Determining whether agricultural soils act as sinks or sources of greenhouse gases (GHGs) requires the quantification of variations in the pools and fluxes of soil organic carbon (SOC) and nutrients, e.g. nitrogen (N), as well as the associated soil microbial responses. In this study, soil was collected from experimental plots of maize (Zea mays) under conventional, minimum or strip tillage treatments established in a sloping field (~10%) of loamy soil in SW England, UK, where maize had been cultivated conventionally for 12 years. Topsoil (0–10 cm) cores were collected from the top, mid, bottom and foot slope positions to investigate soil C, N and microbial properties. The impact of conventional management on potential GHG emissions was assessed by incubating soils collected from the top, mid and bottom slope positions from the conventional treatment. Contents of SOC and total N were greatest at the top slope position and soil mineral N (NO₃⁻-N and NH₄⁺-N) concentrations were greater at the bottom and foot slope positions in all treatments. Biomarker phospholipid fatty acids (PLFA) for Gram positive bacteria and fungi were relatively ¹³C-enriched at each slope position regardless of treatment, indicating preferential utilization of organic matter from maize (C₄) rather than SOC (C₃). Around 70% of carbon incorporated into total PLFA was derived from C₃-SOC at the slope foot, indicating that more SOC older than 12 years was being mineralized at the depositional position. Effluxes of N₂O and CO₂, and total GHG emission were greatest from the incubated soils sampled from the bottom slope position, suggesting that conditions in depositional positions of regularly ploughed sloping arable fields may have increased the potential for mineralization and denitrification. We conclude that the C sink potential of the depositional positions of slopes may be diminished by coincidental GHG emissions.

要确定农业土壤是充当温室气体（GHG）的汇源还是汇源，就需要量化土壤有机碳（SOC）和养分（例如氮）的通量和通量的变化，以及相关的土壤微生物响应。在这项研究中，土壤是从玉米的实验田（玉米）中收集的。），在英国西南英格兰（通常种植玉米12年）的坡地（约10％）的壤土（约10％）下，进行常规，最少或条带耕作。从顶部，中部，底部和脚下斜坡位置收集表土（0-10厘米）岩心，以调查土壤的碳，氮和微生物特性。通过孵化从常规处理的顶部，中部和底部斜坡位置收集的土壤，评估了常规管理对潜在温室气体排放的影响。顶坡位置SOC和总N含量最大，土壤矿质N（NO ₃ ^-- N和NH ₄ ⁺-N）浓度在所有处理中的底坡和脚坡位置都较大。无论处理如何，革兰氏阳性细菌和真菌的生物标记磷脂脂肪酸（PLFA）在每个斜坡位置都相对富集¹³ C，表明优先利用玉米中的有机物（C ₄）而不是SOC（C ₃）。掺入总PLFA中的碳中约70％来自坡脚处的C ₃ -SOC，这表明在沉积位置矿化了12年以上的SOC。N ₂ O和CO _2的流出从底部斜坡位置采样的温育土壤中，总GHG排放量最大，这表明规则耕作的倾斜耕地的沉积位置中的条件可能增加了矿化和反硝化的潜力。我们得出的结论是，同时发生的温室气体排放可能会降低斜坡沉积位置的C汇潜力。