Temporal variation in mineral nitrogen in soil as influenced by incorporation of legume or cereal residues under submergence or well drained conditions

A laboratory study was conducted at the Indian Agricultural Research Institute, New Delhi on a sandy clay loam soil of pH 7.9 and organic C content of 0.34% to study the effect of incorporating Sesbania or Vigna legume residues or wheat straw at 15 and 30t ha^?1 on temporal variation in ammoniacal and nitrate‐N in soil under submergence and well drained conditions. Under submergence most mineral N was present as ammoniacal‐N, while under well drained conditions it was present as Nitrate‐N. The content of ammoniacal N in soil was the highest after 30 days of incubation and declined thereafter under submergence. On the other hand under well drained conditions the mineral‐N (mostly nitrate) content in soil at 30 DAI was very little and showed increases only later, reaching the highest level at 90 DAI. Application of wheat straw specially at 301 ha^?1 level resulted in immobilization of native soil‐N. These results show that rice which is grown under submergence can be transplanted soon after incorporation of legume residues, but for wheat or other crops which are grown under well drained condition a time interval of 30 days or more needs to be provided before sowing the crop.     

Interaction effects of nitrogen and phosphorus fertilizer on nitrogen mineralization of wheat residues in a calcareous soil

Abstract

Because of the high pH of the soil in semiarid regions, phosphorus adsorption is unfavorable. So, considerable amounts of phosphorus fertilizers are used annually, where this fertilizer may affect the plant residues' decomposition. To examine the interaction effects of nitrogen and phosphorus on nitrogen mineralization in calcareous soil, a factorial experiment was performed in a completely randomized design with three replications. The first factor consisted of various C:N ratios (20, 40, and 60 or three levels of nitrogen N₁:0, N₂:11, and N₃:43?kg N ha^?1, respectively) and the second factor consisted of various C:P ratios (87, 174, and 260 or three levels of phosphorus P₁:0, P₂:12, and P₃:45?kg P ha^?1, respectively), under incubation conditions. The results indicated that the cumulative mineral nitrogen content in all treatments, except for N1P2 and N1P3 treatments, started from a positive amount and remained positive until the end of the incubation period. The highest amount of cumulative mineral nitrogen among treatments was related to N3P1 treatment, while the lowest was associated with N2P3 treatment. Mineralization of nitrogen during 60?d of incubation was the dominant phenomenon, except for the N1P2 and N1P3 treatments which remained in the organic phase. The effect of phosphorus on the cumulative mineralization of nitrogen was significant. With increasing the amount of phosphorus, the total inorganic nitrogen diminished. Nitrogen release begins earlier with lower C:N ratios, and therefore the available nitrogen can be released more quickly to the plant. It is generally concluded that, in calcareous soil, the use of nitrogen fertilizer to adjust C:N ratio and to improve the mineralization of wheat residues will be a suitable option.     

土壤压实对土壤物理性质及小麦氮磷钾吸收的影响

为了研究土壤压实对土壤物理性质以及小麦养分吸收情况的影响,在2006和2007年进行了两轮田间试验.试验中,先用旋耕机对田块进行旋耕,耕深10cm,然后使用手扶式、轮式、履带式拖拉机在旋耕后的田块中通过1次(T1)、2次(T2)、4次(T3)以对土壤进行压实处理,对照组(T4)不作任何压实处理.压实处理后再次对土壤表层进行浅旋耕,耕深5 cm,耕后用播种机进行小麦播种,小麦品种为南京-601.试验结果发现,次表层土壤的压实处理显著影响次表层土壤的容重,孔隙度,小麦蛋白质含量以及植物中N、P、K的含量.除次表层的土壤容重在T3组中最大,T4组中最小外,其他参数值在T4组中最大,T3组中最小.并且,随着次表层土壤压实程度的增加,几乎所有的参数(土壤容重除外)都有所减少.不过,与第一年相比,参数值在第二年略有增加.总之,土壤压实严重破坏土壤结构,不利于小麦对养分的吸收.     

矿区复垦土壤种植小麦的重金属安全性

为分析矿区充填复垦土壤种植农作物的生态安全性,以中国徐州市柳新矿区复垦场地为例,对照当地农田土壤,对充填场地种植小麦不同部位As、Cd、Cr、Cu、Hg、Pb、Zn 7种重金属元素含量进行检测,分析了Cd、Cr在成熟小麦不同器官中的分布、富集情况,并利用单项污染指数法和综合指数法对小麦籽粒进行了风险评价。结果表明,三场地中Cd 和Hg在未成熟苗中的含量小于成熟茎中的含量,Cr、Cu和Zn则与之相反,Pb和As的含量规律性不太明显;复垦场地小麦未成熟根的重金属含量都小于成熟根中的含量;比照地中除Cr 和Zn之外,其余元素在未成熟根中的含量均大于成熟根的含量;参照粮食污染限量标准,小麦籽粒中Cd和Cr含量均超标。风险评价显示三场地小麦籽粒中Cd、Cr单项污染指数达到轻度至重度水平,综合污染指数处于轻度污染至中度污染水平之间。该研究对矿区粮食安全的监控具有重要的实际应用价值。     

Decomposition and nitrogen mineralization from legume and non-legume crop residues in a subarctic agricultural soil

An understanding of the C and N dynamics of crop residues is important for efficient nutrient management. The present experiment was conducted to determine the rate of mass and N loss from alfalfa, faba bean, barley, and rape crop residues in a subarctic agricultural soil. Mass, C, and N losses were measured from residues contained in mesh bags and placed on the soil surface or buried 15 cm below the surface. The mass loss from October, 1988, to May, 1989, was the same for surface and buried alfalfa, barley, and rape residues, averaging 40, 20, and 61%, respectively, while surface and buried faba bean residue sustained 30 and 40% mass loss, respectively. The mass loss of the buried residues continued over the summer but not of those placed on the soil surface, resulting in an average 23% greater mass loss of the buried materials after 1 year. The N loss from October to May was similar from the surface and from the buried placements for the alfalfa, faba bean, and rape residues, averaging 11.3, 10.3 and 38.4 g N kg^-1 residue, respectively, while the surface and buried barley lost 2.9 and 4.2 g N kg^-1, respectively. The C:N ratio of all of the residues increased during the winter. These data indicate that the rate of decomposition and N mineralization from crop residues in subarctic environments can equal that measured in temperate climates. Furthermore, the concurrent loss of mass and N combined with an increase in the C:N ratio of the residues suggests that physical rather than biological processes were functioning during the winter. Most of the mass and N loss from these residues occurred during the winter, out of phase with crop demand, thereby creating the potential for N loss from the system and inefficient use of crop residue N.     

Phosphate sorption isotherms for fertilizer p needs of sweet corn (Zea mays) grown on a high phosphorus fixing soil

Abstract

Phosphorus sorption isotherms were used to estimate phosphorus fertilizer rates on a phosphorus fixing Alfic Fragiorthod soil from north Idaho. Five rates ranging from 0–584 kg/ha corresponded to sorption equilibrium solution levels from 0.06 to 0.20 ppm P. Yield of sweet corn (variety Spancross) grown two successive years was related to the sorption equilibrium solution P level. Whole plant weight, weight of ears, number of ears, and ear size approached maximum when the sorption equilibrium solution P level was near 0.13 ppm. The P content of leaves at early tassel stage increased with increasing sorption equilibrium solution P in a nearly straight line relationship. The leaves contained 0.27% P when the sorption equilibrium solution P was 0.13 ppm, the level producing maximum yield. The 0.20 ppm P resulted in 0.41% P in corn leaves.     

Phosphorus acquisition and wheat growth are influenced by shoot phosphorus status and soil phosphorus distribution in a split‐root system

Root proliferation and greater uptake per unit of root in the nutrient‐rich zones are often considered to be compensatory responses. This study aimed to examine the influence of plant phosphorus (P) status and P distribution in the root zone on root P acquisition and root and shoot growth of wheat (Triticum aestivum L.) in a split‐root soil culture. One compartment (A) was supplied with either 4 or 14 mg P (kg soil)^–1, whereas the adjoining compartment (B) had 4 mg P kg^–1 with a vertical high‐P strip (44 mg kg^–1) at 90–110 mm from the plant. Three weeks after growing in the split‐root system, plants with 4 mg P kg^–1 (low‐P plants) started to show stimulatory root growth in the high‐P strip. Two weeks later, root dry weight and length density in the high‐P strip were significantly greater for the low‐P plants than for the plants with 14 mg P (kg soil)^–1. However, after 8 weeks of growth in the split‐root system, the two P treatments of compartment A had similar root growth in the high‐P strip of compartment B. The study also showed that shoot P concentrations in the low‐P plants were 0.6–0.8 mg g^–1 compared with 1.7–1.9 mg g^–1 in the 14 mg P kg^–1 plants after 3 and 5 weeks of growth, but were similar (1.1–1.4 mg g^–1) between the two plants by week 8. The low‐P plants had lower root P concentration in both compartments than those with 14 mg P kg^–1 throughout the three harvests. The findings may indicate that root proliferation and P acquisition under heterogeneous conditions are influenced by shoot P status (internal) and soil P distribution (external). There were no differences in the total root and shoot dry weight between the two P treatments at weeks 3 and 5 because enhanced root growth and P uptake in the high‐P strip by the low‐P plants were compensated by reduced root growth elsewhere. In contrast, total plant growth and total root and shoot P contents were greater in the 14 mg P kg^–1 soil than in the low‐P soil at week 8. The two P treatments did not affect the ratio of root to shoot dry weight with time. The results suggest that root proliferation and greater P uptake in the P‐enriched zone may meet the demand for P by P‐deficient plants only for a limited period of time.     

Application of low‐phosphorus‐containing legume residues reduces extractable phosphorus in a tropical Ultisol

Application of legume green manure (GM) is suggested to be effective in increasing the availability of native soil phosphorus (P) and the dissolution and utilization of phosphate rock (PR)‐P by food crops. Experiments were conducted to study the dynamics of extractable P (P extracted by Bray‐1‐extracting solution) of an Ultisol amended with or without GM residues of contrasting P concentrations in the absence of growing plants. In two separate experiments, GM residues of Aschynomene afraspera (a flood‐tolerant legume) and of Crotalaria micans (upland) with varying P concentrations were added to an acidic soil amended with PR‐P or triple superphosphate (TSP) in plastic bottles. Soil moisture was brought to field capacity of the soil in the upland experiment and saturated with distilled water in the lowland setup. This was done to simulate aerobic upland and anaerobic lowland soil conditions in the relevant plastic bottles. Only P concentration of the residues added varied, while lignin and C : N ratios were similar. A temperature of 25°C was maintained throughout the experiment. Changes in soil extractable Bray‐1‐P were measured at the end of the incubation period (60 or 80 d). In the aerobic soils, extractable P in the combined PR+GM or TSP+GM treatments was significantly lower than in the PR‐ or TSP‐ treated soils. The amendment with GM residues alone significantly increased Bray‐1‐P over the unamended control in the case of the inorganic P‐fertilized GM residues. The trend in extractable P was similar in the soils incubated under anaerobic conditions. However, in the case of PR, concentrations of P extracted by Bray‐1 solution did not significantly change in the presence or absence of GM. The results suggest that the incorporation of GM residues with low P concentration does not lead to a net P release in upland or lowland soils. These results have implications for nutrient cycling in farming systems in W Africa as most of the soils are poor and very low in available P.     

Utilization by wheat crops of nitrogen from legume residues decomposing in soils in the field

Ground ¹⁵N-labelled legume material (Medicago littoralis) was mixed with topsoils in confined microplots in the field, and allowed to decompose for 7 and 5 months in successive years (1979, 1980) before sowing wheat. The soil cropped in 1979 (and containing ¹⁵N-labelled wheat roots and legume residues) was cropped again in 1980.The results support evidence that ungrazed legume residues, incorporated in amounts commonly found in southern Australian wheat growing regions, contribute only a little to soil available N and to crop N uptake, even in the first year of their decomposition. Thus mature first crops of wheat, although varying greatly in dry matter yield (2.9-fold) and total N uptake (2.4-fold), took up only 27.8 and 20.2% of the legume N applied at 48.4 kg ha^?1, these corresponding to 6.1 and 10.8% of the N of the wheat crops. The availability of N from medic residues to a second wheat crop declines to <5% of input. For both first and second wheat crops, uptake of N from legume residues was approximately proportional to legume N input over the range 24.2 to 96.8 kg ha ^?1.The proportional contributions of medic N to soil inorganic N, N released in mineralization tests, and to wheat crop N, differed between seasons and soils, but for a given crop did not significantly differ between tillering, flowering and maturity. In both years, grain accounted for 52–65% of the total ¹⁵N of first crops, roots for < 5–6%. In neither year did the amounts of N or ¹⁵N in the tops change significantly between flowering and maturity, despite a gain in tops dry matter in 1979; by contrast N and ¹⁵N of roots decreased significantly during ripening in both years. Wheat plants at tillering contained about 75% of the N and ¹⁵N taken up at flowering. The amounts of legume-derived ¹⁵N in mature first wheat crops were equivalent to 82–88% of the amounts of inorganic ¹⁵N in the soil profiles at sowing. Wheat straw added at the rate of 2.5 t ha^?1, 2 months before sowing, decreased the uptake of N (15%) and ¹⁵N (18%) by wheat in a nitrogen responsive season.     

Estimation of maximum permissible levels of cadmium in a light soil by using cereal plants

A pot experiment was conducted in a greenhouse to establish the threshold level of Cd in a light soil planted with cereals. During three consecutive years barley, wheat, rye, and corn were grown in the soil treated with 2.5; 5; 25 g g^–1 of Cd applied in sulphate form. The Cd concentration of 5 g g^–1 (plus native Cd content of the soil) was considered as the maximum permissible Cd level in a soil for the soil-plant systems studied. Besides the estimation of total Cd concentrations, several forms of Cd in soils (exchangeable, carbonate, Fe-Mn oxides, organic, and residual) were determined by mean of sequential extraction to define the phytoavailable form of Cd in the soil. The Cd concentration in studied plants increased with the doses of this metal in soil but to different extents for various plant species and various plant parts. The highest Cd enrichment ratios (ER) were found for wheat and corn leaves (2 to 3), whereas, the lowest ERs were detected for corn and rye grains (0.05 to 0.2) grown at the treated soils. All samples of the control plants had ER below 1. A close relationship was found between Cd content of plants and the exchangeable form of Cd in soil, which indicates that this form of the element is readily available for plants. The proposed maximum permissible level of Cd (5 g g^–1 of added metal plus native Cd content of soils) in light soils proved to be too high for cereal plants. The threshold concentration for light soil should not exceed 3 g g^–1.     

Grain legume effects on soil nitrogen mineralization potential and wheat productivity in a Mediterranean environment

The objective of this work was to provide evidence on the effects of faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) on the dynamics of soil N availability and yield parameters of wheat (Triticum turgidum L. var. durum) in a legume–wheat rotation in comparison with the effects of the more extensively studied common vetch (Vicia sativa L.). Soil samples were taken from field plots just before wheat sowing and incubated in the laboratory to assess N mineralization potential, soil respiration and N immobilization after incorporation of legume residues. Soil after vetch cultivation showed the highest residual N and mineralization potential (120 mg N kg^?1 soil), the greatest CO₂ release and the smallest N immobilization. Smaller mineral N release (80 mg N kg^?1 soil) was shown by soil after faba bean cultivation, which, however, would be capable to support an average wheat production without fertilization. Soil after chickpea and wheat cultivation manifested no differences in residual N and mineralization or immobilization potential. Laboratory results were well correlated with grain yield and N uptake during the second season of rotation in the field. All legumes resulted in significant yield surpluses and provided N credit to the following unfertilized wheat.     

生物炭对潮土磷有效性、小麦产量及吸磷量的影响

为探究玉米秸秆生物炭对潮土磷素有效性、小麦产量及吸磷量的影响,采用室内盆栽试验,在潮土中添加0、0.2%、1.0%和5.0%(即CK、MB_(0.2)、MB_(1.0)、MB_(5.0)处理)4个水平的生物炭,分析了不同生物炭用量下潮土磷素有效性、小麦产量及磷素吸收的变化特征。结果表明,随着时间的推移,同一处理下土壤有效磷(AP)含量均逐渐减少,但总体变化不大。在3个关键生育期,土壤AP含量均随生物炭用量的增加而增加;与CK处理相比,成熟期MB_(0.2)、MB_(1.0)和MB_(5.0)处理的土壤AP含量分别显著增加了11.3%、30.5%和167.1%。土壤AP含量与土壤pH、电导率(EC)及有机碳(SOC)含量呈极显著正相关,与土壤磷酸酶活性则呈显著负相关。研究还发现,MB_(1.0)和MB_(5.0)处理产量较CK均显著增加,其中MB_(1.0)处理产量增幅最大,达33.7%。小麦收获后,籽粒磷含量、吸磷量随生物炭用量的增加而增加,其中MB_(5.0)处理的籽粒磷含量和吸磷量均显著高于其它处理,增幅范围分别为21.4%～30.8%、23.0%～68.9%;而处理间植株磷含量和吸收量均无显著性差异(P0.05)。因此,施入中、高量(MB_(1.0)、MB_(5.0))生物炭有利于提高潮土磷素有效性、小麦产量及籽粒磷素吸收。     

水磷互作对黑垆土春小麦生长及产量的影响

在温室条件下进行了黑垆土水磷互作对春小麦生长及产量影响的研究。结果表明,水分和磷素对春小麦苗期与抽穗期内株高和叶面积皆有一定影响,但交互作用的表现不同;适宜的水分与磷素配合既满足了春小麦物质生产过程中对水分和营养元素的需求,又促进了春小麦生长发育,提高了生物产量、经济产量及水分生产效率,从而可以达到以水促磷和以磷促水的目的;而缺水高磷组合或高水低磷组合均不利于春小麦生长发育,其产量与水分生产效率也较低。     

Effect of one phosphorus rate placed in different soil volumes on p uptake and growth of wheat

Abstract

The volume of soil treated with P fertilizer affects P uptake by the crop. Earlier studies have shown that the stimulation of root growth in P‐fertilized soil was similar for both corn (Zea mays L.) and soybean (Glycine max L. Merr). The objective of this research was to determine the effect of fertilizer P placement on P uptake and shoot and root growth of spring wheat (Triticum vulgare L.). Wheat was grown for 34 days in Raub silt loam (Aquic Argiudolls) in a controlled climate chamber. One rate of phosphate per pot, 150 mg P per three kg of soil, was mixed with 2, 5, 10, 20, 40 and 100% of the soil in the pot. The P was equilibrated with moist soil for 5 days at 70°C followed by 21 days at 25° C before transplanting 8‐day‐old wheat plants into each 3 L pot. The P stimulation of root growth in the P‐treated soil was similar to that for corn and soybeans. The effect could be described by the equation y = x^0.7 where y is the fraction of the root system in the P‐fertilized soil where P is mixed with x fraction of the soil. The greatest P uptake and plant growth occurred when added P was mixed with 20% of the soil.     

Effect of legume and legume-festulolium mixture and their mulches on cereal yield and soil quality in organic farming

ABSTRACT

Research was conducted to determine the effects of perennial legume and their mulches on cereal grain yield and the alterations to clay loam Cambisol properties. The perennial legumes (Trifolium pratense L., Medicago sativa L.) as well as their mixtures with festulolium (x Festulolium) were studied in conjunction with their aboveground biomass management methods: removal from the field (cut twice for forage), mixed management (the first cut was for forage, the second and third cuts were mulched) and mulching (four times) in an organic arable farming system. Mulching of legumes biomass resulted in a higher total nitrogen (N) used for green manure. A similar amount of N was accumulated for lucerne and lucerne-festulolium mulch when using mulching and mixed management. Legumes used for mulching caused the amount of mineral N in soil to increase in late autumn (62.7–82.9 kg ha^–1) and decrease in spring (39.5–64.0 kg ha^–1). This mineral N had a positive impact on crop yield (r = 0.68–0.71*); however, mineral N in autumn had a negative impact on soil sustainable organic compounds (r = ?0.71*). The results indicate that the most suitable treatment was the legume-festulolium mixture, which used the biomass under mixed management.     

Distribution and recovery of nitrogen from legume residues decomposing in soils sown to wheat in the field

Unground ¹⁵N-labelled medic material (Medicago littoralis) was mixed with topsoils at 3 field sites in South Australia, allowed to decompose for about 8 months before sowing wheat, and then for a further 7 months until crop maturity. The site locations were chosen to permit comparisons of recoveries and distribution of ¹⁵N in soils (organic N and inorganic N to 90 cm depth) and wheat (grain, straw and roots to 20 cm depth) in areas where rainfall (and wheat yields) differed greatly. Soils differed also in their texture and organic matter contents. Recoveries of applied ¹⁵N in wheat plus soil were 93.1% from a sandy loam (Caliph) and 92.3% from a sandy soil (Roseworthy) despite differences in rainfall and extent of leaching of the ¹⁵NO₃^? formed from the decomposing medic residues. From a heavy clay soil (Northfield), which received the highest rainfall, the ¹⁵N recovery was 87.7%. The loss of ¹⁵N at this site was not due to leaching, as judged by ¹⁵NO₃^? distribution in the soil profile at seeding and crop maturity.Wheat plants took up only 10.9–17.3% of the ¹⁵N added as legume material. Percentage uptakes of ¹⁵N were not related to grain yields. The proportions of wheat N derived from decomposing medic residues were 9.2% at Caliph (input medic, N, 38 kg N ha^?1), 10.5% at Roseworthy (input medic N, 57 kg N ha^?1), and only 4.6% at Northfield (input medic N, 57 kg N ha^?1). Most (51–70%) of the ¹⁵N recovered in wheat was accounted for in the grain. Inorganic ¹⁵N in the soil profiles was depleted during the cropping phase, and at wheat harvest represented from 0.6 to 3.1% only of ¹⁵N inputs. The major ¹⁵N pool was soil organic ¹⁵N accounting for 71.9–77.7% of ¹⁵N inputs.We conclude that, in the context of N supply from decomposing medic tissues to wheat crops, the main value of the legume is long-term, i.e. in maintaining soil organic N concentrations to ensure adequate delivery of N to future cereal crops.The N of the wheat was not uniformly labelled, root N being generally of the highest atom% enrichmensts, and straw N of the lowest. Nevertheless, at the Roseworthy site, the enrichments of wheat N were similar to those of NO₃^? N in the profile at seeding, indicating that the proportions of ¹⁴N and ¹⁵N in the inorganic N pool did not change appreciably during the cropping period. By assuming equilibrium at this site, we calculate that during 15 months decomposition the soil plus legume delivered about 189 kg N ha^?1, of which 93.2 kg ha^?1 (49.3%) was taken up by the wheat, 37.2 kg ha^?1 (19.7%) was immobilized or remained as fine root residues, and 17.3 kg ha^?1 (9.2%) remained as inorganic N in the soil profile; 41.7 kg ha^?1 (22.1%) was unaccounted for in the soil-plant system, and was probably lost via inorganic N. Thus about 6.5 kg inorganic N ha^?1 was supplied by the soil plus medic residues per 100 kg dry matter ha^?1 removed as wheat grain.     

Chemical changes and phosphorus release during decomposition of pea residues in soil

To study C chemistry and nutrient dynamics in decomposing residues and P dynamics at the residue-soil interface, young pea (Pea-Y) and mature pea (Pea-M) residues were incubated in a sandy soil with low P availability. The study was conducted in microcosms in which the residues were separated from the soil by a nylon mesh. Controls consisted of microcosms without residues. Residues and the soil in the immediate vicinity of the nylon mesh were sampled after 5, 15, 28, 42 and 61 days. Residue chemistry was studied by ¹³C nuclear magnetic resonance (NMR) spectroscopy and determination of C, N and P concentrations. Compared to Pea-M, Pea-Y was characterised by higher N and P concentrations, higher percentage of proteins, esters, fatty acids and sugars, and was more easily decomposable in the first 15 days. Pea-M residues had a greater percentage of cellulose and other polysaccharides than Pea-Y and showed a more gradual loss in dry weight. Differences in C chemistry and N and P concentration between the residues decreased with time. The decomposition of Pea-Y and Pea-M residues resulted in an increase in microbial P in the residue-soil interface compared to the control, but available P was increased only in the vicinity of Pea-Y residues.     

Grain legume pre-crops and their residues affect the growth, P uptake and size of P pools in the rhizosphere of the following wheat

Legumes have been shown to increase P uptake of the following cereal, but the underlying mechanisms are unclear. The aim of this study was to compare the effect of legume pre-crops and their residues on the growth, P uptake and size of soil P pools in the rhizosphere of the following wheat. Three grain legumes (faba bean, chickpea and white lupin) were grown until maturity in loamy sand soil with low P availability to which 80?mg P kg^?1 was supplied. This pre-crop soil was then amended with legume residues or left un-amended and planted with wheat. The growth, P uptake and concentrations of P pools in the rhizosphere of the following wheat were measured 6?weeks after sowing. In a separate experiment, residue decomposition was measured over 42?days by determining soil CO₂ release as well as available N and P. Decomposition rates were highest for chickpea residues and lowest for wheat residues. P release was greatest from white lupin residues and N release was greatest from faba bean residues, while wheat residues resulted in net N and P immobilisation. The growth of the following wheat was greater in legume pre-crop soil without residue than in soils with residue addition, while the reverse was true for plant P concentration. Among the legumes, faba bean had the strongest effect on growth, P uptake and concentrations of the rhizosphere P pools of the following wheat. Regardless of the pre-crop and residue treatment, wheat depleted the less labile pools residual P as well as NaOH-Pi and Po, with a stronger depletion of the organic pool. We conclude that although P in the added residues may become available during decomposition, the presence of the residues in the soil had a negative effect on the growth of the following wheat. Further, pre-crops or their residues had little effect on the size of P pools in the rhizosphere of wheat.     

不同豆科植物对黄土高原弃土场的改良效果

为了探究豆科植物种植初期对黄土高原地区弃土场的改良效果,本文采用野外模拟弃土场和实验室测定相结合的方法,在弃土场上种植柠条、白三叶、红豆草、草木樨和紫花苜蓿5种豆科植物,研究1年后弃土场土壤的水分和养分状况.结果表明:各小区种植植物1年后,土壤水分状况有了明显的改善;土壤养分硝态氮质量分数增加,有机质、速效钾的质量分数除了草木樨有所增加以外,其他均减少,速效磷的质量分数均减少,土壤中的速效钾由于植物生长消耗而减少,但其质量分数丰富,足以满足植物生长的需要;土壤中的铵态氮和硝态氮质量分数表现为表聚作用,且硝态氮的质量分数均大于铵态氮;植被对土壤的改良程度依次为白三叶＞柠条＞红豆草＞紫花苜蓿＞草木樨.因此,种植豆科植物可以有效的改善土壤的水分和氮素营养,为今后弃土场土壤改良提供一定的理论参考.     

Chemical forms of cadmium in a calcareous soil treated with different levels of phosphorus and cadmium and planted to spinach

The objective of the investigation was to evaluate the effect of applied phosphorus (P) and cadmium (Cd) on Cd chemical forms determined by sequential extraction and the relationship between these forms and plant responses, i.e., dry weights, concentration, and total uptake of Cd and P in a greenhouse experiment. Treatments consisted of five levels of Cd (5, 10, 20, 40 and 80 mg kg^?1 soil as cadmium sulfate) and four levels of P (0, 15, 30 and 60 mg kg^?1 soil as monocalcium phosphate), which were added to the soil and left to equilibrate for 1 month under greenhouse conditions. Spinach seeds (Spinacea oleracea L., cv Viroflay) were sown and then grown for 8 weeks. The chemical composition in the aerial part of the pant and soil was determined. Application of Cd decreased plant dry matter and increased Cd concentration in the plant, whereas at each level of applied Cd, P increased plant dry matter and decreased plant Cd concentration. All chemical forms of Cd in soil, as determined by a fractionation method, were increased following Cd application, the highest being the carbonatic form. Phosphorous application decreased exchangeable and carbonatic forms of Cd, whereas it increased other forms.