Application of Precision Agriculture Technology for Managing Irrigation of Drought Tolerant Corn

Principal investigators

 A study was conducted at the Texas Agricultural Experiment Station in Bushland with the objective to evaluate the drought tolerance of five corn varieties grown under different irrigation regimes.  The goal of this research is to identify the optimum irrigation regime that would minimize waste of precious irrigation water, reduce pumping expenses and at the same time maximize yield.

 The field study was conducted at the USDA-ARS, Conservation & Production Laboratory, Bushland, Texas.  ive corn varieties having different drought tolerance levels, (Pioneer 33R87, Pioneer 3341, Pioneer 3162, Pioneer 3489, and Pioneer 3346) were planted in twelve-row plots on April 22, 1998.  Irrigation was supplied by a center pivot irrigation system, with 60" drops equipped with LEPA nozzles.

The land under the center pivot was farmed in a circle to reduce runoff and improve irrigation distribution uniformity.  Different amounts of water were applied based on PET recommendations, 75% of PET and 50% of PET.  Multiple infrared thermometers (IRTs) were directly attached to the center pivot to record real time plant stress conditions while the pivot was moving (Figure 1) and plant water status was determined weekly using thermocouple psychrometers.

        On June 26, and July 31, 1998, 2 meters subplots were harvested and plant's fresh and dry weight was determined to monitor plant growth.  On September 29, 1998, plots were harvested using a combine equipped with GPS yield monitoring device.  In addition to the combine harvest, each plot was manually harvested and grain yield calculated.

Environmental conditions were particularly dry this year, making this one of the hardest years for growing a high yielding corn crop.

Table 1 shows the differences in fresh and dry weight among the five varieties at two harvest dates.  On June 26, Pioneer 3346, 3162 and 33R87 had significantly higher fresh biomass than Pioneer 3341, however, by the second harvest only 33R87 had significantly higher fresh weight than all other varieties.  Pioneer 3341 always had the lowest dry weight.

The effect of irrigation treatment on the fresh and dry weight of the 5 varieties at two harvest dates is shown in table 2.  No significant differences were found between the treatment irrigated at 50 and 75 % PET at the first harvest date.  This suggests that if water is a limiting factor and 100 % PET cannot be achieved, growers could water their crop at the beginning of the season using 50 % of the recommended PET and obtain plant growth similar to a crop irrigated at 75 % PET.

A significant interaction between variety and irrigation treatment was found at the final harvest (Table 3).  All five varieties performed similarly when irrigated at 100 % PET.  At 75 % PET, 3341 had significantly lower yield than all other varieties and at 50 % PET 3341 and 3162 had a significant reduction in yield.



Table 1: Fresh and dry weight (in grams) differences among five Pioneer corn varieties at two harvest dates.

June 26 harvest		July 31 harvest
Fresh weight (g)	Dry weight (g)	Fresh weight (g)	Dry weight (g)
9 Pioneer 3346	1678.7   A	391.47 AB	3605.6    B	1089.17 AB
7 Pioneer 3162	1626.8 AB	424.63    A	3882.3 AB	1211.11   A
5 Pioneer 33R87	1600.4 AB	391.23 AB	4236.1    A	1166.67   A
8 Pioneer 3489	1429.4 BC	391.22 AB	3620.3    B	1136.67 AB
5 Pioneer 3341	1352.6    C	310.46    B	3683.9    B	989.44     B

The number preceding the variety name is a drought tolerance value assigned by Pioneer.  The higher the value is the more drought tolerant the variety is.
Means followed by the same upper case letter within a column are not significantly different.



Table 2:  Fresh and dry weight (in grams) differences among three irrigation regimes at two harvest dates.

	June 26 harvest		July 31 harvest
	Fresh weight (g)	Dry weight (g)	Fresh weight (g)	Dry weight (g)
100% PET	1716.49 A	437.47 A	4449.9 A	1280.17 A
75% PET	1487.60 B	352.82 B	3769.3 B	1120.67 B
50% PET	1408.56 B	356.65 B	3197.7 C	955.00   C

Means followed by the same upper case letter within a column are not significantly different.



Table 3: Yield differences (bu/acre) among five Pioneer corn varieties.

	100 % PET	75 % PET	50 % PET
9 Pioneer 3346	138.50 A a	116.37  A ab	90.71   A b
7 Pioneer 3162	152.22 A a	109.29  A   b	34.07   B c
5 Pioneer 33R87	156.19 A a	127.88  A ab	100.44 A b
8 Pioneer 3489	158.41 A a	119.02  A   b	97.35   A b
5 Pioneer 3341	146.02 A a	79.20    B   b	27.00   B c

The number preceding the variety name is a drought tolerance value assigned by Pioneer.  The higher the value is the more drought tolerant the variety is.
Means followed by the same upper case letter within a column are not significantly different.
Means followed by the same lower case letter within a row are not significantly different.

Limited irrigation had no effect on the yield of 3346 and 33R87.  These two varieties did not significantly reduce their yield when irrigated at 75 % PET compared to their yield at 100 % PET indicating more drought tolerance.  This result is of particular importance considering that growers could achieve high yield by watering their crop at 75% of the recommended rate.  Such an irrigation regime would greatly save water and increase growers’ profits by reducing the cost of pumping.

Table 4 shows the mean leaf water potential data taken during the growing season.  Leaf water potential is an indicator of plant water stress.  More negative values indicate a higher water stress.  These results follow the same trend of the yield data.  No significant differences were found among varieties when the crop was irrigated at 100 % PET, however, as water became limited, 3341 and 3162 showed a higher level of stress, indicating that these varieties are not suitable to withstand water stress.

Table 4: Leaf water potential differences (Bars) among five Pioneer corn varieties.

	100 % PET	75 % PET	50 % PET
9 Pioneer 3346	-1.5 A	-8.2  A	-12.5   A
7 Pioneer 3162	-1.9 A	-7.9  A	-15.8   B
5 Pioneer 33R87	-2.1 A	-7.5  A	-12.4  A
8 Pioneer 3489	-2.0 A	-7.9  A	-12.7   A
5 Pioneer 3341	-1.8 A	-10.5    B	-17.2   B

The number preceding the variety name is a drought tolerance value assigned by Pioneer.  The higher the value is the more drought tolerant the variety is.
Means followed by the same upper case letter within a column are not significantly different.

Figure 1.  Infrared thermometers were effective in differentiating water stress treatments

The south end of the figure shows a lower canopy temperature due to the center pivot irrigating while temperature was being measured.  The red, orange and green areas represent areas where the crop was irrigated at 50 %, 75 % and 100 % PET respectively.  Further data interpretation is needed to verify if IRTs can distinguish among the different varieties.

On average yield data are low this year, however the severe drought allowed us to detect significant treatment and varieties differences.  Particularly, in the month of July it was very difficult to maintain the crop at the PET level.  This probably was the principle reason for lower yields in many irrigated corn field experiments.  In addition, southwestern corn borer pressure was high and resulted in excessive plant lodging.  There was also a massive outbreak of corn smut that contributed to lower yields.  However, even with these difficulties, this study produced encouraging results, indicating varieties that could perform well in limited irrigation and the feasibility of introducing remote sensing instrumentation for detecting plant stress and managing irrigation accordingly.  Just from the results of this year study it is easy to see the potential savings in water and associated pumping costs that a grower could achieve by implementing water-saving measures in conjunction with drought tolerant varieties.

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