Short-term changes in chemical and microbial characteristics of paddy soil in response to consecutive addition of organic ameliorants in a rice–rice–vegetable rotation system

With regard of the problems of soil acidification and soil degradation caused by high intensive planting in south China, a 2-year pot experiment consisting of six harvests under a rice–rice–vegetable rotation cropping system was conducted to assess the effects of NPK+ rice straw (RS) and combined application of RS with peanut bran, biochar, and organic fertilizer on soil chemical and microbial characteristics in paddy soil. The control treatment received chemical fertilizer alone. Results showed that RS and the combination of RS with organic ameliorants, especially NPK+ rice straw + biochar (RSBC) treatment led to the greatest improvement of soil pH, soil organic carbon, microbial biomass carbon, and total nitrogen (TN) content, and urease (UE), acid phosphatase (ACP) and catalase (CAT) activities concurrently without yield sacrificing, which inferred that RSBC treatment could be an effective measure to alleviate soil acidification, boost carbon sequestration and nutrients content as well as soil enzyme activities in rice-rice-vegetable rotation system. Besides, Pearson’s correlation analysis showed that soil mineral nitrogen (N_min) content was negatively related to pH, and the available potassium (AK) content was positively related to UE and CAT activity but negatively related to ACP activity. Canonical correspondence analysis demonstrated the N_min and AK explained 27.2% and 13.7% of the variation in microbial species, respectively. Therefore, it is believed that soil N_min and AK content could be the primary factors of soil microbial properties under the rice-rice-vegetable rotation system.

针对中国南方高强度种植引发的土壤酸化与土壤退化问题，本研究开展了为期2年、稻-稻-蔬菜轮作体系下共6次收获的盆栽试验，以评估氮磷钾（NPK）配施水稻秸秆（rice straw, RS）、以及RS与花生麸、生物炭、有机肥配施对稻田土壤化学及微生物特性的影响。对照组仅施用化肥。研究结果显示，RS及其与有机改良剂配施的处理，尤其是NPK+水稻秸秆+生物炭（RSBC）处理，可在不降低作物产量的前提下，显著提升土壤pH值、土壤有机碳、微生物生物量碳、全氮（total nitrogen, TN）含量，以及脲酶（urease, UE）、酸性磷酸酶（acid phosphatase, ACP）和过氧化氢酶（catalase, CAT）活性。这表明RSBC处理可作为稻-稻-蔬菜轮作体系中缓解土壤酸化、提升固碳能力与养分含量，以及改善土壤酶活性的有效措施。此外，皮尔逊相关性分析显示，土壤矿质氮（N_min）含量与pH值呈负相关；而速效钾（available potassium, AK）含量与UE、CAT活性呈正相关，与ACP活性呈负相关。典范对应分析表明，N_min与AK分别解释了微生物群落27.2%和13.7%的变异。因此，本研究认为，在稻-稻-蔬菜轮作体系下，土壤矿质氮与速效钾含量可能是影响土壤微生物特性的核心因素。