North Dakota State University
NDSU Extension Service

No. 183, July 2000
http://www.ext.nodak.edu/extnews/snouts

Field Days Scheduled at NDSU Research Extension Centers
Manage Your Irrigation Systems Carefully in July and August
Follow Irrigation Research on the Web
Irrigation Scheduling Software Available
Knowing Daily Crop Water Use is Valuable Information
Soil Sampling for Salinity or Sodicity in Irrigated Fields
Ten Years of High Value Crop Research
Tech Tip – Checking the Timer on Electric Powered Center Pivots

Field Days Scheduled at NDSU Research Extension Centers

These field days showcase the latest research being carried out by scientists with the North Dakota Agricultural Experiment Station and the NDSU Extension Service. Each station has various tours planned so call to find out the day's events.
MDT – Mountain Daylight Time.

Manage Your Irrigation Systems Carefully in July and August

Up to this point in the growing season we have been receiving a steady supply of rainfall. However, variable rainfall events can fool you into thinking that there is enough water in the root zone and delay starting the irrigation system until it is too late.

July and August constitute the high water use period for irrigated crops. For average weather conditions, most irrigated crops will use between 0.25 and 0.3 inches of water each day. To determine when to turn on the irrigation system and schedule irrigation, it is important to know how much rain is received at each field and have some estimate of the daily water use of your irrigated crop. To measure rainfall, I recommend having two accurate rain gages (at least 2-inch diameter opening). One should be in the southeast corner of the field and one should be located in the northwest corner. I recommend these locations because during the summer about half the rain comes from the south and half comes from the west.

Follow Irrigation Research on the Web

In recent issues of this newsletter, the irrigation water management research under the two-tower pivot at the Carrington Research/Extension Center has been described several times. This web address

http://www.ageng.ndsu.nodak.edu/crec/iwm_crec.htm  

will give you can get a better view of the research. Soil moisture readings from some of the research plots for each high value crop will be displayed and updated as we progress through the growing season. In addition, we will include pictures of the crops at different stages of their growth.

Irrigation Scheduling Software Available

Collaboration between NDSU and the University of Minnesota Extension Service has produced a computerized version of the "Checkbook" irrigation scheduling methods used in each state. The program allows you to select which state you are in and the nearest historical weather data location to your fields. The software creates a spreadsheet based work document for each irrigated field which look very much like the soil moisture balance sheets shown in the bulletins from each state. A feature of the software allows you to graphically show the status of the soil moisture in the field that can be used to predict irrigation dates.

The software is designed to run on machines running Windows 3.1 or higher. We are selling the program along with a detailed operating manual for $30. For more information about the program, please contact me or call (701) 231-7236.

Knowing Daily Crop Water Use is Valuable Information

With variable rainfall events it sometimes becomes difficult to determine when to irrigate and how much water to apply. As the crop approaches the high water use period (July and August) these can become critical decisions. Too much water may leach fertilizer from the root zone and too little water can produce crop stress. Either way, crop yields suffer.

A system of scheduling irrigation must be followed. Scheduling using the "Checkbook" method requires the irrigator to measure rainfall amounts, record irrigation amounts and obtain an estimate of the daily crop water use. Using these data, a soil moisture balance sheet is used to determine the daily soil moisture deficit. This method is called the checkbook method because it is very similar to how you balance your bank checkbook. If you think of rain and irrigation amounts as deposits and crop water use as withdrawals from the "soil water bank" then you have the idea. The procedure is outlined in NDSU Extension circular, AE-792, Irrigation Scheduling by the Checkbook Method, available from your county extension office.

The most difficult part of the process is obtaining the daily crop water use values. Fortunately there are two relatively easy ways to obtain these numbers. AE-792 contains tables that provide estimates of the daily crop water use for the most common irrigated crops in North Dakota. All you need is a record of the daily maximum temperature and the number of weeks past emergence. If you have an Internet account, more accurate estimates of daily crop water can be obtained at:

http://www.ext.nodak.edu/weather/ndawn  

At this Website you can obtain crop water use tables or maps for alfalfa, turf grass, corn, drybean, wheat, barley, potato, sugarbeets, sunflowers and soybean. The soybean and sunflower crop water use values were added this year. The reason I say they are more accurate than the values in crop water use tables of AE-792 is that local daily weather values are used to calculate the crop water use. You can either select crop water use tables for any of the 52 NDAWN weather stations and a particular crop or you can view maps of North Dakota with crop water use values superimposed at the location of each weather station. All you need to do is select the nearest emergence date of the crop of interest and a color-coded map will appear. Summary maps for the previous 2,3,4,5,7 and 10 days are also available.

Knowing crop water use, using the checkbook method and monitoring soil moisture on a regular basis (every two weeks) will help you optimize your irrigation water management and provide the best yield possible.

Tom Scherer (701) 231-7239
NDSU Extension Agricultural Engineer
tscherer@ndsuext.nodak.edu 

Soil Sampling for Salinity or Sodicity in Irrigated Fields

One of the negative effects of irrigation is the concentration of minerals in the soil. The degree to which this occurs is determined by the quality of the irrigation water and the type of soil irrigated. The North Dakota Irrigation Guide defines the limits of soil and water compatibility. Soils that exceed these limits are not recommended for irrigation. Some soils may be irrigated if certain management recommendations are followed and they are regularly tested for salinity and sodicity. Regular soil testing encompasses a number of approaches. The most appropriate approach depends on the site conditions in each irrigated field.

Regular soil testing for salinity and sodicity are intended to determine whether irrigation causes increases in soluble salts and sodium. In general, soil salinity will begin to have noticeable effects on crop yields when the electrical conductivity (EC) of the soil saturation extract is 4 deci-Siemens per meter (dS/m) in the rooting zone. When the sodium adsorption ratio (SAR) of the soil saturation extract exceeds 13, soil physical conditions deteriorate and cause significant reductions in crop yields. The goal of regular soil testing is to detect and control salinity and sodicity long before these levels are reached.

The most critical layer of soil that must be monitored is the surface few inches. Most plants are least resistant to salinity and sodicity during germination and early growth stages. Changes that occur from irrigation are most likely to occur from the surface downward. The topsoil should be sampled on a more frequent interval than the soil from deeper layers. Soluble salts may fluctuate substantially between seasons due to water movement; therefore, it is important that surface samples are taken during germination and seedling emergence. The SAR is a reflection of cation exchange complex, so is not influenced by seasonal changes in water content. Sample timing for SAR is not as important as for salinity.

Sampling should be done prior to the first year of irrigation so that a baseline is established. Sampling for salinity and sodicity under irrigation is different than soil fertility sampling. The goal is to determine where salts or sodium are increasing in the field and at what rate. Composite sampling as done for soil fertility does not accomplish this goal. I suggest that the field be sampled on a grid that covers the portion of the field that has soils recommended for regular monitoring by the North Dakota Irrigation Guide.

Samples should be taken at no greater than a 500 ft interval. If the sampling grid encompasses an unirrigated corner, it should be sampled to serve as a control or comparison. The grid should be adjusted so that problem areas, such as low spots or areas next to saline or sodic soils, are identified and monitored. Sample locations should be marked (on an aerial photo or with GPS) so that soil samples are taken from approximately the same location in subsequent years. The first year of sampling should include a sample from the 0 to 6 inch depth, 6 to 24 inch depth, and 24 to 36 inch depth at each of the grid nodes. EC should be determined on the saturated extract of all three depth increments and SAR on the top two increments. Subsequently, every three years EC and SAR should be determined for the 0-6 inch increment and EC for the 6 to 24 inch increment. Every 6 years SAR should also be determined on the 6 to 24 inch increment and EC should be determined on the 24 to 36 inch increment.

Monitoring of irrigated fields consisting of mostly of irrigable soils with smaller inclusions of nonirrigable saline or sodic soils may be necessary. Irrigation may contribute to expansion of salinity or sodicity into the irrigable soils. Monitoring soils along the edges of these problem areas using the sampling depth increments and intervals suggested above will help determine the rate of encroachment.

Every irrigated field is unique and soil quality monitoring requirements will vary. Many fields are predominantly irrigable soils that require no monitoring. Some fields will require monitoring in only small portions of the field. Whatever the situation is, it is important that consideration of soil monitoring be included in the planning stages of the irrigation system. If it is determined to be needed, implementation of regular soil monitoring will most definitely help the irrigator maintain the productivity of the soil.

Bruce Seelig (701) 231-8690
NDSU Extension Water Quality Specialist
bseelig@ndsuext.nodak.edu

Ten Years of High Value Crop Research

One of the main purposes for research at the Oakes Irrigation Research Site (OIRS) is to evaluate non-traditional crops, such as vegetables, which can be adapted for commercial production under irrigation in North Dakota. The research has focused on variety trials and the agronomic practices needed to successfully grow these high value crops. In this report I will detail some of the research that has been done to meet this objective.

When we started working with carrots about 10 years ago, the thing that caught our attention was the high yields. Average carrot yield (for processing) in the United States is 22 tons/acre. Yields in our plots at the OIRS often surpassed 50 tons/acre. Carrot quality was also as good or better than carrots grown in other areas of the U.S. Over the past 10 years we have experimented with row spacing, plant population, variety selection, cover crops, weed control, and seed bed preparation. We have also cooperated with NDSU main campus faculty on disease and insect control, fertility, and storage of carrots. Seedbed preparation consists of subsoiling and usually making beds, although in sandy soils the beds may not be necessary.

Carrots can be planted with two or three rows per bed with the beds spaced four and a half feet, center to center. Carrots used for processing, cello pack, or cut and peel should be planted at 400,000, 800,000, and 1,200,000 seeds/acre, respectively. Treflan (trifluralin) applied pre-plant and incorporated, followed by Lorox (linuron) applied pre-emergence and post-emergence gave good weed control. Leafhoppers must be controlled to prevent infection with the aster yellows virus. Spraying a fungicide, such as Benlate, on the carrots one week before harvest reduced storage rot due to white mold. Most varieties of carrots grow well in North Dakota. Some we have found that grow especially well are Bolero, Prime Cut, and Primo.

Cabbage also grows extremely well in North Dakota. Yields in our plots averaged 50 to 60 tons/acre (U.S. average yields are 26 tons/acre for processing). The quality is excellent. In our trials, Charmant, Gideon, and Bronco were the best hybrids for the fresh market, while Fresco, Cheers , Bravo , and Bronco were the best hybrids for processing. Hybrids listed by seed companies with relative maturities of greater than 97 days (transplant) or 115 days (direct seed) generally had trouble forming marketable heads. All our cabbage was direct seeded with a specialty planter. It could also be transplanted. Cabbage should be planted at about the same time as spring wheat. Planting later than May 15 in our studies reduced yield and quality. Treflan (trifluralin) applied pre-plant and incorporated followed by Lentagran (wetable powder formulation of pyridate) at the 4-leaf growth stage and hand weeding gave the best weed control. A barley cover crop planted at the same time the cabbage is planted protects the cabbage from wind abrasion but should be killed when it is 6 to 8 inches tall to prevent competition with the cabbage. Cabbage must be cooled immediately after harvest to maintain quality. We did this by putting the cabbage in boxes, stacked on pallets, in a refrigerated truck and drawing air through it.

Onions are not as high yielding, compared to other areas of the U.S., as are carrots or cabbage. Still they can be more profitable than potatoes if managed correctly. Our major research with onions at the OIRS has been with hybrid evaluation, cover crops, and weed control. Cover crops are necessary to protect the onions from wind erosion. Barley, seeded at the same time the onions are seeded and killed when 6 to 8 inches tall, does a good job of protecting the onions while not competing with the onions. Hand weeding in the onions has been reduced from about 30 hours/acre to zero through research at the OIRS and farmer adaptation and experimentation. This represents a tremendous reduction in input costs. Weed control usually consists of spraying Prowl (pendimethalin) just after the onions emerge, followed by 28% N when onions have one true leaf. Fusilade (fluazifop-P), sprayed when the barley cover crop is 6 to 8 inches tall, kills the barley and grass weeds. When onions have two true leaves, and again when they have 5 true leaves, a combination of Buctril (bromoxynil) plus Goal (oxyfluorfen) is sprayed. Prowl or Dual (metolachlor) applied when onions have 4 to 5 true leaves helps with season long weed control.

When vegetables are rotated with corn and soybean, herbicides applied to corn and soybean can carry over and injure vegetables planted in subsequent years. We determined the carryover injury to vegetables from five herbicides; nicosulfuron (Accent), flumetsulam (Broadstrike), clopyralid (Stinger), imazethapyr (Pursuit), and imazamox (Raptor) applied to corn or soybean. One year after herbicide application, nicosulfuron injured cabbage, onion, and red beets; flumetsulam injured cabbage and squash; imazethapyr injured cabbage, onion, red beet, and tomato; and imazamox reduced squash stand. Clopyralid did not carryover to injure vegetables planted one year later. Please note that some labels for these herbicides are more restrictive, as far as time to wait before planting vegetables, than what my research suggests should be the waiting period

Potatoes were not injured by any carryover herbicide any year. There was no injury to any vegetables two years after herbicide application. The low rate of injury to vegetables in this study was due to conditions, such as low clay and soil organic matter content and adequate soil moisture, which promoted dissipation of these herbicides from the soil.

Other research conducted at the OIRS showed that rimsulfuron (Matrix or Shadeout) controlled hairy nightshade in potatoes and tomatoes, but did not control black nightshade. Vegetable varieties adapted to commercial production in North Dakota have been identified for cabbage, carrot, onion, sweet corn, pumpkin, winter squash, tomato, pepper, oriental vegetables, broccoli, garden pea, and red radish. For a more complete report of the research conducted at the OIRS, see the annual reports printed each year (I will send you a copy if you want). You can view the 1996, 1997, 1998, (and soon the 1999) annual reports on the Internet at: http://www.ag.ndsu.nodak.edu/oakes/oakes.htm

Richard Greenland (701) 742-2189
Supervisor, Oakes Irrigation Research Site
rgreenla@ndsuext.nodak.edu

Tech Tip –

Checking the Timer on Electric Powered Center Pivots

The amount of water applied to a crop by a center pivot is controlled by the speed of the end tower. The amount of time the end tower is moving is determined by the setting of the percent timer in the pivot control panel. The new computerized control panels use electronic timers, but most panels use an electro-mechanical timer. Electro-mechanical percent timers are low cost ($25 to $50), readily available and prone to mechanical wear. A percent timer that causes the end tower running time to fluctuate can cause over or under application of irrigation water. Good irrigation management requires an accurate estimate of the application amount applied during irrigation. It is especially important during the fruiting stage (grain filling, corn ear formation, potato tuber bulking, etc) of crops.

To check the accuracy of a percent timer (whether electro-mechanical or electronic), all you need is a view of the wheels on the end tower, a stopwatch and the percent timer setting. For example, if you set the timer to 40%, then the end tower should move 24 seconds out of each minute (0.4 x 60 seconds). Viewing the movement of the end tower wheels and using the stopwatch can check this. Some pivots don't move a continuous 24 seconds but move 12 seconds in each 30 second interval. Either way, the time of movement should add up to 24 seconds in each minute. Measure the movement for at least 3, one-minute periods. If the movement time fluctuates, change the timer. It will save you some future headaches and make your water application amounts reliable.

Tom Scherer (701) 231-7239
NDSU Extension Agricultural Engineer
tscherer@ndsuext.nodak.edu

Water Spouts, No. 183, July 2000

NDSU Extension Service, North Dakota State University of Agriculture and Applied Science, and U.S. Department of Agriculture cooperating. Sharon D. Anderson, Director, Fargo, North Dakota. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. We offer our programs and facilities to all persons regardless of race, color, national origin, religion, sex, disability, age, Vietnam era veterans status, or sexual orientation; and are an equal opportunity employer. This publication will be made available in alternative formats for people withdisabilities upon request, 701/231-7881.

North Dakota State University
NDSU Extension Service