Jolene F. Ward, B.S.
Corporate Secretary

A Practical Look At Soil Productivity
By Dr. Ray Ward, Certified Soil Scientist

    Every now and then, the professionals at Ward Laboratories, Inc. in Kearney, Nebraska are asked why two fields in close proximity to one another can produce dramatically different yields with the same type of management practices.
    The coffee shop answer to that question may be bad luck … in reality, the answer may rest with soil productivity. The fact of the matter is, different soil types require different management practices to produce maximum yields.
    I have had the opportunity to witness this process on our family farm in southeast Nebraska over the last 10 years. I have monitored the yields of these two dry land fields with a high producing silt loam soil and a lower producing silt loam with a clay subsoil. Over that decade of observance, soybeans ranged from 30.2 bushels to 49.2 bushels, while corn ranged from 100.1 bushels to 139.6 bushels.
    In many cases the difference is a result of the soil’s ability to absorb water for the plant to use. In the lower yielding clay subsoil, water permeability may be as low as .06”/hour or 0.6” every 10 hours. Conversely, the permeability of the silt loam soil is .6”/hour or 6” over a 10 hour period.
    The higher yielding silt loam field has an available water holding capacity of 2 1/2”/foot where the clay subsoil can hold only 1 3/4”/foot.
    Simply put, more water holding capacity and better permeability translates into more water for the plant to use.
    So, as producers establish “management zones” on their fields, soil types should be a major consideration in the development of plans to address production in those management zones. Different soil types require different management.
    Additional information about soil types in your fields can be found at your local NRCS office through the County Soil Survey Manual.

    While many alfalfa producers view the last cutting of the year as the end of another long growing season and a chance to stock up on winter feed, a longer term view should be considered as well.
    Current research indicates the timing for the last cutting of alfalfa and other forage in the fall could have a dramatic impact on the start your crop gets the following spring according to Kearney, Nebraska soil scientist Dr. Ray Ward.
    Dr. Ward says documented research indicates that alfalfa should enter winter dormancy with high levels of carbohydrates in the root reserves. To accomplish this, the last cutting should be complete four to five weeks before the average date for the first killing frost, defined as two consecutive days of 24 to 26 degree temperature.
    Dr. Ward continued by saying that alfalfa, as a perennial plant, initiates regrowth after each cutting. The level of carbohydrates fluctuates with each cutting and during regrowth. Normally, a plant’s root system is fully “recharged” four to five weeks after harvest, even in the fall. As a consequence, harvesting four to five weeks prior to frost will allow ample time for the plant to grow and recharge in preparation for the winter dormancy.
    During early growth after harvest an alfalfa plant uses up large amounts of carbohydrates from the tap root of the plant. After a plant reaches six to eight inches photosynthesis “kicks in” recharging the plant’s root system.
    Studies indicate that up to 50% of the available carbohydrates are used to support the plant’s survival during the winter months. It is extremely important, Dr. Ward said, to allow enough time for regrowth before the first killing frost to fully recharge the root system with carbohydrates.
    In short, careful timing on the part of a producer can insure good winter survival and rapid spring growth for next year’s alfalfa.

    To say that the distribution of plant nutrients is highest at or near the surface of the soil is generally true. To say that the surface is where the nutrients stay during the growing season is a whole different story.
    As we analyze the table following this article, we clearly see a higher concentration of nutrients at 0-2” depth, then tends lower as deeper samples are analyzed. The table below is a soil analysis for a Hastings silt loam soil on our family farm that was limed two years ago at a rate of 1.6 tons/acre. Additionally all phosphorus and zinc has been broadcast on this field. In reality, producers could apply phosphorus and zinc in band below the surface with very little difference in the soil analysis as well. This field has been no tilled for 16 years.
    The process after application is very simple. Plants take up the nutrients they need to grow from any sources available. In the fall, we usually harvest just the grain allowing the nutrient filled residue such as stalks, plant leaves and roots to fall to the ground. As the plant residue decomposes, nutrients in the residue return to the soil, normally at or just below the soil surface.
    This natural process happens every growing season. It clearly explains why the nutrient values are highest near the soil surface.