Biofertilization of wheat with algal biomass reducing soil nitrous oxide emission without yield penalty in desert agroecosystems

Biofertilizers (biologically-based fertilizers) are used by humanity to supply crops with limiting nitrogen (N) and phosphorus (P) from the beginning of agriculture in an ancient Egypt. Recently, interest to use biofertilizers and specifically algal-based fertilizers is rising due to a) potential for cultivation of algae in water treatment systems and therefore recycling of nutrients and b) potential to improve stress tolerance and drought resistance of cultivated crops. While beneficial effects of biofertilization on crop performance in laboratory experiments have been reported, none of previous studies considered the environmental effects neither the harvestable yield of agricultural crops in field. To address this knowledge gap, we have designed a replicated field experiment with common wheat (T. aestivum) grown on three soils: loess (clay soil) - typical to the Negev desert, loamy sand - typical to the northern parts of Israel, and sandy loam - typical to the coastal plain of Israel; all areas are used for wheat production. The wheat was irrigated by sprinkle irrigation and fertilized either by inorganic UAN (urea-ammonium-nitrate, 32%; IF) or untreated microalgae mix (Scenedesmaceae spp.; AF) at rate of 10 g N m-2. During the growth season we have measured soil nitrous oxide (N2O) emissions using static chambers coupled with Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) analyzer (ABB - Los Gatos Research, CA) and soil inorganic N dynamics in 0-15 cm soil layer. We have hand-harvested wheat and measured biomass production, grain yields, and carbon isotopic composition (δ13C) of the wheat straw to assess the effect of biofertilization on the wheat productivity and water-use efficiency (WUE). We have found that while vegetative growth (total biomass) was higher in the IF treatment the grain yield was equal in both IF and AF treatments and was affected by the soil type. The N2O emissions followed similar trend in both treatments; high emissions post-fertilization and low emissions throughout the grows season with total emissions lower in the AF treatment. Surprisingly, cumulative emissions were trivial, with emission factors ranging from 0.0002 and 0.14 percent of applied fertilizer N across different soils in both treatments. Our results showing that a) soil N2O emissions are trivial in irrigated wheat cropping system in the Negev desert, and b) biofertilization by microalgae is promising management option.