General recommendation of hydrogel in soil is nearly 8-15 kg/ha. Which means, in only 15 cm furrow slice, only 6 ppm of hydrogel conc. in soil. I want to know that how that minute amount be practically improving soil binding and water holding properties?
Hydrogel is effective in short duration and less water requirement crops. It may be more effective in winter season crops where evaporation rate is very less as compared to other season crops. Generally its seed treatment is more effective and application below the seed is also effective.
Hydrogels have the water absorptive capacity up to 300 times the weight of substances indicating that the each kg of added hydrogel can hold upto 300 ltr water and release slowly according to the water gradient. Application of 10 kg per acre can only retain 3000 ltr water against the evapo-transpirational demand of 12000-16000 ltr per day (@ 3 - 4 mm ET) in field crops. Hence, applicability of hydrogels are limited to field crops where the entire land area is occupied by crop plants.
However, hydrogels have practical applicability in widely spaced plantation crops with watering only to the basin and shade on watering area.
If we add @ 10 kg/acre or 25 kg/ha, the rate is actually near 120 ppm. Isn't is too low to be effective?
Hydrogels are costing from INR 200 to 2000 / kg. Application above 25 kg/ha increases cost of production and the marginal returns reduce drastically. Further, majority of the hydrogels available in market are inorganic compounds, their impact on soil also needs consideration.
These are less effective in high evaporative demand seasons and high water requirement crops.
Every time you apply hydrogel, you have to take in account soil water content, roots system and irrigation / climate. There is no low to apply an hydrogel, just a specific calculation depending on those parameters.
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