Drought Effects on Nitrogen Provisioning in Different Agricultural Systems: Insights Gained and Lessons Learned from a Field Experiment

Abstract

Most nitrogen (N) in organic fertilizers must be mineralized to become available to plants, a process in which microorganisms play crucial roles. Droughts may impact microorganisms associated with the N cycle, negatively affecting N mineralization and plant N supply. The effects of drought on N-related processes may further be shaped by the farming system. We buried 15N-enriched plant material and reduced precipitation in conventionally and organically (biodynamically) managed wheat fields. On two sampling dates, we evaluated the soil water content, plant parameters and the plants’ 15N isotope signature. We intended to study the microbial communities associated with the N cycle to link potential treatment effects on plant N provisioning with characteristics of the underlying microbial community. However, floods impaired the experiment after the first sampling date, and the molecular work on the microbial communities was not performed. Focusing on the pre-flooding sampling date, our data suggested that processes associated with N transformation are sensitive to drought, but the role of the farming system needs further investigation. Since the underlying research question, the set-up and the lessons learned from this study may guide future experiments, we presented improvements to the set-up and provided ideas for additional analyses, hoping to promote research on this topic.

Conventional agriculture and not drought alters relationships between soil biota and functions

“…However, negative effects of reduced precipitation are persistent for several groups of soil biota (e.g. microbes 20 ) and soil functions 21 , 22 independent of the ecosystem. The strength of drought effects partly depends on the drought intensity and duration 23 .…”

Beneficial Microorganisms Affect Soil Microbiological Activity and Corn Yield under Deficit Irrigation

“…The concentration of mineral nitrogen (N), as ammonium (NH 4 + ) or NO 3 − , increased due to the water deficit. In previous works, higher concentrations of mineral N were also observed in soil under water deficits [5,8,49]. Water restriction possibly decreased the rate of N absorption and accumulation by corn, providing higher levels of mineral N in the soil and decreasing the levels of this nutrient in the leaves.…”

“…The water deficit imposed by the 50% ETc water depth reduced corn's growth and leaf area, as well as the nitrogen content in the leaves. Drought stress causes a decrease in cell turgor, which is essential for proper cellular metabolism, such as photosynthesis, enzymatic activity [3,4], and nutrient absorption [5]. In addition, under water deficit, nitrogen contact with the roots, through diffusion and mainly by mass flow, can be reduced [42], decreasing the uptake of this nutrient by the plant [5].…”

“…Drought stress causes a decrease in cell turgor, which is essential for proper cellular metabolism, such as photosynthesis, enzymatic activity [3,4], and nutrient absorption [5]. In addition, under water deficit, nitrogen contact with the roots, through diffusion and mainly by mass flow, can be reduced [42], decreasing the uptake of this nutrient by the plant [5]. On the other hand, regardless of the irrigation level, the inoculation of plants with Bacillus subtilis promoted an increase of 13% in the leaf area index and 12% in the N content of the leaves compared to the treatment without the inoculation.…”

“…Water stress negatively affects plants' physiological and biochemical processes that restrict growth, development, and productivity [3,4]. Drought causes a decrease in cell turgor, which is essential for proper cellular metabolisms, such as photosynthesis, enzyme activity, and nutrient uptake [4,5].…”