Sergey Ariskin, Chief Process Engineer, Agrotrade Company LLC
The high content of soil clods when harvesting potatoes has become a serious problem for farmers in the 2020 season. In some farms, up to half of the crop transported from the field was clods of soil. This significantly reduced the productivity of receiving complexes during storage. Basically, the clods had to be picked manually on conveyors. Even so, part of the land was put into storage. According to our observations, in some farms its content in the crop loaded into storage reaches 20 ... 25%.
What is the key reason for the appearance of a significant amount of lumps during cleaning? Of course, this is the compaction of the soil during pre-planting and planting. We will not consider the topic of soil degradation as a result of the impact of the travel systems of agricultural machines. In potato production, the use of wide low-pressure tires and caterpillar drives is not yet possible. It is also impossible to refuse from tillage implements with active working bodies. These two factors lead to the destruction of the soil structure (soil aggregates). Unstructured soils are susceptible to caking and, as a consequence, the formation of lumps.
Agronomists know that moisture is the main culprit for significant soil compaction during spring field work. Moisture-saturated soil compresses easily. The relaxation period of soil after compaction, as a rule, lasts much longer than the growing season of potatoes. If we put compacted soil into the ridge, we are very likely to get lumps during harvesting.
There is such a concept as the LOWEST SOIL MOISTURE CAPACITY (HB) - the maximum amount of moisture that the soil in its natural bedding can hold in a suspended state after the free outflow of gravitational water stops. Expressed in% of the weight or volume of the soil. It is determined by the granulometric, mineralogical and chemical composition of the soil, its structure, density, porosity - factors that we, again, cannot promptly influence. Figuratively speaking, this is no longer dirt, but when the soil is squeezed in this state, the lump does not collapse when it falls to the ground.
The optimal timing of soil cultivation is the period when the soil is in a state of so-called physical ripeness. For heavy loamy soils it is 40 ... 70% HB, for light - 40 ... 60%. If you translate this into the percentage of moisture in the soil, you get 12 ... 24%, depending on the type of soil.
Table 1. Intervals of soil moisture for high-quality processing
Humidity limit | ||||
Lower, tillage is difficult, it is impossible to destroy lumps, dust | Top, sticky soil, formation of compacted clods | Agrotechnically acceptable for tillage | For high quality finish and lowest resistance | |
Sod-podzolic | 11 | 22 | 12 ... 21 | 15 ... 18 |
Forest gray | 14 | 24 | 15 ... 23 | 17 ... 18 |
Chernozems | 13 | 25 | 15 ... 24 | 15 ... 18 |
Chestnut | 12 | 24 | 13 ... 23 | 14 ... 16 |
Chestnut solonetzic | 12 | 21 | 13 ... 20 | 16 ... 17 |
Gray-brown and brown | 13 | 21 | 14 ... 20 | 15 ... 17 |
Sierozem | 14 | 21 | 12 ... 24 | - |
As can be seen from Table 1, the admissible period for soil preparation and planting is the time when soil moisture is within an average of 15 ... 20%. This is about 7-10 days.
Spring 2020 was rainy and long in many regions. Planting potatoes in some farms was delayed almost at the end of June. Often, potatoes were planted in waterlogged soil. This led to the formation of lumps.
What can be done?
In our opinion, first of all, get rid of the plow sole. Plow to varying depths annually. The most effective is deep loosening with chisel plows. Alternatively, the installation of soil-dredging shares behind the plow body. Almost all plow manufacturers offer this equipment in their product lines. But, unfortunately, few people know about this. In practice, we have not seen plows with such equipment. The destruction of the soil base significantly improves the water balance in the soil - moisture is better retained in the lower layers, there is no soaking in the lowlands. The soil becomes physically ripe faster.
Preplant tillage
It is hardly worth doing cover harrowing at a time when the soil is waterlogged. The tractor running system will certainly compact the soil, and it is unlikely that this compaction will be removed in the future. The same applies to cultivation with tine cultivators. Wet overcompacted lumps turned out to the surface after drying cannot be destroyed even by milling machines.
Experienced agronomists know that the gap between tillage with milling machines (vertically milling or horizontally milling) and planting should be minimal. In dry windy weather, with a large gap, moisture is lost. In a rainy spring, a cultivated, but not planted area can stand for several days. The soil is self-compacting, planting is often started at high humidity. This will definitely lead to lump formation.
Planting potatoes
Planters' coulters and disc harrowers work intensively on the soil. In wet planting conditions, when the soil is heavier than at physical ripeness, compacted lumps are formed, the seedbed is compacted. The most unpleasant thing is that these lumps are next to and above the seed tuber. It is not possible to destroy them during combing with a milling machine. The ridge former loosens the soil ONLY IN THE INTER-ROWS, in the row the lumps remain in their original form.
From all of the above, we can conclude that it is impossible to avoid lump formation by any technical and agrotechnical methods in conditions of a waterlogged spring. Only adherence to optimal agro-terms will help minimize this problem.
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