Effect of Starch-based Hydrogel on Early Growth of Corn
Seed coating with highly absorbent polymers can potentially improve the water availability for early growth of seeds under dry conditions and therefore prevent associated delays in the emergence and reduced crop stand. The limited number of studies on hydrogel seed coatings have shown that their effect on seed growth is not always beneficial, and varies with plant species, amount of hydrogel used and amount of available water in the growing medium. The current work studied the effect of hydrogel seed coating on the early growth of corn using starch-based biodegradable hydrogels. The hydrogels were prepared from potato starch (PS) and waxy corn starch (WCS) by an aqueous esterification-cum-crosslinking reaction with succinic anhydride using dimethylaminopyridine as a catalyst, followed by neutralization of ester carboxylic acid. The formation of the required chemical bonds in starch after the preparation procedure was verified by Fourier transform-infrared spectroscopy. The water absorption capacity of the hydrogels was determined in distilled water (PS: 260 g/g, WCS: 199 g/g) and 0.9% NaCl solution (PS: 18 g/g, WCS: 38 g/g). The saline absorption capacity of the hydrogel under a load of 4.9 kPa was also measured (PS: 7 g/g, WCS: 6 g/g). The effect of the hydrogel as a seed coating on the early growth of corn seeds was tested in a series of experiments. In a preliminary experiment using WCS hydrogel, the germination behavior of hydrogel film-coated corn seeds was compared under water stress with uncoated seeds. The hydrogel-coated seeds showed an improved rate of germination. In the following study that used PS hydrogel, the emergence and early growth of seed corn were tested for the effect of two factors – hydrogel loading per seed (1.1, 2.6 and 4.2%) and watering level (92-93%, 82% and 77% of field capacity or FC). A significantly higher rate of emergence was observed in coated seed than uncoated seeds at the 77% FC watering. The rate of emergence was significantly higher for hydrogel-coated seeds but the three coating levels were similar. This study could therefore not determine the effect of different levels of hydrogel loading on the seeds. At higher watering levels of 93% and 82%, the emergence of the coated seeds did not differ from the uncoated seeds. The hydrogel coating did not have a significant effect on root and shoot dry biomass after 14 and 21 days of sowing. In the final study using PS hydrogel, the emergence of uncoated and hydrogel-coated seeds (4.2% level) was tested at a lower watering level (65% FC). The hydrogel coating showed no improvement in the rate of emergence at this level of watering. It was therefore concluded that the hydrogel coating improved the rate of seed emergence only at moderate limitations of water in the growth medium, which might be attributed to a higher amount of water available due to the coating. The hydrogel coating did not improve emergence at high or very low soil water content. The hydrogel coating did not have a significant effect on the post-emergence growth of corn plant which indicates that hydrogel coating’s contribution to plant’s water requirements diminishes rapidly once the plant gains wider access to soil water through its root system. In future work, a study on the kinetics of hydrogel biodegradation and the associated loss of absorption property can give insights into its maximum functional life in the soil. The hydrogel coating levels may be selected to have a wider range to improve the resolution of the effect of different levels. Finally, the seed pelleting method may be checked for variability in the deposition of the hydrogel among the seeds and, if required, the coating method improved. The hydrogel deposition should have minimal variability among the seeds of a treatment level and should be suitable to implement significantly different treatment levels of hydrogel loading.
Ambrose, Purdue University.
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