Relevance of the Postharvest Period to Soil N2o Emissions from Semiarid Cropping Systems : A Meta-Analysis

In this study, a meta-analysis was carried out to address the quantitative relevance of considering postharvest nitrous oxide (N 2 O) measurements in herbaceous crops (excluding rice) and using static chambers (i.e., noncontinuous measurements). We compiled data from 17 studies carried out in semiarid Spain, thus yielding 157 observations under several conditions of soil texture, crop system (rainfed versus irrigated), tillage, type of crop or nitrogen (N) fertilizer management (i.e., N application rate, use inhibitors or split N applications). In comparison with measurements during the cropping period, we analysed the potential significant differences between maximum N 2 O fluxes, cumulative emissions and N 2 O emission factors (EFs) when considering the postharvest period. The relevance of the postharvest period was significantly higher in rainfed (winter) crops (i.e., those in which the postharvest period occurs during dry summer conditions) than in irrigated (summer) crops (i.e., those in which the postharvest period occurs during colder and more humid autumn-winter conditions). Thus, the average ratios between maximum fluxes (postharvest/preharvest) were 4.0 (0.0–45.4) and 0.2 (0.0–1.3) in rainfed and irrigated crops, respectively. In irrigated crops, cumulative fluxes when considering the postharvest period were not significantly different from those considering only the preharvest period, and an average 23% increment of cumulative emissions during the postharvest period could be assumed in N fertilized crops. The average N 2 O EFs in the studies included in this meta-analysis were 0.17% (0.00–0.88) and 0.23% (0.00–0.99) when not considering and when considering the postharvest period, respectively. The postharvest maximum N 2 O pulses were statistically similar in unfertilized plots and fertilized plots, thus suggesting that the intensity of these N 2 O hot moments occurring after postharvest soil rewetting was barely influenced by N management. This study may contribute to improving N 2 O measurement protocols using static chambers and to re-evaluating N 2 O EFs in semiarid areas