优化施肥方式提高覆膜栽培冬小麦籽粒蛋白质含量的机制

Plastic film mulching (PM) increased dryland wheat yield, but reduced the grain protein content. The main reasons for the decline in grain protein content were the insufficient supply of soil water and nitrogen (N) and the weakening of root absorption capacity after flowering. At present, the PM is typically carried out by fertilizing, rotary tilling, ridging, mulching plastic film on the ridge, and planting wheat in the furrow. Because the position of the ridge is higher than the distribution of wheat roots, the soil water and N in 0-10 cm soil layer under the ridge is not easily to be utilized by wheat, resulting in insufficient soil water and N supply after flowering. In response to this problem, optimizing chemical fertilizer application in PM would be used to improve the capacity of soil water and N supply and root absorption after flowering, thus increase above-ground N uptake and grain protein content. The methods including 15N isotope tracer method and field in situ sampling were used to explore: (1) soil N and water spatial distribution and dynamic changes after flowering, (2) the spatial and temporal distribution of roots, and the absorption, transport and utilization of N of post-flowering, and (3) protein formation and accumulation of wheat grain. Results obtained in the project will identify the agronomic and nutrient mechanisms for optimizing fertilizer application to increase grain protein content and provide a theoretical basis for high-yield and high-quality production of dryland wheat.

覆膜栽培增加了旱地小麦产量，但降低了籽粒蛋白质含量。前期研究表明小麦花后土壤水氮供应不足、根系吸收能力弱化导致的花后地上部吸氮量低是覆膜栽培降低籽粒蛋白质含量的主要原因。目前的覆膜栽培通常是肥料撒施后旋耕、起垄，垄上覆膜、沟内种植小麦。由于垄的位置高出了小麦根系分布范围，以至垄下0-10 cm土层的水氮不易被吸收利用，导致种植于沟内的小麦花后土壤水氮供应不足。针对这个问题，本项目提出优化施肥方式能改善覆膜栽培小麦花后土壤水氮供应强度和根系吸收能力，进而提高小麦地上部吸氮量和籽粒蛋白质含量的科学假设。采用15N同位素示踪法和田间原位取样法，研究小麦花后土壤氮素和水分空间分布与动态变化，确定小麦根系时空分布及其花后对氮素的吸收、转运和利用，结合土壤温度与小麦籽粒蛋白质形成和累积过程的协同分析，查明优化施肥方式提高覆膜栽培小麦籽粒蛋白质含量的农学和营养机制，为旱地小麦高产优质生产提供理论依据。

土壤瘠薄和水分不足是西北旱区作物生产的主要限制因素。覆膜栽培通过改善土壤水热条件提高产量，广泛应用于我国农业生产。然而，传统覆膜栽培（PM1）花后土壤养分供应不足，小麦籽粒蛋白质含量降低。优化施肥方式是解决当前问题有效途径之一。因此，布设田间试验，分析小麦花后土壤水氮空间分布及动态变化，基于15N同位素示踪查明花后小麦对氮素的吸收转运，结合籽粒蛋白形成累积过程，分析优化施肥方式增加小麦籽粒蛋白质含量的机制。结果表明，相对于传统平作，膜侧沟内施肥（PM2）和种侧膜下施肥（PM3）增加小麦籽粒产量12%和17%，未降低小麦籽粒蛋白质含量。与PM1相比，PM2小麦籽粒产量和蛋白质含量提高4%和7%，PM3提高9%和13%。相对于PM1，PM2开花和收获期麦行0-20 cm土层肥料氮供应增加188%和114%，且花后28天麦行0-10 cm土层储水量增加9%，从而增加花后0、14和28天麦行0-10 cm土层根重密度10%，46%和14%。因此，PM2花后0、14和28天茎叶来自肥料的氮吸收增加44%，42%和47%，从而增加茎叶花后28天总氮吸收量22%，促进花后28-48天茎叶氮素转运和籽粒氮累积，增加花后35天和收获期醇溶蛋白21%和20%。相对于PM1，PM3增加开花至收获期麦行0-20 cm土层硝态氮累积44-114%，增加开花和收获期0-10 cm土层肥料氮供应107%和80%；同时增加花后28天和收获期麦行20-40 cm土层储水量6%和8%，以及生育期平均土壤温度0.12 oC；从而提高花后0、14和28天麦行0-10 cm土层根重密度25%，39%和21%。因此，PM3花后14、28和48天籽粒来自肥料的氮吸收增加89%、82%和51%，以至于花后21、28、35天和收获期醇溶蛋白增加17-28%，从而提高小麦籽粒蛋白质含量。总之，优化氮管理能够实现旱地农业覆膜栽培小麦高产优质。