不同施肥模式下设施菜田土壤团聚体养分和微生物量特征

Characteristics of nutrients and microbial biomass in soil aggregates under different fertilization modes in greenhouse vegetable production

【目的】针对设施蔬菜生产中普遍存在的化肥施用严重超量、化肥与有机肥配施模式不合理等现象,利用日光温室蔬菜有机肥/秸秆替代化肥模式定位试验,研究了不同施肥模式对设施菜地土壤团聚体养分、微生物量碳氮含量的影响,为设施蔬菜优质高效生产和减量施用化肥提供科学依据。【方法】将25%或50%的无机氮肥用玉米秸秆或猪粪中氮替代,进行温室蔬菜田间定位试验。试验共设5个处理(各处理等氮、等磷、等钾):1)全部施用化肥氮(4/4CN);2) 3/4化肥氮+1/4猪粪氮(3/4CN+1/4MN);3) 2/4化肥氮+2/4猪粪氮(2/4CN+2/4MN);4) 2/4化肥氮+1/4猪粪氮+1/4秸秆氮(2/4CN+1/4MN+1/4SN);5) 2/4化肥氮+2/4秸秆氮(2/4CN+2/4SN)。在定位试验第6年冬春茬黄瓜季拉秧期采取耕层土壤样品,分析土壤团聚体分布规律和稳定性,并测定各粒级团聚体中土壤养分和微生物量碳、氮含量。【结果】设施菜地土壤团聚体以250~1000μm团聚体和> 2000μm团聚体为主,其含量分别平均为32.0%和38.4%。较4/4CN模式,有机肥/秸秆替代化肥模式提高了土壤大团聚体(> 250μm)比例。配施秸秆模式对土壤团聚体分布影响相对较大,并显著提高土壤团聚体机械稳定性,平均重量直径(MWD)和平均几何直径(GMD)分别提高6.1%和11.2%。在<250μm团聚体、250~1000μm团聚体、1000~2000μm团聚体和> 2000μm团聚体中,不同有机肥化肥配施模式(3/4CN+1/4MN、2/4CN+2/4MN、2/4CN+1/4MN+1/4SN、2/4CN+2/4SN)土壤有机碳含量较4/4CN模式分别增加36.8%~89.6%、34.9%~100.3%、29.5%~69.2%和21.7%~72.1%,分别平均增加69.8%、76.6%、56.9%和49.2%。不同施肥模式对有机碳、全氮、硝态氮、速效磷的影响规律基本一致。土壤有机碳、全氮主要分布在250~1000μm团聚体和> 2000μm团聚体中,平均分别占土壤有机碳储量的34.1%、35.2%和土壤全氮储量的34.0%、36.4%。土壤硝态氮在250~1000μm团聚体与1000~2000μm团聚体中含量较高,土壤速效钾、微生物量碳氮含量表现为随土壤团聚体直径的增大而提高,而速效磷则随土壤团聚体直径的增大而降低。【结论】设施菜田土壤团聚体优势粒级为> 2000μm团聚体和250~1000μm团聚体,配施秸秆模式显著提高土壤团聚体的机械稳定性。有机肥/秸秆替代化肥模式提高土壤各级团聚体有机碳、全氮、硝态氮和速效磷含量。设施菜地土壤有机碳氮主要分布在250~1000μm团聚体和> 2000μm团聚体中,而微生物量碳、氮含量随土壤团聚体直径的减小而呈增加的趋势。

【Objectives】Excessive application of chemical fertilizers or unreasonable combined application of chemical and organic fertilizers is a common practice in greenhouse vegetable production. Therefore, a fixed-site greenhouse vegetable fertilization experiment was carried out to study effects of partial substitution of chemical fertilizer with organic amendments on nutrient and soil microbial biomass carbon (MBC) and nitrogen (MBN) distribution of soil aggregates in order to provide a scientific basis for high quality and efficient vegetable production in greenhouse and fertilizer reduction.【Methods】The greenhouse field experiment was started in 2009, with 25% or 50% nitrogen of inorganic fertilizer replaced by nitrogen of corn straw or pig manure. Soil samples were collected from each plot at 0–20 cm depth during the uprooting stage of the 11th growing season (winter-spring cucumber) in the sixth year. The distribution and stability of soil aggregates, nutrient and MBC and MBN contents of soil aggregates were determined.【Results】1) The predominant size fractions in greenhouse vegetable soil were 250–1000 μm fractions and > 2000 μm fractions, which accounted for 32.0% and 38.4% on average by weight, respectively. Compared with 4/4CN treatment, organic amendments increased the proportion of >250 μm fractions. And soils amended with straw had a relatively large impact on the distribution of soil aggregates, following with a significantly improvement in soil aggregate stability. The MWD and GMD values in straw-treated soil were 6.1% and 11.2% higher than those in 4/4CN-treated soil, respectively. 2) The organic carbon content in organic-amended soil (3/4CN + 1/4MN, 2/4CN + 2/4MN, 2/4CN + 1/4MN + 1/4SN, 2/4CN + 2/4SN) was much higher than that in the 4/4CN treatment with the increasing ranges of 36.8%–89.6%, 34.9%–100.3%, 29.5%–69.2% and 21.7%–72.1% in < 250 μm fractions, 250–1000 μm fractions, 1000–2000 μm fractions and > 2000 μm fractions, respectively, which was respectively averagely increased by 69.8%, 76.6%, 56.9% and 49.2% compared with that of 4/4CN treatment. Actually, effects of the organic amendments on soil organic carbon, total nitrogen, nitrate nitrogen and available phosphorus were basically the same. 3) The organic carbon and total nitrogen in 250–1000 μm fractions and > 2000 μm fractions were the main sources of the organic carbon and nitrogen in the soil, which accounted for 34.1% and 35.2% of the total organic carbon stocks, and 34.0% and 36.4% of the total nitrogen stocks, respectively. 4) The content of soil nitrate nitrogen was higher in 250–1000 μm fractions and 1000–2000 μm fractions than that in other aggregate fractions. Soil readily available potassium, MBC and MBN contents increased with the increasing of soil aggregate-size, whereas soil available phosphorus decreased with the increasing of soil aggregate-size.【Conclusions】The predominant size fractions in greenhouse vegetable soil were 250–1000 μm fractions and > 2000 μm fractions. And soil aggregate stability was significantly improved by partial substitution of chemical fertilizer with straw. Partial substitution of chemical fertilizer with organic amendments increased the content of organic carbon, total nitrogen, nitrate nitrogen and available phosphorus in soil aggregates. The organic carbon and total nitrogen were mainly stored in 250–1000 μm fractions and > 2000 μm fractions, while MBC and MBN contents increased with the decreasing of soil aggregate-size.