Part 2
Continuation. Beginning in the magazine "Potato System" No. 1, 2021
As mentioned in the first part of this article, the use of sprinklers does not lead to the formation of runoff and soil erosion, if the irrigation project is done correctly.
Nevertheless, the operation of irrigation equipment still has an effect on the condition of the soil, and sometimes it is quite noticeable - for example, in cases where the intensity of sprinkling exceeds the rate of infiltration.
Water stagnation can be avoided by installing a different type of sprinkler on the machine or changing the pressure. These changes will allow watering over a larger area, reducing the rate and at the same time doing it more often.
However, there are often cases when the rate of water application was initially calculated correctly, but the formed soil crust interferes with the absorption of moisture. The crust can be dealt with by applying polyacrylamide (PAM) to the surface of the field. The polymer prevents soil compaction and thus prevents erosion.
It is also possible to increase the rate of water infiltration with the help of loosening and other methods of soil cultivation, including the method of reservoir cultivation (its essence lies in the fact that depressions are made between the ridges in the soil to prevent water flow).
In the state of Idaho (USA), on potato fields equipped with pivot irrigation systems, a study was conducted during three growing seasons, the purpose of which was to study the effect of anti-erosion tillage methods (in comparison with standard ones) on the uniformity of moisture distribution over the field and crop yield indicators.
Experimental plots in the fields were selected in such a way that part of the areas under the extreme spans of the irrigation system, where the highest irrigation rates were observed, were cultivated according to the standard scheme, and part - by the reservoir cultivation method.
The soil was a silty loam, and the topography of the plots varied from almost flat to 5% of the slopes.
The irrigation systems were equipped with sprinklers on the discharge hoses (tubes), sprinklers on the boom and rotating with a working pressure of 138 kPa.
In three years, the introduction of the reservoir treatment method has led to a decrease in losses from runoff to less than 1% of the applied water (provided that they remained intact).
The average soil moisture increased by 18%. In addition, statistical analysis showed that the introduction of special treatment significantly increased the percentage of available water in the upper 65 cm of the root zone (P = 0.01). The use of polyacrylamide for soil treatment (PAM) increased yields by 21%, and the content of commercial tubers increased to 64% in conventional plots and to 68% in reservoir plots. Thus, the reservoir type of tillage significantly increased the yield, but the types of sprinklers did not have a significant effect on this indicator.
Previously, polyacrylamide (PAM) applied to furrow irrigated fields at a rate of about 1 kg per hectare is known to enhance infiltration and control water erosion. PAM dissolved in water contacts the soil surface and prevents shear-induced delamination by increasing the adhesion of particles, thereby preventing runoff transfer.
Based on this fact, many growers are interested in using PAM in areas where sprinkler machines work. Note that when introducing sprinkling, it is very important to correctly adjust the droplet size and irrigation intensity so that the soil structure does not collapse. Otherwise, the surface of the soil is covered with a crust, which leads to a decrease in the rate of moisture absorption, the subsequent drainage of water and the loss of part of the fertile land.
Field studies show that significant and long-term enhancement of infiltration, as well as control of runoff and erosion, can be achieved in all studied soil types with a single application of 1 kg of PAM per hectare. In silty loams, Fluvisol PAM treatment reduced erosion by about 64%, in fallow areas - by 76%, infiltration increased by 34% and 18%, respectively. On sandy soils, the results with Fluvisol were more impressive: the application of PAM reduced soil erosion by 98% (96% in fallow areas) and increased infiltration by 47% and 45%, respectively.
What does PAM do? When used in accordance with the NRCS standard, polyacrylamide increases infiltration in addition to almost completely eliminating furrow erosion. The increase in the percentage of infiltration depends on several properties of the soil, especially its texture. In silty loamy soils, there is an increase in net infiltration by about 15% and an increase in lateral moistening of ridges from shallow furrows between low flat beds.
PAM maintains a more permeable pore structure while forming surface compaction during irrigation, which allows for increased infiltration and increases yields in sloping areas. This fact is explained by the fact that PAM holds the topsoil in place (and with it also holds phosphorus, nitrogen, pesticides).
Can PAM go through sprinklers? Experiments in Washington and Idaho have shown that distributing PAM directly through sprinkler systems reduces surface flooding and runoff and promotes more even plant growth through more even water distribution. The researchers estimated the cost of PAM at $ 5-8 per acre.
When considering the potential benefits of PAM, this ability to increase water uptake without runoff or puddles and surface crusting becomes especially valuable in hot summer conditions when pivots are difficult to meet crop water requirements due to design constraints during heat peaks.
Do I need to make any irrigation changes when using PAM? Yes. PAM promotes a higher infiltration rate throughout the entire irrigation process, so if the irrigation pattern is not adjusted, some areas may receive excess moisture.
In fields with a slope (> 2%), the soil infiltration rate is usually lower and the water moves quickly across the field. The improved infiltration and longer furrow travel time as a result of PAM treatment will not be a problem in this case. However, on very steep slopes, PAM can increase net infiltration to justify a reduction in set watering times (i.e. more water will enter the soil in a shorter time).
In fields with shallow furrows (0-0.5%), and especially in non-passable furrows, infiltration can be relatively high and the advance time with PAM can be excessively long, resulting in irregular irrigation. The problem will be especially acute if the inflow is not increased. PAM allows farmers to increase inflow without increasing losses from furrow erosion. Increasing the initial flow volume significantly shortens the advance time and equalizes the soak time for the top and bottom of the field.
Polyacrylamide can control water erosion, but the results of its use, like the results of many other agricultural practices, will vary from field to field.
Based on materials from the site potatoes.news