Superabsorbent hydrogels are a particular class of gels, obtained by chemical stabilization of hydrophilic polymers in a tridimensional network. Hydrogels have been widely proposed over the last 40 years for agricultural use with the aim to ameliorate water availability for plants, by increasing water holding properties of growing media (soils or soilless substrates). Most of the traditional hydrogels on the market are acrylate-based products, thus not biodegradable. Due to the increasing attention for environmental protection issues, biodegradable hydrogels arise lively interest for potential commercial application in agriculture. In this study, we evaluated a novel class of cellulose-based superabsorbent hydrogels, totally biodegradable and biocompatible, for agricultural use. The objectives of the tests carried out were: 1) to verify the ability of the hydrogel to modify the water retention properties of the growing media (soils and soilless substrates); 2) to study the effects on the growth of plants grown on media amended with the hydrogel. Water retention curve of a sandy soil amended with 0, 0.5, 1.0 and 2.0% (w/w) of hydrogel was determined using a Richard's pressure plate apparatus. The hydrogel modified the soil water retention properties. The soil moisture at field capacity increased with the highest hydrogel percentage up to 400% compared to the not amended soil, and at wilting point (-15bar) was similar to that at field capacity of the not amended soil. When added to perlite, a low water holding capacity soilless substrate, 1 or 2% (w/w) of hydrogel increased the container capacity of 28 and 48%, respectively, with no decrease of air capacity. Tests revealed absence of phytotoxicity of the hydrogel, and cultivation trials on cucumber (on soil) and sweet basil (in soilless conditions) showed a general overall enhancement of plant growth and quality when hydrogel was added to growing media. The tested hydrogel showed to be suitable for potential use in agriculture. Its employment should be further evaluated under a cost-effective perspective

ISHS International Symposium on Growing Media and Hydroponics WAYS OF REDUCING ROCKET SALAD NITRATE CONTENT

The adoption of closed soilless systems is useful in minimizing the environmental impact of the greenhouse crops. Instead, a significant problem in closed soilless systems is represented by the accumulation of ions in the recycled nutrient solution, in particular the unabsorbed or poorly absorbed ones. To overcome such problem, we: 1) studied the effect of several values of the electrical conductivity (EC) of nutrient solution in a NFT (Nutrient Film Technique) system on a cherry type tomato crop, and 2) define a NS (called recovery solution), based on the concept of “uptake concentration” and transpiration-biomass ratio, that fits the real needs of the plant with respect to water and nutrients. Three levels of EC set point (SP), above which the NS was completely replaced (SP5, SP7.5, and SP10 for the EC limit of 5, 7.5 and 10 dS m-1, respectively), were established. The SP10 treatment yield was not different from other treatments, and it allowed a better quality of the berries (for dry matter and total soluble solids) and higher environmental sustainability due to a lower discharge of total nutrients into the environment (37 and 59% with respect to SP7.5 and SP5, respectively).The recovery solution used in the second trial allowed a more punctual NS management, by adapting to the real needs of the crop. Moreover, it allowed a lesser amount of water and nutrients to be discharged into the environment and a better use of brackish water, due to a more accurate management of the EC of the NS. The targeted management, based on transpiration-biomass ratio, indicates that, in some stages of the plant cycle, the nutrient solution used can be diluted, in order to save water and nutrients. With such management a closed cycle can be realized without affecting the yield, but improving the quality of the tomato berries.