The main reason for this conclusion was due to high variability within
each treatment. It is believed that ‘border effect’ had an impact
on the plots. The production function given above indicates a water-use
efficiency of 0.0195 Mg/ha of field corn produced for each mm of water
used by the crop, above a threshold of 312 mm.
DEVELOPMENT OF A CROP COEFFICIENT CURVE
FOR FIELD CORN IN SOUTHEAST ARIZONA
The objective of this study was to develop a crop coefficient curve for field corn as a function of heat units, and to subsequently compare the experimentally determined crop coefficient curve to the existing crop coefficient curve in the Arizona Irrigation Scheduling (AZSCHED) software. The study was performed with subsurface-drip-irrigated field corn in Southeast Arizona. AZSCHED determined irrigation amounts and frequencies based on inputs of weather data, water holding capacity of the soil, management allowed depletion, and application efficiency. A water balance approach was used to develop an experimentally determined curve. The study shows that the crop coefficient curve for field corn in AZSCHED did not represent the crop coefficient estimated from field data.
Figure 3: Comparison of Kc Curves
for Field Corn
Figure 4 Kc Curves for Original and Modified AZSCHED Models
Conclusions
The shape of the crop coefficient curve for field corn in AZSCHED was different than the experimentally determined curve. The crop coefficient curve that was modified to fit the data from the field is believed to be a better representation than the original curve in AZSCHED. Although the modified curve is shifted to the right with an increased peak, the seasonal water requirement is actually lower for the modified curve. It is important to note that these conclusions are based on one season of data.
Effect of Salinity on Corn Yield, Plant Growth and Root Development
Several studies have been performed on the effect of salts on corn, but only few under subsurface drip irrigation and arid conditions. In addition, many of these experiments were conducted in greenhouse and organic soils. As a consequence of this, the study of the effect of salinity on corn under field conditions is essential.
This Study had four objectives i.e. to analyze: a) the salinity effects on grain yield, plant growth and root development of field corn, b) the effect of salts application on silking and tasseling, c) the salinity response function for field corn under arid conditions and d) the distribution of salts within the root zone.
Results
Figure 5. Salinity yield response function for field corn.
Conclusion
Corn yield, shoot growth, plant height and root development decreased with salt applications. While silking and tasseling were delayed in those plots that salt solution was injected. All these variables were analyzed statistically and there was significant difference between the four treatments during the different growth stages for the two corn seasons established.
Although the highest concentration
of salts was accumulated in the shallow layer, salinity greatly affected
distribution of corn roots in the soil and this influenced the uptake of
water and nutrients. During the vegetative stage of the plant, roots grew
rapidly. After this stage root growth generally increased at a slower rate
than shoot growth and after the reproductive stage root dry mass declined,
which has been associated with the translocation of N in the roots to the
developing ear.
The corresponding response function
of field corn to salinity was
Y = 9.276 – 0.51(ECe – 1.32)
ECe > 1.32
Y = 9.276
Objective 2 . To improve , modify, and evaluate microirrigation system design and components for natural resource protection and optimum production
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
USEFULNESS OF FINDINGS
Production function, crop coefficient, and the water use efficiency of corn is established for arid environments under SDI. The result can be used as benchmark for irrigation design and management in growing corn in arid areas of the world.
The salinity study reveled that corn under subsurface drip irrigation can tolerate higher salinity levels than what is reported in the literature. This is a significant finding in that it will help farmers save water by using poor quality water and lower leaching fraction and achieve a good yield level.
Determining the threshold salinity value
for corn and the yield reduction per unit of salinity under subsurface
drip irrigation will help farmers also develop best management practices
necessary when using poor quality water for SDI.
WORK PLANNED FOR 2004
To participate in developing the new project proposal and carry out research on the specific objectives relevant to Arizona’s irrigated agriculture.