Abstract
While mineral fertilization increases agricultural yields, it also bears the risk of contaminating non-target ecosystems and negatively affecting soil chemical parameters and microbial communities. This calls for alternative and more sustainable agricultural practices that reduce the use of fertilizers. Flood pulse irrigation could be an alternative to mineral fertilization of hay meadows, since it increases the yield with little or no application of fertilizer. However, the positive and negative implications of flood pulse irrigation on soil chemical parameters and particularly soil microbial communities are still largely unknown. In this study, we assessed shifts in soil microbial communities (SMC) as a response to changes in soil chemical parameters after flood pulse irrigation and/or fertilization of meadows. We determined soil chemical (Corg, Ntot, water extractable N, P, K, pH) and microbial (phospholipid-derived fatty acids, PLFA) parameters of 12 meadows in a 2 × 2 factorial design, comprising flood pulse irrigation and fertilization. Corg, Ntot, and water content as well as microbial biomass were higher in flood-irrigated than in non-flooded soils. Soil microbial biomass positively correlated with Corg, Ntot, and water extractable N. Gram-negative bacteria significantly increased, whereas the fungi/bacteria ratio significantly decreased in flood-irrigated soils compared to non-flooded soils. Arbuscular mycorrhizal fungi were positively correlated with soil pH. Flood pulse irrigation seemed to promote the build-up of a larger soil carbon and nitrogen pool as well as higher water content and microbial biomass. By this, it potentially mitigated negative mineral fertilization effects such as changed soil pH and reduced carbon use efficiency. We conclude that flood pulse irrigation may represent a sustainable alternative to mineral fertilization.
Highlights
Flood pulse irrigation is a traditional method to increase the yields of hay meadows using the water of adjacent streams for a short-term (i.e., 2–4 day) flood pulse [1]
Our results suggest that flood pulse irrigation in extensively used hay meadows has a positive effect on soil fertility
The tendency of an enhanced build-up of soil organic carbon and nitrogen pool and significantly higher water contents are accompanied by significant effects on the microbial community composition upon flood pulse irrigation
Summary
Flood pulse irrigation is a traditional method to increase the yields of hay meadows using the water of adjacent streams for a short-term (i.e., 2–4 day) flood pulse [1]. This can be caused either by an improved plant growth and, respectively, increased root carbon deposition and litter input [3], or by organic matter accumulation due to reduced degradation efficiency of microbial communities if large soil zones become anaerobic [5] The latter would significantly reduce the hay yield due to oxygen deficiencies for plant roots. An optimal water management would keep the water content in a range that plant available water capacity can be maximal exhausted, while oxygen supply keeps soil conditions in an oxic state These optimal conditions support microbial carbon mineralization, which may level out an increased carbon input [6]. The negative effects of flood pulse irrigation on certain groups within the SMC are possible, even when anoxic conditions are not reached
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