Application of two beet vinasse forms in soil restoration: Effects on soil properties in an arid environment in southern Spain

Organic soil amendments are being increasingly examined for their potential in soil restoration. Two beet vinasse forms (fresh, BV, and composted with a crushed cotton gin compost, CV) were applied annually for a period of four years to a Xerollic Calciorthid soil located near Seville (Guadalquivir Valley, Andalusia, Spain) in order to evaluate the efficiency of these organic amendments in soil restoration. The effects of these amendments on plant cover, soil's physical (structural stability, bulk density), chemical (exchangeable sodium percentage), and biological properties (microbial biomass, soil respiration and enzymatic activities such as dehydrogenase, urease, BBA-protease, â-glucosidase, phosphatase and arylsulfatase) were determined. Organic wastes were applied at 5, 7.5, and 10 t organic matter ha−1 rates, respectively. After 4 years of successive soil amendment, the percentage of plant cover decreased 58.3% in BV-amended soils whereas increased 86% in CV-amended soils with respect to the unamended soil. The application of fresh beet vinasse had a detrimental impact on the soil's physical (structural stability decreased 25.2% and bulk density increased 22.9% with respect to the control soil), chemical (exchangeable sodium percentage increased 86.9%), and biological properties (microbial biomass, soil respiration, and dehydrogenase, urease, BBA-protease, â-glucosidase, phosphatase and arylsulfatase activities decreased by 44.9%, 26.2%, 17.6%, 14.8%, 11.1%, 5%, 63% and 59.6%, respectively, probably because high quantities of monovalent cations, such as Na+, and fulvic acids were introduced into the soil by the vinasse, thus destabilizing its structure. However, when beet vinasse was co-composted with a cotton gin crushed compost, the resulting compost had a positive effect on the soil's physical (structural stability increased 26.5% and bulk density decreased 26.3% with respect to the control soil), and biological properties (microbial biomass, soil respiration, and dehydrogenase, urease, BBA-protease, â-glucosidase, phosphatase and arylsulfatase activities increased by 57.1%, 76.4%, 98.4%, 98.2%, 99.8%, 99.4%, 89.8% and 92.3%, respectively, with respect to the control soil). While the application of CV protect the soil and will contribute to its restoration, the application of BV deteriorates the soil and therefore does not contribute to its restoration.