Soil Fertility & Water Use

Sidedressing Corn, Sunflower
Sidedressing corn (a practice usually reserved for sandy soils prone to leaching) should start when the corn is tall enough that clods do not cover the young plants. Usually 4-8 leaf corn is ideal. Corn can physically be sidedressed until the equipment starts snapping off stalks, but it’s better to apply it earlier than that. If the crop becomes too tall to sidedress by knifing in anhydrous, liquid N can be applied through drop tubes from a high-clearance sprayer, with booms rigged to the same width as the planted rows.  Sunflowers can be sidedressed when clod movement danger is past, to when they are too tall to physically get through. Usually 6-18 inches is best.

—Dave Franzen, NDSU extension soil specialist

Topdressing N on Small Grains
Topdressing N deficient small grains from emergence to the 6-leaf stage may serve to increase yield provided a timely rain incorporates the application prior to jointing. Topdressing after the 3-leaf stage may help head size, spikelet number and kernel number decision, all of which are yield component decisions that the wheat plants make.

Hot and/or dry weather later on, particularly at 4-5 leaf stage and at pollination, will modify any improvements that the N additions would make. Also, whatever topdressing strategy is employed, it must rain following application before the 6-leaf stage for the fertilization to be effective.

Topdressing from jointing through the watery ripe stage of grain development will often serve to increase protein content of grain, but will have little if any effect on yield. Applications of N past the watery ripe stage would have no effect on real grain protein content.

Topdressing applications, if made, should be conducted using liquid N (UAN, 28-0-0) applied with streamer bars to reduce leaf burning and crop injury. Streamer bars concentrate the application into bands, which tend to drive most of the fertilizer to the soil surface rather than coat the leaves, where it could damage the leaf tissue and cause “burn”. A concentrated band also slows the rate of urea volatilization from the urea portion (the N in UAN is about 50% urea) of the UAN.

The ammonium nitrate half of the UAN solution is not subject to volatilization, making UAN a preferred fertilizer over dry urea for this type of application. Application with streamer bars most effectively avoids burning on calm days. The danger of burn increases as the wind increases. Under windy conditions, the wind breaks the stream apart and converts it into a poor broadcast application, coating leaves and increasing burn. Do not broadcast the UAN; the burn will be great and may cause a yield reduction in some cases.

If dry urea is used, it might be wise to also have it coated with Agritain®, which is a tried, tested and proven urease inhibitor, and gives about 10 days of protection from volatility.

Whichever source is used, rain is required to move the N into the soil so that roots can utilize it. About 1/4 inch of rain is needed in bare soil to accomplish this, and with residue, the more rainfall is needed, particularly if there is a thatch cover. If rain does not fall until after the 6-leaf stage, yield will not be enhanced.

If the intent of a mid-season application is to increase protein, consider that the largest increase you are likely to see in protein as a result of a mid-season addition of nitrogen is probably no more than one whole percent increase, i.e., for example, an increase from 13 to 14%. The only exception that is likely to occur is in sites that were very nitrogen-deficient at the time of planting. By the time the wheat crop starts heading out, it has accumulated nearly all of the nitrogen that will eventually show up in either grain yield or protein. Consequently, nitrogen applications for enhancing protein should be made as soon after tillering as possible and before flowering and pollination, if at all possible.

– North Dakota State University, Montana State
University Extension Service

Textural Soil Class	Steady infiltration rate inches/hour
Sands	>0.8
Sandy loams	0.4-0.8
Loams, fine sandy loams	0.2-0.4
Clay loams, silty clay loams and clays	0.04-0.2
Sodic clay soils	<0.04

When to Apply Split N Applications in Wheat
Split applications (planting and in-season N) may be considered when conditions favor a yield potential higher than the original yield goal, or when weather patterns favor nitrogen loss.  This includes sandy soils with increased water for nitrogen leaching, and under heavy soils with high temperatures and reduced denitrification. Otherwise, research has indicated no consistent increase in yield from an in-season application of N on spring wheat if enough was present at the beginning of the season.  Thus, in-season or split applications may have a place where N loss is known, in irrigated sandy soils or sandy soils with high yield potential, or where there is higher yield potential. Otherwise, there is no advantage to routinely include split applications of N in a fertility management plan.

– George Rehm, University of Minnesota extension
nutrient management specialist

Water Infiltration Rates
The volume of water that can enter an area of surface soil is called the infiltration rate. The amount of rainfall that can enter the soil is sometimes greater initially than later on during the rain. If the soil is well aggregated, as in a no-till field, water enters more quickly until larger pores are saturated. If the soil contains more clay and is cracked, filling the cracks with water initially results in initially high infiltration until the clay becomes saturated, swells and closes the cracks.

Once the pores are filled and cracks are closed, the texture of the soil becomes the most limiting factor in water infiltration. The force of the rain, the presence of shallow limiting layers, such as compacted tire tracks or tillage pans also restrict the downward flow of water. But in the absence of these factors, texture is the key to water infiltration. The following chart contains general numbers from “An Introduction to Soil Physics,” by D. Hillel, 1982. The values are useful to demonstrate the magnitude of water infiltration. Individual soils will vary around these values.

Heavy rains that occur in the Red River Valley can illustrate how soil type can affect the infiltration rate. In a clay soil, 24 hours of ponding may result in only ½ inch of water infiltration. Several days are needed to absorb 3-4 inches of ponded water.

—Dave Franzen, NDSU, extension soil specialist

Crop Water Use And Hot Weather
Crop water use, also called evapo-transpiration or ET, is an estimate of the amount of water transpired by the plants and the amount of evaporation from the soil surface around the plants. A plant’s water use changes with a predictable pattern from germination to maturity. All crops have a similar water use pattern, although crop water use can change with each growing season due to changes in climatic variables (high temperature, amount of sunlight, humidity, wind) and soil differences between fields (root depth, soil water holding capacities, texture, structure, etc.). The water use efficiency in the following table (translated as seed production per inch of water use by the plant when water is limiting) represents the response of adequately fertilized crops.

Approximate acreage yield, water use and water use
efficiency of some crops commonly grown in the Northern Plains.

CROP AVERAGE YIELD/A AVERAGE WATER USE, INCHES WATER USE EFFICIENCY YIELD/A/INCH H2O Alfalfa 5 tons 24 0.2 ton Grain Corn 120 bu 21 6 bu. Potatoes 400 cwt 20 20 cwt Sugarbeets (Sugar) 3.2 tons 19 0.2 ton Soybeans 35 bu 16 2.2 bu. Spring Wheat 40 bu 15 2.7 bu. Sunflower 1500 lb. 14 110 lb. Flax 25 bu. 12 1.7 bu. Pinto Beans 2200 lb. 12 180 bu. Barley 55 bu 11 5 bu. Source: J. W. Bauder and M. J. Ennen, NDSU Soil Science Dept.

Water Use of Wheat
A wheat crop of about 50 bushels per acre has a water requirement that is about equivalent to 10 inches. However, because water also evaporates from the soil surface, the actual amount of water needed to produce a crop is higher. Under most conditions in the Northern Plains, small grains will need between 14 and 16 inches of soil moisture per season, depending on climactic conditions and the length of the growing season.

Daily crop water use, also called evapotranspiration or ET, depends on canopy development and will generally peak between heading and early dough stage. Daily ET during this peak period can range from 0.10 to 0.30 inches depending on air temperature and cloud cover.  The table below shows estimated daily ET rates for spring wheat in central Minnesota at different stages of growth and selected maximum daily air temperature ranges. As weather is variable by location, so too will daily ET estimates vary by location. Real-time estimated daily crop ET may be observed over the Internet during the growing season at: ndawn.ndsu.nodak.edu.

Determining Yield Probability Based On Soil Moisture
Studies at NDSU have indicated that 5 inches of water is needed by wheat to reach the heading growth stage. After this requirement is met, each additional inch of water will produce 4-7 bushels of wheat. The water can be provided by soil or rainfall.

Sandy soils hold about 1 inch of plant available water, clay soils about 2 inches and loam soils 2.25 inches per foot of soil at field capacity. Average May, June, July rainfall in North Dakota is about 8 inches. Rainfall, depending on crop growth stage, is more efficiently used in June than in other months, which may provide increased yields above predicted yields.

– NDSU

Total Water Available Wheat Yield Bu/A Barley Yield Bu/A 8 12-21 21-30 9 16-28 28-40 10 20-35 35-50 11 24-42 42-60 12 28-49 49-70 13 34-56 56-80 14 38-63 63-90 15 42-70   16 46-77

Drought Stress in Corn
The effect of drought on corn growth and yield varies considerably depending on its timing and severity. Corn is most sensitive to drought during flowering, most specifically 1 to 22 days after silking. When corn is severely stressed prior to flowering, silk growth is delayed and pollen shed will occur before the silks have emerged resulting in barrenness. The corn plant has the capacity to store considerable reserves in the stem, but the developing ear cannot draw upon these reserves until about three weeks after pollination.

During the first stage of moisture stress, the upper leaves curl or roll towards the midrib during the hottest part of the day. If stress continues, premature leaf death begins at the bottom of the plant and proceeds upward. Leaf death is the first sign of permanent damage to the plant. With severe stress, the upper leaves roll so tightly that they appear like “onion leaves.” With less leaf area capable of photosynthesis, grain filling is slowed even while maturing at an accelerated pace. Carbohydrates that had been stored in the stem earlier in the season are moved to the developing ear.

Not surprisingly, drought stressed crops are more prone to lodging because of poor stalk health. There may be some kernel abortion in the tips of the ears, but for the most part, kernel numbers are not reduced significantly with late season drought. Yield losses will largely be due to reduced kernel size and reduced test weight. The amount of reduction will be related to the amount of stress prior to harvest.

– NDSU

Applying N in the Fall
Fall anhydrous ammonia application should wait until about October 1 and only when soil temperature at 4 inches in depth, taken between 6-8 a.m. is below 50 degrees F. Application of anhydrous before these conditions usually results in conversion of N to nitrate, which leads to leaching losses in late winter, early spring and denitrification in heavy soils. Application even after these conditions is not totally without risk, but the chances of going into freeze-up with mostly ammonium N are greatly increased.

Application of banded urea should be delayed until about one week following conditions favorable for anhydrous application. Incorporated broadcast urea should be delayed two weeks after conditions are favorable for anhydrous application.

– Dave Franzen, NDSU, extension soil specialist

Don’t Short Your ’05 Crop: Soil Sample This Fall
Not knowing how much N is available in the soil for your ’05 crop is like throwing money away, shorting the crop of its yield potential or allowing unused soil N to go to waste.

Following a drought, phosphorus and potassium levels are likely to be similar to what they were the previous year, according to David Franzen, NDSU extension soils specialist.  However, the amount of residual nitrogen would be expected to be quite high. The only way to really know for sure is soil testing in the fall or early spring. 

Soil sampling is also valuable in evaluating other production factors such as soil pH, which can influence the effectiveness of some herbicides, notes George Rehm, University of Minnesota extension soils specialist.

For more information on soil sampling and soil nutrient management, see the University of Minnesota web site, www.extension.umn.edu . Click on the “farm” link, then “soil nutrient management.”  NDSU has soil sampling and fertility information online at www.ext.nodak.edu/extpubs/soilfert.htm .

Critical Growth states for major crops ¹

Crop	Critical period	Symptoms of water stress	Other considerations
Alfalfa	Early spring and immediately after cuttings	Darkening color, then wilting	Adequate water is needed between cuttings
Corn	Tasseling, silk stage until grain is fully formed	Curling of leaves by mid-morning, darkening color	Needs adequate water from germination to dent stage for maximum production
Sorghum	Boot, bloom and dough stages	Curling of leaves by mid-morning, darkening color	Yields are reduced if water is short at bloom during seed development
Sugar beets	Post-thinning	Leaves wilting during heat of the day; abnormal dark green color	Most sensitive to moisture shortages in early growing stages but peak moisture use comes later in the season when they have complete ground cover
Soybeans	Bloom and fruit set	Leaf wilting	Any stress from R4-R6 (late pod development/early seed fill) causes more yield reduction than at any other time
Small grain	Boot and bloom stages	Dull green/bluish color, rolled up leaves; firing of lower leaves	Small grain crop injury from drought stress can appear similar to herbicide injury symptoms
Potatoes	Tuber formation to harvest	Wilting during heat of the day	Water stress during critical period may cause cracking of tubers
Sunflower	Preplant, bud and bloom	Leaf wilting	Most sensitive to moisture stress during flowering; least sensitive during vegetative period (emergence to early bud)
1 NRCS Colorado Irrigation Guide, NDSU, Colorado State University

See the NDSU web site www.ag.ndsu.nodak.edu/drought/drought.htm for more information on coping with drought and dry conditions, covering various crop and livestock issues, with good links to other drought-related web sites as well.