氮磷在水稻土不同发生层中的穿透性研究

Transport of phosphorus and nitrogen species in different genetic horizons of paddy soils

为了解氮磷在不同类型水稻土发生层中的迁移特性,从浙江省宁波市和湖州市采集了27个水稻土主要发生层的原状土柱,通过饱和稳定流土柱运移试验,测定了氮和磷在不同发生层中的运移穿透曲线,用平均穿透点评估了NO-3-N、NH+4-N和PO34--P在各发生层中的穿透性。结果表明,氮和磷在各发生层中的穿透能力依次为:NO-3-N>NH+4-N>PO34--P;NO-3-N在各发生层中的穿透能力依次为:漂洗层(E层)>渗育层(P层)>表土层(A层)>腐泥层(M层)>潴育层(W层)>潜育层(G层)>犁底层(Ap层),NO-3-N的穿透能力主要与土壤饱和导水率有关,随饱和导水率增加而增强;NH+4-N穿透能力依次为:E层>P层>A层>W层>M层>Ap层>G层,NH+4-N穿透能力主要与饱和导水率和粘粒有关,迁移受粘粒明显阻滞;PO34--P穿透能力依次为:E层>W层>P层>M层>A层、Ap层>G层,PO34--P穿透能力主要受氧化铁等氧化物和粘粒的阻滞。

Breakthrough experiments were performed on 27 undisturbed soil columns, which were taken from different genetic horizons of paddy soils in Ningbo and Huzhou of Zhejiang, to study the gravity downward transport （mobility） of NO3^--N, NH4^＋-N and PO4^3--P in the soil samples. The mean breakthrough points （volumes of void column at 0. 5） of NO3^--N, NH4^＋ -N and PO4^3- P were estimated from the respective breakthrough curves to evaluate the relative mobility of those species in the soil columns. NO3^--N was found to be the most mobile species, followed by NH4^＋ -N and PO4^3- -P. The order of declining mobility of NO3^- -N in the horizons was albic layer〉percogenetic layer〉 cultivated layer〉muck layer 〉 hydrogric layer 〉 gleyed layer 〉 plowpan; the order of declining mobility of NH4^＋ -N was： albic layer〉percogenetic layer〉cultivated layer〉hydrogric layer〉muck layer〉plowpan〉gleyed layer and that of PO4^3--P was： albic layer〉 hydrogric layer〉 percogenetic layer〉 muck layer〉 cultivated layer, plowpan〉 gleyed layer. The correlation analysis results have shown that the mobility of NO3^--N was positively related to hydraulic conductivity of the soil samples; the soil of a higher conductivity was more mobile and had a smaller mean breakthrough point. The mobility of NH4^＋ -N was also positively related to the soil＇s hydraulic conductivity but negatively related to its clay content. The mobility of PO4^3- -P was reduced by the amorphous iron oxides present in the soil sample.