苹果氮素高效利用的根层土壤氮素调控机制

Appling nitrogen at high rate year by year in apple production in China not only results in low N use efficiency but also brings problems about soil degradation and environmental pollution. So, how to realize high yield and high nitrogen use efficiency cooperatively is very important. From bloom stage to pre-harvest stage, the required N of tree growth mainly comes from soil, so the nitrogen supply intensity in root layer is the key to safeguard the nitrogen requirement and the core of reduced nitrogen losses. We hypothesis that there may be exist a suitable nitrogen concentration in root layer which can meet the required N quantity of apple at different development stages, and can minimize nitrogen losses. Therefore, this study intends to study the effects of root layer soil nitrogen concentration on tree growth, then combination of nitrogen demand rule in different development stages, to establish a theoretical root layer soil nitrogen suitable concentration, further validated by field experiment and feedback adjustment, explore the prolific apple root layer suitable nitrogen concentration range and the corresponding control measures, in order to realize the improvement of high yield and high nitrogen use efficiency cooperatively.

近年来，我国苹果园氮肥用量持续增加，过量施氮不仅导致氮肥利用效率低，还带来了土壤质量下降和环境风险增大等问题，因此在苹果高产条件下如何实现氮肥高效利用具有非常重要的意义。从花期到采收前，果实生长发育所需的氮素主要来自于土壤，根层氮素供应强度既是保障苹果氮素需求的关键，又是降低氮素向环境损失的核心。我们设想如果能把根层土壤氮素浓度维持在既可以满足不同生育时期苹果对氮素的需求，又可以最大限度地减少氮素损失的范围内，则有可能实现苹果产量和氮肥利用效率的协同提高。因此，本研究拟研究根层土壤氮素浓度对树体生长发育的影响机制，依据不同生育期苹果氮素需求规律，建立理论的不同生育期的适宜根层土壤氮素浓度，进一步通过田间试验进行验证和反馈调节，探寻高产苹果根层适宜的氮素浓度范围和相应的调控措施，以实现苹果产量与氮肥利用效率的协同提高。

项目针对当前苹果生产中苹果高产和氮素高效难以协调的问题，基于苹果氮素需求规律，以根层氮素调控为核心，以矮化苹果为研究对象，采用水培、盆栽和田间试验开展了苹果年周期氮素需求规律及累积动态、苹果根层氮素适量稳定供应机制、苹果关键生育期氮素供应限量阈值和苹果根层氮素调控措施研究。主要结果表明，萌芽后30~60 d、120~150 d和150~180 d是6年生烟富3/SH6/平邑甜茶氮素积累与对肥料氮素吸收的最大效率期。苹果生育初期新生器官中结构性氮含量最高，果实在迅速膨大时对营养性氮有较高需求。适量稳定供氮通过提高叶片硝酸还原酶活性、Rubisco活性和Z+ZR、GA3含量，改善了苹果幼苗光合性能，增加了光合产物向根的分配，促进了根系对氮素的吸收。基于植株对肥料氮的吸收利用、氮素土壤残留和土壤氮库盈亏平衡，提出了基于土壤氮素平衡的氮素供应限量标准，萌芽至新梢旺长期、营养转换期和果实膨大期土壤氮素供应限量标准分别为59.27 kg/ha、51.30 kg/ha和77.20 kg/ha。通过应用控释氮肥、增施黄腐酸和生物炭，果园生草以及合理负载协调地上部营养生长与生殖生长和膨大期氮素总量控制、分次施氮技术可实现根层氮素稳定供应，协同实现苹果生长与氮素高效利用。