Nitrogen effects of non-legume catch crops

Nitrate leaching during the winter period can be reduced and often prevented by growing catch crops after the harvest of a main crop. However, catch crops which effectively take up residual nitrogen do not necessarily show good nutrient effects on a succeeding main crop. The objective of this experiment was to investigate how the content of soil mineral nitrogen in spring was affected by the time of incorporation of non-legume catch crops and how the yield and nitrogen uptake of a succeeding main crop was influenced. The yield of spring sown onion and white cabbage was significantly increased by catch crop growing the previous autumn. The nitrogen effect of Italian ryegrass corresponded to 50–100 kg N per ha in the vegetables. However, the yield of spring barley was not significantly affected by the nitrogen released from decomposing catch crops. During decomposition of non-legume catch crops, grown at a high level of nitrogen fertility, nitrogen immobilization did not occur.     

Effect of Catch Cropping on Phosphorus Bioavailability in Comparison to Organic and Inorganic Fertilization

ABSTRACT

Phosphorus (P) is a limited resource and its efficient use is a main task in sustainable agriculture. In a 3-year field experiment the effects of catch cropping [oil radish (Raphanus sativus), buckwheat (Fagopyrum esculentum), serradella (Ornithopus sativus), ryegrass (Lolium westerwoldicum), and phacelia (Phacelia tanacetifolia)] of organic fertilization (cattle manure and biowaste compost) and of inorganic fertilization (Triple-Superphosphate) on plant and soil parameters were investigated on a P-poor loamy sand in Northeast Germany. The catch crops were sown in September and remained on the plots until next spring. Then the main crops oilseed rape (Brassica napus), spring barley (Hordeum vulgare), or spring wheat (Triticum aestivum) were cultivated. The yield and P uptake of the main crops were determined. Furthermore, in the soil the organic matter content, pH, phosphorus (P) in soil solution (Psol), double-lactate and oxalate P content, P sorption capacity, and degree of P saturation were measured. All applied forms of fertilizer affected the P contents in soil and the yields and P uptakes of main crops. For green fertilization especially phacelia was found to contribute to the P supply of the main crops, since it increased the P uptake as well as the P contents in soil significantly. The cultivation of ryegrass led to a reduction of the P availability in soil. For example, in average of the three years the Psol content was 0.35 mg L^{? 1}when phacelia was cultivated and 0.22 mg L^{? 1} when ryegrass was cultivated. The cultivation of phacelia had a comparable effect on soil and plant parameters as the organic and mineral fertilization. An improved P availability and P utilization by catch cropping can reduce the need for external P input which may help to save the limited P resources worldwide.     

Leaching of N,P and glyphosate from two soils after herbicide treatment and incorporation of a ryegrass catch crop

During 2005–2007, studies were carried out in two field experiments in southwest Sweden with separately tile‐drained plots on a sandy soil (three replicates) and on a clay soil (two replicates). The overall aim was to determine the effects of different cropping systems with catch crops on losses of N, P and glyphosate. Different times of glyphosate treatment of undersown ryegrass catch crops were examined in combination with soil tillage in November or spring. Drainage water was sampled continuously in proportion to water flow and analysed for N, P and glyphosate. Catch crops were sampled in late autumn and spring and soil was analysed for mineral N content. The yields of following cereal crops were determined. The importance of keeping the catch crop growing as long as possible in the autumn is demonstrated to decrease the risk of N leaching. During a year with high drainage on the sandy soil, annual N leaching was 26 kg/ha higher for plots with a catch crop killed with glyphosate in late September than for plots with a catch crop, while the difference was very small during 1 yr with less drainage. Having the catch crop in place during October was the most important factor, whereas the time of incorporation of a dead catch crop did not influence N leaching from either of the two soils. However, incorporation of a growing catch crop in spring resulted in decreased crop yields, especially on the clay soil. Soil type affected glyphosate leaching to a larger extent than the experimental treatments. Glyphosate was not leached from the sand at all, while it was found at average concentrations of 0.25 μg/L in drainage water from the clay soil on all sampling occasions. Phosphorus leaching also varied (on average 0.2 and 0.5 kg/ha/yr from the sand and clay, respectively), but was not significantly affected by the different catch crop treatments.     

Measured and simulated availability and leaching of nitrogen associated with frequent use of catch crops

Abstract. Results are presented from three years (1992-1995) of a field leaching experiment on a sandy soil in south-west Sweden. Plots of spring cereals, either with or without an undersown perennial ryegrass catch crop, were compared for nitrogen leaching and nitrogen status in soil. Both treatments were ploughed in spring, and other tillage regimes were also identical. Measurements of nitrogen leaching from drains, nitrogen uptake in crops and mineral nitrogen in the soil were made. Two coupled, simulation models, which describe water flow and nitrogen transformations and transport in soil, were used to interpret data and to calculate the nitrogen budget and nitrogen mineralization in the soil.
Nitrogen leaching was 40 50% less in the catch crop treatment compared with the control during years when the establishment of the catch crop succeeded. In the third year of the experiment nitrogen leaching was actually greater in the catch crop treatment (7 kg N/ha). This increase was caused by a poorly established catch crop coinciding with enhanced mineralization of previous catch crop residues. There was no simulated change in soil organic nitrogen in either of the treatments. Simulations showed increased nitrogen mineralization during April-July after incorporation of plant material in spring, especially in the catch crop treatment. However, the increased nitrogen mineralization probably occurred too late for the released nitrogen to be fully available to the main crop.     

Cover crop growth and impact on N leaching as affected by pre‐ and postharvest sowing and time of incorporation

In Northern Europe, cover crops are traditionally established before spring crops by undersowing, but some cover crops might also have an effect if preharvest sown before spring crops and even winter crops. The effects of cover crop sowing date, sowing technique and succeeding main crop on biomass production, N uptake, nitrate leaching and soil inorganic N were tested in lysimeters and in the field. Cruciferous cover crops (oil radish, white mustard) were sown preharvest by broadcasting into winter wheat in July and were allowed to grow until a following winter wheat was established in September. Other preharvest cover crops were left in place until late autumn. For comparison, the same cruciferous cover crops were established postharvest after light harrowing. Perennial ryegrass undersown in spring barley was also included. Aboveground N uptake in preharvest cover crops amounted to a maximum of 24 kg N/ha in September before sowing winter wheat. When left until late autumn, preharvest oil radish took up a maximum of 66 kg N/ha, and ryegrass and postharvest cover crops 35 kg N/ha. Preharvest establishment of cruciferous cover crops before a spring‐sown crop thus seems promising. The soil was depleted of inorganic N to the same extent in late autumn irrespective of cover crop type, sowing time and technique within winter wheat or spring barley. However, the reduction in nitrate leaching of preharvest cover crops incorporated after 2 months and followed by winter wheat was only half of that achieved by cover crops left until late autumn or spring.     

Cover crops and their erosion-reducing effects during concentrated flow erosion

Cover crops are a very effective erosion control and environmental conservation technique. When cover crops freeze at the beginning of the winter period, the above-ground biomass becomes less effective in protecting the soil from water erosion, but roots can still play an important role in improving soil strength. However, information on root properties of common cover crops growing in temperate climates (e.g. Sinapis alba (white mustard), Phacelia tanacetifoli (phacelia), Lolium perenne (ryegrass), Avena sativa (oats), Secale cereale (rye), Raphanus sativus subsp. oleiferus (fodder radish)) is very scarce. Therefore, root density distribution with soil depth and the erosion-reducing effect of these cover crops during concentrated flow erosion were assessed by conducting root auger measurements and controlled concentrated flow experiments with 0.1 m topsoil samples. The results indicate that root density of the studied cover crops ranges between 1.02 for phacelia and 2.95 kg m^− 3 for ryegrass. Cover crops with thick roots (e.g. white mustard and fodder radish) are less effective than cover crops with fine-branched roots (e.g. ryegrass and rye) in preventing soil losses by concentrated flow erosion. Moreover, after frost, the erosion-reducing potential of phacelia and oats roots decreased. Amoeba diagrams, taking into account both below-ground and above-ground plant characteristics, identified ryegrass, rye, oats and white mustard as the most suitable species for controlling concentrated flow erosion.     

Animal manure slurries as a source of nitrogen for cereals; effect of application time on efficiency

Abstract. Field experiments undertaken at 14 sites, on a range of soil types, in lowland England, during the cropping years 1989–1993, tested the effectiveness of cattle or pig slurry as a source of nitrogen for cereal cropping. Slurry was applied in autumn, winter and spring, to autumn and spring sown cereal crops. Assessments included slurry nitrogen efficiency relative to N in spring applied fertilizer in terms of both grain yield and grain protein production, apparent crop recovery and content of mineral nitrogen in soil profiles. Crop response to nitrogen was poor at seven sites where high residues of soil mineral nitrogen (SMN) were present. On the seven responsive sites, spring slurry applications proved more efficient (mean 40%) as a source of N than autumn (mean 24%) or winter applications (mean 32%). These differences were smaller than reported in a number of other studies, probably as a result of relatively low excess winter rainfall, resulting in less nitrate leaching during the period of the investigation. Rapid incorporation into the topsoil of slurry applied in autumn, increased (28 kgN/ha) the SMN of samples taken early in the winter. However this increase did not lead to a consistent improvement in crop N uptake. Slurry dressings, whenever applied, can be expected to make a significant contribution to the N requirement of the succeeding crop and need to be taken into account when calculating the appropriate spring fertilizer application.     

Simulating nitrate retention in soils and the effect of catch crop use and rooting pattern under the climatic conditions of Northern Europe

This model analysis of catch crop effects on nitrate retention covered three soil texture classes (sand, loamy sand, sandy loam) and three precipitation regimes in a temperate climate representative of northern Europe (annual precipitation 709–1026 mm) for a period of 43 years. Simulations were made with two catch crops (ryegrass and Brassica) with different rooting depths, and soil N effects in the next spring were analysed to 0.25, 0.75 and 2.0 m depth to represent the catch crop effect on following crops with different rooting depths. Nitrate retained without a catch crop was generally located in deeper soil layers. In the low precipitation regime the overall fraction of nitrate retained in the 0–2.0 m soil profile was 0.23 for the sandy soil, 0.69 for the loamy sand and 0.81 for the sandy loam. Ryegrass reduced leaching losses much less efficiently than Brassica, which depleted nitrate in the 0–0.75 m soil layer more completely, but also in the deeper soil layer, which the ryegrass could not reach. A positive N effect (N_eff, spring mineral N availability after catch crop compared with bare soil) was found in the 0–0.25 m layer (that is shallow rooting depth of a subsequent main crop) in all three soil texture classes, with on average 10 kg N/ha for ryegrass and 34 kg N/ha for Brassica. Considering the whole soil profile (0–2.0 m deep rooting of next crop), a positive N_eff was found in the sand whereas generally a negative N_eff was found in the loamy sand and especially the sandy loam. The simulations showed that for shallow‐rooted crops, catch crop N_eff values were always positive, whereas N_eff for deeper‐rooted crops depended strongly on soil type and annual variations in precipitations. These results are crucial both for farmers crop rotation planning and for design of appropriate catch crop strategies with the aim of protecting the aquatic environment.     

苏南稻田4种冬绿肥养分特性及对翻压前土壤无机氮的影响

为充分利用苏南冬闲稻田发展适宜绿肥作物种植,在大田试验条件下,研究了毛叶苕子（Vicia villosa Roth）、 光叶苕子（Vicia villosa var.）、 紫云英（Astragalus sinicus L.）和肥田萝卜（Raphanus sativus L.）4种绿肥作物的生长、 营养特性,比较分析了绿肥作物翻压前不同处理间耕层土壤无机氮含量与构成的差异。结果表明,在绿肥作物翻压期,4种绿肥作物均达到较高生物量和养分累积量,鲜重、 干重分别为24.8 30.7 t/hm2和3.6 4.2 t/hm2,不同绿肥作物间无显著差异。 4种绿肥作物的吸氮量为69.8 136.4 kg/hm2,毛叶苕子最高,肥田萝卜最低。吸磷量为7.1~11.3 kg/hm2,肥田萝卜最高,紫云英最低。吸钾量为117.6~151.3 kg/hm2,毛叶苕子最高,光叶苕子最低。与对照冬闲相比,种植绿肥作物不同程度地降低了耕层土壤无机氮含量（平均降低38.9 kg/hm2）,其中硝态氮含量下降明显,铵态氮含量均较对照土壤有增加趋势（平均提高6.5 kg/hm2）,毛叶苕子和光叶苕子处理铵态氮含量增加显著。4种绿肥作物均适合苏南冬闲稻田种植,能潜在降低无机氮的损失风险和为后季水稻作物生长提供养分。     

Simulation of nitrogen dynamics in farmland areas of Denmark (1989–1993)

Abstract. Each year since 1986 information has been collected about the farming systems at intersections of a nationwide 7 km square grid in Denmark. These management data and corresponding soil analyses were used in the model DAISY to simulate water and nitrogen dynamics. The model was validated with respect to harvested dry matter yield and nitrogen content in the soil. Simulated nitrate leaching from farmland areas from 1 April 1989 to 31 March 1993 was related to precipitation zones, soil type, fertilizer strategies and cropping systems. The mean simulated nitrate leaching for the whole of Denmark was 74 kg N/ha/yr, with a large yearly variation in the period considered. The simulated nitrate leached from soils with a sandy subsoil corresponded to 51% of the applied fertilizer, twice that leached from soils with a loamy subsoil. The application of pig manure resulted in average leaching losses of 105 kg N/ha/yr. The simulated nitrate leaching losses at sites where only artificial fertilizer was applied were in the following order: cereal with undersown grass < crop followed by winter cereal or winter rape < cereal or rape without a catch crop < root crops without a catch crop. Where only artificial fertilizers were applied, the simulated mean annual leaching was 59 kg N/ha from spring barley and 40 kg N/ha from winter wheat. A map of simulated nitrate leaching in Denmark was produced using a Geographical Information System.     

施氮量和土壤含水量对黑麦草还田红壤氮素矿化的影响

目标 氮素矿化是决定土壤供氮能力的重要生态过程,养分添加和水分在调节土壤的氮转化方面起着重要的作用。探讨施氮和土壤水分对黑麦草还田过程中土壤氮素矿化的影响有利于进一步优化红壤旱地作物生产的水肥管理。 【方法】 通过室内培养试验,研究了施氮量 (0、60、120 mg/kg) 和土壤含水量 (15%、30%、45%) 对红壤旱地黑麦草还田过程中土壤净硝化量、氨化量和氮矿化量的影响。 【结果】 土壤含水量15%时,施氮有利于提高黑麦草还田初期土壤净硝化量,施氮量120 mg/kg抑制了黑麦草还田后期土壤硝化作用。在30%土壤含水量时,施氮量120 mg/kg明显抑制了黑麦草还田后期土壤硝化作用。土壤含水量45%抑制了黑麦草还田初期不同施氮水平下土壤净硝化量,但增加了黑麦草还田91 d时土壤净硝化量,且施氮量60 mg/kg下的净硝化量显著高于120 mg/kg水平下的。土壤净氨化量在整个黑麦草还田过程中均为正值,且呈现多次升高-降低的往复动态变化。土壤净氨化量在三种土壤含水量下均表现为施氮条件下的显著高于不施氮处理。土壤含水量的增加有利于提高施氮量120 mg/kg下黑麦草还田初期土壤的氨化作用,但降低了黑麦草还田后期土壤净氨化量。相比不施氮,三个含水量条件下的施氮处理在黑麦草还田过程中的大部分阶段都显著增加了土壤净氮矿化量,土壤含水量30%条件下土壤净氮矿化量的变化最大。相比土壤含水量15%,30%含水量促进了黑麦草还田中期 (13～57 d) 土壤净氮矿化量的增加,45%含水量抑制了黑麦草还田后期 (73～91 d) 土壤净氮矿化量。 【结论】 红壤区旱地黑麦草还田时应合理施入化学氮肥 (60 mg/kg),在黑麦草还田初期保持较高的土壤含水量 (45%) 能够抑制土壤的氮矿化作用,还田中后期适当降低土壤含水量 (30%)有利于增加土壤氮素的矿化。      

Catch crop biomass production,nitrogen uptake and root development under different tillage systems

Catch crops are generally regarded as an efficient tool to reduce nitrate leaching. However, the benefits need to be balanced against potential adverse effects on the main crop yields. The objectives of the study were to study three contrasting catch crops, that is, dyer's woad (DW) (Isatis tinctoria L.), perennial ryegrass (RG) (Lolium perenne L.) and fodder radish (FR) (Raphanus sativus L.) under three tillage systems. For that, we used a tillage experiment established in 2002 on a Danish sandy loam. The tillage treatments were direct drilling (D), harrowing to 8–10 cm (H) and ploughing (P). Above‐ground biomass production and N uptake were measured in the catch crops and the main crop. Catch crop root growth was studied using both minirhizotron and core methods. Soil penetration resistance was recorded to 60 cm depth. Fodder radish and RG produced up to 1800 kg/ha dry matter and DW 900 kg/ha. The nitrogen uptake in November was 55, 37 and 31 kg N/ha for FR, RG and DW, respectively, when averaged across the 2 yr of study. The yield of the spring barley main crop was in general highest where FR was grown as a catch crop. Ploughing tended to result in highest yields although differences were only significant in 2008. The minirhizotron root measurements showed that the crucifers FR and DW achieved better subsoil rooting than RG. In contrast, the soil core data showed no significant difference between FR and RG in subsoil root growth. Our study highlights the need for further studies on subsoil root growth of different catch crops.     

Alysimeter study of the effects of a ryegrass catch crop, during a winter wheat/maize rotation, on nitrate leaching and on the following crop

The effects of an intercrop catch crop (Italian ryegrass) on (i) the amounts and concentrations of nitrate leached during the autumn and winter intercrop period, and (ii) the following crop, were examined in a lysimeter experiment and compared with that from a bare fallow treatment. The catch crop was grown in a winter wheat/maize rotation, after harvest of the wheat, and incorporated into the soil before sowing the maize. A calcium and potassium nitrate fertilizer labelled with ¹⁵N (200 kg N ha^?1; 9.35 atom per cent excess) was applied to the winter wheat in spring. Total N uptake by the winter wheat was 154 kg ha^?1 and the recovery of fertilizer-derived N (labelled with ¹⁵N) was 60%. The catch crop (grown without further addition of N) yielded 3.8t ha^?1 herbage dry matter, containing 43 kg N ha^?1, of which 4.1 % was derived from the ¹⁵N-labelled fertilizer. Two-hundred kg unlabelled N ha^?1 was applied to the maize crop. During the intercrop period the nitrate concentration in water draining from the bare fallow lysimeters reached 68 mg N1^?1, with an average of 40 mg N1^?1. With the catch crop, it declined rapidly, from 41 mg N I^?1 to 0.25 mg N I^?1, at the end of ryegrass growth. Over this period, 110 kg N ha^?1 was leached under bare fallow, compared with 40 kg N ha^?1 under the catch crop. ¹⁵N-labelled nitrate was detected in the first drainage water collected in autumn, 5 months after the spring application. The quantity of fertilizer-N that was leached during this winter period was greater under bare fallow (18.7% of applied N) than when a catch crop was grown (7.1 %). In both treatments, labelled fertilizer-N contributed about 34% of the total N lost during this period. With the ryegrass catch crop incorporated at the time of seedbed preparation in spring, the subsequent maize grain-yield was lowered by an average of 13%. Total N-uptake by the maize sown following bare fallow was 224 kg N ha^?1, compared with 180 kg ha^?1 with prior incorporation of ryegrass; the corresponding values for uptake of residual labelled N were 3% (bare fallow) and 2% (ryegrass) of the initial application. Following the maize harvest, where ryegrass was incorporated, 22.7% of the previous year's labelled fertilizer addition was present in an organic form on the top 30 cm of lysimeter soil. This compares with 15.7% for the bare fallow intercropping treatment. Tracer analyses showed overall recoveries of labelled N of 91.7% for the winter wheat/ ryegrass/maize rotation and 97% for the winter wheat/bare fallow/maize rotation. The study clearly demonstrated the ecological importance of a catch crop in reducing N-leaching as well as its efficient use of fertilizer in the plant-soil system from this particular rotation. However, the fate of the organic N in the ploughed-down catch crop is uncertain and problems were encountered in establishing the next crop of maize.     

Improving mineral nitrogen control by combining catch crops,fertilisation, and straw management in a clay loam soil

This experiment was conducted on a clay loam Cambisol and set out to determine the effects of combining catch crops, variable fertilisation levels, and straw management on the productivity of a spring barley-catch crop agrosystem, on the enrichment of soil with organic matter and nitrogen (N), and on soil mineral N control. Research was carried out in a spring barley (Hordeum vulgare L.) crop without catch crops, with undersown red clover (Trifolium pratense L.), and with post-crop white mustard (Sinapis alba L.). The barley was unfertilised, fertilised at moderate rates or at high rates. Straw was managed by either removing it from the field or chopping and spreading it. The quantity of organic matter and N incorporated into the soil depended on the fertilisation level of the barley crop. Soil mineral N stocks in the spring were reduced when straw was used together with red clover. When white mustard mass was incorporated alone in the autumn during ploughing, soil mineral N was reduced in the spring; however, when it was incorporated with straw, the effect was the opposite. Soil mineral N content is controllable when organic matter components are combined according to their decomposition rates, masses, and incorporation times.     

Nitrogen conserving potential of successive ryegrass catch crops in continuous spring barley

Abstract. The nitrogen (N) conserving effects of Italian ryegrass ( Lolium multiflorum L.) undersown as a nitrate catch crop in spring barley ( Hordeum vulgare L.) were evaluated over a ten-year period in outdoor lysimeters (1.5 m deep, diam. 1 m) with sandy loam soil. Spring barley grown every year received 11.0 or 16.5 g N m⁻² before planting or was kept unfertilized. The N was given either as calcium ammonium nitrate or as ammoniacal N in pig slurry. From 1985 to 1989, ryegrass was undersown in the barley in half of the lysimeters while barley was grown alone in the remaining lysimeters. The grass sward was left uncut after barley harvest and incorporated in late winter/early spring. From 1990 to 1994 all lysimeters were in barley only.
Barley dry matter yields and crop N offtakes were not affected by the presence of undersown ryegrass, although grain yields appeared to be slightly reduced. After termination of ryegrass growing, N offtake in barley (grain+straw) was higher in lysimeters in which catch crops had been grown previously.
The loss of nitrate by leaching increased with N addition rate. Regardless of N dressing, ryegrass catch crops halved the total nitrate loss during 1985–1989, corresponding to a mean annual reduction in nitrate leaching of 2.0–3.5 g N m⁻². From 1990 to 1994, lysimeters previously undersown with ryegrass lost more nitrate than lysimeters with no history of ryegrass. The extra loss of nitrate accounted for 30% of the N retained by ryegrass catch crops during 1985–1989.
It is concluded that a substantial proportion of the N saved from leaching by ryegrass catch crops is readily mineralized and available for crop offtake as well as leaching as nitrate. To maximize benefits from ryegrass catch crops, the cropping system must be adjusted to exploit the extra N mineralization derived from the turnover of N incorporated in ryegrass biomass.     

Ergebnisse von Simulationsrechnungen mit einem Bodenstickstoffmodell zur Düngung und zum Zwischenfruchtbau in Trinkwasserschutzgebieten

Results of computer simulations on fertilization and catch cropping problems in water protection areas by means of a soil nitrogen model A simple model of the nitrogen turnover in soil is presented. The model was validated by field experiment time series. The simulation results showed that dividing of the mineral nitrogen fertilization during spring for root crops or maize as well as shortening the first spring nitrogen fertilization for winter cereals diminished the leaching of nitrate only in extremely wet springs on sandy soils. The great importance of winter catch cropping in a cereal-root crop or a cereal-maize rotation on all soils and the necessity to avoid liquid manuring during late summer and early autumn, especially on sandy soils without catch cropping, are demonstrated. The results underline the predominant influence of the weather conditions on nitrate leaching.     

Green manuring with clover and ryegrass catch crops undersown in spring wheat: effects on soil structure

Abstract. The objective of the present study was to investigate the potential of undersown catch crops to counteract soil degradation after autumn ploughing. Italian ryegrass (Lolium multiflorum Lam.) and white clover (Trifolium repens L.) were undersown in spring wheat on a loam soil in southern Norway, allowed to grow as cover crops after grain harvest and ploughed in to 20 cm depth as green manure in late October. Ryegrass prevented a collapse of the ridged plough furrow profile during winter, which occurred on grain monoculture and white-clover plots. Also, it tended to improve the water stability of aggregates, aggregate size distribution, bulk density, and pore volume in soil sampled in May. The preservation of the plough furrow profile was mainly attributed to enmeshment by an extensive system of fine roots and less to rhizosphere and microbial effects on aggregate stability. The results showed that ryegrass catch crops may give rapid structure improvements that are likely to contribute appreciably to easier seedbed preparation and less soil degradation in arable farming systems, even if the soil is ploughed in autumn.     

施氮量对土壤无机氮分布和微生物量氮含量及小麦产量的影响

在高肥力土壤条件下,研究了施氮量对土壤无机氮分布和微生物量氮含量及小麦产量的影响。结果表明,小麦生长期间,施氮处理0100.cm土层硝态氮积累量显著大于不施氮处理;当施氮量大于150.kg/hm2时,随施氮量增加,0100.cm土层硝态氮积累量显著增加;随小麦生育进程推进,施氮处理上层土壤硝态氮下移趋势明显,至小麦成熟时,施氮1952～85.kg/hm2处理60100.cm土层硝态氮含量显著大于其它处理。小麦生长期间,0100.cm土层铵态氮积累量较为稳定,施氮处理间亦无显著差异。与不施氮肥相比,施氮提高小麦生长期间040.cm土层土壤微生物量氮含量;当施氮量小于240.kg/hm2时,随施氮量增加,土壤微生物量氮含量增加。小麦的氮肥利用率随施氮量增加而降低;施氮1051～95.kg/hm2,收获时小麦植株吸氮量、生物产量、子粒产量和子粒蛋白质含量提高;而施氮量大于240.kg/hm2时,小麦生育后期的氮素积累量降低,收获时植株吸氮量、生物产量和子粒蛋白质含量降低。说明本试验条件下,施氮1051～50.kg/hm2可满足当季小麦氮素吸收利用,获得较高的子粒产量和蛋白质含量。继续增加施氮量,土壤微生物量氮含量增加,但土壤中残留大量硝态氮,易淋溶损失。     

Assessment of selenium mineralization and availability from catch crops

Selenium (Se) release from four plant species (Indian mustard, fodder radish, Italian ryegrass and hairy vetch) was measured under controlled leaching conditions and in a pot incubation experiment as part of a study of the potential for using these plant species as Se catch crops. Catch crops may reduce Se leaching and, by subsequent release of Se from the plant material, increase the available Se for succeeding crops. Plants grown both without and with Se addition (250 g Se/ha) were tested. In the leaching experiment, frozen plant material was incorporated into soil columns and incubated at room temperature for up to 19 weeks. The results showed that Se concentrations in the leachate were higher when Se‐enriched plant material was incorporated in the soil, indicating Se mineralization. When non‐enriched plant material was added to the soil, Se concentrations in the leachate were generally lower than that in the control, indicating Se immobilization. In the pot incubation experiment, the results were consistent with those from the leaching experiment. The addition of enriched plant material increased Se concentration in Indian mustard plants compared with unamended soil. However, the addition of plant materials grown without Se significantly decreased Se concentrations in plant dry matter, again indicating Se immobilization. Fertilizer application with inorganic Se as selenate did not affect Se concentrations either in the leachates or in the plants grown in the pot incubation. Thus, the results show the potential of catch crops to increase Se mineralization and uptake in succeeding crops.     

Untersuchungen zur Stickstoff-Immobilisation in mineralisch gedüngten Ackerböden aus Löß während der Vegetationszeit von Winter-Weizen

Experiments on nitrogen immobilization in minerally fertilized soils from loess during the growing season of winter wheat The nitrogen regime has been simulated during the growing period of winter wheat 1984/85 on a stagnigleyic cambisol using a simple, functional computer model. The model includes N mineralization from soil organic matter, transport of water and nitrate as well as growth of wheat and N uptake by the crop. Simulation starts at harvest of the previous crop. Simulated and measured N supply (soil mineral nitrogen plus N uptake by the plant) were in good agreement between september and december 1984. On this loess plot as well as on 10 other ones an over-estimation of mineral nitrogen in the soil up to 40 kg/ha was observed with beginning of december/january 1984/85 reflecting a seasonal trend. Experiments with ¹⁵N enriched Ca-nitrate 1984/85 on microplots of the same field point to a non-consideration of nitrogen immobilization. Fertilizer-N-immobilization amounted up to 35 kg/ha in the soil and to further 15 kg/ha in the straw material. The pool of fixed ammonium was of no importance with respect to the mobilization-immobilization-turn-over of fertilizer nitrogen. Experiments 1988/89 on microplots of a colluvial loess soil indicate a change of biomass nitrogen being responsible for the seasonal N-immobilization. An increase of biomass-N of about 30 kg/ha was observed under the growing wheat crop. An additional N-immobilization of nearly 40 kg/ha was observed with straw incorporation. A similar increase of microbial biomass nitrogen under winter wheat has been observed during the growing period 1987/88.