地表滴灌水氮耦合对毛白杨幼林生长及土壤水氮分布的影响

Coupling effects of water and nitrogen on tree growth and soil water-nitrogen distribution in young Populus tomentosa plantations under surface drip irrigation

为探究地表滴灌水氮耦合对毛白杨生长及土壤水氮分布的影响,以2年生三倍体毛白杨人工林为研究对象,研究2种灌水处理(W20、W45)和3种施氮水平(80、150、220 kg/(hm2·a))下滴头正下方0～80 cm土层土壤含水率(soil water content,SWC)和无机氮(Nmin)的动态变化规律,结合林木生长情况,明确2年生三倍体毛白杨最佳水氮耦合策略。结果表明:W20处理能显著促进4-7月林木胸径生长(P<0.05),水氮因子尚未表现出交互作用(P>0.05)。灌溉能显著影响SWC,旱季(4月底至6月中旬)W20处理平均SWC达到11.3%,较空白对照(CK)提高37.5%;雨季(6月下旬至8月初)SWC受降雨影响整体提升,处理间差异不显著(P>0.05)。旱季Nmin在0～80 cm土层逐渐积累,集中分布在0～20 cm表土层,且随施氮量增加而增加;雨季Nmin向深土层移动,W20处理Nmin出现深层淋溶,W45处理各土层Nmin分布均匀,其中W45N150处理0～80 cm土层Nmin平均质量分数达到44.27 mg/kg,显著高于其他处理(P<0.05)。生长季末各处理Nmin均增加,在土层中产生积累。综上,N150处理能保证整个生长季内0～80 cm土层充足的氮素含量,结合林木生长情况判断,4-7月W20处理能显著促进毛白杨幼林生长(P<0.05),8月份开始W45处理即可满足林木生长对水分的需求。

Soil water and nitrogen nutrients are key factors affecting forest growth,especially for young triploid Populus tomentosa.Water and fertilizer factors have synergistic effects,water deficit can inhibit the absorption of nutrients in forests,and excessive irrigation can easily cause nutrient leaching.Although excessive fertilization can improve the water and nitrogen use efficiency under certain conditions,the large amount of nitrogen remaining in the soil is bound to pollute the environment.At present,many scholars have simulated the soil moisture and nitrogen transport under drip irrigation through indoor soil column simulation test.The research on soil water and nitrogen transport in the field is mainly concentrated in the agricultural and horticultural field,and the key is to monitor nitrogen leaching and nitrogen balance.In the field of forestry,due to the complexity of field conditions and the simplification of evaluation indicators,most studies focus on the effects of different water-nitrogen coupling strategies on tree growth and physiological indicators,few researches were on the distribution of water and nitrogen in root zone.In order to explore the effects of water and nitrogen coupling treatments on growth of Populus tomentosa and water-nitrogen distribution in soil,a field experiment was conducted about 2-year-old triploid Populus tomentosa to investigate the effects of two irrigation levels(W20,W45)and three fertilizer levels(N80,N150,N220)coupling treatments on increment of diameter at breast height(DBH),dynamic distribution of soil water content(SWC)and mineral nitrogen content(Nmin)in 0-80 cm soil depth under drip emitter in growing season.Results showed that W20 treatment promoted the growth of DBH during April to July significantly(P<0.05),the interaction of irrigation and fertilizer factors was not significant(P>0.05).SWC was influenced greatly by irrigation treatment,which showed that the SWC of W20 treatment had reached 11.3%in dry season(from the end of April till the middle of June),37.5%higher than blank control.There was no significant difference in different treatment(P>0.05)in rainy season(from the late June to early August),because SWC was influenced greatly by precipitation.Nmin was accumulated in 0-80 cm soil layer during dry season,especially in 0-20 cm soil layer,which showed positive correlation with fertilization.Nmin moved from topsoil towards deep soil in rainy season,which leached below 80 cm soil layer in W20 treatment and increased uniformly in 20-80 cm soil layers in W45.The average Nmin in 0-80 cm soil layer reached to 44.27 mg/kg in W45N150 treatment in rainy season,which was significant higher than other treatments(P<0.05).Nmin accumulated in 0-80 cm soil layer at the end of growing season.To sum up,N150 treatment can provide adequate nitrogen content in 0-80 cm soil layer in growing season.Combined with the growth of young trees,W20 treatment can promote the growth significantly during April to July(P<0.05),and W45 treatment can meet the water demand for growth of the tree after July.