培养条件下微纳米增氧水添加对新疆砂壤土硝化作用的影响

为了提升氮素利用效率和生产能力，采用室内培养试验方法，研究不同土壤含水率（田间持水量的30%、60%、100%及175%）条件下增氧水处理对土壤硝化作用的影响，并分别利用硝化动力学方程和硝化作用强度定量评价NH4+-N和NO3--N含量的动态变化特征，比较NH4+-N初始消耗速率、NH4+-N最大消耗速率、达到最大消耗速率所用时间以及NO3--N平均生成速率的变化。结果表明：粉质砂壤土氮素转化以硝化作用为主；随着含水率的升高，土壤硝化作用强度呈现先增加后降低的趋势，并在田间持水量条件下达到最大。在不同含水率条件下增氧水处理对土壤硝化作用的影响具有显著差异（P<0.05）。与常规水处理相比，在田间持水量的60%条件下，增氧水处理对土壤硝化过程的促进作用更为明显，NH4+-N最大消耗速率提高了8.9%，最大消耗速率出现时间提前，NO3--N平均生成速率增加，硝化作用更强；而在田间持水量条件下，增氧水处理的土壤NH4+-N消耗没有显著差异，仅NO3--N平均生成速率增加；田间持水量的175%条件下，增氧水处理土壤NH4+-N最大消耗速率降低了21.5%，最大消耗速率出现时间滞后，但NO3--N平均生成速率没有显著变化。该研究提出了增氧水处理促进氮素转化作用的最适水分条件，为发展农业高效水肥利用技术提供了理论依据。     

温度和水分对典型香型烟区植烟土壤氮素矿化的影响

为探究典型香型烟区植烟土壤氮素矿化特征及其与温度和水分的关系,采用室内培养试验研究了土壤温度(15、28、37℃)和土壤相对含水量(50%、65%、80%田间持水量)对云南大理、贵州毕节、河南许昌3个典型香型产区植烟土壤氮素矿化的影响。结果表明:不同地区植烟土壤矿质氮和矿化速率变化规律与温度和水分密切相关。3个产区植烟土壤的矿质氮含量和矿化速率均随着温度的升高而升高,在同一温度条件下,以土壤有机质含量较高的云南大理土壤矿化量较大,有机质含量较低的河南许昌土壤矿化量较小。不同地区植烟土壤含水量与氮素矿化的关系不尽相同,土壤相对黏重的贵州毕节土壤以50%田间持水量处理土壤氮素矿化量和矿化速率最大,以80%田间持水量处理最不利于氮素矿化;而质地相对较轻的河南许昌土壤和云南大理土壤均为在65%田间持水量条件下最有利于氮素矿化,以50%田间持水量处理氮素矿化量较小。基于一级动力学方程的模拟,3个植烟土壤的潜在矿化氮库(N0)都随温度的增加而提高,总体以28～37℃的培养温度较为适宜,低于15℃不利于土壤有机氮的矿化,3个植烟土壤的N0以云南大理最高,河南许昌最低;土壤矿化速率常数(K)以云南大理最大。土壤相对含水量也对N0有一定影响,且土壤温度和含水量对不同土壤氮素矿化量和矿化速率均存在显著的互作影响,合理调控土壤温度和土壤相对含水量,可以有效调节不同生态烟区土壤氮素矿化动态变化。     

黄土高原土壤水分性质及其分区

黄土高原土壤具有很好的调节作物供水的功能,这和土壤的水分性质有关。本文研究了土壤的持水性能、有效性能和移动性能等。影响黄土高原土壤水分性质的主要因素是土壤质地。文内绘制了包括五个质地带的土壤质地分区图。田间持水量在轻壤土、中壤土和重壤土范围内均为20%±2,未表现出明显相关。萎蔫湿度则几乎完全决定于土壤质地。文内绘制了田间持水量和萎蔫湿度的等值线图。土壤水物理蒸发影响深度可达2-3米。两米土层内物理蒸发失水量轻壤土和中壤土达田间持水量的25-35%;具有下伏粘化层的重壤土,60厘米以下矢水量不大于10%。后者为作物准备了较多的储水。文内列出了不同质地土壤的水分特征曲线的经验方程,所有资料汇总于土壤水分性质表中。本研究结果为合理利用土地提供了基础数据。     

生物炭基肥和水分胁迫对花生产量、耗水和养分吸收的影响

为了探究不同生物炭基肥施用量下水分胁迫对花生栽培的应用潜力,运用自动遮雨棚花生盆栽试验,对不同生物炭基肥施用量(0,750,1 500kg/hm2)和不同水分胁迫程度(常规控水,70%~75%田间持水量;中度水分胁迫,60%~65%田间持水量;重度水分胁迫,50%~55%田间持水量)对花生产量、耗水和其养分吸收特征的影响进行研究。结果表明:施入750,1 500kg/hm2生物炭基肥可提高0—15cm土层土壤铵态氮和速效钾含量、植株地上部分氮钾养分吸收和水分生产率;除重度水分胁迫外,其他两种控水水平均能提高土壤速效钾含量,促进植株营养吸收,进而提高产量;中度水分胁迫下,施入750,1 500kg/hm2生物炭基肥,较无生物炭基肥可显著提高植株地上部分氮钾吸收,增产40.48%和37.71%,提高水分生产率53.8%和9.9%。研究结果可为生物炭基肥在干旱地区花生生产的应用方面提供理论依据。     

添加生物质炭对红壤水稻土有机碳矿化和微生物生物量的影响

通过室内培育试验,研究了添加生物质炭对江西红壤水稻土有机碳矿化和微生物生物量碳、氮含量的影响。结果表明:红壤有机碳矿化速率在培育第2天达最大值后迅速降低,培养7天后下降缓慢并趋于平稳;添加生物质炭降低了土壤有机碳的矿化速率和累积矿化量,培养结束时,不加生物质炭的对照处理中有机碳的累积矿化量分别比添加0.5%和1.0%生物质炭的处理高10.0%和10.8%。此外,生物质炭的加入显著提高了土壤微生物生物量,添加0.5%生物质炭处理的土壤微生物生物量碳、氮含量分别比对照高111.5%～250.6%和11.6%～97.6%,添加1.0%生物质炭处理的土壤微生物生物量碳、氮含量分别比对照高58.9%～243.6%和55.9%～110.4%。相同处理中,干旱的水分条件下(40%田间持水量)微生物生物量要高于湿润的水分条件(70%田间持水量)。同时,添加0.5%和1.0%的生物质炭使土壤代谢熵分别降低2.4%和26.8%,微生物商减少了43.7%和31.7%。     

生物炭对粉黏壤土水力参数及胀缩性的影响

该文选取2种粒径（细炭0.013～0.048 mm、粗炭0.3～0.7 mm）的生物炭,以2种质量百分比（3%、6%）施入一种粉黏壤土,通过测定不同粒径生物炭及施加比例下土壤的水分特征曲线、饱和水力传导度、收缩性及饱和膨胀率,研究生物炭对粉黏壤土水力参数及胀缩性的影响。结果表明,2种粒径及添加比例的生物炭均降低了粉黏壤土的持水能力。但4种添加生物炭处理相互之间持水能力差异不显著。生物炭可降低粉黏壤土中极微孔隙和中大孔隙的比例,提高微孔隙和小孔隙所占的比例。生物炭的添加降低了该粉黏壤土的饱和含水率和凋萎系数。细炭对粉黏壤土的田间持水率没有显著影响,粗炭降低了粉黏壤土的田间持水率。两种粒径的生物炭均可提高粉黏壤土的有效含水率,并降低离心失水过程中土壤的收缩,在这2方面细炭的影响效果比粗炭显著;细炭的添加对粉黏壤土饱和膨胀率没有显著影响,粗炭则降低了粉黏壤土的饱和膨胀率。2种粒径生物炭的添加均降低了该粉黏壤土的饱和水力传导度。3%和6%的添加比例在大部分研究指标中未表现出明显差异。该研究可为生物炭在土壤环境修复应用方面提供一定的理论指导。     

土壤水分和氮添加对3种质地紫色土氮矿化及土壤pH的影响

为正确认识土壤水分、质地和外源氮添加对紫色土氮矿化作用和土壤pH的影响,以西南地区典型的紫色土为研究对象,通过90d的室内恒温(25℃)好气培养,研究了3种质地(粘土、粉粘壤土和砂土)紫色土在不同含水量(55%,65%和75%田间持水量)和尿素氮添加水平(0mg/kg土和250mg/kg土.)条件下,土壤氮矿化作用和pH的变化。结果表明:前30d的累积矿化氮量可占培养期间(90d)的78.48%~91.55%,且各处理的土壤累积矿化氮量和净矿化速率均随着培养时间的延长而快速增加;第30~90d,土壤累积矿化氮量增长缓慢,净矿化速率迅速下降并趋于稳定。土壤累积矿化氮量和净矿化速率在各培养阶段均随土壤水分含量的增加而逐渐增大,其中75%WHC(75%田间持水量)和75%WHC+U(75%田间持水量+尿素)处理的矿化作用最强。土壤质地从一定程度上对土壤的矿化产生影响,但其影响并不显著。外源氮添加能促进土壤氮矿化,其净氮矿化量和净矿化速率在各培养阶段均极显著(p0.01)高于未加氮处理,分别为未施氮处理的1.68~4.56倍,0.60~6.47倍。外源氮添加使土壤pH显著下降,55%WHC+U、65%WHC+U和75%WHC+U处理分别下降了0.57,0.66,0.72个pH单位,土壤有酸化趋势。土壤pH值与土壤氮素净矿化速率呈极显著线性相关,净矿化速率对pH变化贡献巨大。总之,土壤含水量增加和外源氮添加均促进了土壤氮矿化,增加了土壤矿质氮含量,同时外源氮添加也加速了土壤pH下降,土壤有酸化趋势。     

生物炭对东北黑土持水特性的影响

为探究生物炭对东北黑土持水特性的影响,系统研究3种添加比例(2%、5%、10%)、3种粒径(0.25、0.5、1 mm)的杨木炭和竹炭对3种质地东北黑土(壤土、砂壤土、砂土)田间持水量和含水率的影响规律,构建添加生物炭黑土的水分特征曲线,并采用Van-Genuchten和Broods-Corey模型进行拟合。结果表明:生物炭能显著提高不同质地东北黑土的持水能力,黑土的田间持水量与生物炭的添加比例呈显著正相关,而与生物炭的粒径呈负相关,0.5 mm和1 mm粒径的生物炭对黑土田间持水量的影响差异不显著,杨木炭显著优于竹炭,0.25 mm、10%添加比例的杨木炭对东北黑土持水能力的提高效果最优,壤土、砂壤土、砂土3种质地黑土的田间持水量和饱和含水率分别可提高64.97%、66.42%、69.39%和47.60%、38.93%、31.18%;Van-Genuchten模型能更精确的模拟添加生物炭黑土的水分特征曲线,最佳离心时间为100 min,三次函数曲线能够较好的拟合添加生物炭黑土的体积含水率与离心吸力之间的多元动态关系,为生物炭对各种质地东北黑土水分运动规律的深入研究提供理论依据。     

炭基肥对老茶园土壤有机碳矿化温度敏感性的影响

采取室内恒温培养法,以施用炭基肥（BF）、不施炭基肥（CK）的40a茶园土壤为研究对象,设定15℃、25℃和35℃共3种不同温度场景,连续监测土壤有机碳（soil organic carbon,SOC）矿化特征并分析有机碳矿化温度敏感性,为评估老茶园固碳减排及障碍消减提供参考。结果表明：（1）炭基肥提升了温变场景下茶园土壤pH值和SOC含量。15℃、25℃和35℃培养温度下,BF处理的土壤pH值较CK处理分别增加0.45、0.07和0.28个单位;BF处理的SOC含量较CK处理分别提高22.19%、16.65%和25.50%。（2）炭基肥增加了温变场景下茶园SOC累计矿化量、潜在矿化势（CS）及土壤呼吸强度,对SOC矿化呈现正激发效应。15℃、25℃和35℃培养温度下,BF处理的SOC累计矿化量较CK处理分别提高15.61%、46.51%和36.89%。BF处理的CS值随温度升高呈现先增加后减少的变化趋势,25℃培养温度下BF处理的CS值较15℃和35℃培养温度下分别提高147.11%和29.21%。（3）炭基肥降低温度升高处理下茶园SOC矿化温度敏感性。25～35℃温度范围内,BF处...     

生物炭添加对黄土高原典型土壤田间持水量的影响

为确定生物炭添加对黄土高原典型土壤水分条件的影响,利用威尔科克斯法,室内条件下测定2种生物炭类型(苹果树枝生物炭和锯末生物炭)及3种生物炭添加比例(2％,5％,10％)对黄土高原3种典型土壤(填)土、黄绵土、风沙土田间持水量的影响.结果显示:(填)土、黄绵土、风沙土添加生物炭后田间持水量分别平均增加2.77％,3.09％,4.17％,显著高于不施炭处理(p＜0.05).苹果树枝生物炭对3种土壤田间持水量提高程度平均值为4.67％,显著高于锯末生物炭2.02％的提高程度;生物炭添加量与土壤田间持水量增加程度成正比例关系,添加量越大,土壤田间持水量增加程度越高,其中,苹果树枝生物炭10％添加量对3种土壤田间持水量的增加程度最大.研究表明,生物炭添加可以显著提高土壤田间持水量,不同种类生物炭及添加量对土壤田间持水量影响差异较大.     

Organic carbon mineralization responses to temperature increases in subtropical paddy soils

Purpose

Understanding organic carbon mineralization and its temperature response in subtropical paddy soils is important for the regional carbon balance. There is a growing interest in factors controlling soil organic carbon (SOC) mineralization because of the potential for climate change. This study aims to test the hypothesis that soil clay content impedes SOC mineralization in subtropical paddy soils.

Materials and methods

A 160-day laboratory incubation at temperatures from 10 to 30 °C and 90% water content was conducted to examine the dynamics of SOC mineralization and its temperature response in three subtropical paddy soils with different clay contents (sandy loam, clay loam, and silty clay soils). A three-pool SOC model (active, slow, and resistant) was used to fit SOC mineralization.

Results and discussion

Total CO₂ evolved during incubation following the order of clay loam > silty clay > sandy loam. The temperature response coefficients (Q ₁₀) were 1.92?±?0.39, 2.36?±?0.22, and 2.10?±?0.70, respectively, for the sandy loam soil, clay loam soil, and silty clay soil. But the soil clay content followed the order of silty clay > clay loam > sandy loam. The sandy loam soil neither released larger amounts of CO₂ nor showed higher temperature sensitivity, as expected, even though it contains lower soil clay content among the three soils. It seems that soil clay content did not have a dominant effect which results in the difference in SOC mineralization and its temperature response in the selected three paddy soils. However, dissolved organic carbon (DOC; representing substrate availability) had a great effect. The size of the active C pool ranged from 0.11 to 3.55% of initial SOC, and it increased with increasing temperature. The silty clay soil had the smallest active C pool (1.40%) and the largest Q ₁₀ value (6.33) in the active C pool as compared with the other two soils. The mineralizable SOC protected in the silty clay soil, therefore, had even greater temperature sensitivity than the other two soils that had less SOC stabilization.

Conclusions

Our study suggests that SOC mineralization and its temperature response in subtropical paddy soils were probably not dominantly controlled by soil clay content, but the substrate availability (represented as DOC) and the specific stabilization mechanisms of SOC may have great effects.     

不同质地土壤上烤烟氮素积累、分配及利用率的研究

【目的】土壤质地能概括反映土壤内在的肥力特征,对土壤养分供应具有调控作用,是影响农田中土壤氮素供应和氮肥利用的重要因素。本试验通过在皖南烟区3种质地(壤土、黏壤、砂壤)土壤上施用等量氮肥来研究其对烤烟不同生育期的氮素吸收、积累及利用特征的影响,旨在为烟田土壤改良及烤烟合理施肥提供理论依据。【方法】在皖南烟区现代农业科技园的典型壤土、黏壤和砂壤土上分别建立田间试验,采用15N田间微区试验和室内分析相结合的研究方法,在烤烟的团棵期(移栽后38 d)、现蕾期(移栽后53 d)、平顶期(移栽后64d)和成熟期(移栽后103 d),采集长势一致的烟株样品,测定烟株各部位的生物量,并采用凯氏定氮法检测其全氮含量,采用ZHTO2型同位素质谱仪测定其15N丰度。【结果】皖南烟区壤土和黏壤土上烤烟总氮和肥料氮积累均随生育期呈单峰变化,在烤烟平顶期达最大,总氮积累量分别为4.25 g/plant和3.96 g/plant,肥料氮积累量分别为2.34 g/plant和2.54 g/plant,而砂壤土上烤烟到成熟期其总氮和肥料氮的积累量达到最大,分别是5.64 g/plant和2.73 g/plant,均显著高于同时期的壤土和黏壤;壤土、黏壤和砂壤土上烤烟均以叶部肥料氮占总氮比例及氮素分配率较高,茎部次之,根部最低;不同质地土壤上烤烟氮肥利用率与肥料氮的积累动态具有一致的变化趋势,其中壤土和黏壤在平顶期最大,分别为34.5%和40.7%,之后壤土利用率缓慢下降,黏壤下降幅度较大,而砂壤土上烤烟氮肥利用率在生育期内呈上升趋势,至成熟期最大,为43.7%。【结论】不同质地土壤上烟株对氮素的吸收利用顺序为砂壤壤土黏壤,黏壤土在烤烟生育期内供氮能力较弱,应合理调控土壤氮的矿化及增加肥料氮的供应;砂壤土氮肥利用率较高,应严格控制氮肥的施用量。     

Soil carbon responses to past and future CO2 in three Texas prairie soils

Changes in soil carbon storage could affect and be affected by rising atmospheric CO₂. However, it is unlikely that soils will respond uniformly, as some soils are more sensitive to changes in the amount and chemistry of plant tissue inputs whereas others are less sensitive because of mineralogical, textural, or microbial processes. We studied soil carbon and microbial responses to a preindustrial-to-future CO₂ gradient (250–500 ppm) in a grassland ecosystem in the field. The ecosystem contains three soil types with clay fractions of 15%–55%: a sandy loam Alfisol, a silty clay Mollisol, and a black clay Vertisol. Soil and microbial responses to atmospheric CO₂ are plant-mediated; and aboveground plant productivity in this ecosystem increased linearly with CO₂ in the sandy loam and silty clay. Although total soil organic carbon (SOC) did not change with CO₂ treatment after four growing seasons, fast-cycling SOC pools increased with CO₂ in the two clay soils. Microbial biomass increased 18% and microbial activity increased 30% across the CO₂ gradient in the black clay (55% clay), but neither factor changed with CO₂ in the sandy loam (15% clay). Similarly, size fractionation of SOC showed that coarse POM-C, the youngest and most labile fraction, increased four-fold across the CO₂ gradient in the black clay, but increased by only 50% across the gradient in the sandy loam. Interestingly, mineral-associated C, the oldest and most recalcitrant fraction, declined 23% across the gradient in the third soil type, a silty clay (45% clay). Our results provide evidence for priming in this soil type, as labile C availability and decomposition rate (measured as soil respiration and soil C mineralization) also increased across the CO₂ gradient in the silty clay soil. In summary, CO₂ enrichment in this grassland increased the fast-cycling SOC pool as in other CO₂ studies, but only in the two high-clay soils. Priming in the silty clay could limit SOC accumulation after prolonged CO₂ exposure. Because soil texture varies geographically, including data on soil types could enhance predictions of soil carbon and microbial responses to future CO₂ levels.     

Nitrogen availability to grain sorghum from organic and inorganic sources on sandy and clayey soil surfaces in a greenhouse pot study

In a greenhouse pot study, we examined the availability of N to grain sorghum from organic and inorganic N sources. The treatments were¹⁵N-labeled clover residues, wheat residues, and fertilizer placed on a sandy clay loam and loamy sand soil surface for an 8-week period. Soil aggregates formed under each soil texture were measured after 8 weeks for each treatment. Significantly greater ¹⁵N was taken up and recovered by grain sorghum in sandy clay loam pots compared with loamy sand pots. Greater ¹⁵N recovery was consistently observed with the inorganic source than the organic sources regardless of soil texture or time. Microbial biomass C and N were significantly greater for sandy clay loam soil compared with the loamy sand. Microbial biomass ¹⁵N was also significantly greater in the sandy clay loam treatment compared to the loamy sand. The fertilizer treatment initially had the greatest pool of microbial biomass ¹⁵N but decreased with time. The crop residue treatments generally had less microbial biomass ¹⁵N with time. The crop residues and soil texture had a significant effect on the water-stable aggregates formed after 8 weeks of treatments. Significantly greater water-stable aggregates were formed in the sandy clay loam than the loamy sand. Approximately 20% greater water-stable aggregates were formed under the crop residue treatments compared to the fertilizer only treatment. Soil texture seemed to be one of the most important factors affecting the availability of N from organic or inorganic N sources in these soils.Contribution from the MissouriAgricultural Experiment Station, Journal Series No.12131     

Dynamics of 15N-labeled ammonium sulfate in various inorganic and organic soil fractions of wetland rice soils

Summary The dynamics of basally applied ¹⁵N-labeled ammonium sulfate in inorganic and organic soil fractions of five wetland rice soils of the Philippines was studied in a greenhouse experiment. Soil and plant samples were collected and analyzed for ¹⁵N at various growth stages. Exchangeable NH₄ ⁺ depletion continued after 40 days after transplanting (DAT) and corresponded with increased nitrogen uptake by rice plants. Part of the applied fertilizer was fixed by 2:1 clay minerals, especially in Maligaya silty clay loam, which contained beidellite as the dominant clay mineral. After the initial fixation, nonexchangeable ¹⁵N was released from 20 DAT in Maligaya silty clay loam, but fixation delayed fertilizer N uptake from the soil. Part of the applied N was immobilized into the organic fraction. In Guadalupe clay and Maligaya silty clay loam, immobilization increased with time while the three other soils showed significant release of fertilizer N from the organic fraction during crop growth. Most of the immobilized fertilizer N was recovered in the nondistillable acid soluble (alpha-amino acid + hydrolyzable unknown-N) fraction at crop maturity. Between 61% and 66% of applied N was recovered from the plant in four soils while 52% of fertilizer N was recovered from the plant in Maligaya silty loam. Only 20% – 30% of the total N uptake at maturity was derived from fertilizer N. Nmin (mineral N) content of the soil before transplanting significantly correlated with N uptake. Twenty-two to 34% of applied N was unaccounted for possibly due to denitrification and ammonia volatilization.     

不同质地小麦根际土壤有机碳、氮含量及特性研究

测定了两种不同质地土壤小麦根际土及非根际土中不同形态有机碳、氮的含量及特性。结果表明,粘壤土及砂质壤土两种不同质地土壤小麦根际土中有机碳、可溶性有机碳(WEOC),土壤全氮、可溶性有机氮(WEON)、游离氨基酸及硝态氮和铵态氮均显著高于非根际土;根际土及非根际土中WEON的含量均高于硝态氮及铵态氮含量,其在根-土界面氮素转化中的作用值得关注。不同质地土壤相比,粘壤土中各指标的含量均显著高于砂质壤土。根际土有机碳矿化累积量及矿化率均高于非根际土;培养期间粘壤土释放的CO2量明显低于沙质壤土,这可能与粘壤土粘粒含量高,对土壤有机碳的保护作用有关。     

Response of soil exchangeable and crop potassium concentrations to variable fertilizer and cropping regimes in long-term field experiments on different soil types

Annual potassium (K) balances have been calculated over a 40‐year period for five field experiments located on varying parent materials (from loamy sand to clay) in south and central Sweden. Each experiment consisted of a number of K fertilizer regimes and was divided into two crop rotations, mixed arable/livestock (I) and arable only (II). Annual calculations were based on data for K inputs through manure and fertilizer, and outputs in crop removal. Plots receiving no K fertilizer showed negative K balances which ranged from 30 to 65 kg ha^?1 year^?1 in rotation I, compared with 10–26 kg ha^?1 year^?1 for rotation II. On sandy loam and clay soils, the K yield of nil K plots (rotation I) increased significantly with time during the experimental period indicating increasing release of K from soil minerals, uptake from deeper soil horizons and/or depletion of exchangeable soil K (K_ex). Significant depletion of K_ex in the topsoil was only found in the loamy sand indicating a K supply from internal sources in the sandy loam and clay soils. On silty clay and clay soils, a grass/clover ley K concentration of ～2% (dry weight) was maintained during the 40‐year study period on the nil K plots, but on the sandy loam, loam and loamy sand, herbage concentrations were generally less than 2% K.     

Soil organic matter, effects on soils and crops

Abstract. Manurial treatments and cropping history have remained unchanged for many years in classical and long-term experiments at Rothamsted and Woburn, in some cases for more than 100 years. Soil samples taken periodically have been analysed to follow changes in organic carbon content with time and treatment. Data presented here clearly show effects of carbon input and soil texture on equilibrium organic matter content.
Until recently increasing amounts of soil organic matter had little effect on yields of arable crops especially if fertilizer nitrogen dressings were chosen correctly. However the yield potential of many crops has increased and various agronomic inputs have become available to achieve that potential. Yields of many crops are now larger on soils with extra organic matter both on the sandy loam at Woburn and the silty clay loam at Rothamsted. Some of the effect appears to be related to extra water holding capacity, some to availability of nitrogen in ways which cannot be mimicked by dressings of fertilizer N, and some to improved soil physical properties. Responses to fertilizer N have been larger on soils with more organic matter.     

基于HYDRUS-2D模型的玉米高出苗率地下滴灌开沟播种参数优选

开沟播种是一种可显著提高地下滴灌春玉米出苗率的新型播种方式,为了优化该技术模式,该文通过两年田间试验分析了地下滴灌玉米出苗率与灌水后种子处土壤有效饱和度(effective saturation)的关系,并基于HYDRUS-2D构建了地下滴灌开沟播种土壤水分运动模型,以90%玉米出苗率为前提,研究了不同土质和土壤初始含水率条件下3个技术参数——开沟深度、滴灌带埋深和灌水量对种子处土壤有效饱和度的影响.结果表明:1)出苗率随土壤有效饱和度线性递增,土壤有效饱和度不小于0.77时,出苗率超过90%;2)地下滴灌开沟播种HYDRUS-2D模型模拟精度较高,模拟得到的土壤有效饱和度随开沟深度增大而增大,随滴灌带埋深增大而减小;3)满足土壤有效饱和度为0.77所需的出苗水灌水量随土壤黏粒含量、土壤初始含水率和开沟深度增大而减小,随滴灌带埋深增大而增大.当表层土壤初始含水率为40%田持~60%田持时,开沟深度每增加5cm,砂壤土的出苗水灌水量减小15~20mm,粉壤和粉黏土的出苗水灌水量减小6~18mm;滴灌带埋深由30cm增大到35cm时,砂壤土的出苗水灌水量增大16~21mm,粉壤和粉黏土的出苗水灌水量增大4~14mm.不同埋深和开沟深度下,当表层土壤初始含水率由40%田持增大到60%田持时,砂壤土的出苗水灌水量减小9~14mm,粉壤和粉黏土的出苗水灌水量减小9~19mm;4)综合考虑土壤质地、玉米根系分布、机械作业、耗能、耕作深度和土壤水深层渗漏以及土壤初始含水率,玉米地下滴灌适宜的滴灌带埋深为30~35cm,开沟深度为10~15cm,灌水量范围为25~67mm.农业生产者可以根据当地实际情况对以上3个技术参数进行合理配置.     

土壤质地对柱花草生长发育、生物量及土壤肥力变化的影响

采用大田试验的方法,在云南省元谋县小雷宰流域内壤土、砂壤土和重壤土3种质地土壤上,以热研5号柱花草为材料,研究土壤质地对柱花草生长发育、生物量及土壤有机质、有机碳、全氮和全磷的影响。试验结果表明:3种土壤质地上种植柱花草,柱花草地上部和地下部生长量和生物量表现幼苗期增加缓慢,而分枝期后增加快的趋势。壤土耕性好,兼有砂土和重壤土的优点,有利柱花草地上部分的生长发育,柱花草地上部生长量、生物量及改善土壤肥力方面显著高于重壤土。砂壤土有利于柱花草根系向深层土壤生长,柱花草地下部生长量、生物量及根瘤显著高于种植在重壤土。在3种土壤质地种植柱花草后,土壤有机质、有机碳、全氮和全磷均有上升趋势。综合而言,通气性和保肥保水能力居中的壤土更适合柱花草的生长发育及干物质的积累。