Abstract
AbstractUnder the hot and moist conditions of irrigated agriculture in the arid subtropics, turnover of organic matter is high, which can lead to considerable carbon (C) and nitrogen (N) losses. Therefore, sustainable use of these soils requires regular manure application at high rates. To investigate the contribution of consecutive manure applications to an arid sandy soil to various soil N pools, goat manure was isotopically labeled by feeding 15N‐enriched Rhodes grass hay and applied to the soil during a two‐year field experiment. In the first year, soils received 15N‐labeled manure to distinguish between soil‐derived and manure‐derived N. In the second year, these plots were split for the application of either 15N‐labeled or unlabeled manure to discriminate N derived from previous (first year) and recent (second year) manure application. Soil samples (of control and 15N‐manured soil) were collected at the end of the first and the second year, and incubated in two laboratory experiments with labeled or unlabeled manure. At the beginning of Experiment 1, 7% of total N, 11% of K2SO4 extractable N, and 16% of microbial biomass N were derived from previously field‐applied manure. While the application of manure during incubation increased microbial biomass N by 225% and 410% in the control soil and the previously field‐manured soil, respectively, N2O emissions were more affected on the control soil, releasing considerable amounts of the soil N‐pool (80% of total emissions). In Experiment 2, 4% of total N, 7% of K2SO4 extractable N, and 7% of microbial biomass N derived from previously applied manure, and 4%, 8%, and 3% from recently applied manure, respectively. Microbial biomass N and N2O‐N derived from manure declined with time after manure application, whereas in Experiment 1 this tendency was only observed for microbial biomass N.
Highlights
The interaction between high temperatures, frequent irrigation, and tillage often leads to high microbial activity and a subsequent rapid organic matter turnover and nutrient losses in the tropics and subtropics (Austin et al, 2004; Conant et al, 2011; Fiedler et al, 2016)
3 Results In Experiment 1, concentrations of soil organic C (SOC), K2SO4 extractable C, and microbial biomass C increased with increasing number of manure applications (Co1 < CoM < Mm = MM; Tab. 2) and significantly changed during the incubation experiment
While SOC generally decreased during the experiment, K2SO4 extractable C increased on control soils and remained relatively constant on field-manured soils, whereas microbial biomass C increased in all treatments
Summary
The interaction between high temperatures, frequent irrigation, and tillage often leads to high microbial activity and a subsequent rapid organic matter turnover and nutrient losses in the tropics and subtropics (Austin et al, 2004; Conant et al, 2011; Fiedler et al, 2016). Considerable carbon (C) and nitrogen (N) volatilization losses in irrigated semi-arid and arid soils have been documented (Wichern et al, 2004a; Buerkert et al, 2010; Siegfried et al, 2011; Goenster et al, 2014) Despite these reported losses, the repeated application of animal manure can stabilize or increase soil organic C (SOC) and N concentrations of top-soils (Craswell and Lefroy, 2001; Lal, 2006; Siegfried et al, 2011; Ingold et al, 2015), which is important for soil fertility and sustainable crop production. Frequent wet–dry cycles induced by flood-irrigation can further intensify min-
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