Evaluation of the Effects of New Environmental Additives Compared to Mineral Fertilizers on the Leaching Characteristics of Some Anions and Cations under Greenhouse Plant Growth of Saline-Sodic Soils

The aim of this study was to determine and monitor the influences of organic and biological additives compared to mineral fertilizers on leaching characteristics of anions and cations, also to know more about the ability of these additives to make complexes with dissolved and toxic salts to decrease soil salinity.

Salt-affected soils comprise of saline and sodic soils which differ in origin, physico-chemical properties and the constraints to plant growth. Due to the presence of excess soluble salts (e.g. sodium (Na⁺) and chlorides (Cl^-)).

Ten treatments were established, including two levels of spent grain (environmental organic wastes from the beer industry), S1(10 g of spent grain / kg soil) and S2 ( 20 g of spent grain / kg soil); two levels of compost M1(10 g of compost / kg soil) and M2 ( 20 g of compost / kg soil); mixed M1 with S1 (M1S1); inoculation of Azospirillum brasilense (A1); inoculation A1 with S2 (A1S1); inoculation A1 with M1 (A1M1); 20:20:20 of N, P, and K fertilizers (NPK), and control (CK, without any additives). All treatments were mixed with 30 kg soil pots under greenhouse conditions, corn (Zea mayz L.) seeds were sown in the soil pots. The most relevant nitrogen and salt in soil leachates were collected and analysed every 20 days for 100 days. The soil leachates were collected under plant growth from pots by closed system.

The result revealed that organic additives such as A1 and S2 treatments effectively decreased soil pH, soil EC, and reduced NaCl concentration in soil leachates. The Ca²⁺ and K⁺ cations in the soil leachates were not stable at high levels of organic additives. Soluble NO₃^- and NH₄⁺ were significantly lower in A1, S2, and A1S1 treatments than in NPK, M2, and CK treatments. Soil treatment with A1 and S2 significantly improved the soil chemical environment by increasing the Cation Exchange Capacity (CEC) and soluble and exchangeable-K⁺ and thus limited entry of Na⁺ into the exchange complex in soil and consists complex with soluble Na⁺ as sodium humate form.

In the final, the highest nitrogen use efficiency with the least NO₃^- and NH₄⁺ losses in saline-sodic soil was also found in S2 and A1 treatments. Moreover, under this bio-organic fertilization way, NO₃^- concentrations in soil leachates was outside of danger of damaging the environment. Thus, spent grain with Azospirillum were suggested to be the optimal fertilizer with the lowest nitrogen leaching losses, best yield, quality, and the least groundwater environmental risk under corn (Zea mays L.) organic and bio-organic cultivation comparing with chemical cultivation.