Differences in soil organic carbon stocks and fraction distributions between rice paddies and upland cropping systems in China

Purpose

A large body of research suggests that rice (Oryza sativa L.) cropping facilitates soil organic carbon (SOC) storage, while the stability of the sequestered carbon is still not well understood. The objective of this study was to determine the differences in SOC stocks and fraction distributions between rice paddies and upland cropping fields and their variation in different rice cropping areas.

Materials and methods

Data from the national soil survey were analyzed to assess the differences in SOC contents between paddy and upland cropping fields at the regional scale. In addition, three pairs of rice and upland cropping systems were selected in Heilongjiang [single rice vs. single corn (Zea mays L.) cropping], Jiangsu [rice-wheat (Triticum aestivum L.) vs. corn-wheat cropping], and Jiangxi (double rice vs. double corn cropping) provinces, representing the major cropping patterns in China. Physical fractionation techniques were used to investigate the differences in SOC stocks and distribution among different pools between rice-based cropping systems and non-rice cropping systems in China.

Results and discussion

SOC concentrations were, on average, 74.9% higher at the regional scale and 56.8% higher at the field scale in paddy than in upland cropping fields. Carbon proportion of particulate organic matter within microaggregates increased from 14.4% in upland cropping soils to 25.3% in paddy soils at the Heilongjiang site and from 12.4 to 25.5% at the Jiangxi site. Meanwhile, the free silt and clay-associated carbon was significantly greater in paddy than in upland cropping soils at the both sites. Nevertheless, SOC distribution did not markedly differ between paddy and upland cropping fields at the Jiangsu site where rice was rotated with winter wheat annually.

Conclusions

As compared to upland cropping or rice-upland crop rotation, continuous rice cropping, such as single and double rice cropping, could favor SOC stabilization by occlusion within microaggregates and adsorption to the silt and clay outside microaggregates, which may promote the long-term storage of SOC in paddies.     

低氮胁迫下小麦抑草作用的化感效应与资源竞争分析

化感效应和资源竞争在作物抑草中起重要作用。为区分低氮胁迫下小麦抑草作用的化感效应与资源竞争,以强化感小麦品种‘115/青海麦’、‘92L89’和弱化感小麦‘抗10103’为材料,设置氮水平为25 mg·L-1、50mg·L-1、100 mg·L-1和200 mg·L-1的水培试验,通过小麦与看麦娘共培、应用含小麦根系分泌物的小麦-看麦娘共培液处理看麦娘,分别测定了小麦对看麦娘的生物干扰作用、化感效应及资源竞争效应。结果表明,不同化感潜力的小麦对看麦娘的抑制能力存在显著差异,抑制率大小为‘115/青海麦’(55.1%~73.9%)‘92L89’(48.9%~65.9%)‘抗10103’(15.4%~45.5%),且抑制率随氮水平的降低而增大。在小麦的抑草作用中,化感效应与资源竞争并存。低氮胁迫条件下,强化感小麦抑草能力增强主要通过提高化感效应实现;弱化感小麦抑草能力增强主要通过提高资源竞争实现。不同化感潜力小麦的抑草作用在低氮胁迫下表现出不同的生态策略。小麦抑草作用的化感效应均随氮水平降低而增大,其抑制率随氮水平的变化可用一元二次方程加以拟合。     

两级螺旋排肥装置的设计与试验

为了改变现有排肥装置对肥料形态特征要求高的缺陷及改善排肥效果,该文设计了一种两级螺旋排肥装置,研究了装置的排肥原理,建立了排肥螺旋的单圈排肥量的数学模型,分析了两级螺旋排肥装置的相关参数,并通过试验测试与分析了两级排肥装置的排肥性能。试验结果表明,在10~200 r/min转速范围内,对于芭田复合肥、水稻专用肥及吸潮后的芭田复合肥和水稻专用肥,两级螺旋排肥装置每分钟内的排肥量随转速的增加而增大,并呈线性关系,整体决定系数大于0.998,排肥螺旋的单圈排肥量的极差、标准差及变异系数较小,对于含水率2%的芭田复合肥和含水率5.6%的水稻专用肥的单圈排肥量的变异系数小于0.025;吸潮后含水率较高的芭田复合肥和水稻专用肥的单圈排肥量的变异系数整体上不大于0.040。同时,通过数学模型计算出的单圈排肥量与实际单圈排肥量一致较好,该模型能准确表达此类两级螺旋排肥装置的单圈排肥量。因此,该研究能有效地改善排肥效果,降低对肥料形态特征的要求,为同步播种施肥机具及变量施肥机具的研究与设计提供了参考依据。     

长期定位施肥对夏玉米钾素吸收及土壤钾素动态变化的影响

以长期定位试验为平台,夏玉米品种郑单136为材料,设置CK（不施肥）,NP（施氮、 磷肥）,NPK（施氮、 磷、 钾肥）和1.5MNPK（小麦季施高量氮、 磷、 钾肥+有机肥,玉米季仅施用化肥）4个处理,研究夏玉米钾素吸收规律及生育期内土壤钾素动态变化。结果表明,生育期内施钾与不施钾处理夏玉米干物质积累量均一直增加,在成熟期达到最大值; 在施用氮、 磷肥的基础上增施钾肥不但可以提高夏玉米地上部干物质积累量,同时也可以提高叶片及茎秆中的钾素含量,进而提高夏玉米整个地上部吸钾量;而在氮、 磷、 钾肥基础上增施有机肥,对夏玉米干物质积累无显著影响,但可显著提高茎秆及叶片的钾素含量和地上部钾素吸收总量。夏玉米钾素吸收主要集中在灌浆期之前,在灌浆期达到最大值,之后钾素出现回流现象。夏玉米收获后与播种前相比,土壤水溶性钾和交换性钾含量无明显下降或者略有增加,而非交换性钾明显下降,非交换性钾是夏玉米钾素吸收的主要形式。夏玉米吸钾量与播种前土壤3种形态的钾素含量呈显著正相关。因此,增施钾肥对于改善夏玉米生产,维持土壤钾素平衡及实现农业可持续发展具有深远意义。     

沂蒙山区小流域坡耕地土壤颗粒结构与养分退化特征

为探讨坡耕地土壤退化程度及其与坡度的关系,在沂蒙山区选择典型小流域,通过测定流域内不同坡度坡耕地、弃耕地与生态林地的土壤颗粒组成、分形维数、土壤养分质量分数的变化及其相关性,研究坡耕地土壤颗粒结构与养分退化特征。结果表明：1）所有土地利用类型,土壤砂粒体积分数最高,黏粒体积分数最低,平均值分别为70．81％、0．75％;2）土壤颗粒分形维数、有机质质量分数为生态林地〉弃耕地〉坡耕地;3）坡耕地土壤颗粒分形维数随坡度增加而减小,其大小与土壤粉粒和黏粒体积分数分别呈极显著、显著正相关;4）所有土地利用类型,土壤有机质质量分数与砂粒体积分数显著负相关,与粉粒和黏粒体积分数显著正相关,土壤氮、磷、钾养分质量分数与土壤颗粒体积分数相关性不显著;5）研究区土壤具有粗骨性砂土的物理特性,坡耕地耕作或坡度加大会增强土壤粉粒和黏粒的流失,导致土壤颗粒分布的均匀性及其分维数下降,水肥保蓄性能和养分质量分数降低。     

根外施钾对苹果树光合速率的影响研究

试验研究金矮生苹果树生育期根外施K对其光合速率的影响结果表明 ,根外施K可促进光合速率 ,一定程度缓和“午休”现象。苹果生育期 5～ 10月份 5次根外施K对促进与延长当年苹果树光合速率和营养积累有显著作用 ,其效应优于根外 1次施K和 3次施K处理 ,每次施K作用持续时间达 2 5d左右。     

长期不同施肥处理水稻土磷素在剖面的分布与移动

稻麦轮作黄泥土施肥试验始于1980年,共布置不施肥、纯化肥、有机肥(猪粪或菜籽饼)、化肥加有机肥、氮肥加秸秆、氮肥加有机肥加秸秆等14种处理。2003年11月麦季取土壤样品分析结果表明:(1)与无肥处理相比,施磷处理和有机肥处理耕层土壤全磷(TP)含量皆有显著增加,并且表现出向下迁移的迹象,有机肥配施NPK化肥处理土壤磷的迁移可达30 cm深度,其余施磷处理均至25 cm。(2)大部分施磷处理在表层0~25 cm内无机磷(I-P)总量发生显著性变化,Ca2-P由于其溶解性强可迁移到30 cm以下,Al-P、Fe-P、Oc-P(闭蓄态磷)的迁移可达25 cm,Ca8-P至20 cm;Ca10-P含量只在有化肥P输入的6个处理的0~15 cm耕层土壤中有显著性增加。(3)土壤有机磷(O-P)含量的变化小于无机磷的变化,只有无机磷配施有机肥的3个处理和仅施PK化肥的处理,其耕层土壤有机磷发生显著性增加。     

吉林省无公害中药材种植基地土壤环境质量评价

对吉林省7个无公害中药材规范化种植示范基地土壤环境质量现状评价结果显示,这7个基地各项污染指标均符合国家标准规定,单项污染指数和综合污染指数均<1,土壤环境质量为2级,适宜建立无公害中药材种植基地。     

Added nitrogen interaction as affected by soil nitrogen pool size and fertilization – significance of displacement of fixed ammonium

Displacement of NH₄⁺ fixed in clay minerals by fertilizer ¹⁵NH₄⁺ is seen as one mechanism of apparent added nitrogen interactions (ANI), which may cause errors in ¹⁵N tracer studies. Pot and incubation experiments were carried out for a study of displacement of fixed NH₄⁺ by ¹⁵N‐labeled fertilizer (ammonium sulfate and urea). A typical ANI was observed when ¹⁵N‐labeled urea was applied to wheat grown on soils with different N reserves that resulted from their long‐term fertilization history: Plants took up more soil N when receiving fertilizer. Furthermore, an increased uptake of ¹⁵N‐labeled fertilizer, induced by increasing unlabeled soil nitrogen supply, was found. This ANI‐like effect was in the same order of magnitude as the observed ANI. All causes of apparent or real ANI can be excluded as explanation for this effect. Plant N uptake‐related processes beyond current concepts of ANI may be responsible. NH₄⁺ fixation of fertilizer ¹⁵NH₄⁺ in sterilized or non‐sterile, moist soil was immediate and strongly dependent on the rate of fertilizer added. But for the tested range of 20 to 160 mg ¹⁵NH₄⁺‐N kg^–1, the NH₄⁺ fixation rate was low, accounting for only up to 1.3 % of fertilizer N added. For sterilized soil, no re‐mobilization of fixed ¹⁵NH₄⁺ was observed, while in non‐sterile, biologically active soil, 50 % of the initially fixed ¹⁵NH₄⁺ was released up to day 35. Re‐mobilization of ¹⁵NH₄⁺ from the pool of fixed NH₄⁺ started after complete nitrification of all extractable NH₄⁺. Our results indicate that in most cases, experimental error from apparent ANI caused by displacement of fixed NH₄⁺ in clay is unlikely. In addition to the low percentage of only 1.3 % of applied ¹⁵N, present in the pool of fixed NH₄⁺ after 35 days, there were no indications for a real exchange (displacement) of fixed NH₄⁺ by ¹⁵N.     

几种天然生物防腐剂对生鲜罗非鱼片防腐效果研究

以细菌总数、TVB-N为指标,比较了生姜、大蒜、溶菌酶、乳酸链球菌素、茶多酚、ε-聚赖氨酸、鱼精蛋白、壳聚糖等8种天然生物防腐剂对生鲜罗非鱼片的防腐效果。结果表明,8种天然生物防腐剂对生鲜罗非鱼片均有一定防腐作用,最佳防腐浓度分别为:生姜体积分数20 mL/100 mL,大蒜60 mL/100 mL,溶菌酶质量分数0.5%,茶多酚0.6%,乳酸链球菌素1.0%,鱼精蛋白0.6%,壳聚糖1.2%,ε-聚赖氨酸0.6%。其中,生姜、大蒜和壳聚糖的防腐效果相对较好。