施氮水平对旱塬覆沙苹果园土壤酶活性及果实品质的影响

研究土壤酶活性及果实品质在不同氮肥水平下的变化规律,探讨氮肥施用量对土壤酶活性与果实品质相关性的影响,为旱塬覆沙苹果园合理施氮、提高氮素利用率及降低土壤环境污染建立科学依据。通过田间试验,以‘长富2号’为试验材料,设置5个氮素水平(对照0、165、330、495和660kg/hm~2,分别简写为CK、N1、N2、N3和N4),并于2017年测定土壤全氮含量、土壤酶活性与果实品质。结果表明:土壤全氮随着施氮量增加而升高;0～20和 20～40 cm土层中脲酶和磷酸酶活性在N2处理下均达到最大值,而蔗糖酶活性则于N3处理下最高;40～60 cm土层中过氧化氢酶活性随氮肥增施呈上升趋势。在330～495 kg/hm~2施氮范围内,与对照相比,增施氮肥能够显著提高果实横径、可溶性固形物、可滴定酸、维生素C及总糖含量(P0.05)。随着施氮量增加,果实产量呈先降后升趋势。土壤过氧化氢酶(除 20～40 cm土层)、蔗糖酶活性与果实可溶性固形物含量具有极显著相关性(P0.01),与可滴定酸和 40～60 cm土层中维生素C含量具有显著相关性(P0.05)。综合分析认为,330～495kg/hm~2为旱塬覆沙苹果园合理施氮范围,对提高土壤酶活性及氮肥利用率效果显著,并有利于改善果实品质。

Effects of nitrogen fertilizer levels on soil enzyme activity and fruit quality of sand-covered apple orchard in Loess Plateau of Eastern Gansu

Abstract: Large-scale application of nitrogen fertilizer has made a great contribution to improving crop yield. However, excessive nitrogen application is a common and serious problem in orchards, not only reduces nitrogen use efficiencies of trees, but also causes potential environmental problems. Accordingly, reasonable nitrogen application is an important strategy for increasing yield and maintaining a sustainable agroecosystem. The objective of this research was to elucidate the variation regularity of soil enzyme activity and fruit quality in apple orchard, and their correlations were analyzed, so as to provide a scientific basis for reasonable nitrogen application, enhancing nitrogen utilization rate, and reducing the environmental pollution. In this study, a field experiment was conducted with ''Nagafu 2'', and five nitrogen fertilizer treatments (Control: CK, 165 kg/hm2: N1, 330 kg/hm2: N2, 495 kg/hm2: N3, and 660kg/hm2: N4) was established in 2015. The soil total nitrogen content, soil enzyme activity, and fruit quality were measured in 2017. The results showed that the soil total nitrogen content was enhanced with increasing nitrogen application in the same soil depth, and yet it decreased with increasing of soil depth. It suggested that the effect of sand-covered on fertilizer conservation was obvious and the utilization of nitrogen fertilizer was improved. In soils at depth of 0-20 cm and >20-40 cm, the maximal activities of soil urease and phosphatase occurred under N2 treatment, while the maximal activity of invertase occurred under N3 treatment. The soil catalase activity was higher with increasing of nitrogen application in >40-60 cm soils. Compared with the control, the fruit horizontal diameter, soluble solid, titratable acidity, vitamin C, and total sugar content increased significantly when the nitrogen application rate was 330-495 kg/hm2 (P<0.05). With the increasing of nitrogen application, fruit yield decreased first and then increased. Excessive fertilization could significantly increase fruit yield (P<0.05). The soil urease, invertase, and phosphatase activities, as well as most quality index of apple were suppressed when nitrogen fertilizer application exceeded 495 kg/hm2. Significant (P<0.05) or remarkably significant (P<0.01) correlation was found between activities of soil catalase (except > 20-40 cm soil depth) and invertase and contents of soluble solid, titratable acidity. It is noteworthy that three kinds of soil enzyme activies have a significant negative correlation with soluble solid (P<0.05). Urease activity was significantly correlated with fruit yield (P<0.05), but was no significantly correlated with invertase activity (P>0.05). Therefore, invertase activity could be used as an indicator of soil fertility in sand-covered apple orchard. All of these results demonstrated that the optimal nitrogen fertilizer application could significantly (P<0.05) enhance soil enzyme activities and nitrogen utilization efficiency, and then improved fruit quality and yield in sand-covered apple orchard. According to the relationship between soil enzyme activity and apple fruit quality, the optimal nitrogen fertilizer application should be 330-495 kg/hm2. It could create a good soil biochemical environment for stable and high yield of apple orchards, and could also further improve the health of agricultural ecosystem.