ISSUE 13   August 13, 2009

SPRING STRIP-TILL IN HEAVY SOIL?

Last summer (2008), fall strip-till in heavy soils in the Valley looked wonderful. In my plots on a Fargo soil, the strip-till corn and sugarbeets were taller, healthier and ultimately yielded much more than conventionally tilled treatments. Last fall the soil was too wet for fall strip-till preparation. The strip-till unit was used only the day before seeding and even though the unit was set for 3-4 inches deep, it still brought up muddy, cloddy soil and produced an inadequate seedbed. The results for corn and sugarbeet this year have been less than desirable. Stand count in sugar beet has been 25% lower in strip-till than conventional till; stand count in corn was 2% lower and a full leaf stage behind all season; tassel emergence on August 3 was 40% for conventional till and only 7% for strip-tillage. These disappointing statistics do not mean that strip-till in general is a poor practice, but it does mean that spring strip-till in heavy clay soils in wet springs certainly is a poor practice. The conventionally tilled plots in standing stalks consisted of two passes with a disc set 4 inches deep three days before seeding, and one pass with a field cultivator set about 2 inches deep the day before seeding. Sugarbeet stand after these operations was very good. In soybean stubble, one pass with the disc set 4 inches deep three days before seeding, and one pass with a field cultivator set about 2 inches deep the day before seeding also made a good seedbed for corn. Hopefully, we will have a dry September/October for harvest and strip-till preparation; but if we do not, prepare a plan B and let the strip-till unit sit next spring.

 

POTASSIUM PROBLEMS INCREASE

The number of crop potassium (K) deficiency symptom problems has increased lately. This region has a history of good soil K levels; however, intensive soybean cultivation has decreased soil levels over recent years. Potassium deficiency symptoms are almost always seen in lower leaves, with leaf margins yellowing, and as the deficiency progresses, the yellowing moves towards the middle of the leaf. Recall that N deficiency is seen in lower leaves also, but the yellowing starts at the veins and leaf tips and then progresses along the veins and out to the leaf edges. Although soil test K levels are a good general predictor of possible K needs, the soil test K values can vary due to soil moisture during the growing season and at the time of sampling. Research is being conducted in several states to determine whether soil drying at the laboratory makes the test results more or less variable over time for a specific soil. In the meantime, growers should periodically test their for K, especially if they grow crops other than small grains. Corn is especially sensitive to low K levels particularly in no-till and ridge-till systems. A recent Plant Diagnostic Lab canola sample was K deficient. Soybeans are not as sensitive to K as corn, but growing soybean certainly hastens a soils K level decline. The good news is that recently potash prices have dramatically declined recently, and although they are higher than they were several years ago, they are in the realm of affordibility for most crop prices if required.

 

MID-LATE SEASON NUTRIENT ISSUES

In wetter, cooler years, it is not unusual that some soybeans in highly calcareous, and especially saltier soils do not green-up from iron deficiency chlorosis (IDC). This is a year when areas of certain fields will not green-up at all. These areas will struggle to make 10 bu/acre. In some areas of the state, small areas of IDC have also appeared in dry bean (see figure). The symptoms in dry bean are similar to soybean, but usually much less severe. A plant analysis of the leaves provide a good diagnosis of the problem. The Fe level in these plants was 0.15 ppm, which is below the 0.2 ppm threshold. To obtain a proper plant sample for Fe, take the leaves, and while fresh, wash with distilled water (never tap water) and then dry. Any soil on the leaves will contaminate the sample and render the leaf analysis useless for Fe diagnosis.


Iron deficiency chlorosis symptoms on
dry beans. Upper leaves are most affected
with interveinal yellowing.
Photo from
Wells county courtesy of Greg Endres,
Carrington R & E Center.

Potassium problems in crops, especially soybean continue to be diagnosed. The deficiency symptoms on soybean are yellowing of older leaves, starting at the leaf margins and moving towards the center of the leaf. These symptoms might be mis-diagnosed as drought symptoms. Plant tissue analysis will help confirm the deficiency symptoms. Plant washing is not needed for K analysis, and may actually leach K from plant tissue. Growers of soybean and other non-small grain crops on loam and coarser textured soils need to become more aware of their soil K values now and in the future. Years of soybean, corn and non-small grain production has seriously reduced many soil K levels in the state and K fertilizer may need to increase as the growers plan future crops.

Sulfur deficiency is being noted in soybean across the state. I observed a soybean field near Rugby on August 7 that has been a pale yellow color for at least a month, according to the grower. Nodule formation was normal. The soil was a coarse loam to sandy loam in texture. With the rainfall of last fall, higher than normal snowfall and snow-melt this spring, sulfur deficiency in all crops was likely in most areas of the state. Unfortunately, soybean is one of those crops that tends to not be fertilized. This practice may be one reason for several consultants and extension staff to note this general yellowing of soybean - not related to lack of nodulation and IDC seen across the state this summer. There is no research that I can find that suggests in-season remedies for S deficiency in soybean. Obvious solutions such as foliar ammonium sulfate or ammonium thiosulfate applications will cause severe leaf burning and are most definitely NOT RECOMMENDED. A research study is being implemented out of Carrington that might help our understanding of foliar or post-emergence options in this crop.

 

SOIL SAMPLING AFTER HARVEST

With winter wheat harvest under way and spring grain harvest around the corner, soil sampling season cannot be far behind. Sampling behind the combine for small grains is a good way to obtain a better surface soil sample for P, K, soil pH and zinc. It is also a good way to make certain that soil sampling is conducted should the later fall become wet as in 2008. Some are hesitant to sample too early (before October) because the values might change. In the one definitive research effort in North Dakota that considered this issue, the researchers found that in after August sampling, sometimes the values increased later, some decreased later, and some stayed the same. After October sampling, sometimes values increased, some decreased and some stayed the same. Their experiences lead me to recommend that the activity of sampling is important and that earlier is not better or worse than sampling later. The only difference is that when sampling earlier after small grains/canola, a better surface sample is taken and the sampling actually will get done more regularly than waiting, and waiting and waiting.

After field peas/lentils, waiting until mid-September may have an advantage due to increased soil mineralization following these crops. The mineralization will slow once soils cool.

Consider zone sampling this year to better evaluate field nutrient levels. It is a proven method of improving fertilizer application efficiency in this region. Fertilizer is less expensive this year than last, but most nutrient prices are still higher than in most earlier years.

Dave Franzen
NDSU Extension Soil Specialist
david.franzen@ndsu.edu


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