土壤耕作方式对双季稻产量构成与穗镉积累的影响

为比较研究不同土壤耕作方式(翻耕、旋耕、免耕)对南方双季稻区水稻产量构成与稻穗镉积累分配特性的影响,探讨镉污染稻田双季稻最优土壤耕作方式,2015—2017年,以"陵两优211"与"威优46"为早、晚稻供试品种,在湖南省湘潭县易俗河镇中度镉污染稻田(全镉含量0.86 mg/kg)开展定位试验,比较研究了双季免耕、双季翻耕、双季旋耕、早旋晚免、早翻晚免5种土壤耕作方式下土壤有效镉含量、双季稻的产量构成与穗镉积累分配情况。结果表明:(1)双季稻产量以双季翻耕处理最高,早翻晚免处理次之,双季旋耕与早旋晚免处理再次之,双季免耕处理最低;翻耕处理产量最高的原因在于其有效穗数与每穗粒数较高。(2)齐穗期至成熟期,穗镉含量一般呈增长趋势;第1年早晚稻齐穗期穗镉含量以免耕处理最高,但免耕能明显降低水稻齐穗至成熟期穗镉含量的增长速率;早晚稻成熟期穗镉含量一般以翻耕处理较高,免耕与旋耕处理较低,免耕与旋耕处理有差异但在不同年份与季别间表现不尽相同。(3)成熟期稻穗各部位镉含量趋势表现为枝梗谷壳糙米;第1年糙米镉含量以免耕处理较高,但第2,3年呈现免耕处理低于翻耕与旋耕处理的趋势。(4)第1年早、晚稻穗镉累积量均以旋耕处理较低,但第2,3年均以免耕处理较低。(5)较其他处理而言,双季免耕明显提高了土壤有效镉含量,双季旋耕则降低了土壤有效镉含量。3年定位试验表明,土壤耕作方式对镉污染稻田土壤有效镉含量、双季稻产量构成与稻穗镉积累分配有明显影响,从保证双季稻产量、降低稻米镉含量与轻简省工的角度出发,早翻晚免是中度镉污染双季稻田的最优土壤耕作方式。

Effects of Soil Tillage Methods on Yield Components and Cadmium Accumulation in Panicles of Double-cropping Rice

To compare the effects of different soil tillage methods (ploughing, rotary tillage and no tillage) on rice yield composition and cadmium accumulation and distribution traits in rice panicles in southern double-cropping rice fields, and to explore the optimal soil tillage method for double-cropping rice in cadmium-contaminated rice fields, taking "Lingliangyou 211"and "Weiyou 46"as early and late rice varieties, the available cadmium content in soil, rice yield components and spike cadmium accumulation and distribution of double-cropping rice under five soil tillage methods (double-cropping no-tillage, double-cropping ploughing, double-cropping rotary tillage, ploughing in early rice and no-tillage in late rice, rotary tillage in early rice and no-tillage in late rice) were studied in Yisuhe Town, Xiangtan County, Hunan Province in 2015 to 2017. The experimental field was cadmium-contaminated rice fields, and the total cadmium content was 0.86 mg/kg. The results showed that the yield of double cropping rice was the highest in the treatment of double-cropping ploughing, followed by the treatments of ploughing in early rice and no-tillage in late rice, double-cropping rotary tillage and rotary tillage in early rice and no-tillage in late rice, and that of no-tillage in double cropping rice was the lowest. The highest yield of ploughing treatment was due to the higher number of effective panicle and grains per panicle. (2) The cadmium content in panicle generally showed an increasing trend from full heading to maturity stage. In the first year of early and late rice, the cadmium content in panicle at full heading stage was the highest in no-tillage treatment, but no-tillage could significantly reduce the growth rate of cadmium content in panicle from full heading to maturity stage. The cadmium content in panicle at maturity stage was higher in ploughing treatment and lower in no-tillage and rotary tillage treatment, there were difference between no-tillage and rotary tillage treatment, but they were different among years and seasons. (3) Cadmium content in different parts of rice panicle at maturity stage followed the order of branches > husks > brown rice. The cadmium content in brown rice was higher in no-tillage treatment in the first year, but in the second and third years, that of no-tillage was lower than that of ploughing and rotary tillage. (4) The cadmium accumulation in panicle of early and late rice was lower in rotary tillage treatment in the first year, but it was lower in no-tillage treatment in the second and third years. (5) Compared with other treatments, double-cropping no-tillage significantly improved the soil available cadmium content, while double-cropping rotary tillage decreased the soil available cadmium content. The three-year locational test showed that soil tillage methods had a significant impact on available cadmium in soil, yield components and cadmium accumulation and distribution in rice panicles of double-cropping rice in cadmium-contaminated paddy field. From the perspective of ensuring the yield of double-cropping rice, reducing cadmium content in rice and saving labor, ploughing in early rice and no-tillage in late rice was the optimal soil tillage method for medium cadmium-contaminated double-cropping rice fields.