Manure has a wide range of environmental and nutrient based benefits. When properly applied to soil it has the potential to make crops grow and thrive. In order for proper application to take place it is first necessary to understand something about the structural makeup and nutrient composition of manure. Manure begins as organic material that was once alive such as plant or animal tissue. Organic material remains classified as such until it is introduced to the soil where it undergoes decomposition. During decomposition organic material is converted by microorganisms into the next usable phase known as organic matter.
One person who is quite knowledgeable on the topic of organic matter is a vegetable and berry specialist at the University of Vermont Extension, Vern Grubinger. He says there are three forms of organic matter that can be found in the soil and each one is determined by the time it takes for it to completely decompose.
The first form is known as humus or passive organic matter. Humus is the final product of decomposition and may take hundreds or even thousands of years to develop. It is made up of dark, organic material that forms in soil when plant and animal matter decays. Grubinger notes humus is further enriched by worm castings and excrement left behind by burrowing animals such as moles.
Humus usually represents the majority of total soil organic matter but, because it is not biologically active, it provides very little food for soil organisms and therefore has little influence on soil fertility. Despite this limiting characteristic, humus contributes numerous physical benefits to the soil.
According to Grubinger a second form of organic material found in soil is active organic matter. Active organic matter differs from passive organic matter because it is associated with a lot of biological activity. The reason for this is because it is primarily made up of fresh plant and animal residues that have been broken down within a short period of time. It can take as little as a few weeks to as much as several years for active organic matter to form.
Slow organic matter is the third form and it is somewhere in between active and passive organic matter. It consists primarily of detritus, which is a mixture of non-living particulate organic material and attached microorganisms which act as decomposers. Slow soil organic matter is somewhat resistant to decay and may take several years to a few decades to completely break down.
Both active and slow organic matter contribute greatly to soil fertility because their breakdown results in the release of plant nutrients.
According to Eddie Funderburg, a soil and crop consultant with Noble Research Institute in Ardmore, OK, three important physical benefits from organic matter are water-holding capacity, soil structure aggregation and erosion prevention.
Organic matter has excellent water-holding capacity, says Funderburg. As a matter of fact, it has the ability to absorb and hold up to 90 percent of its weight in water, which it subsequently releases back into the surrounding plant roots.
Funderburg goes on to say organic matter causes soil to clump and form soil aggregates which further help to improve soil structure. With better soil structure, the infiltration of water through the soil improves significantly, which in turn improves the soil’s ability to take up and hold water.
Erosion prevention is a property of organic matter that is not widely known about, says Funderburg. He points to data used in the universal soil loss equation, which indicates that increasing soil organic matter even as little as one to three percent can reduce erosion 20 to 33 percent because of increased water infiltration and stable soil aggregate formation caused by organic matter.
Physical benefits are not the only reason to utilize organic material. Recent agronomy information put forth by the Cornell University Cooperative Extension points out that there are chemical and biological benefits as well.
One important chemical benefit of organic matter is that it accelerates decomposition of soil minerals over time, making the nutrients in the minerals available for plant uptake.
In order for plants to thrive they rely on soil to provide an optimal pH range between 5.5 and 7.0. This can be hard to maintain but a second benefit of organic matter is that it plays a key role in improving the soil’s ability to resist pH change.
A third chemical benefit provided by organic matter is its ability to hold onto and supply over time essential positively charged nutrients such as magnesium. This concept is also known as the cation exchange capacity.
When it comes to biological benefits organic matter provides food for the living organisms in the soil. It also enhances soil microbial biodiversity and activity, which can help in the suppression of diseases and pests. Finally, organic matter enhances pore space through the actions of soil microorganisms. This helps to increase infiltration and reduce runoff.
Among the many nutrients found in manure none are more crucial to plants than nitrogen, phosphorus and potassium.
Nitrogen is an essential nutrient for plant growth, development and reproduction. It is a major component of chlorophyll and an important element of amino acids. Without proteins, plants wither and die. Furthermore, nitrogen acts as a catalyst for other needed minerals.
Phosphorus is important because it helps a plant convert other nutrients into usable building blocks with which to grow. Whenever the supply of phosphorus is lacking, plants are unable to complete their production cycle as expected.
Potassium is associated with movement of water, nutrients, and carbohydrates in plant tissue. Potassium is also involved with enzyme activation within the plant that affects protein, starch and adenosine triphosphate production or ATP. A deficiency of potassium ions can impair a plant’s ability to maintain these crucial processes.
Grubinger says that without good soil management practices active organic matter in the soil can diminish as soon as a year or two. In order to effectively maintain the same level of active organic matter a constant supply of fresh organic materials is required.
Grubinger recommends the use of crop roots, crop residues and cover crops. These three types of crops tend to enhance organic matter accumulation by providing the nitrogen needed for decomposition of freshly added organic materials. Legume cover crops especially benefit organic materials such as corn stover, cereal straw and heavily bedded manure, which are all know to be high in carbon and nitrogen.
Going along with Grubinger, Cornell University Cooperative Extension offers some additional useful soil management practices that help to maintain or increase soil organic matter levels.
First, the Extension points out how standard intensive tillage practices turn the soil over and expose organic matter to the air where it undergoes increased mineralization rates and erosion losses. To avoid this, the Extension advocates the use of conservation tillage practices such as zone tillage or no-till.
A second soil management practice that the Extension supports is the rotation of annual row crops with perennial grass or legume sods. This practice reduces erosion and helps build up organic matter as a result of the decomposition of the root mass.
Finally, the Extension advises against soil compaction because it increases waterlogging and suggests a soil management plan that helps maintain proper pH to enhance microbial activity and decomposition of freshly added materials.