有机肥替代化肥比例对椪柑生长发育、产量和土壤生物学特性的影响

  【目的】  通过研究等氮磷钾养分条件下，有机肥替代化肥比例对椪柑生长、养分吸收、产量和土壤微生物性状的影响，提出适宜的有机替代比，为柑橘化肥减量与提质增效技术提供理论依据。  【方法】  于2019、2020年在重庆连续进行田间试验，供试材料为15年生枳砧台湾椪柑(Citrus reticulata Blanco cv. Ponkan)。设置CK (不施肥)、FP (单施化肥)、T1 (有机替代率为氮10%、磷25%、钾18%)、T2 (有机替代率为氮15%、磷38%、钾27%)、T3 (有机替代率氮20%、磷51%、钾36%)、T4 (有机替代率为氮30%、磷76%、钾54%)共6个处理，除CK外，各施肥处理的氮、磷、钾养分一致。调查分析椪柑生长、养分吸收、产量和肥料贡献率及土壤微生物特性。  【结果】  1)与FP相比，有机肥替代处理(T1至T4)增加了根系量、根系活力和枝梢生长量，显著增加了细根(直径0～0.5 mm)比例，且增加幅度随有机替代比的增大而提高；有机替代处理的春梢叶片SPAD、P_n、PI_abs和PI_total等较FP处理均有不同程度的提高，并随有机替代比的增大呈先升后降的趋势；以T2和T3处理对椪柑生长发育较好；2) 2019和2020年有机肥替代处理的枝梢和果实N、P和K积累量相比FP有一定程度的增加，且随有机替代比的增加均呈先升后降的趋势；2019和2020年各有机肥替代处理较FP处理平均增产了7.2%～26.4%和2.0%～36.9%，肥料贡献率比FP处理分别提升了5.2%～45.4%和3.3%～54.9%，但随有机替代比的增加呈先升后降的趋势，以T2和T3处理促进养分积累和增产的效果较好；3)有机肥替代处理的根际土壤脲酶、蔗糖酶活性及可培养的细菌和放线菌数量较FP均有所增加，且随有机替代比的增大而增加，7月时达最大，而土壤可培养真菌数量表现出先增后减的趋势，以T3和T4处理对土壤微生物特性较好。  【结论】  等氮磷钾养分情况下，有机肥替代化肥促进了椪柑侧根根系特别是细根和春、秋枝梢的生长发育，改善了叶片的光合作用，提高了枝、叶、果对养分的积累和椪柑产量，改善了果园土壤生物学特性。本试验条件下，以有机替代15%～20%的氮肥、38%～51%的磷肥和27%～36%的钾肥的效果最好。

Effects of partial substitution of chemical fertilizer with organic fertilizer on Ponkan growth and yield and soil biological properties

  【Objectives】  We studied the effects of substituting chemical fertilizer with organic fertilizer on growth, nutrient accumulation and yield of Ponkan, and soil microbial properties under equal nutrient supply. We determined the appropriate quantity of organic fertilizer that can be substituted for chemical fertilizer, providing the theoretical basis for reducing the latter and enhancing the efficiency of agricultural technology.   【Methods】  Using 15-year-old Taiwan Ponkan (Citrus reticulata Blanco cv. Ponkan) grafted on Poncirus trifoliata (L.) as test material, field experiments were conducted in 2019 and 2020 in Chongqing. The six treatments included no fertilizer application [i.e., control (CK)], pure chemical fertilizer application (FP), N, P and K substitution ratio of 10%, 25%, and 18% (T1), substitution ratio of 15%, 38%, and 27% (T2), substitution ratio of 20%, 51%, and 36% (T3), and substitution ratio of 30%, 76%, and 54% (T4). Except for CK, the treatments’ N, P and K nutrient input was consistent. The growth, nutrient accumulation, yield and fertilizer contribution to yield and soil microbial properties were analyzed.   【Results】  1) The root activity and growth of branches with organic fertilizer were higher than FP. Organic fertilizer application (P<0.05) increased the proportion of fine roots (0–0.5 mm). Compared with FP, SPAD, P_n, PI_abs and PI_total were promoted to a certain extent, increasing with organic fertilizer application at first and subsequently decreasing. Moreover, T2 and T3 recorded higher Ponkan growth than other treatments. 2) In 2019 and 2020, branch accumulation and fruit N, P and K in the organic fertilizer substitution treatments was higher than FP. However, there were fluctuations in the recorded increase. Compared with FP, the yield in each organic fertilizer substitution treatment increased by 7.2%–26.4% and 2.0%–36.9%, respectively, compared with FP, and the fertilizer contribution rate increased by 5.2%–45.4% and 3.3%–54.9%. With increasing organic fertilizer application, fruit yield and fertilizer contribution rate fluctuate, with T2 and T3 recording higher values. 3) Sucrase and urease enzyme activity and the number of cultivatable bacteria and actinomycetes treated with organic fertilizer were higher than FP, reaching the highest in July and increasing with organic fertilizer application. The number of cultivatable soil fungi increased at first and subsequently decreased, with T3 and T4 having higher soil microorganisms.   【Conclusions】  Substituting chemical fertilizer with organic fertilizer under equal nutrient supply can promote the growth and development of lateral roots, especially fine roots and spring and autumn shoots, enhance the photosynthesis of leaves, improve nutrient accumulation in leaves, twigs and fruits, especially yield of Ponkan and promote soil microbial characteristics. Overall, the optimum substitution ratio was 15% to 20% for N, 38% to 51% for P, and 27% to 36% for K.