01.09.2012

Mulch for soil protection

Agricultural producers are constantly seeking ways for reduction the rate of fertilizers, crop protection chemicals and fuel consumption, especially in a situation when the prices for agricultural inputs are climbing up. The price for these inputs is constantly growing and the fertility of the soil continues to deteriorate. Thus, the cost-price of yield is also getting higher. How can we restore humus content in the fertile layer of the soil without additional financial inputs? The farming practice showed that the only wise decision for both soil and farmer is conservation agriculture.

Mulch... Its importance for restoration of the fertile layer of the soil is hard to overestimate, though the necessity of the mulch layer is always questioned.
The specialists of Agro-Soyuz know the importance of a mulch layer to increase the yield based on their own experience.

The mulch is the foundation of conservation agriculture

One of the primary objectives of an agronomist is to protect the soil and minimize environmental risks during crop production.
It is widely accepted that the bare soil is gradually losing its fertility under the influence of wind, rain and sun. Moreover, its structure is ruined and it becomes prone to sealing. Crop residues spread across the field will protect the soil from overheating and excessive drying during hot summer, while in winter they protect winter crops’ roots from freezing.

Rain drops are also harmful for the bare soil. On the one hand they compact it influencing water infiltration and on the other hand, the rain drop striking the soil destroys it and leads to soil erosion. Sometimes we can see the effect of «rice» fields, when the soil is flooded and water doesn’t infiltrate. After drying destroyed soil particles (in other words — dust) are blown away with the wind, which sometimes moves them over very long distances. Sometimes due to a destroyed soil structure water cannot infiltrate deeper than 5-7 meters. Crop residues covering the soil can mitigate the effect of rain drop forces and protect the soil from water erosion.

Mulch on the soil surface acts like animal’s fur — holds immobile air and limits vapor exchange between the soil and atmosphere. Air humidity under the mulch layer is much higher than that above it (obviously, excluding rain or increased humidity situations).

Water accumulation and storage are very important for yield establishment. Water will quickly evaporate from the bare soil, so it is almost impossible to manage soil moisture under conventional tillage, whereas, under conservation agriculture it is possible to reduce moisture evaporation from the soil and «take» it through the leaf surface. This is exactly how the process of establishment of future yield is running. Each crop uses a specific amount of moisture in order to produce a unit of product. The more water it used, the higher is the yield. That’s why our objective is to run as much water through a crop as possible and prevent its evaporation from the soil. The mulch is a good help in this process. Actually, availability of water is critical for crops produced in arid areas. If you leave crop residues and mulch on your fields in fall, it will retain snow in winter, reduce evaporation of moisture in spring and protect the soil from overheating in summer.

You may say that water accumulation during hot and dry summer is good. But what would you do, when it is time for seeding, but the soil covered with mulch is still wet? Our experience of work under different climatic conditions shows that in areas with extra moisture there is no need to wait till the soil gets a little drier if it is covered with mulch. An example from Novosibirsk region where they have cool and wet spring and short and hot summer: in spring of 2010 the only farm that seeded 100% of its fields had a mulch layer on the soil surface. The machines could drive on the mulch, while the neighbors were waiting till the soil gets drier. The mulch also prevented the soil from sticking to the wheels.

Another challenge facing farmers that implement conservation agriculture is weeds. Mulch helps to control weeds. First of all, when weeds drop their seeds, they do not fall onto soil, but fall into the mulch layer. In other words, a seed is «hanging», it has no contact with the soil and it will have hard time emerging, since it will need to grow through a thick mulch layer. Moreover, «fresh» weeds seeds are in deep dormancy and only those that are resting in the soil at 5-10 cm depth are ready to germinate.

If you don’t «take» them out of there, some of them will not have enough energy to emerge through the soil and the mulch layer covering it. The seed bank will gradually shrink, since we create more difficult conditions for their emergence. In the long run this results in significant reduction of frequency of application and the amount of crop protection chemicals.

Proper nutrition and availability of water makes crops healthy and this means that they can compete with weeds themselves. In other words any contribution to crop’s health is a contribution to weed control, since the biggest enemy of a weed is a crop itself due to its ability to perform biological weeds control.

Where the mulch starts

Mulch represents the residues of commercial and cover crops, which create a protective layer on the soil surface. A crop rotation is a good help in pests, diseases and weeds control. The crop rotation is selected keeping a lot of different nuances in mind, such as moisture level, weed infestation, a desired amount of crop residues and the situation in the market. At the same time crop sequence means a sequence of crop residues. In order to obtain different crop residues it is necessary to diversify the crop rotation. For example, if your crop rotation consists of only corn, you will accumulate a huge and a very thick layer on the soil, which is incorrect. If your crop rotation consists of only soybeans, your field will be bare.

It is known that residues of different crops are decomposing differently and require different amount of time for decomposition. For example, corn residues require about 3 years for decomposition, grain crops — 1.5-2 years, sunflower will decompose during a year, whereas canola and soybeans are quickly decomposed — you’ll see almost no residues by spring. We should balance and control accumulation of mulch to obtain a cover, which is easily managed.

Of course, mulch does not exclude using of fertilizers, but the rate of fertilizers can be reduced with time reducing production costs and improving grain quality, as we apply organics instead of mineral artificially created fertilizers.

The root system of brassica crops, such as canola and mustard can convert unavailable phosphorus and potassium compounds into easily available forms for next crops. After canola and mustard harvest the residues of these crops leave these nutrients in the soil, but in available for and at achievable depth.

Moreover, bare soil stimulates quick oxidation of organic matter, i.e. its mineralization. Plant feeders also do not live on the bare soil, they hide from the drying sun at field edges and shelterbelts, where they can hunt. The mulch layer creates favorable conditions for life and proliferation of hunting insects.

Annual sequence of grain and broadleaf crops breaks the life cycle of harmful insects and diseases, which attack crops that continuously grow on the same field. Planning a crop rotation, pay attention to the interaction of crops, e.g. corn stalks have an allelopathic effect on barley stand.

Each time, when we «move» crops from one field to the other, we change the environment of pests, diseases and weeds. It is important that the crop rotation consists of both commercial crops and those that improve soil fertility and structure without tillage.

Managing crop residues

Start managing crop residues — the foundation of zero-tillage — during harvest. There are 3 criteria to control harvest quality under conservation agriculture: cutting height (not less than 10-20 cm), keeping the type of the harvested crop and the seeding dates of the next crop in mind, optimum chopping of a non-commercial part of harvest (less than 5 cm) and even distribution of straw over the field. It is very important that the soil cover is even, otherwise windrows and heaps will interfere with the following seeding operation. If an opener cannot cut through a thick layer of residues, the seeds will be «hanging» inside the mulch layer, leading to empty spots in the field. Where the mulch layer is thin, weeds will take the opportunity for intensive growth. After harvest there should be an even and thick cover of crop residues. To achieve this, grain harvesters are equipped with straw choppers, and the width of spreading should be the same as the width of the combine header. It is preferable to use a stripper header.

This header strips the standing heads of grain crops with «combs» located in the stripper drum of the header. Thus, only grain with a small admixture of straw and small stems flows through the combine, increasing its ability to separate grain compared with harvest with a traditional header. This means that the combine’s capacity will increase 25-50%. Furthermore, a combine with a stripper header can work early in the morning and late at night as wet and stiff straw is left in the field and doesn’t get into the combine’s separator.

A stripper header can solve several problems of harvest simultaneously. It leaves standing stubble, solving the problem of even distribution of crop residues. This is an ideal environment for direct seeding machines. The evenness of distribution and even the color of residues influence the speed of soil warming in spring and cooling in autumn.

Standing stubble protects the crop stand from wind and temperature fluctuations. At the same time, high stubble is sometimes a concern for farmers, who use a sweep opener for seeding as it may block. If a farmer has a disc drill, (s)he will have no problems with this situation; but not all the farmers have this type of machine. As a rule, these are the farms that convert to conservation technologies and disc their soils after harvest. Obviously, this is far away from the «true» direct seeding into an undisturbed soil (the main principle of conservation agriculture), but this is a temporary measure until the farmer buys a disc drill, which will do this job.

This article tells you about one the most important elements of zero-tillage, i.e. the mulch. We hope that this information will help you to make a correct choice in favor of conservation agriculture. The experience of last decades shows that in order to be successful (not just chasing a quick profit) in agriculture and improve soil fertility in the long run, we should cooperate with the nature and not fight with it.