连续种植不同绿肥作物的土壤团聚体空间分布及稳定性特征

为探讨连续种植绿肥对土壤团聚体的影响,以箭筈豌豆（Vicia sativa L.）、肥田萝卜（Raphanus sativus L.）、蓝花苕子（Vicia cracca L.）、毛叶苕子（Vicia villosa Roth）、光叶苕子(Vicia villosa var.)为研究对象,分析了连续种植不同绿肥作物下的土壤团聚体组成、空间分布及稳定性特征。结果表明：连续种植绿肥能够提高 0~40 cm土层不同粒径土壤机械稳定性团聚体、水稳性团聚体含量,不同绿肥作物显著提高的土壤团聚体在粒径大小及空间分布上不相同。并且连续种植绿肥有利于土壤水稳性大聚体（>0.25 mm）的形成,>5 mm 粒级的土壤水稳性团聚体的增加对土壤水稳性大团聚体积累的影响较为突出,其中肥田萝卜的土壤水稳性大团聚体含量最高。另外,连续种植绿肥还显著降低了 0~20 cm 土层的土壤团聚体破坏率（9.24%~38.19%）,土壤团聚体破坏率表现为毛叶苕子<肥田萝卜<蓝花苕子<箭筈豌豆<光叶苕子,而对土壤平均重量直径的影响表现不同,肥田萝卜、毛叶苕子有利于 0~20 cm 土壤平均重量直径的提升,蓝花苕子、肥田萝卜对 20~40 cm 土壤的平均重量直径有显著的提高,肥田萝卜对土壤平均重量直径的促进作用在空间上更深,而光叶苕子降低了土壤平均重量直径。     

不同植茶年限土壤团聚体的分布特征及稳定性研究

在野外调查的基础上,结合室内分析对不同植茶年限土壤团聚体的组成及稳定性进行了研究,结果表明：（1）不同植茶年限的土壤团聚体数量,在干筛处理下总体呈现出随粒径的减小先降低后增加再降低的趋势;而湿筛处理下,总体呈现随粒径的减小先减小后增加再减小再增加的趋势;微团聚体则总体呈现随粒径的减小而减小的趋势;植茶年限对土壤团聚体大小分布状况无显著影响;（2）风干团聚体和水稳性团聚体中>5mm粒径团聚体含量均随植茶年限增加呈现先增加再减小的趋势,其中植茶20~22年时最大,而<5mm粒径分布则相反;（3）不同植茶年限,风干团聚体与水稳性团聚体平均重量直径（MWD）、几何平均直径（GMD）值均为植茶20~22年时最大,而分形维D值则最小,且MWD、GMD及D值在不同植茶年限下多呈显著差异,表明植茶年限与土壤团聚体稳定性之间存在较大的相关性。     

不同类型茶园土壤团聚体组成特征及稳定性研究

采用野外调查和室内分析相结合的方法,对武夷山市5种主要土壤类型（黄壤、红壤、潮砂土、高山草甸土、紫色土）茶园的土壤团聚体组成及其稳定性特征进行了研究。结果表明：茶园土壤大团聚体含量均随土层加深呈减少的趋势,微团聚体含量则相应上升。黄壤、高山草甸土、紫色土>5 mm的大团聚体含量最高,所占比例在18.07%~89.23%;红壤和潮砂土土壤团聚体含量则以<0.25 mm微团聚体含量最高,所占比例为37.16%~63.91%。茶园土壤R0.25（>0.25 mm水稳性团聚体）含量在36.08%~97.23%之间（均值为73.60%）;高山草甸土平均质量直径（MWD）和几何平均值（GMD）均显著高于其他土壤类型,黄壤和紫色土次之,潮砂土最低,分形维数（D）的变化趋势则相反。相关分析表明,土壤团聚体组成及稳定性指标与土壤有机碳、全氮、全磷、容重、孔隙度、砂砾、粉粒有显著相关性,与土壤C/N、全钾、pH、粘粒的相关性不明显。     

A staggered maize–legume intercrop arrangement robustly increases crop yields and economic returns in the highlands of Central Kenya

Smallholder farmers in East-Africa commonly intercrop maize (Zea mays L.) with grain legumes to maximize utilisation of land and labour, and attain larger crop yields. Conventionally, one legume line is intercropped between each pair of maize lines. This study evaluated the potential of a modified two-by-two staggered arrangement (MBILI) to increase crop yields and economic benefits in two sites in Central Kenya with contrasting soil fertility levels during 7 consecutive seasons. Common beans (Phaseolus vulgaris L.), cowpea (Vigna unguiculata (L.) Walp.) and groundnut (Arachis hypogaea L.) were grown as legume intercrops. The MBILI system resulted in increased maize yields in both sites, and increased cowpea yields in the poor site. In the fertile site, using beans as an intercrop was most profitable, and the MBILI system increased net benefits by 40%, relative to the conventional system. In the poor site, groundnut and cowpea were better adapted, and the MBILI system increased net benefit by 12–37%. Positive effects of the MBILI system were most pronounced in the poor site, but occurred independent of soil fertility level. Rainfall amounts and distribution varied widely, but the MBILI system increased yields both under conditions of ample and inadequate rainfall. N balances were negative with beans and groundnut, but neutral with cowpea as the intercrop. A modest N fertilizer application is therefore essential to sustain yields in the long term, especially when beans or groundnuts are intercropped. In conclusion, the MBILI system, when combined with adjusted nutrient inputs, resulted in superior and robust improvements in crop yields and economic benefits, relative to the conventional intercropping system.     

On-farm evaluation of the ‘push–pull’ technology for the control of stemborers and striga weed on maize in western Kenya

The ‘push–pull’ technology is a novel pest management strategy developed for control of stemborers and striga weed, Striga hermonthica, in maize-based farming systems in eastern Africa, where maize is intercropped with desmodium, a forage legume, and Napier grass is planted as a border crop. Desmodium repels stemborer moths while Napier grass attracts them. Desmodium also suppresses the parasitic striga weed through a series of mechanisms ranging from shading to allelopathy through the root system. The technology is currently being disseminated among smallholder farmers in eastern Africa and adoption rates are rising. Our on-station studies have reported efficacy of this technology against the two pests resulting in increased grain yields. The current study was conducted between 2003 and 2006 in 14 districts in western Kenya to assess effectiveness of the technology under farmers’ own conditions. Twenty farmers from each district, who had adopted the technology, were randomly selected for the study. Each farmer had a set of two plots, a ‘push–pull’ and a maize monocrop. Seasonal data were collected on percentage of maize plants damaged by stemborers, the number of emerged striga, plant height and grain yields. Similarly, farmers’ perceptions on the benefits of the technology were assessed using a structured questionnaire. Stemborer damage and striga counts to maize plants were significantly lower in the ‘push–pull’ plots than in the maize monocrop plots. Similarly, maize plant height and grain yields were significantly higher in the former. Farmers rated the ‘push–pull’ technology significantly superior in having reduced stemborers and striga infestation rates and increased soil fertility and grain yields. These results demonstrate that the technology is equally effective in controlling both pests with concomitant yield increases under farmers’ conditions in the districts studied.     

秸秆还田对玉米产量和土壤团聚体组成及有机碳分布的影响

研究秸秆还田对土壤团聚体组成、有机碳分布及玉米产量的影响,为秸秆合理利用与土壤培肥提供科学依据。采用田间定位试验的方法,研究秸秆还田(SNPK)和生物炭还田(BNPK)处理对玉米产量,土壤团聚体组成及其有机碳分布的影响。结果表明,与常规施肥相比,SNPK和BNPK处理4年后玉米产量分别提高6.95%和4.83%;SNPK和BNPK处理均提高了0~20 cm土层2 mm团聚体含量,降低0.25 mm团聚体含量,均降低21~40 cm土层中2 mm团聚体含量;SNPK处理提高0~20 cm土层有机碳含量14.11%,BNPK处理对土壤有机碳提高不明显,二者均提高0~20 cm土层中0.25~1 mm和0.25 mm粒级中的有机碳含量;SNPK处理明显提高0~20 cm土层2 mm粒级团聚体对有机碳的贡献率,BNPK处理对各粒级团聚体对有机碳的贡献率影响不明显。长期秸秆还田和生物炭还田能够改变土壤团聚体的分布,有利于土壤结构的形成,提高土壤固碳能力,增加玉米产量。     

不同类型茶园土壤团聚体有机碳分布特征研究

采用野外调查和室内分析相结合的方法,研究福建省武夷山市5种不同类型茶园土壤（黄壤、红壤、潮砂土、高山草甸土、紫色土）团聚体有机碳分布特征。结果表明：5种类型茶园土壤各粒级团聚体有机碳含量均随土壤层次的加深呈现降低的趋势;2个土层中,5种类型茶园土壤团聚体有机碳含量均以＞5 mm粒径最高,随着土壤团聚体粒径的增加,团聚体有机碳增加;黄壤、高山草甸土和紫色土茶园均以＞5 mm粒径团聚体有机碳储量和贡献率最高,而潮砂土则以＜0.25 mm粒径最高;土壤有机碳含量与各粒径团聚体有机碳含量呈极显著正相关（相关系数为0.95～0.98）。     

THE EFFECT OF WHITE CLOVER AND NITROGENOUS FERTILIZER ON THE PRODUCTION OF A SWARD

Data from an experiment already reported (2) are used to examine a statistical method proposed by Walker et al . (8) for apportioning the nitrogen harvested in grass in a grass/ legume sward to legume, fertilizer and soil. Multiple regressions of the yield of N in the grass (G_n) upon N harvested in the associated legume (C_n) and N applied in fertilizer (F_n) were highly significant; but they were very variable, mainly because of the strong (negative) correlation between C_n and F_n. In some cases the coefficient for clover N was negative, in some cases the coefficient for fertilizer N exceeded unity; and the residual constant varied widely among 4 sets of plots on the same soil. The interpretation of such equations in physical terms is criticized on these grounds. The use of pure grass swards in conjunction with mixed swards gave estimates of the recovery of fertilizer N, and of the transfer of N from clover to grass, which agreed better with other published data than did the coefficients in a multiple regression. A simple regression of the estimate of transferred N in the grass upon the N harvested in the clover yielded a second constant. This constant, which varied considerably from one series of plots to another, is thought to indicate interactions between the various sources of N, which would be attributed to a direct effect of soil N if the multiple regressions were interpreted as Walker et al . suggest.     

Land Equivalent Ratio of Groundnut-Fingermillet Intercrops as Affected by Plant Combination Ratio,and Nitrogen and Water Availability

Abstract

Field experiments were conducted to characterize intercropping advantages in groundnut-fingermillet intercrop in relation to crop combination ratios, soil moisture and nitrogen (N) availability. Three intercrops in 1 : 2, 1 : 1 and 2 : 1 alternating rows of groundnut and fingermillet were examined for their growth and yield in comparison with their respective sole crops in 1996. The effect of well watered (W) and water stressed (D) conditions on the intercropping advantage was also examined for 1 : 1 intercrops in 1995 and 1996. Fertilizer N was applied at the rate of 20 kg ha^?1 in 1995 and 50 kg ha^?1 in 1996. The total above-ground biomass (DM) and its land equivalent ratio (LER) were highest in the 1 : 1 combination ratio. The DM production of intercropped fingermillet was higher in 1996 with higher N than in 1995 with low N application, while those of groundnut were similar in both years. The intercropped groundnut exhibited significantly higher DM production after the fingermillet harvest. The LERs in grain yield were higher in 1996 (1.43 under W and 1.45 under D), than in 1995 (0.87 under W and 1.22 under D). Also, LERs were consistently higher under D than W conditions. Water stress severely reduced the leaf area index (LAI) of fingermillet at a low N, especially in the later stages, whereas higher N alleviated the water stress effect. A close linear relationship was observed between LAI and leaf area (LA) per unit leaf N both for groundnut and fingermillet, with intercrops producing larger LA per unit leaf N than sole crops. Intercropping maintained higher ability in leaf net photosynthesis and transpiration of groundnut up to later stages, and significantly reduced water evaporation from the soil surface under the canopy than sole cropping of fingermillet. These results suggest that three processes associated with the intercropping yield advantages in the groundnut-fingermillet intercrop; 1) higher leaf photosynthesis and vigorous growth of groundnut after the fingermillet harvest, 2) higher LA production per unit N and 3) efficient water use. In conclusion, interspecific shading was considered to be the key mechanism associated with these processes, leading to the intercropping advantages. The degree of the interspecific shade and its effect on growth and yield depended on the available soil N and water.     

磷肥用量对土壤速效磷及玉米产量和养分吸收的影响

通过两年田间肥料定位试验,研究北疆灰漠土区不同磷肥用量对土壤速效磷含量以及玉米生长和养分吸收的影响。结果表明,不施磷肥或施磷量较低（75 kg/hm²）时,土壤速效磷含量显著降低;施磷量为150 kg/hm²时土壤速效磷含量基本维持平衡;施磷量为300 kg/hm²时土壤速效磷在0～40 cm土壤积累明显。施磷肥可显著增加玉米干物质量,施磷量超过150 kg/hm²干物质量增加不明显。玉米植株的氮素和磷素积累量随施磷量增加而显著增加,磷肥对玉米植株磷素养分的分配影响不大,但可显著促进氮素向子粒的转运,氮素在子粒的分配比例显著增加。施磷肥可显著提高玉米产量,施磷量为150 kg/hm²可维持土壤速效磷平衡并获得高产,是该区玉米的适宜磷肥用量。     

Effects of pesticides and fertilizer on invertebrate populations of grass and wheat plots in Kent in relation to productivity and yield

At a site in Kent, perennial ryegrass (Lolium perenne) variety S24 and Italian ryegrass (L. multiflorum) variety RVP, wheat varieties Armada and Norman, and the original mixed grass ley were grown in small plots during 1982–84. Two toxic pesticides (phorate and aldicarb) were applied to half the total number of plots three times each year to eliminate soil invertebrate populations. Fertilizer was also applied to most plots. The yields of the crops, grown with and without pesticide, and the effects of the fertilizer were compared. Grass herbage yield was measured on three occasions during the summers of 1983 and 1984. Wheat grain yields were also determined in 1983. During the first year significant differences were not apparent in grass dry matter yield between pesticide-treated and non-treated plots, but significant differences were found in the second year. The perennial ryegrass was more susceptible to pest damage than the Italian ryegrass or the grass ley. Grass yields varied between cuts and in relation to variety and pesticide treatment, yields tending to be greater in untreated plots. Fertilizer treatment greatly increased grass dry matter yields, particularly with the Italian ryegrass. The effects of pesticide treatment on both wheat varieties varied although some yield enhancement was evident. Invertebrate animal populations in pesticide and fertilizer-treated plots were also assessed in autumn 1982, spring and autumn 1983 and spring 1984. In contrast to pesticide treatment, fertilizer treatment had little effect on soil invertebrate populations. Nematode populations were reduced at each sampling occasion by the pesticide treatment. Slug populations were initially unaffected but were subsequently reduced. Leatherjackets, by far the most abundant pest in both grass and wheat plots, were markedly affected by pesticides on all sampling occasions. Generally, fewer soil-dwelling dipterous larvae were recovered in spring than in autumn. Stem-boring dipterous larvae were virtually absent.     

不同培肥方式对茶园土壤团聚体中有机碳和全氮分布的影响

通过长期定位试验,研究不施肥（CK）、100%化肥（CF）和50%化肥+50%有机肥+豆科植物（IF）等3种处理对茶园黄红壤团聚体及其有机碳（TOC）和全氮（TN）分布的影响。结果表明,各处理均以≥2βmm水稳性团聚体占优势,其质量分数高达54.95%~66.97%;同时,该级水稳性团聚体中TOC、TN储量分别是相应全土总量的33.31%~45.45%和33.76%~46.60%。其中,不同粒径水稳性团聚体TOC和TN的贡献率在IF和CF处理中的大小排序为（≥2βmm）>（<0.5~0.25βmm）>（<1~0.5βmm）>（<2~1βmm）>（<0.25~0.106βmm）,而在CK中为（≥2 mm）>（<1~0.5βmm）>（<0.5~0.25βmm）>（<2~1βmm）>（<0.25~0.106βmm）。与CK相比,IF处理可显著（P<0.05）提升≥2βmm水稳性团聚体的含量和平均重量直径,增加该粒径水稳性大团聚体中TOC和TN的含量及储量。而且,≥2βmm水稳性团聚体含量与全土TOC、TN含量均呈极显著（P<0.01）的正相关。但是,IF处理土壤不同粒径团聚体的C:N比值一般比CK低。综上表明,处理IF不仅能增加土壤及其水稳性团聚体中TOC和TN的含量及储量,而且提高水稳性团聚体的稳定性,是茶园黄红壤固碳供氮的合理培肥模式。     

A COMPARISON OF THE REACTION OF DIFFERENT GRASS SPECIES TO FERTILIZER NITROGEN AND TO GROWTH IN ASSOCIATION WITH WHITE CLOVER. II. YIELD OF NITROGEN

Seven species or varieties of grass, and a mixture of 3 of them, were sown in pure swards, treated with 4 levels of nitro-chalk (0, 17·5, 35, and 70 Ib N/ac/cut) and cut 4 or 5 times each year. Each species and the mixture were also sown with white clover, and the effect of fertilizer N on the yield of N in each grass was compared with the effect of clover on the yield of N harvested from the grass/clover swards.
The regression line for response in yield of N with increasing levels of fertilizer N showed slight, but significant, upward curvature. The grasses differed in their uptake of N from the soil, S37 cocksfoot and S48 timothy showing relatively high uptakes, and the ability of each grass to take up fertilizer N was usually related to its uptake of N from the soil. Differences in the yield of dry matter between the species, at a similar level of N, are discussed, and it was concluded that perennial ryegrasses were most efficient and Agrostis tenuis was least efficient in using the N taken up in the production of DM.
In general, there were no significant differences between the yields of N of the grass/clover mixtures; the N yields of the grass components were significantly different and tended to be inversely related to the N yields of clover.
Grasses which gave high yields of N with fertilizer were also high yielding when grown in association with clover. Pure grass swards required more than 200 Ib fertilizer N/ac/yr in order to yield the same amount of N as the grass/clover swards. The amount of N estimated to have been derived by grass from clover (indirect effect of clover) increased each year; it was highest with S37 cocksfoot and lowest with Irish perennial ryegrass, averaging 46 and 23 Ib N/ac/yr, respectively.     

应用Le Bissonnais法研究茶园土壤团聚体稳定性

采用野外调查和室内分析相结合的方法,应用Le Bissonnais法研究茶园土壤团聚体稳定性。结果表明：（1）不同植茶年限茶园土壤>5 mm团聚体含量均表现为湿润扰动处理（81.05%~95.62%）>慢速湿润处理（64.18%~89.31%）>快速湿润处理（17.62%~24.26%）,团聚体平均质量直径（MWD）、几何均重直径（GWD）和偏倚系数（C_S）值也具有相同的变化规律,表明茶园土壤团聚体的崩解机制主要是快速湿润时孔隙内封闭的空气压力作用,快速湿润处理更接近茶园土壤实际情况;（2）快速湿润处理下,土壤团聚体稳定性对茶树连作的响应存在明显差异。随着植茶年限的增加,土壤团聚体MWD、GMD和C_S值先降低后升高,在植茶23 a时最低。表明茶园土壤团聚体稳定性在植茶23 a时最弱;（3）在快速湿润处理下,茶园土壤团聚体稳定性与土壤有机质和粘粒含量呈显著正相关。表明茶园土壤有机质和粘粒含量升高有利于土壤团聚体的形成和稳定性增强。因此,在茶园管理中应加强铺草覆盖,减弱消散作用对团聚体的破坏,植茶16~23 a时需增施有机肥料,以提高茶园土壤团聚体稳定性。     

LAND RESTORATION WITH PULVERIZED FUEL ASH

Experiments were carried out with different depths of added topsoil, with different methods of cultivation and with different rates of application of fertilizers on an ash disposal site near Newark. Good yields of hay and wheat were obtained and were shown to vary systematically with the treatment of the plots. Good yields of wheat were obtained with a top dressing of 125 kg N/ha even on bare ash but, in contrast with the yields of DM from grass, yields of grain tended to increase with increasing depth of added soil. This pattern appeared to be influenced by the variations in spring rainfall. There appeared to be no adverse effects of uptake of trace elements from the ash.     

Effects of mulching,N-fertilization and intercropping with Desmodium uncinatum on Striga hermonthica infestation in maize

The parasitic weed Striga hermonthica is a major constraint to maize production in sub-Saharan Africa and causes serious food insecurity. We discovered serendipitously an effective control method for the weed that involves intercropping cereals with the fodder legume, silverleaf desmodium, Desmodium uncinatum (Jacq.) DC., through mechanisms that involve soil shading and nitrogen fixation. In the current study we investigated long-term effects of inorganic nitrogen (N), mulching and D. uncinatum, singly and in combinations, on S. hermonthica infestation, maize plant growth and grain yields. Treatments comprised sole maize with and without 120 kg N/ha; sole maize plots covered with maize straw (i.e. mulching), with and without N; and maize–D. uncinatum intercrop, with and without N. Intercropping maize with D. uncinatum gave the most significant suppression of S. hermonthica, with addition of N only minimally enhancing its effect. Similarly, mulching significantly suppressed S. hermonthica, although to a much less extent. Application of N both to sole maize and mulched plots reduced seasonal S. hermonthica infestations but the effect was largely insignificant. The effect of D. uncinatum was again notable as it dramatically increased maize plant height and grain yields, with the addition of N only minimally improving both effects. Application of N and mulch, singly and in combination, to the sole maize crop generally enhanced plant height and grain yields, although to a less extent, with the effect of N on grain yields being statistically insignificant during most of the cropping seasons. These results confirm the efficacy of D. uncinatum in S. hermonthica suppression leading to better growth and yields of maize. The effects of N application, mulching and a combination of both treatments in S. hermonthica control in maize were also observed, although these effects were much weaker. The results and their implications are discussed in the context of smallholder cropping systems in the region.     

Planting date and nitrogen management interactions in irrigated maize

It is becoming increasingly important to develop economically and environmentally sound nitrogen fertilizer management practices. The objective of this experiment was to determine the optimum N application time-crop planting time combination(s) at two N rates which would maximize N fertilizer use efficiency (NFUE) and maintain high grain yields of irrigated maize (Zea mays L.) in the western Corn Belt of the USA. Maize was planted three times at biweekly intervals during 1979–1981 on a Typic Argiudoll in eastern Nebraska. The ¹⁵N-depleted (NH₄)₂SO₄ was applied at rates of 90 or 180 kg N/ha in a band midway between maize rows at planting, or at the 4-, 8-, or 16-leaf growth stage during 1979–1980. Control plots (no N fertilizer applied) were maintained in each planting date. No N was applied during 1981 to allow study of residual treatment effects. Grain dry-matter yield and total N and fertilizer N (FN) contents of grain were determined, and NFUE was calculated as the fraction of FN in grain to applied FN.Very high N supply by the soil resulted in small effects of FN on yield and NFUE during the first year of treatment. According to the response surface analysis, greatest NFUE (52%) in concert with high grain yield (11.2 Mg/ha, the predicted maximum) would have been achieved by applying the low N rate at the 13- to 14-leaf growth stage to maize planted during the week before the average date of 10 May. Due to lower soil N supply the 2nd year of treatment, most corn with 90 kg N/ha did not produce near-maximum grain yields. However, yields within 10% of maximum were obtained when 90 kg N/ha was applied to the early planting at the 14- to 16-leaf stage, and NFUE was 67–71% with this treatment. Maximum NFUE with the application of 180 kg N/ha was only 44%. Recovery of residual FN in this silty clay loam soil was an important factor in the improvement of NFUE with delayed N applications the second year of treatment. In 1981, recovery of residual FN generally increased with a previous delay in N application time and was not greatly influenced by planting time. Early planting in combination with a modest rate of N applied very late during vegetative growth provided maximum recovery of FN in harvested grain, while maintaining high grain yields.     

RESPONSE OF GRASSLAND TO NITROGENOUS FERTILIZER IN THE WEST OF ENGLAND

Extensive replicated plot experiments were carried out at Henley Manor Farm from 1956–1961 to obtain accurate measurements of herbage production and response to nitrogenous fertilizers under West of England conditions. 356 plots were used; use of the herbage by both cutting and grazing was studied. The principal results are: Grass/ clover swards (containing approx. 35% clover) grown without nitrogenous fertilizer averaged 75 cwt dry matter per acre per annum. Application of nitro-chalk to initially grass/clover swards reduced the clover content of the herbage. About 133 lb N/annum was required by an all-grass sward to equal the production of a grass/clover sward without N. Attempts to increase production of grass/clover swards by using N for early growth and relying on clover for mid-season growth were unsuccessful in 2 out of 3 years. Swards (initially grass/clover) gave significant increases in total dry-matter production from regular use of the lowest level of N (26.0 or 34.7 lb N/acre/cut or graze) in 44 out of 49 cases. Extremely high yields were obtained from the heaviest use of N (104.2 lb N/acre/silage cut). 52.1 lb N/acre/cut or graze was the optimum rate of application on ail-grass and grass/clover swards. Up to about 350 lb N/acre/annum the dosage-response curve was very nearly straight for all-grass and grass/clover swards. On the grazed plots herbage left ungrazed amounted on average to only 6% of the total. The health of all stock on the high nitrogen plots (as well as all others) was excellent.     

等氮量投入下有机无机肥配施对玉米产量及氮素利用的影响

以1989年建立的国家黑土肥力与肥料效益监测基地的长期肥料定位试验为研究平台,研究等氮条件下有机无机肥长期配施对玉米产量及氮肥利用率的影响。研究结果表明,长期氮磷钾肥配施(NPK)及氮磷钾肥与有机肥配施(牛粪+NPK、秸秆+NPK)有利于玉米产量的提高,与不施肥(CK)相比,分别提高192.0%、218.3%和192.6%。NPK、牛粪+NPK及秸秆+NPK处理氮肥农学利用率、氮肥偏生产力均显著高于单施氮肥处理。经18年长期定位试验,与试验初期相比均能提高土壤有机质含量、全氮含量及碱解氮含量,以牛粪+NPK处理效果最好,分别增加46.6%、28.6%和36.8%。施用牛粪及秸秆后土壤pH值年纪间变化不大,长期施用化肥土壤pH值降低。     

氮肥用量对土壤养分含量、春玉米产量及农学效率的影响

采用田间试验,设置5种施氮水平,研究不同氮肥用量对土壤养分含量、春玉米产量和氮肥利用的影响。结果表明,优化施氮(N150)、优化施氮配施有机肥(N150+M)处理可增加土壤速效养分含量;土壤水分和温度受不同氮肥用量影响较小。N150和N150+M处理玉米增产幅度较大,增产率分别为19.44%和16.67%;N150处理的氮肥农学利用率最高,高量施氮处理(N180)最低;减量施氮(N120)与N150处理的氮肥偏生产力较高。优化施用氮肥处理,不仅可以增加土壤速效养分含量,保障速效养分对春玉米的及时供给,同时还可以增加春玉米产量,提高氮肥利用效率。