ISSUE 12 July 23, 1998
LODGED GRAIN AND EXCESS N
Because of the storms across the state during the last few weeks, there is lodged grain in many fields. In areas subject to intense storms, lodging may consume a great portion of the field, but in most situations, the lodging is confined to low areas in the fields, such as waterways or depressions, or to old building/feed lots. Excessive soil N levels can cause weaker plant stems as growth is lush, but at the expense of strong cell wall structure. Higher organic matter soils have greater rates of N mineralization compared to lower organic soils, and soil N may tend to be higher in these areas because of leaching from higher landscape positions into low positions.
The lodging in many fields is an indicator of the variable nature of soil N. Taking note of the areas in which grain is down now will help samplers avoid these high N areas if taking a composite sample, or can help to guide the sampler toward zones of higher N for a variable rate application now or in the future.
High pH development over the last 10 years?
Some producers have noted higher pH levels now than in tests from about 10 years ago. There is a feeling that soil pH can be changed drastically by soil moisture differences in a decade due to human activity or climate. Real soil pH levels between pH 6.9 and 4.8 can change relatively rapidly during a 10 year span if high rates of N or manure are applied which lead to acidification. It is not uncommon to lower pH levels about 0.1 pH unit per year where 200 lb/acre of N as an ammonium source are applied annually. However, once the soil pH reaches about 7, soil carbonate levels help the soil resists changes downward or upward in pH. Some producers have noted pH levels in the low 7's about 10 years ago, and now see levels close to or over pH 8. So how is this possible?
In these situations, real pH change is unlikely. Ten years ago, the region was suffering one if its worst droughts in memory. In dry soils, taking a 0-6 inch soil sample is very difficult. It is likely that the soil sample was on the light side of a truly 6-inch deep soil sample. This is important, because many of our regional soils have subsoils close to the surface (within 8-12 inches) where there are very high levels of carbonates with a pH of 8 to 8.4. Now, these soils are being resampled coming out of CRP in a moist to wet environment and it is easy for the soil probe to take soil from 6 inches+. Only a few soil cores with some soil containing high levels of free carbonates will produce a very high soil pH.
Movement of carbonates upward significantly in the soil naturally can take hundreds of years. The soil carbonate development that produced the carbonate levels in our soils and subsoil layers took an estimated 5-8 thousand years. However, erosion of low pH topsoil and inconsistencies of soil core depth are usually the culprits in wide soil pH differences between years.
Dr. Dave Franzen
NDSU Extension Soil Specialist