Search

Summary: Quantifying short‐ and long‐term availability of animal manure nitrogen (N) is of practical interest to ensure adequate crop yield, minimize N pollution and reduce inputs of mineral‐N fertilizer. We measured short‐term carbon (C) and N dynamics after one or six repeated additions to soil (every 56 days) of ammonium sulphate (AS) and undigested (PS) and anaerobically digested (DPS) pig slurry in a laboratory incubation experiment. Soil CO2 emissions, pH and mineral N (ammonium + nitrate) were measured during the period of 0–56 days following fertilizer additions. An accompanying experiment was conducted with similar but 15N‐labelled fertilizers to measure soil mineral N 56 and 112 days after one, three or six repeated additions, and to estimate the increase in slurry available N after repeated additions. Nitrogen from slurries potentially available for plants (77–91, 44–58 and 57–66% of added N for AS, PS and DPS, respectively) was close to that supplied in mineral form with the fertilizer, indicating negligible net mineralization of slurry organic N, after both one and repeated additions. In fact, soil mineral N increased in most of the treatments because of repeated additions, but the increases were small, on average 0.5–2.1% of added N per period of 56 and 112 days. Calculations of availability of fertilizer N based on unlabelled N were equally precise compared with those estimated with 15N, but trends over time were more variable. We conclude that many repeated additions (simulating a long manuring history) are needed to obtain a marked increase in available slurry N, even under controlled conditions. Highlights: We studied slurry decomposition after single or repeated additions in two laboratory incubationsWe used unlabelled and 15N‐labelled pig slurries to estimate N availabilityN potentially available for plants was close to that supplied in mineral form with slurriesSlurry N availability increased with repeated additions, but residual effects were small for both slurries [ABSTRACT FROM AUTHOR]

Alternative management practices such as no-tillage compared to conventional tillage are expected to recover or increase soil quality and productivity, even though all of these aspects are rarely studied together. Long-term field experiments (LTEs) enable analysis of alternative management practices over time. This study investigated a total of 251 European LTEs in which alternative management practices such as crop rotation, catch crops, cover crops/green manure, no-tillage, non-inversion tillage and organic fertilization were applied. Response ratios of indicators for soil quality, climate change and productivity between alternative and reference management practices were derived from a total of 260 publications. Both positive and negative effects of alternative management practices on the different indicators were shown and, as expected, no alternative management practice could comply with all objectives simultaneously. Productivity was hampered by non-inversion tillage, FYM amendments and incorporation of crop residues. SOC contents were increased significantly following organic fertilizers and non-inversion tillage. GHG emissions were increased by slurry application and incorporation of crop residues. Our study showed that alternative management practices beneficial to one group of indicators (e.g. organic fertilizers for biological soil quality indicators) are not necessarily beneficial to other indicators (e.g. increase of crop yields). We conclude that LTEs are valuable for finding ways forward in protecting European soils as well as finding evidence-based alternative management practices for the future; however, experiments should focus more on biological soil quality indicators as well as GHG emissions to enable better evaluation of trade-offs and mutual benefits of management practices. [ABSTRACT FROM AUTHOR]

Repeated applications of animal slurry to soil can lead to residual nitrogen ( N) effects from mineralization of organic N carried over from the previous year and from remineralization of previously immobilized N. We studied the effect of repeated slurry applications on soil mineral N ( SMNt: nitrate- N plus soluble, exchangeable and non-exchangeable ammonium- N) dynamics in a simplified, aerobic laboratory incubation. The experiment evaluated the effects of up to four applications (84-day intervals) of two different liquid cow slurries, ammonium sulphate and water (unfertilized control, CON) to sandy loam and clay loam soils. The slurries came from heifers ( HEI) and lactating dairy cows ( COW). Both soil types showed net N mineralization in HEI during each 84-day interval after application (3-6% of slurry- N), whereas decomposition of COW induced net N immobilization at 16% of slurry- N. The effect observed for COW might have come from its larger C to organic- N ratio. After each application to the clay loam soil, 36-64% of the ammonium applied was not recoverable at day 0 because of ammonium fixation by clay minerals, and an average of 20% of fertilizer- N was measured as non-exchangeable ammonium at day 84. Recovery of N applied with both HEI and COW at day 84 increased significantly with subsequent applications to clay loam soil, but not to sandy loam soil. Residual effects in clay loam soil ranged from 2 to 11% of applied N, which probably resulted from slow mineralization of recalcitrant organic fractions in the slurry and partial stabilization of microbial by-products within the soil. Highlights A novel incubation approach was used to study residual N effects of ammonium sulphate and slurries., Fertilizers were applied one, two, three or four times to a sandy loam ( SL) and a clay loam ( CL) soil., Residual N effects were small; less slurry NH4-N was available in CL than SL because of clay fixation., Mineralization of residual slurry- N and stabilization of microbial by-products were slow. [ABSTRACT FROM AUTHOR]

Soil organic matter ( SOM) improves soil physicochemical and biological properties, and the sequestration of carbon in SOM may mitigate climate change. Soil organic carbon ( SOC) often decreases in intensive cropping systems. Incorporation of crop residues ( CR) may be a sustainable management practice to maintain the SOC levels and to increase soil fertility. This study quantifies the effects of CR incorporation on SOC and greenhouse gas ( GHG) emissions ( CO2 and N2O) in Europe using data from long-term experiments. Response ratios ( RRs) for SOC and GHG emissions were calculated between CR incorporation and removal. The influence of environmental zones ( ENZs), clay content and experiment duration on the RRs was investigated. We also studied how RRs of SOC and crop yields were correlated. A total of 475 RRs were derived from 39 publications. The SOC increased by 7% following CR incorporation. In contrast, in a subsample of cases, CO2 emissions were six times and N2O emissions 12 times higher following CR incorporation. The ENZ had no significant influence on RRs. For SOC concentration, soils with a clay content >35% showed 8% higher RRs compared with soils with clay contents between 18 and 35%. As the experiment progressed, RR for SOC concentration increased. For N2O emissions, RR was significantly greater in experiments with a duration <5 yr compared with 11-20 yr. No significant correlations were found between RR for SOC concentration and yields, but differences between sites and study durations were detected. We suggest that a long duration of crop residue incorporation is a win-win scenario under a continental climate. We conclude that CR incorporation is important for maintaining SOC, but its influence on GHG emissions should be taken into account as well. [ABSTRACT FROM AUTHOR]