Dealing with Drought

Lynn Jensen

OSU Malheur County Extension

Clint Shock

OSU Malheur Experiment Station

When water is plentiful we usually arrange our time for irrigation practices around our other farming practices. As an example, most growers change their furrow irrigation sets at 12 or 24-hour intervals because it is convenient and efficiently manages labor. When water is short, we need to rethink some of our practices and make water stretch to obtain the maximum benefit. After all, water is our second most important resource behind the land itself. You need to realize that you are exchanging management and labor for water. Not all of you are facing serious water shortages this year, but may next year, if the winter is dry. Also, with the current power crises, there will be more and more pressure applied to conserve water and use it for power generation or for endangered species such as salmon and bull trout. The issues affecting the Klamath Basin or similar ones such as Total Maximum Daily Load (TMDL) may only be a few years away from affecting Malheur County.

The ideas below are only suggestions. Hopefully one or more of them will work on your farm. They are not listed in a prioritized order but some of them will have more impact on water savings than others.

§ Leave some ground idle and apply the water to the high value crops. Since irrigation districts have to keep their system charged with water, this idea would have a greater impact if everyone in the district cut back on irrigated acres.

§ Do not over irrigate – sounds simple but is not easily accomplished. Most growers tend to err on the side of excess when it comes to irrigation. Too much water does not have the visual impact that too little does but it wastes soil and fertilizer, as well as water.

§ Use the "ET" (evapotranspiration) charts published by the Bureau of Reclamation AgriMet system. They are available on the Internet at at the Malheur Experiment Station website or directly at . The charts make fairly accurate estimates of crop water use. This can help you estimate when you need to irrigate. (See section of this newsletter about how to use these charts.)

§ Soil moisture monitoring equipment will tell you how much moisture is in the soil. There are several types of sensors available. The most common ones used in this area are Watermark sensors, the Diviner and tensiometers. These instruments, along with ET charts will provide a fairly accurate estimate of irrigation needs.

§ Graph soil moisture readings. We believe that the most important aspect of soil moisture monitoring is to create a graph of the readings. (A sample graph used for Watermark sensors is attached below.) Even if you use a shovel and your fingers for measuring soil moisture, you can graph the readings. This will improve your irrigation accuracy.

§ Some plants handle drought stress better than others. Barley uses less water than wheat. Sugarbeets are able to extract moisture from a greater depth than most crops. Crops such as Russet Burbank potatoes suffer greatly in quality when drought stressed, Shepody potatoes not as much but still more than other crops. Russet Burbank looses tuber grade and fry color with water stress. Shepody and Umatilla Russet varieties loose total yield. Potatoes can be stressed very early, but should not be stressed after setting tubers. Water stress on onions will affect yield, grade and lower the percent of single centers. Wheat and corn lose test weight and yield. For most crops, water stress at the flowering stage is most damaging.

§ Know the water holding capacity of the different soils on your farm. A sandy loam soil will not hold as much water as a silt loam soil, thus it will need to be irrigated more frequently. The lighter sandy loam should not have as much water applied with each irrigation as the heavier soil because it cannot hold as much water. The extra water is lost to leaching.

§ Consider surge irrigation or at least a modified surge program on the first irrigation. The wetting-drying cycle of surge irrigation reduces water loss to deep percolation. Water losses to deep percolation are particularly important on the first irrigation when the soil is friable and takes a lot of water. A modified surge irrigation is when you alternate siphon tubes between rows every couple of hours on the first irrigation. This method can save water and reduce nitrogen loss through leaching.

§ Alternate row irrigation is when you irrigate one side of the bed on one irrigation, the other row or side of the bed on the next one. This practice works well with crops, which are less sensitive to moisture stress.

§ Compact the soft non-traffic rows in furrow irrigated fields so that the infiltration rate is similar to the wheel-traffic rows.

§ Irrigate only the wheel row. Since the infiltration rate in the soft row is usually much higher than the wheel row, irrigating the wheel row will reduce deep movement of the water. This will help keep the water in the root zone.

§ Switch to sprinkler irrigation. This allows you to manage water more efficiently and apply it to the depth needed. Remember that some crops may have increased diseases under sprinklers because the foliage is kept wet. (With today's increased power costs, this may not be a good option unless you can set up a gravity flow system.)

§ Drip irrigation can save you a lot of water, in many cases over half of what you use under furrow irrigation. It will often increase yields as well. It is costly to set up but practical for onions and promising for seed alfalfa. The Malheur Experiment Station is investigating ways to obtain long term benefits from the tape by leaving it in the ground through several cropping cycles. They have an excellent web page titled "An Introduction to Drip Irrigation" at
http://www.cropinfo.net/drip.htm.

§ Change irrigation sets when water reaches the end of the furrow rather than at a specified time of day.

§ Use PAM (polyacrylamide) or straw mulch to improve water infiltration in tight soils.

§ Eliminate deep watering of shallow rooted crops. Crops such as onions and beans have shallow root systems. Frequent, light irrigations can help keep the water in the root zone where the plant can use it.

§ Slightly drought stress the bottom of the field by cutting the water as soon as it reaches the end of the field in order to keep the top end from receiving too much water. Usually we over water the top of the field and cause stress from over watering and nitrogen deficiency from leached nitrogen. Production losses should be similar. Straw the bottom end of the field so that the water that gets there soaks in.

§ Use catch basins to collect runoff and reuse it. Sometimes this involves pumping water to the top of the field or to the next field. The cost of pumping needs to be analyzed to see if it is cost effective.

§ Know the water use requirements of the crops you intend to grow to make sure you have enough water to get an economic yield.

How To Use The AgriMet Crop Water Use Chart

Example

(1) ESTIMATED CROP WATER USE – JULY 16, 2000 ONTO
(2) CROP	(3) START	(4) DAILY CROP WATER USE- (IN) PENMAN ET - JULY 12 13 14 15				(5) Daily Forecast	(6) COVER DATE	(7) TERM DATE	(8) SUM ET	(9) 7 DAY USE	(10) 14 DAY USE
ONYN	401	0.32	0.3	0.29	0.31	0.32	710	820	20.6	2.16	4.3
POTS	501	0.33	0.32	0.3	0.32	0.34	610	820	19.7	2.3	4.28

(1) = Location of weather station ONTO = Ontario, Malheur Experiment Station

(2) = Crop ONYN = Onions POTS = Shepody Potatoes

(3) = Start Date = Crop emergence date

(4) = Amount of water used by the crop each day for the past four days

(5) = Estimate water use for the date on the chart, i.e.. July 16

(6) = Cover date. Date the crop reached full canopy

(7) = Term date. Date irrigation stops or crop is harvested

(8) = Sum ET. Total estimated water use from the beginning of the growing season to the current date.

(9) = 7 day use. Prediction of water needed by crop for the next 7 days.

(10) = 14 day use. Prediction of water needed by crop for the next 7 days.

Estimated water use of selected Malheur County Crops – taken from "ET" values at the Malheur Experiment Station for the 2000 crop year. Depending on the irrigation efficiency of your farming operation, actual water use may be more or less than these values. They are a good, relative guide.

Crop Water use – inches/yr

Alfalfa 45

Pasture 36

Winter Wheat 26

Spring Wheat 26

Sugarbeets 38

Onions 32

Potatoes 30

Beans 24

Field Corn 30

Peppermint 28