渭北旱塬矮砧密植苹果园土壤矿质氮积累与空间分布特征

随着苹果矮砧密植栽培模式的迅速发展,揭示矮砧密植苹果园土壤矿质氮的积累与分布特征对果园科学施肥具有重要意义。本研究以不同树龄(6 a、9 a、12 a)的矮砧密植苹果园为对象,在树下、株间、行间以及树干与行间的中间点位置采集土样,分析土壤硝态氮、铵态氮和矿质氮的积累与分布特征。结果表明:0～300 cm土层土壤硝态氮累积量随果园树龄的增大而增加,不同树龄的果园之间差异显著,表现为6 a＜9 a＜12 a,硝态氮累积量由1729 kg·hm^-2增长到3771 kg·hm^-2;而各树龄果园的铵态氮含量较低,对矿质氮的积累与空间分布特征基本不构成影响。在垂直方向上,硝态氮存在两个累积峰,第2个累积峰所在的土层深度随果园树龄的增大由180 cm下移到220 cm;在水平方向上,行间位置的硝态氮含量随果园树龄的增大由27 mg·kg^-1增长到138 mg·kg^-1,涨幅超过400%,各树龄果园之间差异显著。综上,各树龄果园均存在氮肥施用过量和硝态氮淋溶严重的问题,生产中应减少果园的氮肥施用量,同时应在施肥位置布设防渗措施阻止硝态氮向土壤深层淋溶。

Mineral nitrogen accumulation and its spatial distribution in soils in dense planting dwarf rootstock apple orchard on the Weibei dry plateau,Northwest China

With the rapid development of dense apple tree plantings with the dwarf rootstock cultivation method,determining accumulation and distribution characteristics of soil mineral nitrogen in densely planted orchards with dwarf rootstock is important to enable scientific fertilization of apple orchards.We investigated densely planted apple orchards with dwarf rootstocks and different plant ages(6 a,9 a,and 12 a).We collected soil samples under trees,between trees,between rows,and at the midpoints between the trees and rows,and examined the accumulation and distribution characteristics of nitrate,ammonium,and mineral nitrogen.The cumulative amount of nitrate in the 0-300 cm soil layer increased with plant age.The difference between orchards with different plant ages was significant and showed the trend 6 a<9 a<12 a.The cumulative amount of nitrate increased from 1729 kg·hm^-2 to 3771 kg·hm^-2 with increasing plant age.The ammonium content was low for orchards of all plant ages and had little effect on the accumulation and spatial distribution of mineral nitrogen.There were two accumulation peaks of nitrate nitrogen in the vertical direction.The depth of soil layer where the second accumulation peak was located decreased from 180 cm to 220 cm with increasing plant age.In the horizontal direction,soil nitrate nitrogen content between rows increased from 27 mg·kg^-1 to 138 mg·kg^-1 with increasing plant age,representing a more than 400% increase.The difference between orchards with different plant ages was significant.In summary,excessive usage of nitrogen fertilizer and serious leaching of nitrate were problematic in all orchards with different ages.Less nitrogen fertilizer should be applied,and anti-seepage measures should be used at the fertilization location to prevent the leaching of nitrate to deep layers.