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。     

不同土壤质地和含水率对炭基肥料氮素矿化的影响

为了探究土壤特性对炭基肥料氮素矿化的影响,采用室内培养和大田小区试验,分析了炭基肥在不同土壤质地(砂质壤土、粉砂质壤土、黏土)及含水率(80%、60%、40%田间最大持水量)条件下,氮素矿化动态变化特征。结果表明:在室内培养条件下,对于不同土壤质地,炭基肥在砂质壤土条件下矿化势最高,其次为黏土,最低的为粉砂质壤土;对于不同田间持水量,在粉砂质壤土条件下,炭基肥矿化势最高的为80%田间最大持水量(80%SMC),其次为60%SMC,最低的是40%SMC;在砂质壤土和黏土条件下,炭基肥的矿化势均表现为60%SMC> 80%SMC> 40%SMC。培养状态下粉砂质壤土、砂质壤土、黏土条件下最大氮素有效性分别是34.12%、56.31%、41.14%,而在大田条件下,炭基肥单季氮素最大矿化率在粉砂质壤土、砂质壤土、黏土3种土壤质地下分别是50.61%、32.27%、34.29%。     

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.     

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     

不同质地土壤上玉米养分吸收和分配特征

采用池栽试验在4种质地土壤和2种施肥水平下,研究了玉米植株氮、磷、钾的吸收和分配特征。结果表明,不同质地土壤上玉米植株养分累积量为氮钾磷;不同处理玉米氮、磷、钾的累积量表现为中壤轻壤粘壤砂壤,且各处理间差异达显著水平。不同处理叶片和茎鞘中三元素累积量的变化与单株一致,氮、磷、钾分配以叶片中的比例略高于茎鞘。从后期氮、磷、钾的转移率看,不同质地土壤表现为砂壤轻壤中壤粘壤;不同处理中子粒中氮、磷、钾的含量与产量变化一致,且处理间达显著水平。施肥增加了各种质地土壤上玉米植株及器官氮、磷、钾的累积量和子粒产量,其中砂壤增加幅度最大,轻壤和中壤次之,粘壤最小。同时施肥使得叶片和茎鞘中的氮、磷、钾转移率略有降低。     

肥液浓度对不同形态氮素在土壤中运移转化特性的影响

为揭示肥液(尿素)浓度影响下土壤湿润体中不同形态氮素的运移转化规律,选取黏壤土和砂壤土作为肥液入渗试验供试土壤,量化分析肥液浓度对土壤累积入渗量和不同形态氮素在分布和再分布过程中运移转化特性的影响。结果表明:相同入渗时间内土壤累积入渗量随肥液浓度的增大而增加,Kostiakov公式的入渗系数与肥液浓度呈现线性关系,建立并验证了考虑肥液浓度影响的土壤累积入渗量估算公式,模拟值与实测值具有较高的一致性,两者间的相对误差绝对值均值均8.0%;入渗结束时,土壤湿润体相同位置处的尿素态氮、铵态氮(NH_4~+-N)和硝态氮(NO_3~--N)含量均随肥液浓度的增大而增加;NH_4~+-N主要分布在土壤湿润体深度20 cm以上,尿素态氮和NO_3~--N含量随着湿润体深度的增大呈现下降趋势;再分布过程中,土壤湿润体中尿素态氮含量随再分布时间的增加整体呈现减小趋势,且黏壤土和砂壤土湿润体中的尿素态氮分别在再分布5,3天时基本水解完成;NH_4~+-N含量呈现先增加后减小的趋势,黏壤土湿润体中的峰值约出现在再分布3～5天,而砂壤土约在再分布3天;黏壤土湿润体中NO_3~--N含量呈现先增加后减小的趋势,其峰值约在5～10天,而砂壤土中NO_3~--N含量在再分布10天时,始终保持在较高水平。研究结果为农田灌溉施肥系统的设计和管理提供理论基础和技术支撑。     

豫中不同土壤质地烤烟烟叶色素含量变化的差异

在河南豫中烟区研究了4种典型质地土壤烤烟主栽品种NC89不同生育时期和调制后烟叶质体色素含量变化的差异。结果表明,砂土烟叶β-胡萝卜素和总类胡萝卜素在烤后烟叶样品中含量较高,其余几种色素降解程度均较大;砂壤土烟叶中大部分色素含量在烟株现蕾期至尚熟时下降较为缓慢,成熟采收时下降较为明显,在烤后烟叶中叶绿素、β-胡萝卜素和总类胡萝卜素残留较少,质体色素降解充分;壤土烟叶各种色素含量随生育期推进下降趋势均较明显,烤后烟叶样品中质体色素含量也较低,残留较少;黏土烟叶中各种色素含量在现蕾期至尚熟时含量开始下降,但在成熟采收时含量较高,色素降解程度低,烤后烟叶中叶绿素和类胡萝卜素含量偏高。砂壤土和壤土植烟有利于烤烟香气前体物质的积累和适时转化。     

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。     

Determining differential water movement through ion exchange resin for nitrate leaching measurements

Abstract

The fate of fertilizer N applied to agricultural soils is of growing concern due to the potential for groundwater contamination. The recent development of an exchange resin that specifically absorbs NO₃ has led to the potential for a new technique to measure cumulative NO₃ leaching. The main limitation to the application of the resin technique is the matching of water movement through the resin with that of soil. A soil water movement device was developed to compare water movement through the resin to that of soil. A study was initiated to develop a resin/soil pack with water movement characteristics that closely matches those of natural soils. Three different soil types were used in this study: a Cahaba sandy loam (fine‐loamy, siliceous, thermic Typic Hapludult), a Congaree clay loam (fine loamy, mixed, nonacid, thermic Typic Udifluvent), and a Hiwassee clay (clayey, kaolinitic, thermic Typic Rhodudult). Both pure resin and resin mixed with soil were found to have higher water movement characteristics compared to bulk soil. A resin pack method was found which had water movement characteristics that were not significantly different from that of bulk soil for the three different soil types. The resin pack method is described.     

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.     

Plant Response to Copper Toxicity as Affected by Plant Species and Soil Type

ABSTRACT

A greenhouse experiment was conducted to determine the bioavailability of copper (Cu) in clay loam and sandy clay loam soil. Lettuce (Lactuca sativa) and spinach (Spinacia oleracea) were grown in pots for 45 d. When mature, plants were treated for 15 additional days with 0, 100, 250, 500, or 1000 mg Cu kg^?1 as CuSO₄·5H₂O. After harvest, Cu in soils and plant tissues was determined. In soils, applied Cu raised total and EDTA-extractible Cu. Results also revealed that the amounts of Cu extracted from sandy clay loam soil (80%) were higher than those extracted from clay loam soil (70%). In plants, increasing soil Cu concentration increased plant concentration of the metal. Plant species vary in their capacity for Cu accumulation: Lettuce has a relatively higher potential for Cu uptake and translocation than does spinach. Cu accumulation also differs among plant organs. In lettuce, metal accumulation is higher in roots than in shoots, where 60% to 80% of the total Cu of the plant is located in the roots. However, in spinach, there is no significant difference in Cu content between roots and shoots. The transfer of the metal from soil to plant is higher for plants grown on sandy clay loam soil. For a given rate of applied Cu, metal content in plant tissues is higher on sandy clay loam soil due to its higher transfer coefficient (C_T) from soil to plant. Nevertheless, all crops studied showed a positive linear relationship between extractible soil Cu and plant Cu.     

Lime application to reduce phosphorus release in different textured intact and small repacked soil columns

Purpose

Phosphorus (P) losses from agricultural fields through leaching are the main contributors to eutrophication of lakes and rivers in North America. Adoption of P-retaining strategies is essential to improve the environmental quality of water bodies. The main objective of this study is to evaluate lime as a soil amendment in reducing phosphorus concentration in the leachate from three common soil textures with neutral to alkaline pH.

Materials and methods

Phosphorus leaching from undisturbed soil columns (10 cm in diameter and 20 cm deep) as well as small repacked columns was investigated and compared in this study. Lime (high calcium hydrated lime) at the rate of 1% by air-dried soil mass was applied to the topsoil of the columns. Both sets of experiments followed a full factorial design with two factors of soil texture at three levels (sandy loam, loam, and clay loam) and treatment at two levels (control and limed) with three replicates. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy was performed on the control and limed soil samples to confirm the formation of calcium phosphate compounds.

Results and discussions

For both intact and repacked columns, dissolved reactive phosphorus (DRP) concentrations in the leachates from limed sandy loam and limed loam soil columns was significantly reduced, while DRP in the limed clay loam column leachates was not changed. Elemental mapping demonstrated that in limed sandy loam and loam soils, the calcium loadings on the soil surface were always linked with phosphorus. The formation of calcium phosphate compounds and the increased phosphate adsorption on the soil surface through Ca bridging could be the two main phosphorus-lime retention mechanisms. Total dissolved phosphorus (TDP) in the leachates of limed loam and limed clay loam indoor intact and repacked columns was reduced, while there was no change in that of the sandy loam soil. In finer textured soils, lime can increase TDP retention through the immobilization of organic phosphates.

Conclusions

The impact of lime application on DRP and TDP varied with the soil texture. The lime-induced reduction in the DRP and TDP was variable between the intact and repacked columns demonstrating the importance of soil structure on phosphorus and lime interactions in the soil. Overall, lime application at the studied rate can be considered a promising soil amendment in mitigating phosphorus loss from non-calcareous neutral to alkaline soils.

     

Catch Crop and Animal Slurry in Spring Barley Grown with Straw Incorporation

Abstract

Four rates of straw (0, 4, 8 and 12 t ha^?1 yr^?1) were incorporated in a field experiment with continuous spring barley. The experiment was conducted on a sandy soil (5.5% clay) and a sandy loam soil (11.2% clay). After eight years, the straw incorporation was combined with catch-crop growing with and without winter application of animal slurry and also spring fertilization with mineral fertilizer (0, 50, 100 or 125 kg N ha^?1 yr^?1). The combined experiment was conducted for three lyears on the sandy soil and for four years on the sandy loam soil. The effects on barley dry matter yield and N uptake are presented together with the long-term effects of the straw incorporations on crop growth and soil C and N. Grain yield on the sandy loam was unaffected by straw incorporation. On the sandy soil the highest straw application rates reduced grain yield in the unfertilized barley. When the barley received mineral fertilizer at recommended levels (100 kg N ha^?1 yr^?1), grain yield on this soil was also unaffected by the high straw rates. Including a catch crop had a positive effect on the grain yield of barley on both soils. The total N uptake in grain and straw generally increased with straw application up to 8 t ha^?1 yr^?1. With the highest straw application rate (12 t ha^?1 yr^?1), the total N uptake decreased but still exceeded N uptake in barley grown with straw removal. The barley accumulated higher amounts of N when a catch crop was included. The total N uptake in the barley was significantly higher after animal slurry application. The extra N uptake, however, was much lower than the amounts of N applied with the slurry. Incorporation of straw had only a small influence on N uptake after slurry application. The straw, therefore, was not able to store the applied N during winter. In the two four-year periods before the combined experiment, grain yield on the sandy loam was generally negatively affected by straw incorporations. In the second period, N uptake began to show a positive effect of the straw. On the sandy soil, grain yield and N uptake during the whole period were generally positively affected by the straw incorporations except for the highest straw rate (12 t ha^?1 yr^?1). The sandy loam soil showed higher increases in C and N content after the repeated straw incorporations and catch-crop growing than the sandy soil. When application of animal slurry was combined with the catch crop, no further increases in soil C and N were found relative to soil where a catch crop was grown without slurry application. Large amounts of the N applied with the slurry may therefore have been lost by denitrification or nitrate leaching.     

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.     

Effect of Induced Soil Compaction on Changes in Soil Properties and Wheat Productivity under Sandy Loam and Sandy Clay Loam Soils: A Greenhouse Experiment

The continuous use of heavy machinery and vehicular traffic on agricultural land led to an increase in soil compaction, which reduces crop yield and deteriorates the physical conditions of the soil. A pot experiment was conducted under greenhouse conditions to study the effects of induced soil compaction on growth and yield of two wheat (Triticum aestivum) varieties grown under two different soil textures, sandy loam and sandy clay loam. Three compaction levels [C₀, C₁, and C₂ (0, 10 and 20 beatings)], two textural classes (sandy loam and sandy clay loam), and two genotypes of wheat were selected for the experiment. Results indicated that induced soil compaction adversely affected the bulk density (BD) and total porosity of soil in both sandy loam and sandy clay loam soils. Compaction progressively increased soil BD from 1.19 Mg m^?3 in the control to 1.27 Mg m^?3 in C₁ and 1.40 Mg m^?3 in C₂ in sandy loam soil while the corresponding increase in BD in sandy clay loam was 1.56 Mg m^?3 in C₁ and 1.73 Mg m^?3 in C₂ compared to 1.24 Mg m^?3 in the control. On the other hand, compaction tended to decrease total porosity of soil. In case of sandy loam, porosity declined by 5% and 17% in C₁ and C₂, respectively, and declined in sandy clay loam by 29% and 54%, respectively. Averaged over genotypes and textures, shoot length decreased by 15% and 26% at C₁ and C₂, respectively, and straw yield decreased by 21% and 61%, respectively. The compaction levels C₁ and C₂ significantly decreased grain yield by 12% and 41%, respectively, over the control. The deleterious effect of compaction was more pronounced on root elongation and root mass, and compaction levels C₁ and C₂ decreased root length by 47% and 95% and root mass by 41% and 114%, respectively, over the control. Response of soil texture to compaction was significant for almost all the parameters, and the detrimental effects of soil compaction were greater in sandy clay loam compared to sandy loam soil. The results from the experiment revealed that soil compaction adversely affected soil physical conditions, thereby restricting the root growth, which in turn may affect the whole plant growth and grain yield. Therefore, appropriate measures to avoid damaging effects of compaction on soil physical conditions should be practiced. These measures may include soil management by periodic chiseling, controlled traffic, conservation tillage, addition of organic manures, and incorporating crops with deep tap root systems in a rotation cycle.     

Soil, Water and Yield Relationships in developing Strategies for the Precision Application of Nitrogen Fertiliser to Winter Barley

To investigate on-farm strategies for the site-specific application of nitrogen fertiliser, two hypotheses were tested: that maximum economic output is either obtained by applying more nitrogen to the historically highest yielding soil and less to the lowest yielding soil, or by the reverse strategy.Field experiments were conducted in 1997, 1998 and 1999 on a commercially managed field of winter barley (Hordeum vulgare), comprising a clay loam and a sandy loam, in Cambridgeshire, UK. The experiments were carried out in a strip-based design using on-farm equipment. In all 3 yr, at typical application rates of 100–200 kg[N] ha⁻¹, there were significant differences between the yield of the clay loam and the sandy loam soil. When rainfall in the February to July period of the growing season was higher than average, the sandy loam soil yielded significantly higher than the clay loam soil and the reverse occurred when the rainfall was lower.Despite the above factors, analysis showed that the maximum of the yield response curve for each soil, occurred at the same application rate in each growing season. Given this relationship, there was no economic benefit from variable rate application of nitrogen to different soil units based upon historic yield, or any other form of information.     

Effect of cobalt treatments on dry matter production of wheat and DTPA extractable cobalt content in soils

Abstract

The effect of different concentrations of cobalt added to two soil types, a sandy and a sandy loam soil, was studied on growth performance and tissue cobalt concentration of wheat plants. DTPA‐extractable cobalt was significantly higher in the sandy soil than in the sandy loam soil. Plants grown in the sandy soil accumulated significantly higher amount of cobalt in comparison to plants grown in the sandy loam soil. Roots were significantly richer in cobalt than shoots in both the soil types. Lower (1 μg g^‐1) administration of cobalt resulted in an enhancement in the growth whereas higher (5–625 μg g^‐1) addition inhibited growth. A significant inverse relationship between relative wheat yield and tissue cobalt concentration was observed. The results indicate a possible requirement of cobalt for higher plants.     

不同质地耕层土壤有效态微量元素含量特征

[目的]研究不同土壤质地下耕层土壤有效态微量元素含量特征,为合理制定农田土壤施肥方案和提高土壤养分资源利用率提供依据。[方法]以库车县不同质地耕层土壤(0—20cm)为调查对象,采用统计方法对土壤微量元素有效态含量特征进行分析。[结果](1)土壤有效态微量元素在壤土、砂壤土、黏土、黏壤土及砂土中含量差异显著(p0.05),且壤土和砂壤土的有效态微量元素含量相对较高;(2)土壤微量元素有效性综合指数排列顺序依次为:砂壤土(1.51)砂土(1.44)黏土(1.42)壤土(1.41)黏壤土(1.27);(3)土壤有机质与土壤有效态微量元素均具有极其显著的相关性(p0.01),pH值则与有效铜和有效锰相关显著(p0.05)。[结论]在不同土壤质地下,微量元素铁和锌含量较为缺乏,锰和铜含量则相对较为丰富,故应依据这一特性进行土地科学管理和施肥。     

Simulating corn yields over 16 years on three soils under inorganic fertilizer and hog manure fertility regimes

Abstract

Corn yields (Zea mays L.) on control treatments with inorganic fertilizer and on copper‐enriched hog manure treatments with annual rates up to 168 mt/ha from a 16‐year study were modelled with the Erosion Productivity Impact Calculator (EPIC) simulation model. The field research study was conducted on three diverse soils, a Guemsey silt loam, a Bertie fine sandy loam, and a Starr‐Dyke clay loam. Results indicated that EPIC simulated the manure and fertilizer treatments equally well. EPIC produced simulated yield means that were not different from measured yield means for all treatments (p ≤ 0.05). Goodness of fit tests indicate that simulated yields did not differ from measured yields for all simulation models except the Bertie manure treatment (p ≤ 0.05). For control and manure treatments, simulated yields explained 78% and 89% of variation in measured yields for the Guernsey soil, 55% and 42% for the Bertie soil, and 76% and 70% for the Starr‐Dyke soil, respectively. Overall, these are reasonable yields estimates, but site‐specific soil and other model parameter respecification is critical. Yield modeling with heavy applications of animal manure or inorganic fertilizer is feasible and useful.     

Survival of Pseudomonas solanacearum biovars 2 and 3 in soil: Effect of moisture and soil type

The survival of Pseudomonas solanacearum biovars 2 and 3 in three soils, a Nambour clay loam, a Beerwah sandy loam and a Redland Bay clay, was compared at pressure potentials of ?0.003, ?0.05 and ?0.15 kPa. The soils were inoculated with mutants of P. solanacearum biovars 2 and 3, resistant to 2000 μg streptomycin sulphate ml^?1 and their survival measured every 6 weeks for 86 weeks in the clay loam and clay and for 52 weeks in the sandy loam. Soil populations declined with the initial drying necessary to bring the soil moisture to the specific pressure potentials; the initial counts for biovar 2 varied between 0.20 and 2.00 × 10⁹ cfu g^?1 soil and for biovar 3 between 0.17 and 1.29 × 10⁹ cfu g^?1 soil.The population decline in soil maintained at a constant pressure potential was expressed as the rate of population decline. Biovar 2 declined more rapidly than biovar 3. The rate of population decline of each biovar at ?0.003 and ?0.05 kPa was greater in clay loam than in sandy loam and at all pressure potentials it was greater in clay loam and sandy loam than in clay. There was also a tendency for the rate of population decline of both biovars to decrease in the drier soil treatments.