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, Fv/Fm, RWC and antioxidant activity (superoxide dismutase, peroxidase, and catalase), but increased electrolyte leakage and leaf H2O2 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.
Highlights
Soil amendments are known to promote several plant growth parameters
Our results indicate that exogenously applied S-enriched leonardite (SA1 and SA2) is an effective chemical for improving plant growth and yield of maize plants subjected to P deficiency, water stress or under the combination of both
The present study clearly showed that combined stress caused a considerable decrease in maize yield and yield related traits such as Fv/Fm, chlorophyll content, and leaf relative water content
Summary
In many agro-ecosystems, water scarcity and drought induced phosphorus deficiency limits crop yield significantly. The largest increase in yield and plant traits in relation to humic acid and leonardite application was observed under combined stress situation. 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 high and deficiency of any of the plant nutrients may lead to hamper growth and decrease yield[15]. Plants have developed strategies to alleviate P deficiency[26], which include increased efflux of organic acids[27], altered root structure[28], and enhanced acid phosphatase activity[29]. Humic acid application leads to an increase in some key plant biochemicals such as nucleic acids, vitamins, amino acids, and nutrients, but it improves soil chemical properties[36,37]
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