No. 156, August 1996
------------------------------------------------------- Location Topic Date Time ------------------------------------------------------- Staples, MN* Potatoes August 5 5:30 p.m. Staples, MN* Dry Bean August 15 10:00 a.m. Oakes Field Trials Field Crops August 20 9:00 a.m. ------------------------------------------------------- *Central Lakes Agricultural Center, Staples, MN
Color coded crop water use maps for North Dakota are now available on the internet via the World Wide Web (WWW). If you have an internet access account and a net browser such as Netscape or Microsoft Explorer, then go to this address <http://www.ext.nodak.edu/weather/cropwater/> and check out these maps. They were created to provide accurate estimates of crop water use for the eight major irrigated crops in North Dakota.
The maps are created using weather data from the 49 stations which comprise the North Dakota Agricultural Weather Network (NDAWN). Each weather station on the network is automated and the weather data are retrieved every day. The crop water use estimates are calculated using the weather data from each automated weather station and these numbers are shown on the maps. The crop water use estimates for the eight crops use a reference ET amount (inches of water use per day) calculated with the Jensen-Haise equation. The reference ET amount is adjusted for each crop to produce the estimated crop water use amount.
The crop water use estimates for potato, corn, dry bean, sugarbeet, wheat and barley are calculated using an average emergence date for North Dakota growing conditions. The emergence date and the date or dates of the water use estimates are shown at the top of each map. The water use estimates for alfalfa and turf grass are calculated assuming they began growing on April 1. When a crop is selected, the first map shown is for the previous day (a complete weather day). Below this map, you can select a summary map for the previous 2,3,4,5,7 or 10 days. Any comments about these maps and their use, whether positive or negative, are appreciated.
A field day is planned from 9 am to noon Sept. 4 at the Oakes Management Systems Evaluation Area (MSEA) site. The MSEA site is located on Highway 1, four and a half miles south of Oakes, ND.
The MSEA site is part of a research project designed to answer questions about the relationship between agriculture and ground water quality. Topics to be covered include control of European corn borer, an update on BT corn which is resistant to corn borer, use of remote sensing to measure crop characteristics, site specific farming and the effects of ridge tillage farming practices on ground water quality.
Tom Scherer, (701) 231-7239
NDSU Extension Agricultural Engineer
tscherer@ndsuext.nodak.edu
Water Spouts: www.ext.nodak.edu/extnews/snouts/
The North Dakota Agricultural Products Utilization Commission (APUC) is a state agency which awards value-added agricultural processing, research and marketing grants. Some previous grants include Central Dakota Growers, the High Value Irrigated Crops Task Force and the Nesson Valley Irrigation Project. The commission has a newsletter entitled the APUC News which includes descriptions of the projects which received grants, outlines of project final reports, meeting information and application guidelines. If you are interested in receiving this newsletter contact us at ND APUC, State Capitol, 6th Floor, 600 E Boulevard Ave, Bismarck, ND 58505-0020 or call our office at (701) 328-4760.
Amy Bodine, (701) 328-4760
Accountant, ND APUC
There are a number of water quality myths that continue to be touted as well known facts. One of these goes something like this: "It's been shown over and over again that irrigation causes significant groundwater contamination and if you don't have problems now, it's just a matter of time." Once that statement is accepted as an incontrovertible truth, then the next logical step must be major changes in all irrigation management and stricter regulation in irrigated areas. I would argue that this is an inappropriate reaction based on an inaccurate generalization of the real world.
The simplistic view that makes irrigators the "bad boys" of American agriculture is not justified. Irrigation is just one of many farming systems used to produce crops. There are combinations of natural factors and irrigation management that can cause groundwater contamination; however, this is also true of dryland farming systems.
The point of this discussion is not to absolve irrigators of environmental responsibility nor to distract attention from real problems. However, the inordinate amount of attention that groundwater contamination has received in recent years needs to be placed within the realm of fact.
In North Dakota we know from several monitoring studies that pesticides are rarely detected in groundwater. However, those studies do show that low level contamination does occur sometimes. Few studies of pesticides in groundwater have been able to conclusively link contamination incidence with any specific farming system, including irrigation. However, several investigators have concluded that a large portion of pesticide contaminations were due to poor well construction or inappropriate pesticide handling practices. A general conclusion of several studies including some from North Dakota is that shallow wells are more likely to be contaminated than deep wells.
Considering our present knowledge of pesticides in groundwater, how should irrigation management be approached? The simple answer is, no different than management of any other farming system. The data from monitoring studies provides little support for singling out any particular farming system for special attention. Primary emphasis should be placed on management methods that secure the integrity of the well and the area around it. Secondary emphasis should be placed on management methods that reduce the availability of pesticides to move to groundwater.
The construction and operation of irrigation wells are subject to regulation by the North Dakota Water Commission. Among other things these rules are designed to reduce the potential for groundwater contamination. They should be followed. If pesticides are applied through the irrigation system, state regulations require the use of chemigation equipment that protects against back-siphonage. When pesticides for chemigation are stored near the well secondary containment will reduce the risk of contamination from a leak or spill.
Major factors that determine potential for pesticide contamination of groundwater are the following:
Assessment of these factors helps to determine which areas that would have the greatest potential to contribute to pesticide contamination of groundwater. NDSU Extension Bulletin EB-63 discusses how to do an assessment using these four factors.
If the assessment identifies critical areas for potential contamination, management methods can be selected for those areas that reduce the opportunity for pesticide movement to groundwater. These management methods are often referred to as best management practices or BMPs. Most BMPs are appropriate for both irrigated and dryland farming systems. They are organized into three categories: 1) Improved pesticide application (table 1); 2) Integrated pest management (table 2); and 3) Soil and water conservation practices (table 3). Some BMPs are unique to irrigated agriculture (table 4). These BMPs are discussed in a series of NDSU extension circulars AE-1110 - 1116.
Table 1.Improved pesticide application BMPs.
- Use pesticides with low mobility and persistence.
- Use pesticide formulations that reduce drift losses.
- Adjust spray equipment to give the range in droplet size for optimum coverage of the target.
- Release pesticide spray as close to the target as possible.
- Never apply pesticides during weather conditions that may cause significant drift of small droplets away from the spray target.
- Calibrate application equipment regularly to ensure that the proper amount of pesticide is applied.
- Add petroleum or modified vegetable oil adjuvants to herbicide mixes, when recommended.
- Utilize banded applications of pesticides when possible.
- Utilize methods of pesticide application that target individual pests or improve uniformity of application if possible.
- Use pesticides that can be incorporated into the soil, if possible.
- Avoid pesticide applications prior to intense rainfall events.
- Check mix-water for pH and minerals that may reduce pesticide efficacy.
Table 2.Integrated pest management BMPs.
- Plant pest-resistant cultivars if available.
- Maintain competitive plant growth through the regular use of good agronomic practices.
- Use crop rotation to break pest life-cycles.
- Control volunteer plants that can serve as hosts for certain diseases and insects.
- Use tillage to control pests where appropriate.
- Use biological control of pests when available and when effectiveness has been demonstrated.
- Use preemptive techniques for pest management.
- Optimize timing of pesticide applications according to pest life cycles and economic thresholds of damage.
- Rotate pesticides to prevent development of pest resistance.
Table 3.Soil and water conservation BMPs.
- Utilize animal wastes, if available, as a source of organic matter and as a portion of nutrient inputs.
- Rotate low residue crops with green manure or with high residue crops that return larger portions of organic material to the soil.
- Use reduced tillage methods wherever possible.
- Use tillage to disrupt macropores if preferential movement of pesticides is a source of groundwater problems.
- Use soil conservation practices that reduce the force of wind.
- Use soil conservation practices that reduce the force of runoff water.
Table 4.Irrigation BMPs.
- Schedule irrigations appropriately by accounting for the soil moisture and crop water use.
- Time water applications to avoid water movement beyond the rooting zone.
- Adjust water application amounts to meet varying crop demands at different growth stages.
- Irrigation water must be applied uniformly and accurately.
- The chemigation unit must be calibrated with each use to ensure accurate application of chemicals.
Irrigated agriculture is not going to ruin our groundwater. Combined with certain factors there is potential for pesticide contamination to occur under some irrigated fields. The probability of groundwater contamination can be reduced by following management practices that reduce pesticide availability to water movement. Not all of these practices are appropriate for all conditions and most will need refinement to local conditions. Complete control of our environment will never be possible; however, the general principle of improved management based on increased knowledge will always be worth pursuing.
Bruce Seelig, (701) 231-8690
NDSU Extension Water Quality Specialist
The term site-specific farming means carefully tailoring soil and crop management to fit the different conditions found in each field. Site-specific farming is sometimes called "prescription farming," "precision farming" or "variable rate technology." It has caused a focus on the use of three technologies -- remote sensing, geographic information systems (GIS) and global positioning systems (GPS).
A GIS uses computer technology to store cultural and natural resource information that can be recalled in a geographical format or "map." The maps of different information are often referred to as "layers" because they can be overlaid. These layers of information can be related to exact field locations. Currently, most researchers are able to analyze only a few layers at a time. In the future, more effort will be made to analyze multi-layers of information.
Satellite systems that collect and transmit remotely sensed data important to farmers have been developed. Farmers can analyze the satellite information themselves or contract for this service with various companies. In North Dakota the process of using satellite imaging with farming has begun in the Red River Valley.
Some people incorrectly use the term "GPS" to imply precision farming. GPS makes use of transmitted information from satellites to determine a precise geographical location. The value of knowing a precise location includes: 1) accurate geographic identification of soil properties; 2) fertilizer and pesticides can be prescribed to fit measured soil properties (as opposed to estimated from soil maps); and 3) yield data can be monitored from precise locations as one goes across the field.
The real value of site-specific methods for the farmer is to plan more accurate crop protection programs, adjust fertilizer rates from one part of a field to another based upon localized soil tests, and know the yield variation within a field. These benefits will enhance the overall cost effectiveness of crop production as crop inputs are adjusted to the soil type and stored soil moisture. Only enough inputs are placed in the soil to optimize crop growth without over application or under application.
Currently, the most interest in site-specific farming is with yield monitoring and variable fertilizer application. Both are important. Up to this time, soil testing was performed by taking several samples from different areas in the field. The samples were then mixed together and a composite sample was sent in for testing. This method gave an average for the field. The problem with this method is very few places in a field will be "average." So, some places will be over fertilized and other places will be under fertilized, resulting in inefficient use of fertilizer. Variable fertilizer application allows applying inputs based upon the soils production capabilities.
Yield monitoring is important and allows a producer to see the results of crop production practices over each area in the field. The only other way to obtain yield results was to weigh the entire crop produced and determine an "average" yield. Again, most areas in a field are not average.
Site-specific farming has tremendous capabilities to help improve the efficiency in producing crops. There is a cost for this technology and at the present time, the payback for the system is unknown.
Vern Hofman, (701) 231-7240
NDSU Extension Agricultural Engineer
There are several techniques for estimating corn grain yield prior to harvest. This version was developed by the ag. engineering department at the University of Illinois and is the one most commonly used. A numerical constant for kernel weight is figured into the equation in order to calculate grain yield. Since weight per kernel will vary depending on hybrid and environment, the yield equation should only be used to estimate relative grain yield. For example, yield will be overestimated in a year with poor grain fill conditions, while it will be underestimated in a year with good grain fill conditions.
Step 1. Count the number of harvestable ears per 1/1000th acre. (Table 1)Step 2. Count the number of kernel rows per ear on every fifth ear. Calculate the average.
Step 3. Count the number of kernels per row on each of the same ears, but do not count kernels on either the butt or tip that are less than half size. Calculate the average.
Step 4. Yield (bushels per acre) equals:
(ear #) X (avg. row #) X (kernel #) ----------------------------------- 90
Soybean yield estimates are most accurate within three weeks of maturity, but are still only estimates. Assume 2.5 bean per pod.
1. Determine the number of feet of row needed to make 1/1000 of an acre (Table 1).2. Count the number of plants in ten (10) different randomly selected sample areas. Calculate the average.
Avg. = __________ = A (plants/A)3. Count the number of pods per plant on ten randomly selected plants from each sample area. Calculate the average.
Avg. = __________ = B (pods/plant)4. Calculate pods/acre by multiplying plant population by pods/plant.
A X B = __________ = C (pods/acre)5. Calculate seeds/acre by multiplying pods per acre by an estimate of 2.5 seeds/pod.
2.5 X C = __________ = D (seeds/A)6. Calculate pounds/acre by dividing seeds/acre by an estimate of 2500 seeds/pound.
D ÷ 2,500 = __________ = E (lbs/A)7. Estimate yield by dividing pounds/acre by 60 pounds/bu.
E ÷ 60 = __________ = Yield (bu/A)
Table 1. Length of row equal to 1/1000th acre. An accurate estimate of plant population per acre can be obtained by counting the number of plants in a length of row equal to 1/1000 of an acre. Make at least three counts in separate sections of the field, calculate the average of these samples, then multiply this number by one thousand (1,000). ----------------------------------------- Length of Single Row Row Width to Equal 1/1000 of an acre ----------------------------------------- (inches) (feet) (inches) 6 87 1 7 74 8 8 65 4 10 52 3 15 34 10 20 26 2 28 18 8 30 17 5 32 16 4 36 14 6 -----------------------------------------
You can estimate dry bean yields by knowing the number of seeds per pod, pods per plant and plants per 1/1000th of an acre. At the time of counting seeds and pods, the maturity status of each should be determined.
If a seed or pod will not mature, it shouldn't be counted. Then count the total plants per 1/1000th acre to complete the data collection.
Within a representative and uniform plant stand, randomly select five plants each from at least five randomly selected locations in the field.
Keeping all plant data separate, pull and count the pods from each plant and then count the seeds to determine average seeds per pod for all five replications. These data are combined with the average number of plants per 1/1000th acre.
Average number of seeds per pound --------------------------------- Kidneys 900-1000 Pintos 1400 Great Northerns 1600-1800 Pinks/Small Reds 1600-2000 Navies/Blacks 3000 ---------------------------------
Seeds per pound can vary 10-20% for different varieties within a bean class. If available, use reported estimates for seed number per pound for your variety.
The accuracy of yield estimate can be improved by counting seeds and pods from at least 10 plants per replication.
Duane R. Berglund, (701) 231-8135
NDSU Extension Agronomist
In some areas of North Dakota, concern has been raised over rising salinity and total dissolved solids (TDS) concentrations measured in water samples from some wells. In most cases increasing TDS has been composed of sulfatic salts, including calcium and magnesium sulfate, and in some cases sodium sulfate.
Increased salinity in water can be of concern to users of water. For irrigators sufficiently large salinity can decrease crop water use efficiency and crop yield. Soil salinization problems can result in needs for special management, such as increased water application for flushing salts from the soil profile. If sodium is present, substantial soil damage through slaking and loss of soil structure can occur. Increased salinity is also undesirable from the standpoint of drinking water, where EPA has suggested a maximum TDS guideline of 500 milligrams per liter (mg/L).
Sulfate, which is a primary component of most of the increased salts, is not toxic, although large sulfate concentrations can cause short-term intestinal discomfort and loosening of stool. This, however, is usually a temporary condition. Although an EPA limit of 500 mg/L of sulfate has been suggested, most recent research has indicated that intestinal problems actually occur at higher levels than previously thought. It is unlikely that a mandatory EPA limit on sulfate will be set in the near future. If such a limit is placed, some EPA sources have suggested that it will likely be higher than the proposed 500 mg/L.
Are TDS levels rising? In some wells and in some aquifers, yes. Many theories have been offered to explain these increases in sulfate, including the possible contribution from sulfate fertilizer use. Another theory proposed has been that nitrate leached to the aquifer is denitrified through a process called "autotrophic denitrification," which removes nitrate from the aquifer, but which also oxidizes insoluble sulfide to the highly soluble sulfate form. While these processes are likely occurring, it is unlikely that they are the primary contributors to increased TDS in well water. Other sources are more likely.
North Dakota's soil and underlying geological materials are very high in sulfate, as is much of the northern Great Plains. Shale bedrock and glacial till weathered from shale often contain substantial quantities of sulfate, weathered over thousands of years or oxidized from sulfide minerals weathered from the shale. Water in North Dakota's glacial aquifers generally moves from areas of recharge to areas of discharge at a rate of about 10 to 100 feet per year. Water moving from a recharge area toward a discharge area dissolves and carries an ever increasing salt load as it proceeds on its course. These salts are deposited when the water is evaporated or transpired to the atmosphere in discharge areas.
Discharge areas are very often areas such as shallow lakes, marshes, or land-surface depressions where the water table is near the surface. In discharge areas water evaporates, depositing salts in the soil, or leaving water in more saline water bodies. Discharge areas can also occur at deeper levels where crop roots extract water from the water table, or even greater depths where tree roots extract water form the water table. Discharge areas, which are often identifiable by saline soils, serve as areas for salt accumulation and concentration, thereby preventing salt buildup in the aquifer.
When large-scale ground water withdrawals occur in an aquifer, the flow system changes, even if use does not exceed recharge and when sustainable yield practices are used in allocating water. As water tables decline to lower elevations, former net discharge areas may convert to net recharge areas. Thus, during recharge events, salts formerly deposited in the net discharge areas are flushed downward into the aquifer and toward the wells. The results is that wells near previous discharge areas frequently draw more salty water toward them, and TDS increases with pumping. Sometimes this process can work in reverse. Wells placed in or near salty water sources can become less saline as fresher water is pulled toward them. However, an increase in salinity more frequently occurs because wells are usually placed in locations with better water quality.
Increased TDS in well water is most likely to occur when wells are placed near saline lakes or wetlands, or when wells are placed near aquifer boundaries that are high in salts. Many glacial till materials, or weathered shales, that border or underlie aquifers have high salt concentrations. Observed changes in TDS have ranged from a few mg/L to almost 1,000 mg/L.
To some degree, increasing TDS will be unavoidable in some areas, as long as water is pumped for use. However, work is currently being done to better identify salt source areas, and to better manage the water resource so that problems from rising TDS can be avoided or minimized.
Bill Schuh, (701) 328-2739
Hydrologist, N.D. State Water Commission
It really does matter! You should be checking soil moisture levels on the coarsest textured (sandiest) soil under irrigation. The finer textured (heavier) soils will hold more water and won't reach critical soil moisture deficient levels (when yield loss starts), until after the crop on sandier soil has already started to stress.
The crop will use the same amount of water regardless of soil type (if moisture is available), but coarse textured soils hold less water. Therefore, the PERCENT OF SOIL MOISTURE DEFICIT under an irrigation system will vary with soil type.
The soils under your pivot are usually not uniform. If you check the county soil survey, you will most likely find that you are irrigating a wide range of soil types. The soil type and rooting depth of the crop determine how much moisture can be stored in the soil for the crop to utilize. If you have a shallow layer of very coarse textured soil it may limit root growth as well.
So don't just check soil moisture levels where it is convenient and near the road. Use your soil survey and monitor the coarsest soils to prevent yield loss.
The critical period for soil moisture management is approaching fast for many crops or in the case of most small grains already here. Yield loss from moisture stress varies by crop but generally is most severe for crops suffering during the period from flowering through grain fill.
Use some type of irrigation scheduling such as the Checkbook method to forecast and estimate crop water use in addition to in-field monitoring with a soil probe and other instruments.
The soils that have the lowest water holding capacity will dictate the frequency and amount of irrigation. This information can be obtained from the local NRCS county soil survey.
Detailed information on irrigation scheduling and assistance in starting a scheduling program is available from your local county agent office or Irrigation Specialist.
Jim Weigel, (701) 652-3194
NDSU Extension Area Specialist-Irrigation
No. 156, August 1996
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 with disabilities
upon request, 701/231-7881.
North Dakota State University
NDSU Extension Service