How to improve soil fertility?

The content of organic matter is one of the most important soil fertility indices. Its role in the formation of environmentally sustainable agro-landscapes has long been known, but in pursuit of high yields and economic “profits” the role of mineral fertilizers is increasing, and the balance of organic matter confidently rolling into “bottomless money pit“.

Of course, this does not mean that you need to go straight to the biological or organic farming. The main task is to understand the reasons for the permanent decrease in the content of organic matter in the soil and find ways to solve the problem in order to prevent the decline of natural fertility and, consequently, the potential yield of cultivated crops.

Most people working in the agrarian sector understand the importance of organic matter for the soil. They write about it in various publications, talk at seminars and conferences, and scientific institutions (and not only Ukrainian ones) pay attention to this. What is the reason for the gradual degradation of soils?

The first reason: “Ukrainian soils are the most fertile.” This historical dogma has made up us the hostage of the natural fertility of the soil. Confidence in unlimited properties of soils reduces the need to maintain a decent balance of nutrients and humus to the phrase: ” After us the deluge!” However, long-term intensive soil use leads to a decrease of organic content matter and changes the ratio between its components. In particular, the content of the active fraction from 33-50 to 15-25% decreases (Fig. 1).

Рис. 1. Основні складники органічної речовини ґрунту до використання у сільському господарстві та після довготривалого використання.
Fig. 1 The main components of organic matter before use and after long-term use.
The second reason: the decline of the livestock sector. A few decades ago, livestock farms functioned in the vast majority of villages, and therefore organic fertilizers were introduced in sufficient quantities. For the period of 1990-2017, the cattle population decreased by 85%. As a result, in 2017, about 220 kg of organic matter was introduced per 1 hectare of arable land. It is known that for deficit-free humus balance it is expedient to apply 8-16 t / ha of organic fertilizers depending on the soil-climatic conditions. In addition to carbon, such fertilizers contain the entire spectrum of macro- and micronutrients in a wide range of values.The tendency of development of poultry industry and pig breeding shows the possibility of increasing the amount of organic fertilizers, but they can’t provide the needs of all fields. An alternative can be the cultivation of siderates – crops that can quickly grow vegetative mass. Sederal mass is equivalent to 20-40 t / ha manure. Another plus – the preservation of moisture and nutrients.
The third reason: “crop rotation” remains in theory. The crop rotation has always been on the guard of fertility. Saturation of crop rotation with leguminous crops, the inadmissibility of too large areas under cultivation, the return of crop to one and the same field only after a certain period of time – these and other conditions were created to breach them now. High margin cultures are priority. This, of course, affects the phytosanitary state of crops and soil fertility.
The fourth reason: improper management of process residues. In general, the amount of process residues that remains on the field are not enough for a no-deficit humus balance. But process residue may not stay on the fields. One of the main reasons is the alienation of an unproductive part of the harvest from the field. At best, these process residues will return to the fields in the form of organic fertilizers. In fact, the use of straw for more economically attractive purposes is possible subject to the compensation of alienated “organic”.

Відбілювання ґрунту по–українськи_Суцчасні Агроносми.jpg

The worst case management option is burning of process residues. Of course, there are some advantages in this approach, but there is no case where they won’t outweigh the huge disadvantages. Especially those relating to the destruction of organic matter of the soil. According to the research results of the Agrochemistry department at NUBN, the burning of straw on one of the sites resulted in a decrease of humus content by 0.3%, alkali hydrolyzed nitrogen compounds – by 25 mg / kg compared to the other part of the field. How do you like them apples?

The effect of cultivation on crop residues can be obtained by adjusting the ratio C: N. So, for maize C: N varies in the range from 40 to 70: 1, for cereals – from 60 to 80: 1, and for legumes – from 20 to 40: 1. Crop residues of legumes contribute to faster accumulation of organic matter. For other crops, additional nitrogen fertilization is required to shift the C: N to more optimal performance. If you don’t do this, the microbiota for mineralization processes will use available forms of nitrogen, which will negatively affect the conditions of growth and development of culture.

The fifth reason: plowing is associated with high yields. Any cultivation activates the decomposition of organic matter. Each time the soil is processed, it is in contact with air. Oxygen stimulates or accelerates the action of microbes in the soil, which feed with organic matter. The greatest losses of organic matter are observed precisely when plowing. Due to this method of production, less stable humus is formed and more CO2 emissions are released to the atmosphere.

Вплив обробітку на втрату органічної речовини

Minimization of cultivation is actively promoted in Ukraine. But the primary reason for partial or complete abandonment of plowing is not the loss of organic matter. First, farmers realized the negative impact of plow soles on the growth and development of crops. Secondly, they payed attention to the high costs of fuel and lubricants. Thirdly, there was a need for economical use of moisture. Soil protection cultivation positively effects on the water regime of the soil, including the positive effect of organic matter balance. As you know, organic has sponge properties: it can hold up to 90% moisture from the total mass.

The sixth reason: is the high rates of mineral fertilizers. Cations and anions that are part of their composition have different effect on organic matter. Scientists have found that single charged cations (NH4 +, Na +, K +) have a peptizing effect on organic matter. In other words, the destruction of the valuable structure and the deterioration of the properties of the soil occurs. To understand the consequences of negative effects, it is sufficient to mention the saturation of soil with sodium ions during the process of solubilization.

Organic matter is the most negatively affected by alkali and hydrolytically alkaline fertilizers. In fig. Figure 2 shows the result of the treatment of soils with mineral fertilizer solutions. The darker color of the filtrate indicates the removal of organic colloids. As expected, most fertilizers containing ammonium contributed to darkening of the filtrate. The solution of potassium chloride didn’t have peptic activity. According to research by scientists, other compounds of potassium, in particular, sulfate and carbonate, remove organic colloids (V.I. Filon, 2009).

Рис. 2. Фільтрат після взаємодії наважки чорнозему типового із розчинами добрив: 1 – аміачна селітра, 2 – КАС, 3 – карбамід, 4 – амофос, 5 – калій хлористий, 6 – гранульоване вапно, 7 – сульфат магнію
Fig. 2. Filtrate after interaction with the sample of typical black soil with  fertilizer solutions: 1 – ammonium nitrate, 2 – CAS, 3 – urea, 4 – ammophos, 5 – potassium chloride, 6 – granulated lime, 7 – magnesium sulfate.
The seventh reason: is degradation processes. Reducing the amount of organic matter in the soil provokes the increase of soil degradation, which enhances the mineralization of organic matter. A closed circle is formed. This means that the more degraded the ground – the greater the loss of organic matter occurs. Considerable damage is caused by wind or water erosion. To weaken the influence of the wind erosion managed at the expense of forest protection bands, however, they are in the overwhelming majority in poor condition. Water erosion causes irreparable damage to sloping lands, especially in irrigated conditions.And this is far from a complete list of reasons … The result of each of these factors is a decline in the content of organic matter and humus. If there are several factors, then soil fertility indicators will decrease in geometric progression. For example, the situation is on one of the fields (Fig. 3).
The content of organic matter for the period 2016-2017 decreased by 0.2-0.7% (except for one selection point). The main factors of the possible decrease in the content of organic matter: the alienation of crop residues of winter wheat, the introduction of high standards of mineral fertilizers, the application of plowing. In addition, it is necessary to take into account also the seasonal dynamics of changes in this indicator (first sampling – spring, second sampling – fall).
Рис. 3. Картограма вмісту органічної речовини у ґрунті
Fig. 3. Cartogram of the organic matter content in the soil

During a relatively short period of time with cartograms, 19% of the area with a very high content of organic matter disappeared. There was a redistribution in other areas of provision. The analysis of crop development over the last 4 years (Figure 4) showed that in the zone with an average content of organic matter (2.5% in 2016 and 2.1% in 2017), the NDVI indices were the lowest regardless of crop. Of course, the problems in this zone is not only with the content of organic matter, but it could cause adverse conditions for the growth and development of plants, affecting the physical, chemical, agrochemical and other indicators. Accordingly, the approaches to the fertilizer system in the different productivity zones should be different.

Рис. 4. Показники NDVI на одному і тому ж полі за останніх чотири роки
Fig. 4. NDVI indices in the same field over the past four years.
How to determine if there is a problem with the loss of soil fertility? First, if the factors listed in this material are observed in your field, it already indicates the presence of a risk zone. Secondly, you can roughly calculate the balance of organic matter or humus. But the calculation method includes various coefficients that are averaged. And the accuracy of the calculation is conditional, but it allows you to orientate towards the change in the content of organic matter.The most objective assessment of organic matter balance of the soil can only be given by periodically monitoring its content in each field of the farm. Every 3-5 years, agrochemical diagnostics should be conducted, which will provide a complete answer to the question: what is the vector of fertility? If during this period the content of organic matter has decreased, this indicates the need for complex changes in the approaches to building a fertilizer system.
When carrying out periodic agrochemical analysis it is necessary to observe three key rules:

  1. It’s expedient to do the soil sampling in the same period of the year as the previous one. Indicator of the content of organic matter (as well as for most agrochemical indicators), is cyclist.
  2. Soil sampling should be carried out using as closely as possible method and grid. If the basic sampling was at a depth of 30 sm, then the next samples should be sampled in the same way. Elementary sites into which the field is divided must also coincide;
  3. The laboratory analysis method of soils should be identical. And here it is necessary immediately to focus on the difference in the concepts of “humus”, “organic matter” and “organic carbon”. These are different indicators.

Only 100% compliance with the above points will allow you to compare confidently the data of the two examinations. Even if they were conducted by two different laboratories, institutions or companies. Otherwise, comparison of indicators will be inappropriate.

How to “shift” the balance of organic matter to the positive side? The answer is obvious: to ensure the flow of organic matter in one form or another. And small quantities here can’t help: 2-4 l / ha of humates do not contribute to the rapid restoration of fertility. Biodestructors should be used in the presence of a large mass of process residues. If there is no “food” for microorganisms, they will begin to “eat” organic matter of the soil.

Preservation and reproduction of organic matter is a serious agro-chemical, ecological and social problem. What will our descendants get: fertile black soil or substrate? We give the answer, moreover, today!

Oleksiy Tarasenko, agrochemist at LLC AgriLab

Ihor Bordiuzha, Head of the laboratory of the department of agrochemistry and quality of plant products  at NUBN of Ukraine

Magazine “Агроном”, 2018


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