Can Humic Substances Improve Soil Fertility under Salt Stress and Drought Conditions?

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. Core Ideas Saline irrigation reduces the fertility of Oxisols, mainly in low‐rainfall periods. The combination of humic substances and salinity increased salinity of Oxisols. During low‐rainfall periods, humic substances reduced Oxisol fertility.

Impact of Seed Dressing and Soil Application of Potassium Humate on Cotton Plants Productivity and Fiber Quality

“…However, the composition of humus depends upon abiotic controls, soil biota and the types of input crop and animal residues. The addition of organic amendments, i.e., biochar, organic matter, farmyard manure, compost and especially humic substances in soil with low organic matter status could increase the physical, chemical and biological properties of the soil [8][9][10][11][12][13][14][15][16][17]. soil characteristics vary with land use [18][19][20].…”

Current Understanding of the Use of Alkaline Extractions of Soils to Investigate Soil Organic Matter and Environmental Processes

“…Both organic amendments resulted in increased soil salinity regardless of the salinity of the irrigation water. Suddarth et al (2019) conclude that addition of organic amendments had no benefit during severe drought and saline water irrigation.…”

“…Suddarth et al (2019) designed a 2‐yr field study during severe drought conditions in the northeast semiarid region of Brazil to understand the combined effects of saline irrigation and application of organic C amendments on the Oxisol soil composition and passion fruit ( Passiflora edulis Sims f. edulis ) productivity. It is commonly believed that the addition of an organic amendment such as humic substances can mitigate the impact of drought by increasing soil water‐holding capacity and improving soil structure.…”

Which Traits of Humic Substances Are Investigated to Improve Their Agronomical Value?

“…Hartz and Bottoms showed that fruit yields and biomass weights were not enhanced in response to HS addition to soils [ 17 ]. Suddarth et al also suggested that combined treatment of a HS with irrigation might increase the salt content of soils [ 18 ]. Therefore, imminent discussions are necessary to direct HS research and development toward more practical and reliable agronomic recommendations.…”