Can humic substances improve soil fertility under salt stress and drought conditions?

Authors: SUDDARTH, STELLA - Universidade Federal Da Paraiba (UFPB); Ferreira, Jorge; CAVALCANTE, LOURIVAL - Paraiba University; FRAGA, VANIA - Universidade Federal Da Paraiba (UFPB); Anderson, Raymond - Ray; Halvorson, Jonathan; BEZERRA, FRANCISCO - Paraiba University; MEDEIROS, SHERLY - Paraiba University; COSTA, CASSIO - Universidade Federal Da Paraiba (UFPB); DIAS, NILDO - Federal Rural University Of The Semi-Arid

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2019
Publication Date: 10/31/2019
Citation: Suddarth, S.R., Ferreira, J.F., Cavalcante, L.F., Fraga, V.S., Anderson, R.G., Halvorson, J.J., Bezerra, F.T., Medeiros, S.A., Costa, C.R., Dias, N.S. 2019. Can humic substances improve soil fertility under salt stress and drought conditions? Journal of Environmental Quality. 48(6):1605-1613. https://doi.org/10.2134/jeq2019.02.0071.
DOI: https://doi.org/10.2134/jeq2019.02.0071

Interpretive Summary: The soils of semiarid regions are often poor in carbon and mineral nutrients, both necessary sources of energy for soil microorganisms and plants, respectively. Although the addition of amendments rich in organic matter may improve soil chemical characteristics, the effectiveness of different types and concentrations of organic matter in these amendments is poorly understood for semi-arid soils. This work evaluated the effect of two sources of organic carbon (Humistar® and diluted cow manure) on the chemical characteristics of a semi-arid soil cultivated with passion fruit and irrigated with saline water. The experiment took place in the Brazilian semiarid (northeast region) during the most severe drought in 30 years. Our results with the soil used in this experiment contradict the general idea that organic matter can mitigate the harmful effects of salt in semiarid soils because the addition of both Humistar® and diluted bovine biofertilizer to the soil reduced soil fertility. Although this response may depend on the concentration of humic acids in the amendment, our results suggest that there is no economic return associated with the application of either amendment. This work benefits farmers and land managers who seek to improve soil fertility for farms in semi-arid regions. Organic farmers particularly may benefit as Humistar® is considered an organic amendment, but there are no economic studies to support its purported benefits.

Technical Abstract: Semiarid soils may be poor in organic carbon, a necessary source of energy for soil microorganisms that affect plant growth. Although the addition of organic carbon may improve soil chemical characteristics, the concentration of humic compounds in the organic component may vary and affect soil chemical composition. We evaluated the effect of two sources of humic compounds on a dystrophic yellow Oxisol cultivated with passion fruit (Passiflora edulis Sims f. edulis) and irrigated with saline water during a severe drought in the Brazilian semiarid region. Soil fertility was evaluated during two seasons. A bovine biofertilizer and an organic commercial amendment (Humistar) were used as sources of humic compounds. Salinity resulted in reduced soil fertility, mainly during the lower rainfall period. The combination of humic substances and salinity increased soil salinity. Humistar, more concentrated in humic acid than fulvic acid, increased both acidity and salinity of the Oxisol under study during the lower rainfall period. Our results contradict the general idea that organic matter can mitigate the harmful effects of salts in semiarid soils because the addition of organic sources to the soil, mainly during a severe drought period, may reduce soil fertility. Although this response may depend on the concentration of humic acids in the amendment, our results suggest that the correction of soil chemistry with the application of either amendment to Oxisols under semiarid conditions, mainly during severe drought, is not economically feasible.