Date of Award:

5-1963

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Agronomy

Committee Chair(s)

R. L. Smith

Committee

R. L. Smith

Committee

R. J. Miller

Committee

B. N. Wadley

Abstract

There are many advantages and some disadvantages associated with the fall application of nitrogen fertilizers. The advantages of applying fertilizer at this time appear very convincing. It is easier to get onto the land in the fall. During the fall, farmers usually have more time to apply fertilizer than they do in the spring. In the fall the fertilizer companies offer better services. This is because the fall application of fertilizer lengthens out their season, thus making it possible for them to handle more fertilizer.

The main disadvantage is the fact that it is possible to lose the fall-applied nitrogen before the plants get a chance to use it in the spring. The winter moisture may leach it from the soil or it may be volatilized and lost into the atmosphere.

The use of the ammoniacal form of nitrogen minimizes this disadvantage. The chemical properties of this form of nitrogen are such that it will remain in the soil longer. As a positive ion it is attracted by the soil colloids with forces strong enough to prevent it from being leached from the soil. This attraction also reduces losses by volatilization. However, the autotrophic bacteria, Nitrosomonas and Nitrobacter, oxidize the ammoniacal nitrogen to obtain energy. This process is called nitrification, and the end product is nitrate nitrogen. Nitrate nitrogen has chemical properties which differ from ammonium nitrogen and which might lead to losses from the soil. Nitrate nitrogen, as an anion, is not attracted to the negative soil colloids. This means that it can easily be leached from the soil by the winter moisture or even lost by denitrification into the atmosphere.

The possibility that nitrification might occur, therefore, is of utmost importance when considering the value of applying ammoniacal nitrogen fertilizers in the fall. Some of the environmental factors which influence nitrification are aeration, moisture, and temperature of the soil.

Oxygen is necessary for the microbial nitrification reaction. The fall application of fertilizer is usually accompanied with either plowing or disking, either of which increases the aeration of the soil. It is, therefore, safe to assume that aeration is not the factor that limits the nitrification of fall-applied ammoniacal fertilizers.

Moisture is another factor which influences nitrification. Justice (1961) and others have shown by experimental data that nitrification proceeds even at low moisture content in the soils, moistures that approach the permanent wilting percentage. In this region the soil moisture during late fall and winter is usually adequate for maximum nitrification. The process of nitrification is usually not limited during the winter because of soil moisture.

Nitrification, being a microbial reaction, is sinsitive to temperature. Many soil scientists have shown by laboratory experiments that nitrification decreases as the temperature decreases and usually stops near the freezing point of the soil. Temperature can be assumed as the major factor influencing the rate of nitrification of the fall-applied ammoniacal fertilizers. Although much information is available concerning the influences of temperature on nitrification, information concerning nitrification as it is influenced by the fluctuating fall and winter temperatures in the field is very limited. In the past it has been difficult to subject samples to these field temperatures and still be able to check the nitrification of individual samples. The suggested use of polyethylene bags (Eno, 1958) to hold individual samples makes it possible to obtain the data from field experiments.

Since use of polyethylene bags as containers for soil samples undergoing nitrification is rather new, it is also necessary to compare the results of nitrification in polyethylene bags with the conventional laboratory method.

The objectives of this study were:

  1. Compare the rates of nitrification proceeding in polyethylene bags with those occurring in conventional containers in the laboratory.
  2. Determine nitrification in several soils in polyethylene in the laboratory under conditions that can be compared to fall and spring field studies.
  3. Determine the nitrification that occurs in several soils put into the field in polyethylene at various times during the fall.
  4. Examine the extent and rate of nitrification of several soils in polyethylene bags in the field during the early spring.

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