• ISSN 1008-505X
  • CN 11-3996/S
Volume 27 Issue 10
Oct.  2021
Article Contents

Citation:

Effects of long-term incorporation of milk vetch combined with reduction of chemical fertilizer on yield, quality and soil fertility of early rice in Jiangxi

  •   【Objectives】  This study was conducted to evaluate the effects of incorporating different amounts of milk vetch combined with reduced chemical fertilizer on early rice yield and rice quality in a double rice cropping system in South China, in order to provide a theoretical basis for chemical fertilizer reduction and high-quality rice production in the region.  【Methods】  The 12-years long-term experiment located at Yujiang District of Yingtan City, Jiangxi Province was established in 2008. The seven treatments included winter fallow with no fertilization (CK), winter planting of milk vetch with no fertilization (MV), winter fallow with 100% chemical fertilization (F100, conventional fertilization), 15000 kg/hm2 milk vetch + 80% chemical fertilizer (G1F80), 22500 kg/hm2 milk vetch + 80% chemical fertilizer (G1.5F80), 30000 kg/hm2 milk vetch + 80% chemical fertilizer (G2F80), 37500 kg/hm2 milk vetch + 80% chemical fertilizer (G2.5F80). The effects of milk vetch rate on rice yield, yield components, appearance quality, starch content, protein content, fat content and amino acid composition were analyzed.  【Results】  Under the condition of 20% reduction of chemical fertilizer, different incorporation rate of milk vetch increased rice yield and the effective panicle. Compared with conventional fertilization treatment, the average yields in G2F80 and G2.5F80 treatments were increased by 6.3% and 8.0%, respectively. The yield of G2.5F80 treatment reached 7.17 t/hm2, and the effective panicle was significantly increased by 7.4%, compared with F100. Rate of milk vetch incorporation influenced the physico-chemical properties of soil. G2F80 significantly increased soil organic matter by 13.1% and total nitrogen by 12.8% while maintaining soil available nutrient content, compared with F100 treatment. Low incorporation rate of milk vetch under reduced fertilizer conditions equally reduced the appearance, palatability of rice. However, there was no significant difference in the appearance quality and cooking and eating quality of rice treated with between G2.5F80 and F100 treatments. Compared with F100 treatment, the protein content and total amino acid content in G2.5F80 treatment increased by 19.1% and 59.4%, respectively, and the essential amino acid content in MV treatment increased by 49.8%. The lysine and isoleucine contents of G1.5F80 treatment were the highest, with 147.6% and 145.7% increases compared to F100 treatment.  【Conclusions】  Incorporation of milk vetch under reduced chemical fertilizer application effectively improved soil fertility, thereby improving rice yield and nutritional quality. However, low incorporation rate would decrease the appearance and palatability quality of rice to some extent. Incorporation of 37500 kg/hm2 milk vetch combined with 80% chemical fertilizer elicited superior agronomic performance and nutritional quality.
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Effects of long-term incorporation of milk vetch combined with reduction of chemical fertilizer on yield, quality and soil fertility of early rice in Jiangxi

    Corresponding author: GAO Song-juan, gaosongjuan@njau.edu.cn
    Corresponding author: CAO Wei-dong, caoweidong@caas.cn
  • 1. College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China
  • 2. Institute of Soil & Fertilizer and Resource & Environment, Jiangxi Academy of Agricultural Sciences, Nanchang, Jiangxi 330200, China
  • 3. Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences/Key Laboratory of Plant Nutrition and Fertilizer, Ministry of Agriculture and Rural Affairs, Beijing 100081, China

Abstract:   【Objectives】  This study was conducted to evaluate the effects of incorporating different amounts of milk vetch combined with reduced chemical fertilizer on early rice yield and rice quality in a double rice cropping system in South China, in order to provide a theoretical basis for chemical fertilizer reduction and high-quality rice production in the region.  【Methods】  The 12-years long-term experiment located at Yujiang District of Yingtan City, Jiangxi Province was established in 2008. The seven treatments included winter fallow with no fertilization (CK), winter planting of milk vetch with no fertilization (MV), winter fallow with 100% chemical fertilization (F100, conventional fertilization), 15000 kg/hm2 milk vetch + 80% chemical fertilizer (G1F80), 22500 kg/hm2 milk vetch + 80% chemical fertilizer (G1.5F80), 30000 kg/hm2 milk vetch + 80% chemical fertilizer (G2F80), 37500 kg/hm2 milk vetch + 80% chemical fertilizer (G2.5F80). The effects of milk vetch rate on rice yield, yield components, appearance quality, starch content, protein content, fat content and amino acid composition were analyzed.  【Results】  Under the condition of 20% reduction of chemical fertilizer, different incorporation rate of milk vetch increased rice yield and the effective panicle. Compared with conventional fertilization treatment, the average yields in G2F80 and G2.5F80 treatments were increased by 6.3% and 8.0%, respectively. The yield of G2.5F80 treatment reached 7.17 t/hm2, and the effective panicle was significantly increased by 7.4%, compared with F100. Rate of milk vetch incorporation influenced the physico-chemical properties of soil. G2F80 significantly increased soil organic matter by 13.1% and total nitrogen by 12.8% while maintaining soil available nutrient content, compared with F100 treatment. Low incorporation rate of milk vetch under reduced fertilizer conditions equally reduced the appearance, palatability of rice. However, there was no significant difference in the appearance quality and cooking and eating quality of rice treated with between G2.5F80 and F100 treatments. Compared with F100 treatment, the protein content and total amino acid content in G2.5F80 treatment increased by 19.1% and 59.4%, respectively, and the essential amino acid content in MV treatment increased by 49.8%. The lysine and isoleucine contents of G1.5F80 treatment were the highest, with 147.6% and 145.7% increases compared to F100 treatment.  【Conclusions】  Incorporation of milk vetch under reduced chemical fertilizer application effectively improved soil fertility, thereby improving rice yield and nutritional quality. However, low incorporation rate would decrease the appearance and palatability quality of rice to some extent. Incorporation of 37500 kg/hm2 milk vetch combined with 80% chemical fertilizer elicited superior agronomic performance and nutritional quality.

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  • 水稻(Oryza sativa L.)是我国主要的粮食作物和我国65%以上人口的主食[1-2]。随着国民经济的发展和居民生活水平的提高,我国在提高粮食产量保障粮食安全的同时,也越来越重视稻米品质的提升[3-4]。在当前部分生产者片面追求水稻高产,长期过量且不均衡的投入化肥,造成土壤养分失衡[5]。利用大量冬闲田种植豆科绿肥,是我国南方稻田土壤培肥的重要措施。冬种绿肥能够有效增加作物产量,改善土壤质量,提高土壤肥力和资源利用效率,对粮食生产具有重要作用[6-8],紫云英作冬绿肥配施化肥可优化水稻产量构成因素,提高水稻产量和产量稳定性[6]。冬种紫云英能够有效促进水稻对氮、磷、钾养分的吸收,提高水稻养分累积量[9-11]。氮(N)是植物生长的关键营养元素,氮肥的施用对水稻产量和质量的提高具有关键作用[12]。磷(P)也是作物生长的重要元素,缺磷会直接影响植物光合产物的合成和对其他养分的吸收,增加水稻垩白指标,最终影响稻米产量、品质和食味值[13-14]。与单施化肥相比,冬种紫云英能够显著提高土壤有机质和全氮含量,培育土壤碳库和氮库,增加无机氮、有效磷和速效钾的供应[9,15-17]。冬种绿肥对土壤肥力的改善不仅体现在提升土壤质量等长期效应上,还有增加速效养分供应、促进后茬作物养分吸收的即时效应,对作物增产、提质有重要作用[18-20]。前人针对冬种绿肥提高土壤养分和水稻产量的研究较多,但鲜有冬种紫云英配施化肥对稻米品质影响的报道,冬种绿肥在提高水稻产量的基础上对稻米外观品质、蒸煮食味和营养品质的影响尚不清楚。因此,研究绿肥对水稻产量及稻米品质的影响具有十分重要的意义。本试验依托位于江西双季稻区的长期定位试验,研究冬种紫云英减施化肥在提高土壤肥力和水稻产量的基础上对稻米品质的影响。

  • 1.   材料与方法

      1.1.   试验地概况

    • 定位试验始于2008年,地点位于江西省邓家埠水稻原种场(东经116°85′,北纬28°21′)。早稻生育期内试验点气温与降水量如图1所示,其中2020年早稻生育期内总降水量为763.2 mm,平均气温 26.1℃。土壤类型为低丘红壤发育的红壤性水稻土。试验开始前土壤基础理化性质为 pH 5.82、有机质30.17 g/kg、全氮1.87 g/kg、全磷 0.43 g/kg、全钾31.3 g/kg、碱解氮 144 mg/kg、有效磷3.9 mg/kg、速效钾58.0 mg/kg。供试紫云英品种为赣紫1号,紫云英鲜草含水量为89%,干物质养分含量为N 2.59%、P 0.23%、K 1.86%。供试早稻品种为株二优35。

      Figure 1.  Precipitation and temperature during early rice growth period

    • 1.2.   试验设计

    • 田间试验采用随机区组设计,共设7个处理:1)冬闲不施肥对照(CK);2)不施化肥,冬种紫云英并全部翻压,紫云英还田量为22500 kg/hm2(MV);3)冬闲水稻季施100%化肥(F100);4)冬种紫云英,翻压15000 kg/hm2紫云英+80%化肥(G1F80);5)冬种紫云英,翻压22500 kg/hm2紫云英+80%化肥(G1.5F80);6)冬种紫云英,翻压30000 kg/hm2紫云英+80%化肥(G2F80);7)冬种紫云英,翻压37500 kg/hm2紫云英+80%化肥(G2.5F80)。每处理设3次重复,共21个小区,小区面积21 m2。早稻100%化肥处理为当地农民常规施肥量,分别为N 150 kg/hm2、P2O5 75 kg/hm2、K2O 120 kg/hm2;80%化肥施加量为N 120 kg/hm2、P2O5 60 kg/hm2、K2O 96 kg/hm2。晚稻化肥施肥量均为N 180 kg/hm2、P2O5 75 kg/hm2、K2O 150 kg/hm2;CK处理不施肥,其它处理肥料用量和施用方法相同,肥料类型与早稻相同。

      其中氮、磷、钾肥分别为尿素(N 46%)、过磷酸钙(P2O5 12%)、氯化钾(K2O 60%)。氮肥按照基肥占40%、分蘖肥占30%、穗肥占30%的施肥方式进行施用(分蘖肥在移栽后5~7 天撒施,穗肥在主茎穗长1~2 cm时施用),磷肥和钾肥全部用作基肥。

      CK和F100处理冬季空闲(不种任何作物),其它处理在冬季种植紫云英,紫云英播种量30 kg/hm2。在2019—2020年度,于2019年10月12日采用稻底套播的方式播种紫云英,各处理紫云英在2020年4月10日按各处理所需翻压量进行翻压,4月29日移栽水稻,7月17日收获早稻。各处理早稻生育期:CK和MV处理为108 天、F100处理为109 天、G1F80和G2F80处理为110 天、G1.5F80和G2.5F80处理为111 天。

    • 1.3.   样品采集及指标测定

      1.3.1.   水稻产量、产量构成因素及土壤农化性状
    • 于早稻成熟期(2020年7月17日)进行水稻测产和考种,并采集土壤样品。每小区全区收获测定水稻实际产量,选取100穴调查水稻有效穗数,计算平均有效穗数后选取3穴进行考种,测定每穗粒数、结实率和千粒重等产量构成因素。

      采用5点取样法在各小区内取0—20 cm 耕层土壤样品,剔除石砾和植物残体等杂物,经风干过筛后测定土壤肥力。土壤pH采用5∶1水土比,电位法测定[21];土壤有机质和全氮含量使用C/N元素分析仪(Flash Smart,Thermo Fisher Scientific,美国)测定;土壤有效磷含量采用0.5 mol/L碳酸氢钠浸提—钼锑钪比色法测定[21];土壤速效钾含量采用1 mol/L醋酸铵浸提—原子吸收法测定[21];无机氮(Nmin)采用 2 mol/L氯化钾浸提—连续流动分析仪(SAN++,Skalar,荷兰)测定。

    • 1.3.2.   稻米品质
    • 垩白率、垩白度参照国家标准GB/T 17891-2017《优质稻谷》分析。淀粉含量参照国家标准GB/T 15683-2008《大米直链淀粉含量的测定》分析。

    • 1.3.3.   蛋白质、脂肪和氨基酸
    • 脂肪含量参照国家标准GB/T 14772-2008《食品中粗脂肪的测定》分析。蛋白质含量采用凯氏定氮法[22]分析,测定精米中的含氮量后,再乘以换算系数 5.95,计算稻米中蛋白质含量。氨基酸含量采用5 mL 20 mmol/L 的盐酸溶液萃取1 h后,加入60 μL 硼酸盐缓冲溶液,快速混合,在涡旋状态下加入10 μL AccQ-2A 氨基酸衍生剂后置于55 ℃烘箱内衍生化反应,用高效液相色谱仪(1260,Agilent,美国),AccQ Tag氨基酸分析柱(150 mm×4.6 mm,5 µm,waters公司)测定水解氨基酸含量,分析7种必需氨基酸,即苏氨酸(Thr)、苯丙氨酸(Phe)、亮氨酸(Leu)、甲硫氨酸(Met)、异亮氨酸(Ile)、赖氨酸(Lys)和缬氨酸(Val),以及10种非必需氨基酸,即精氨酸(Arg)、酪氨酸(Tyr)、丙氨酸(Ala)、甘氨酸(Gly)、脯氨酸(Pro)、谷氨酸(Glu)、丝氨酸(Ser)、组氨酸(His)、氨基丁酸(Gaba)和半胱氨酸(Cys)[23]

    • 1.4.   数据统计与分析

    • 采用SPSS 21.0进行方差分析,采用Duncan法进行差异显著性检验(P < 0.05为差异显著)。

    2.   结果与分析

      2.1.   不同紫云英翻压量下的水稻产量及产量构成因素

    • 从2009—2020年的水稻平均产量可知,相比F100处理,G1F80和G1.5F80处理水稻产量无显著差异,继续增加翻压量后产量显著提高,G2F80和G2.5F80处理分别增产6.3%和8.0%,其中G2.5F80处理的产量最高,达7.17 t/hm2。与F100处理相比,不同翻压量紫云英配施80%化肥可提高水稻有效穗数,其中G2.5F80处理有效穗数最高,较F100处理显著提高7.4%。减施化肥20%条件下不同紫云英翻压量处理与F100处理的每穗粒数、结实率和千粒重指标无显著差异,均以G2.5F80处理最高(表1)。

      处理
      Treatment
      产量
      Yield
      (t/hm2)
      有效穗数
      Effective panicle
      (×104/hm2)
      每穗粒数
      Spikelets
      per panicle
      结实率
      Grain filling rate
      (%)
      千粒重
      1000-grain weight
      (g)
      CK3.42 ± 0.35 d128.80 ± 6.38 e80.81 ± 1.94 d83.71 ± 1.03 a26.76 ± 0.12 a
      MV3.81 ± 0.02 c144.72 ± 7.85 d90.50 ± 2.16 c83.23 ± 1.13 a26.78 ± 0.12 a
      F1006.64 ± 0.01 b208.21 ± 10.97 c109.93 ± 2.62 ab84.06 ± 1.17 a26.68 ± 0.14 a
      G1F806.75 ± 0.03 ab212.10 ± 10.57 bc107.58 ± 2.38 b83.93 ± 1.05 a26.69 ± 0.14 a
      G1.5F806.90 ± 0.03 ab214.66 ± 10.53 abc109.83 ± 2.49 ab84.07 ± 1.06 a26.74 ± 0.16 a
      G2F807.06 ± 0.02 a218.43 ± 10.77 ab110.97 ± 1.91 ab83.87 ± 1.15 a26.61 ± 0.18 b
      G2.5F807.17 ± 0.04 a223.63 ± 11.65 a112.45 ± 1.77 a84.89 ± 1.07 a26.89 ± 0.15 a
      注(Note):CK—冬闲不施肥对照 No fertilization; MV—不施化肥,冬种紫云英并全部翻压,紫云英还田量为 22500 kg/hm2 22500 kg/hm2 milk vetch and no fertilization; F100—冬闲水稻季施 100% 化肥 With fallow and 100% chemical fertilization; G1F80—冬种紫云英,翻压 15000 kg/hm2 紫云英 + 80% 化肥 15000 kg/hm2 milk vetch + 80% chemical fertilizer; G1.5F80—冬种紫云英,翻压 22500 kg/hm2 紫云英 + 80% 化肥 (G1.5F80) 22500 kg/hm2 milk vetch + 80% chemical fertilizer; G2F80—冬种紫云英,翻压 30000 kg/hm2 紫云英 +80% 化肥 30000 kg/hm2 milk vetch + 80% chemical fertilizer; G2.5F80—冬种紫云英,翻压 37500 kg/hm2 紫云英 + 80% 化肥 37500 kg/hm2 milk vetch + 80% chemical fertilizer. 同列数据后不同小写字母表示不同处理间差异显著 (n = 5, P < 0.05) Values followed by different lowercase letters in a column indicate significant difference among treatments (n = 5, P < 0.05).

      Table 1.  Rice yield and its components under different incorporation amounts of milk vetch (2009–2020)

    • 2.2.   不同紫云英翻压量下的稻米外观品质

    • 不同紫云英翻压量对稻米外观品质有显著影响(图2)。相比CK和MV处理,F100和翻压紫云英配施80%化肥处理均降低了稻米的垩白率和垩白度,其中F100和G2.5F80处理最低,垩白率分别为14.3%和14.2%,垩白度分别为1.7%和1.8%。与F100处理相比,减量施用化肥条件下紫云英翻压量较低时,提高了稻米垩白度和垩白率。其中G1F80处理垩白率和垩白度分别增加7.9%和20.1%,G1.5F80处理分别增加了4.5%和12.6%,G2F80处理分别增加了5.1%和4.6%,G2.5F80和F100处理相比,稻米垩白率与垩白度没有显著差异。

      Figure 2.  Changes of grain appearance quality under different incorporation amounts of milk vetch

    • 2.3.   不同紫云英翻压量下稻米蒸煮食味和营养品质

      2.3.1.   不同紫云英翻压量下的稻米淀粉含量
    • 与F100处理相比,不同紫云英翻压量均能显著提高直链淀粉含量,降低支链淀粉含量(图3)。其中以G1F80处理直链淀粉含量最高和支链淀粉含量最低,直链淀粉含量为13.90%,相比F100处理提高了10.14%,支链淀粉含量为44.17%,较F100处理降低了10.7%。紫云英与化肥配施处理,随着紫云英翻压量的增大稻米淀粉总量逐渐增加,具体为直链淀粉含量随紫云英翻压量增大而降低,支链淀粉含量随紫云英翻压量增大而升高。

      Figure 3.  Changes of starch content under different incorporation amounts of milk vetch

    • 2.3.2.   不同紫云英翻压量下稻米蛋白质和脂肪含量
    • 与F100相比,单独翻压紫云英(MV)稻米蛋白质含量没有显著变化,而紫云英+减施化肥处理,随着紫云英翻压量的增大,稻米蛋白质含量呈现逐渐增加的趋势(图4),以G2.5F80处理稻米蛋白质含量最高,达8.59%,比G1F80处理显著提高了22.2%,较F100处理提高19.1%。与F100处理相比,紫云英及紫云英配施化肥处理,稻米脂肪含量无显著差异(图4),其中以G1F80处理稻米脂肪含量最低,相较F100处理降低了13.3%。

      Figure 4.  Changes of protein and fat content under different incorporation amounts of milk vetch

    • 2.3.3.   不同紫云英翻压量下稻米氨基酸含量
    • 不同紫云英翻压量对稻米氨基酸总量有不同程度的影响(图5),G2.5F80处理稻米氨基酸总量最高,达13.63 mg/g,相较于F100处理显著升高了59.4%,其次是MV处理,氨基酸总量为12.71 mg/g,相较于F100处理升高了48.78%。非必需氨基酸含量以G2.5F80和G1F80处理较高,分别为12.34 mg/g和11.06 mg/g,较F100处理分别提高了68.1%和50.7% (图5)。

      Figure 5.  Changes of amino acid content under different incorporation amounts of milk vetch

      各处理间必需氨基酸含量无显著差异(图5),其中MV处理的必需氨基酸含量最高,达1.81 mg/g,相较F100处理提高了49.8%,其必需氨基酸中,缬氨酸、苯丙氨酸、甲硫氨酸和亮氨酸含量较高。G1.5F80处理的赖氨酸和异亮氨酸含量最高,相较F100分别提高了147.6%和145.7%。

    • 2.4.   不同紫云英翻压量下的土壤农化性状

    • 试验12年后,MV处理的土壤各指标与CK无显著差异,但与F100相比,除pH和速效钾外,其余指标均显著降低。与CK相比,F100和减施化肥配合翻压不同量紫云英均显著降低了土壤pH,显著提高了土壤有机质、全氮、有效磷和无机氮含量(表2)。与F100相比,G1F80处理显著降低了速效钾含量,G1.5F80处理显著增加了土壤有机质含量(9.21%),G2F80、G2.5F80处理显著增加了土壤有机质和全氮含量,但G2.5F80显著降低了速效钾含量。综合比较对土壤肥力指标的影响,紫云英单独翻压只能维持土壤肥力,减施20%的化肥配合低量或高量紫云英翻压(G1F80、G1.5F80、G2.5F80)与常规化肥用量(F100)的效果相当,但长期减施化肥会显著降低土壤的速效钾含量;只有配施适量紫云英(G2F80)才能在维持土壤速效养分含量的基础上,较施用常规化肥(F100)显著提高土壤的有机质(13.1%)和全氮(12.8%)含量。

      处理
      Treatment
      pH有机质
      Soil organic matter
      (g/kg)
      全氮
      Total N
      (g/kg)
      有效磷
      Available P
      (mg/kg)
      速效钾
      Available K
      (mg/kg)
      无机氮
      Inorganic N
      (mg/kg)
      CK5.46 ± 0.02 a30.39 ± 0.11 d1.91 ± 0.01 e2.43 ± 0.03 b87.33 ± 4.98 ab18.76 ± 0.54 b
      MV5.40 ± 0.03 ab30.82 ± 0.76 d1.96 ± 0.04 e2.20 ± 0.12 b105.67 ± 8.09 a20.28 ± 1.40 b
      F1005.33 ± 0.02 bc33.00 ± 0.38 c2.11 ± 0.02 d9.83 ± 1.16 a89.33 ± 2.73 ab25.07 ± 1.20 a
      G1F805.33 ± 0.05 bc33.79 ± 0.87 c2.19 ± 0.03 cd7.60 ± 1.21 a65.67 ± 5.70 c27.09 ± 1.90 a
      G1.5F805.27 ± 0.04 c36.04 ± 0.70 b2.27 ± 0.04 bc7.60 ± 1.29 a70.00 ± 4.36 bc24.83 ± 0.36 a
      G2F805.26 ± 0.04 c37.33 ± 0.69 a2.38 ± 0.05 a8.07 ± 0.60 a88.67 ± 9.91 ab25.96 ± 1.11 a
      G2.5F805.30 ± 0.03 bc36.12 ± 0.98 ab2.30 ± 0.07 ab9.23 ± 0.27 a56.67 ± 4.48 c26.95 ± 1.41 a
      注(Note):CK—冬闲不施肥对照No fertilization; MV—不施化肥,冬种紫云英并全部翻压,紫云英还田量为 22500 kg/hm2 22500 kg/hm2 milk vetch and no fertilization; F100—冬闲水稻季施 100% 化肥 With fallow and 100% chemical fertilization; G1F80—冬种紫云英,翻压 15000 kg/hm2 紫云英 + 80% 化肥 15000 kg/hm2 milk vetch + 80% chemical fertilizer; G1.5F80—冬种紫云英,翻压 22500 kg/hm2 紫云英 + 80% 化肥 22500 kg/hm2 milk vetch + 80% chemical fertilizer; G2F80—冬种紫云英,翻压 30000 kg/hm2紫云英 + 80% 化肥 30000 kg/hm2 milk vetch + 80% chemical fertilizer; G2.5F80—冬种紫云英,翻压 37500 kg/hm2 紫云英 + 80% 化肥 37500 kg/hm2 milk vetch + 80% chemical fertilizer. 同列数据后不同小写字母表示不同处理间差异显著 (n = 5, P < 0.05) Values followed by different lowercase letters in a column indicate significant difference among treatments (n = 5, P < 0.05).

      Table 2.  Soil basic properties under different incorporation amounts of milk vetch

    3.   讨论

      3.1.   不同紫云英翻压量对土壤农化性状的影响

    • 有研究指出,冬种紫云英能够有效改善土壤农化性状,提高土壤肥力[20, 24-26],培育土壤碳库和氮库[15, 27-29],通过改变土壤氮的形态和土壤微生物群落,提高水稻氮肥利用率,进而促进水稻的生长、发育和产量提升[30-31],对农业生产提供了许多有益的指导。并且冬种紫云英通过扩充土壤养分库容,达到节肥增效的目的[20]。相比单施化肥处理,长期冬种紫云英配施80%化肥显著增加了土壤有机质和全氮含量,增幅达3.95%和1.22%[6]。在本研究中,不同紫云英翻压量配施80%化肥处理较单施化肥均提高了土壤有机质和全氮含量,其中G2F80处理的土壤有机质和全氮最高,相较于F100处理分别显著增加了13.1%和12.8%。翻压紫云英不仅能提升土壤全量养分,而且还能增加速效养分的供应[18,25]。本研究中,与单施化肥相比,翻压紫云英配施减量化肥能够提升土壤无机氮含量,但土壤速效钾含量随翻压量的增加而逐渐减少,主要是由于钾肥的投入量降低,随着绿肥翻压量的增加,总氮的投入相应增加,由此增加了水稻对钾的吸收。可见,减施化肥20%配施紫云英30000 kg/hm2 (G2F80)能够在维持土壤速效养分含量的基础上,较常规化肥(F100)处理显著提高土壤的有机质和全氮含量,改善土壤肥力。紫云英对土壤农化性状的改善,可能是其增加水稻产量和提高稻米营养品质的重要原因。

    • 3.2.   不同紫云英翻压量对水稻产量的影响

    • 大量研究表明,与单施化肥相比,冬种紫云英及减量配施化肥能够提高水稻有效穗数、千粒重、实粒率等产量构成因素[10, 32-33],提高水稻的总分蘖数和有效分蘖数,并提高其叶面积指数,进而促进水稻增产[34]。也有研究指出,化肥和有机肥的配施有利于提高水稻株高、籽粒干质量、分蘖数和水稻中后期干物质累积量,从而促进水稻高产稳产[35-36]。冬种紫云英能够促进水稻的光合作用,通过提高水稻的叶面积指数、光合速率和势粒比,为产量形成提供更多的干物质[10]。在本研究中,适量紫云英翻压量配施80%化肥处理较常规施肥均显著提高了水稻产量,并提高有效穗数、每穗粒数、结实率等产量构成因素,主要原因是长期翻压适量紫云英提升了土壤有机质和全氮含量,提高了土壤对水稻氮、磷、钾养分的稳定供应,进而提高肥料利用率,优化水稻产量及其构成因素,与前人[10,32-33,37]研究结果一致。与单施化肥相比,紫云英翻压量较低时减施化肥水稻结实率和千粒重有所下降,原因可能是长期紫云英低翻压量没有显著提升土壤有机质和全氮含量,以及减施化肥在一定程度上影响了土壤氮磷钾养分的供应。

    • 3.3.   不同紫云英翻压量对稻米品质的影响

    • 稻米品质主要包括外观品质、蒸煮食味品质和营养品质等[38]。稻米品质不仅受遗传因素、环境因素、水分管理、耕作方式和土壤肥力的影响,同时也与施肥方式有密切关系[39]。外观品质通常指水稻的垩白率、垩白度等,垩白指标高的稻米透明度低,碎米率高,影响稻米的经济价值。有研究指出,氮磷钾肥配施或化肥配施有机肥可以降低稻米垩白率和垩白度,提高稻米外观品质[40-41]。稻米的垩白性状与稻米中氮素含量呈负相关[42]。在本研究中化肥减施配合低紫云英翻压量改善稻米外观品质的效果不如常规施肥和化肥减施配合高紫云英翻压量。在紫云英翻压量为30000和37500 kg/hm2时,稻米垩白度和垩白率才与F100处理接近,这也与紫云英翻压量较低时,土壤中的有机质和氮素含量的调节作用不足,减施化肥又影响了水稻的氮素营养有关。当然,早稻生长期经历了低温至高温,灌浆期正值盛夏,温度较高,有可能是生育期差异引起的灌浆不完全导致稻米垩白指标增高[43]

      直链淀粉含量是评价稻米蒸煮食味品质的关键指标,一定范围内较高的支链淀粉含量能够提升稻米的蒸煮食味品质。并且水稻植株体内氮素含量能够影响碳氮代谢过程,最终改变稻米中淀粉和蛋白质的合成和含量变化[44]。有研究指出麦秆覆盖还田和稻草全量还田能够降低水稻直链淀粉含量[45-46],但也有研究指出冬种绿肥在一定程度上增加了稻米的直链淀粉含量[47]。本研究中,与单施化肥相比,减施化肥配施不同翻压量紫云英在一定程度上降低了稻米的支链淀粉含量,提高了稻米的直链淀粉含量。各翻压量紫云英处理对比,G2.5F80处理的直链淀粉含量最低,可能是由于紫云英翻压量较大时在水稻生长后期,土壤氮素含量升高而降低了稻米中的直链淀粉含量[48]。蛋白质含量是评价稻米营养品质的重要指标。适量紫云英+减施化肥能够提升稻米蛋白质含量,可能是紫云英配施化肥能够平衡土壤中的氮素释放速率,改善了土壤的供氮能力,使得水稻生长的各个时期能均衡吸收土壤中的氮素,提高水稻氮素累积量,有助于稻米中蛋白质的形成[49]。紫云英翻压量较低时向土壤中释放的氮素含量有限,随着翻压量的增加,土壤供氮能力增强,稻米蛋白质含量也随之升高。稻米蒸煮食味品质与稻米蛋白质含量呈负相关[50],这是由于较高的蛋白质含量会影响稻米的吸水、膨胀和糊化,从而降低了稻米蒸煮食味品质[51-52]。因此在评价不同紫云英翻压量下稻米的蒸煮食味品质时应综合考虑直链淀粉和蛋白质含量之间的关系。在本研究中,G2F80和G2.5F80处理蛋白质含量较高,但其直链淀粉含量小于14%,说明较高的紫云英翻压量在一定程度上提高了稻米的蛋白质含量,改善了稻米的内在品质但降低了稻米的适口性。

      氨基酸是人类的重要营养物质,关系到人体营养的供给水平,水稻生长过程中的施肥量、施肥方式等都能够极大程度地影响稻米氨基酸含量[53]。有研究指出,土壤中含氮量与稻米氨基酸含量呈正相关[54],并且土壤氮库的培育可以通过增加富含赖氨酸的谷蛋白的比例来提高土壤中的必需氨基酸含量[55],改善稻米营养品质[56]。本研究中,G1.5F80处理的赖氨酸和异亮氨酸含量最高,相较F100处理分别提高了147.6%和145.7%;G2.5F80处理显著提高了稻米总氨基酸含量,MV处理的必需氨基酸含量最高,且赖氨酸含量最高。这可能是由于长期种植翻压紫云英后培育了土壤氮库,提高了土壤综合肥力和土壤质量,进而提高了稻米中氨基酸含量。水稻蛋白质含量与氨基酸含量呈正相关关系[57],G2.5F80处理稻米氨基酸含量显著提升,进而有利于稻米中蛋白质的合成和蛋白质质量的提高,为人体生理功能提供物质资源,促进人体中酶、激素和维生素的合成。

    4.   结论
    • 江西双季稻区,连续多年种植翻压低量紫云英(<30000 kg/hm2)减施20%化肥,虽然没有显著降低水稻产量但是显著降低了稻米的外观和食味品质,对稻米营养品质的改善和土壤肥力提升的效果与常规化肥没有显著差异,但显著降低土壤有效钾含量。种植翻压高量紫云英(≥30000 kg/hm2)减施20%化肥才能有效改善土壤肥力,维持土壤速效养分含量(土壤速效钾可能会有所降低,应注意补充),同时,增加水稻产量,提高稻米外观和营养品质的同时,不降低食味品质。综合起来来看,长期减少20%化肥用量,配合翻压紫云英37500 kg/hm2可以提升江西双季稻区的土壤质量(注意钾素补充)和水稻的高产优产。

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