Sulfur-enriched leonardite and humic acid soil amendments enhance tolerance to drought and phosphorus deficiency stress in maize (Zea mays L.)

Abstract

Soil amendments are known to promote several plant growth parameters. In many agro-ecosystems, water scarcity and drought induced phosphorus deficiency limits crop yield significantly. Considering the climate change scenario, drought and related stress factors will be even more severe endangering the global food security. Therefore, two parallel field trials were conducted to examine at what extent soil amendment of leonardite and humic acid would affect drought and phosphorus tolerance of maize. The treatments were: control (C: 100% A pan and 125 kg P ha −1), P deficiency (phosphorus stress (PS): 62.5 kg P ha −1), water deficit stress (water stress (WS): 67% A pan), and PS + WS (67% A pan and 62.5 kg P ha −1). Three organic amendments were (i) no amendment, (ii) 625 kg S + 750 kg leonardite ha −1 and (iii) 1250 kg S + 37.5 kg humic acid ha −1) tested on stress treatments. Drought and p deficiency reduced plant biomass, grain yield, chlorophyll content, F v /F m , RWC and antioxidant activity (superoxide dismutase, peroxidase, and catalase), but increased electrolyte leakage and leaf H 2 o 2 in maize plants. The combined stress of drought and P deficiency decreased further related plant traits. Humic acid and leonardite enhanced leaf P and yield in maize plants under PS. A significant increase in related parameters was observed with humic acid and leonardite under WS. The largest increase in yield and plant traits in relation to humic acid and leonardite application was observed under combined stress situation. The use of sulfur-enriched amendments can be used effectively to maintain yield of maize crop in water limited calcareous soils. The global climate change simulations suggest fresh water availability will further deplete in many rainfed and irrigated agricultural areas 1 and thus, threatens food security 2. Although hydrological, meteorological and agricultural droughts occur simultaneously and are interrelated with each other, agricultural drought is believed to be the most common 3,4. Water stress causes a variety of responses from physiological to molecular in plants, allowing them to acclimate to harsh ecological conditions 5. Drought susceptibility of plants differs according to the plant species, stress level, and growth stages 6. Considerable yield gaps have been noticed in agricultural systems 7,8 and the availability of good quality water and mineral nutrients is critical for overcoming these yield gaps 9-11. This is principally reasonable for maize crop, one of the main cereals of the globe, covering 26% and 37% of the total cereal cultivated area and production, respectively 12. Maize is known as one of the highest water-requiring crops. Water deficiency imposed at any stage of its development can reduce grain yield significantly 13,14. As it is a fast-growing crop, its requirement for essential nutrients is also high and deficiency of any of the plant nutrients may lead to hamper growth and decrease yield 15. Maize is particularly susceptible to P deficiency, which can suppress growth and grain...

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