Land use conversion from grassland to cropland places unique constraints on ecosystem services and sustainability across the United States. In the northern Great Plains, this process is acute with marginal lands continuously cycling in and out of production. As this trend continues, it remains unclear what the short-term impacts of intermittent cropping are to soil biological properties. This study examines the short-term response of soil microbial biomass and activity during grassland conversion to cropland using conventional tillage (CT) and no-till (NT) practices in comparison to a grassland control. Long-term grassland was converted to cropland for three consecutive years. Following crop harvest, soil samples were gathered to measure the ‘first-year’ impacts to microbial biomass and enzyme activity (beta-glucosidase [BG], beta-glucosaminidase [BGA] and phosphomonoesterase [PHOS]). Conversion of grassland to small grain production did not produce a statistically significant trend for total microbial biomass or bacterial biomass. However, there were strong environmental effects due to yearly fluctuations in precipitation on total microbial biomass, total bacterial biomass and total fungal biomass. The effect of land conversion via CT on fungal biomass was strong and resulted in decreased fungal to bacterial biomass ratios. CT significantly decreased fungal populations over both the grassland and NT by 29 %. All three enzyme activities in the top 7.5 cm were significantly reduced by land conversion via CT during the study year with the highest precipitation. On average, BG and BGA activity in the CT plots were approximately 20 % lower than either the grassland or NT plots. Phosphomonoesterase activity under CT was significantly decreased by 28 % and 18 % compared to grassland and NT, respectively. In the 7.5–15 cm depth interval, BG and BGA activities in the grassland control and NT plots showed vertical stratification, with the CT plots having the highest BG and BGA activities with higher precipitation. There was no effect of land conversion on PHOS activity at the 7.5–15 cm depth. Significant declines in soil microbial biomass and enzyme activity may occur in the first year of grassland conversion to cropland, particularly with tillage, implying reduced C and nutrient cycling potentials. These effects were the strongest for fungal biomass and occurred under conditions of higher precipitation in the semi-arid study site.

从草地到农田的土地利用转换对整个美国的生态系统服务和可持续性构成了独特的限制。在大平原北部，这一过程非常剧烈，边缘土地不断循环进出生产。随着这一趋势的继续，目前尚不清楚间歇作物对土壤生物学特性的短期影响。这项研究调查了常规耕作（CT）和免耕（NT）措施与草地控制相比，草地转化为农田期间土壤微生物量和活性的短期响应。长期的草地已连续三年转化为农田。收获农作物后，收集土壤样品以测量“第一年”对微生物生物量和酶活性的影响（β-葡萄糖苷酶[BG]，β-氨基葡萄糖苷酶[BGA]和磷酸单酯酶[PHOS]）。草地向小谷物生产的转化并未产生总微生物量或细菌生物量的统计学显着趋势。但是，由于降水量对微生物总生物量，细菌总生物量和真菌总生物量的逐年波动，因此具有很强的环境影响。通过CT进行土地转化对真菌生物量的影响很强，并导致真菌与细菌生物量之比降低。CT显着降低了草原和北部地区的真菌种群，降低了29％。在研究年份中，降水量最高的情况下，通过CT进行的土地转换显着降低了顶部7.5 cm处的所有三种酶的活性。一般，CT地块的BG和BGA活性比草地或NT地块低约20％。与草原和北部地区相比，CT下的磷酸单酯酶活性分别显着降低了28％和18％。在7.5–15 cm的深度范围内，草地控制区和NT区的BG和BGA活动表现出垂直分层，其中CT区的BG和BGA活动最高，降水量更高。在7.5–15 cm的深度上，土地转化对PHOS的活动没有影响。在草地转化为耕地的第一年，尤其是耕种，土壤微生物生物量和酶活性可能会显着下降，这意味着碳和养分循环潜力降低。