"黑麦草-水稻"草田轮作系统研究Ⅶ黑麦草残留物的田间分解及营养元素的释放动态

采用尼龙网袋分解法,将一定量的黑麦草根系和地上留茬(统称黑麦草残留物)置于田间耕作层令其自然分解,分别于埋设后11,39,70,109,161和244 d收集尼龙网袋内的样品,洗净,烘干,称重后用于分析全量N、P、K、Ca、Mg、Mn和Fe的含量.结果表明,黑麦草残留物在大田中通过生物降解,将养分释放到土壤中,在后作水稻的生长发育过程中,分解初期的释放量较高,埋设10 d后黑麦草残留物样品中近90%的Ca和37%～50%的C、N、P、K和Fe被释放,Mn和Mg则只有0.4%～13.4%被释放.在早稻生长过程中黑麦草残留物有74.9%被分解,C、N、Mn和Mg的矿化率均在80%以下,表现出一定的缓释效应.晚稻收获时各养分的释放率达到92%～99%.理论上黑麦草根系可以为0～20 cm土层贡献有机质、N、P、K、Fe、Mn、Mg和Ca分别达到865.42 g/kg,26.92 g/kg,1.75 g/kg,23.83 g/kg,2 741 mg/kg,75 mg/kg,162 mg/kg和46 mg/kg.     

德惠市农田黑土肥力评价及施肥措施研究

对吉林省德惠市黑土农田土壤5项指标综合评价的结果表明,土壤速效钾含量、阳离子交换量处于良好级,速效磷含量、土壤有机质含量处于中等级,全N含量处于差级,pH在不同地块差异明显。土壤保肥、耐肥性能好,但土壤肥力严重退化。因此,在施肥上应遵循增施有机肥,增N、控P、保K,配合施用中微量元素的原则,保持黑土的持续生产能力。     

Effects of crop growth and soil treatments on microbial C,N, and P in dry tropical arable land

We studied the dynamics of microbial C, N, and P in soil cropped with rice (Oryza sativa) and lentils (Lens culinaris) in a dryland farming system. The crop biomass and grain yield were also studied. The microbial biomass and its N and P contents were larger under the lentil than under the rice crop. Microbial nutrients decreased as the crops grew and then increased again. Farmyard manure and NPK fertilizer applications increased the level of microbial nutrients, crop biomass, and grain yield by 35–80%, 55–85%, and 74–86%, respectively. However, these applications had no significant effect on most of the soil physicochemical properties in the short term. The microbial biomass was correlated with the crop biomass and grain yield. The calculated flux of N and P through the microbial biomass ranged from 30–45 and 10–19 kg ha^-1 year^-1, respectively. Cultivation of a cereal crop followed by a leguminous crop sustains higher levels of microbial nutrients and hence greater fertility in impoverished tropical arable soils. The soil microbial biomass appears to contribute significantly to crop productivity by releasing nutrients, and applications of manure, either alone or with fertilizers, promote this effect more strongly than the application of NPK fertilizers alone.     

Burrow building in seabird colonies: a soil-forming process in island ecosystems

Soil modification via biopedturbation by burrow-building seabirds was examined in a Mediterranean, island ecosystem. Physical and chemical soil properties were compared between a colony of Wedge-tailed Shearwaters (Puffinus pacificus) and adjacent heath across a 14-month period. When compared to heath soil, the biopedturbated soil was 28% drier (6.04±5.40 vol%), had increased bulk density (by 29% to 1.30±0.11 g cm⁻³, 51% porosity), wetting capacity (by 83% to 0.55±0.83 molarity of ethanol droplet), hydraulic conductivity (by 266% to 398.91±252.04 mm h⁻¹), and a greater range in soil surface temperature (31.7±6.2 °C diurnally to 18.3±3.2 °C nocturnally). Soil penetration resistance was reduced by 26% at a depth of 0–100 mm (326.5±122.4 kPa) and by 55% at 500–600 mm (1116.8±465.0 kPa). Colony soil also had increased levels of nitrate (by 470%), phosphorous (118%), ammonium (102%), sulphur (69%), and potassium (34%), decreased levels of iron (by 50%) and organic carbon (61%), was more alkaline, and had a 78% greater conductivity. Shearwaters deposited guano at a rate of 234.4 kg ha⁻¹ yr⁻¹ (dry mass). Chemical analysis of guano equated this to 50.9, 5.7, 5.5, and 3.6 kg ha⁻¹ yr⁻¹ of nitrogen, potassium, sulphur, and phosphorous, respectively. Experimentally constructed burrows demonstrated that digging alone can alter physical and chemical soil factors, but that changes in the nutrient profile of colony soils are predominantly guano-driven. We argue that the physical impact of seabirds on soil should not be overlooked as a soil-forming and ecosystem-shaping factor in island ecosystems, and that biopedturbation can exert major bottom-up influences on insular plant and animal communities.     

Exploring the spatial relations between cereal yield and soil chemical properties and the implications for sampling

Abstract. In general, agricultural management has focused on differences between fields or on the gross differences within them. Recent developments in agricultural technology, yield mapping, Global Positioning Systems and variable rate applications, have made it possible to consider managing the considerable variation in soil and other properties within fields. This system is known as precision agriculture. More precise management of fields depends on a better understanding of the factors that affect crop input decisions. This paper examines the spatial variation in crop yield, soil nutrient status and soil pH within two agricultural fields using geostatistics. The observed properties vary considerably within each field. The relation between yield and the measured soil properties appears to be weak in general. However, the range of spatial correlation for yield, shown by the variogram, is similar to that of the soil chemical properties. In addition the latter changed little over two years. This suggests that information on the scale of variation of soil chemical properties can be derived from yield maps, which can also be used as a guide to a suitable sampling interval for soil properties.     

森林生态系统中初级生产者-分解者养分的关系

 森林生态系统中,初级生产者和分解者之间的养分关系,是一种既互利又竞争的复杂关系。通过构建初级生产者-分解者系统的养分流动模型,分析分解者增长受碳限制或受养分限制的判断标准。在假定整个系统封闭的前提下,讨论初级生产者与分解者实现共存并保持长久稳定的条件:一是分解者必须受碳限制,这要求分解者较之初级生产者对养分吸收具有更强的竞争力;二是矿化系数与碎屑化系数之比(a41/a23)要足够大于在初级生产者中的碳/养分与在分解者中的碳/养分之比(α/β)。这表明,从化学计量论的角度来看,生态系统的持续和稳定,对碳/养分之比和植物与微生物的竞争能力方面有严格的要求。     

稻作区保护性耕作和小麦种植对土壤养分的影响

该文采用4个处理：常规犁耕-休闲(DTF)、常规犁耕-小麦(DTW)、保护耕作-休闲(CTF)和保护耕作-小麦(CTW)，分析了10年后稻作区保护性耕作和小麦种植对土壤养分的影响。结果表明：在CTW处理下，土壤全N分别较DTF、DTW和CTF处理高10.03%、26.81%和23.17%。土壤碱解N也呈现相同的趋势；土壤全P，CTW处理下较DTF、DTW和CTF处理分别高12.93%、15.86%和21.36%。在0～10 cm土深，CTW处理下土壤有效P分别是DTF和DTW处理下的4.5和2.1倍；土壤全K在4种处理中与全N和P有类似的趋势；与处理DTF相比，Ca₂-P、Ca₈-P、Al-P、Fe-P、O-P和Ca₁₀-P在CTW下的含量迅速增加；代换态、易还原结合态、碳酸盐结合态、有机质结合态和无定形态Fe、Mn和Cu在CTW处理下含量降低，而残渣态Fe、Mn和Cu则增加。代换态和易还原锰结合态Zn在CTW处理下的含量增加，而相应地，无定形态和有机质结合态Zn则显著降低。而且，在有效Fe、Cu和Mn降低的同时，有效的Zn增加；稻作区，保护性耕作和小麦种植不仅增加表土层土壤养分的含量，而且可通过影响P、Fe、Mn、Zn和Cu的形态，缓解Fe和Mn对作物的毒害。     

Dust storm erosion and its impact on soil carbon and nitrogen losses in northern China

There is increased awareness of the environmental impacts of soil carbon (C) and nitrogen (N) losses through wind erosion, especially in areas heavily affected by dust storm erosion. This paper reviews the recent literature concerning dust storm-related soil erosion and its impact on soil C and N losses in northern China. The purpose of our study is to provide an overview of the area of erosion-affected soils and to estimate the magnitude of soil C and N losses from farmland affected by dust storm erosion.According to the second national soil erosion remote-sensing survey in 2000, the area affected by wind erosion was 1.91 million km², accounting for 20% of the total land area in China. This area is expanding quickly as the incidence of heavy dust storms has greatly increased over the last five decades, mainly as a result of the intensification of soil cultivation. The economic and ecological damage caused by wind erosion is considerable. Heavily affected areas show a loss of nutrients and organic carbon in soils and the heavily degraded soils are much less productive. Compared with the non-degraded soil, the C and N contents in degraded soils have declined by 66% and 73%, respectively. The estimated annual losses per cm toplayer of soil C and N by dust storm erosion in northern China range from 53 to 1044 kg ha^− 1 and 5 to 90 kg ha^− 1, respectively. Field studies suggest that soil losses by wind erosion can be reduced by up to 79% when farmers shift from conventional soil tillage methods to no-till. Thus shifting to no-till or reduced tillage systems is an effective practice for protecting soil and soil nutrients. Our study indicates that soil conservation measures along with improved soil fertility management measures should be promoted in dry-land farming areas of northern China. As erosion is a major mechanism of nutrient withdrawal in these areas, we plead for the development of accurate methods for its assessment and for the incorporation of erosion, as a nutrient output term, in nutrient budget studies.     

Variability in soils and vegetation associated with harvester ant (Pogonomyrmex rugosus) nests on a Chihuahuan Desert watershed

The effects of harvester ant (Pogonomyrmex rugosus) nests on the density and cover of spring annual plants and on soil characteristics were measured at three locations characterized by different soils and dominant vegetation on a desert watershed. There were few differences in vegetation and soils associated with harvester ant nests at locations at the base of the watershed where brief periods of flooding and sediment deposition occur at periodic intervals. At mid-slope locations, there were significant increases in total nitrogen, inorganic phosphorus, and cover (biomass) of four species of spring annuals at the edges of nest disks when compared with reference sites. The spring annuals that exhibited increased cover were species that increase biomass as a function of available nitrogen. At a clay-loam, Scleropogon-Hilaria, grassland site, there were significant reductions in the concentrations of Ca²⁺ and Mg²⁺, significant increases in nitrate and total nitrogen, but a significant increase in cover in only one species of annual plant. The data demonstrate that the effects of ants on soil properties and vegetation vary with site location and soil type.     

Direct contribution by soil arthropods to nutrient availability through body and faecal nutrient content

Summary The direct contribution made by soil arthropods to nutrient dynamics was investigated in pine forests that differed in soil nutrient status. Nutrient concentrations (K⁺, Ca²⁺, Mg²⁺, PO ₄ ^3– , N, C) in the most abundant species and groups of arthropods in two Pinus nigra forests were compared, and distinct differences were found among taxonomic groups. In the rank order: collembolans, oribatides, isopods, diplopods, Ca²⁺ and Mg²⁺ concentrations increased, while N and C concentrations decreased. The nutrient concentrations in individuals of the same species but originating from the different forests were similar, except for the isopod Philoscia muscorum. The total and available nutrient concentrations in food and faeces of the collembolan Tomocerus minor and the isopod Philoscia muscorum were compared. The isopod faeces contained relatively less K⁺ and Mg²⁺, and more Ca²⁺, PO ₄ ^3– , and greater N availability, compared with the food material. The collembolan faeces showed a higher availability of all nutrients measured. The N species appeared to be changed by collembolans; their faeces contained high NO ₃ ^– concentrations, while their food contained relatively high concentrations of NH ₄ ⁺ . These findings were examined in relation to their significance for ecosystem functioning. It was concluded that about 12% of the total K⁺, PO ₄ ^3– , N and 2% of the Ca²⁺ in the organic layer was found in the mesofauna. It was calculated that faeces production by the collembolans resulted in a 2.4 times higher NO ₃ ^– availability in the forest floor.