Land-use history,forest conversion,and soil organic carbon in pine plantations and native forests of south eastern Australia

Land-use history – the number, type, and duration of previous land uses – is relevant to many questions regarding land-use effects on soil carbon, but is infrequently reported. We examine the importance of land-use history variables, as well as topographic and edaphic variables, on soil C in a range of forest types – native forest, pine plantations, secondary forest and rehabilitated forest – at three contrasting locations in south eastern Australia. Our comparisons include a novel forest conversion of exotic pine plantations to native, broadleaf forest.Using nested ANOVAs, we detected few differences in soil C concentration indices (total C, microbial biomass C, K₂SO₄–C) and C content among eucalypt-dominated vegetation and pine plantations within each location (0–10 cm depth). However, planned contrasts indicated a 30% decrease in soil C content with conversion of native forest to pine plantation of age 37 years. The reverse land-use change – pine plantation to native, broadleaf forest – was associated with a decrease in soil C concentration and content at one location (40%; age 12–13 years) and no detectable changes at another (to age 7 years). Variable effect between locations of this novel land-use change on soil C could be due to differences in potential productivity, conifer species, and plantation age.We used correlation coefficients and general linear models to identify widely applicable variables for predicting soil C concentration and content at local scales (≤ 20 km²). Within-location relationships with topographic variables were weak and infrequent relative to those with edaphic and land-use history variables. Soil texture was strongly correlated with soil C at each location, although the relative significance of different particle size fractions differed among locations. Electrical conductivity appeared more widely applicable since it was included in C models at two locations. Combining land-use history and edaphic variables produced strong predictive models for soil C concentrations and content at two locations (total r² 0.83 to 0.95). Positive relationships were indicated between soil C and ‘age of current vegetation’ at one location, and negative relationships were indicated with ‘number of land uses’ at another. These data highlight a potential predictive role for land-use history variables in local-scale assessments of soil C in forested landscapes.     

Land-use history has a stronger impact on soil microbial community composition than aboveground vegetation and soil properties

The response of soil microbial communities following changes in land-use is governed by multiple factors. The objectives of this study were to investigate (i) whether soil microbial communities track the changes in aboveground vegetation during succession; and (ii) whether microbial communities return to their native state over time. Two successional gradients with different vegetation were studied at the W. K. Kellogg Biological Station, Michigan. The first gradient comprised a conventionally tilled cropland (CT), mid-succession forest (SF) abandoned from cultivation prior to 1951, and native deciduous forest (DF). The second gradient comprised the CT cropland, early-succession grassland (ES) restored in 1989, and long-term mowed grassland (MG). With succession, the total microbial PLFAs and soil microbial biomass C consistently increased in both gradients. While bacterial rRNA gene diversity remained unchanged, the abundance and composition of many bacterial phyla changed significantly. Moreover, microbial communities in the relatively pristine DF and MG soils were very similar despite major differences in soil properties and vegetation. After >50 years of succession, and despite different vegetation, microbial communities in SF were more similar to those in mature DF than in CT. In contrast, even after 17 years of succession, microbial communities in ES were more similar to CT than endpoint MG despite very different vegetation between CT and ES. This result suggested a lasting impact of cultivation history on the soil microbial community. With conversion of deciduous to conifer forest (CF), there was a significant change in multiple soil properties that correlated with changes in microbial biomass, rRNA gene diversity and community composition. In conclusion, history of land-use was a stronger determinant of the composition of microbial communities than vegetation and soil properties. Further, microbial communities in disturbed soils apparently return to their native state with time.     

油菜秸秆还田腐解变化特征及其培肥土壤的作用

为促进油菜秸秆腐解,推进农村作物秸秆的资源化利用,减少秸秆焚烧对环境的负面影响,培养与提高土壤肥力,采用尼龙网袋和田间试验相结合方法,设置了油菜秸秆不同还田量处理和不同还田深度处理,研究了油菜秸秆腐解百分率和腐解速率变化特征,分析了油菜秸秆还田对土壤性质及作物产量的影响。结果表明,油菜秸秆还田的腐解百分率随时间延长而逐渐增大,秸秆腐解速率则早期快后期慢;随秸秆还田量增加,腐解速率降低,表现为全量还田的秸秆腐解速率<2/3量还田秸秆腐解速率<1/2量还田秸秆腐解速率<1/3量还田秸秆腐解速率;在种植水稻条件下油菜秸秆还田深度在10 cm时腐解速度最慢,在表层还田腐解速度最快,20 cm深还田腐解速度居中。相比对照处理来说,油菜秸秆还田降低了土壤容重,增加了土壤有机质含量,一定程度上提高了土壤氮磷钾含量(P<0.05)。油菜秸秆还田对水稻作物有极显著增产作用(P<0.01),增产幅度在6.02%～21.17%之间。本试验对水稻油菜轮作体系下油菜秸秆还田腐解特征进行的研究可为调控油菜秸秆还田腐解速度,改善农业生态环境提供参数依据。     

Overview on soil fertility management for cereals crops in semi-arid conditions of Spain

The management of the fertilization in integrated production intends to produce good yields and high product quality, while protecting the soil from different processes such as erosion, salinization, and acidification. Principally, it seeks to maintain and improve soil fertility by preventing loss of organic matter and nutrient imbalances, while also preventing surface and groundwater pollution, and the main objective being to produce food of maximum nutritional value. In this paper we assess, in prevailing soil types in central Spain (Cambisol and Regosol), several limiting factors of soil fertility, such as soil compaction due to conservative tillage systems and climatic conditions which influence the vegetation and soil conditions (mainly during the summer). The analysis of integrated fertilization allows us to highlight the importance of maximizing resources and natural production mechanisms. We evaluate the nutritional requirements of crops, aiming to ensure long-term sustainable compatible agriculture which satisfies both the demands of society (concerning environmental protection) and the agricultural productivity requirements. In this context, the official guidelines in Spain have been to meet the standards and requirements established in integrated management programs.     

不同碳氮比有机肥组合对低肥力土壤小麦生物量和部分土壤肥力因素的影响

为了快速提高低肥力土壤肥力,以石麦15为试验材料,通过盆栽实验研究了在低肥力红壤和潮土上不同碳氮比有机肥组合对小麦生物量和部分土壤肥力因素的影响.试验结果表明,施用有机肥和化肥可以明显提高小麦产量和土壤肥力,且有机肥与化肥配施比单施化肥效果更好,其中秸秆、猪粪与化肥配合使用对提高小麦产量与土壤养分作用最为明显,显著高于其它肥料组合.随着有机肥碳氮比的提高,提高小麦产量与改善土壤养分的作用逐渐变小.在潮土上,碳氮比为12.5:1的有机、无机肥料配施组合在提高小麦生物量方面,分别比碳氮比为25:1、40:1的肥料处理平均高24.2%、29.7%,在红壤上则分别为19.8%、21.2%,并且在增加土壤速效养分、脲酶活性、微生物量等地力方面的效果也比碳氮比为25:1和40:1的处理明显.     

Trees on farms and their contribution to soil fertility parameters in Badessa, eastern Ethiopia

Surface (0–15 cm) and subsurface (30–45 cm) soil samples from under canopy, edge of canopy and away from canopy of isolated Cordia africana Lam. and Croton macrostachyus Del. trees and their leaves were examined to investigate leaf nutrient content, root biomass and the contribution of trees on farms to soil fertility parameters in Badessa area, eastern Ethiopia. Leaves of C. macrostachyus had 20% higher P and 25% lower K contents than those of C. africana. The studied species had comparable leaf N content. Both species produced shallow lateral roots that extended beyond the canopy zone. Typically, higher fine root biomass was observed in the surface soils than the subsurface soils. Both species did not affect soil organic C, pH and cation exchange capacity. Surface and subsurface soils under tree canopies had 22–26 and 12–17% higher N, respectively, than the corresponding soils away from tree canopies. Surface soil available P under tree canopies was 34–50% higher than the corresponding soil away from canopies. Available P content of subsurface soil was improved only under C. africana canopy. The available P of surface soil under C. macrostachyus canopy was more than double that for C. africana. Trees of both species increased underneath surface and subsurface exchangeable K by 18–46% compared with the corresponding controls. In conclusion, C. macrostachyus and C. africana trees on farms keep soil nutrient high via protection against leaching, translocation of nutrients from deeper to the surface layer and accumulation of litter, which create a temporary nutrient pool in the surface soils under their canopies.     

Land-use effects on soil carbon and nitrogen in a typical plateau lakeshore wetland of China

Wetland soils (WS) can store a significant amount of soil organic carbon (SOC) and total nitrogen (TN). Surface soils (0–20 cm) were sampled in WS, 20-yr-old conventionally tilled soils (CTS20), 2-yr-old abandoned tilled soils (ATS2), and 6-yr-old abandoned tilled soils (ATS6) to estimate changes in SOC and TN contents due to cultivation and abandonment. Our results showed that SOC and TN contents were significantly higher in WS than those in CTS20, ATS2, and ATS6. As a result of 20-yr cultivation, SOC and TN contents decreased from 43.75 to 24.06 g kg^?1 and from 4.96 to 2.32 g kg^?1, respectively. However, after the abandonment of cultivated wetlands, SOC and TN contents showed a slow increase but the change was not significant among CTS20 and ATS2. The findings of this study suggest that SOC and TN contents in top 20 cm soils of wetlands can be reduced significantly by cultivation, but they are restored slowly after abandonment.     

The effects of a forest fire on soil microfungi

The effects of forest fires on the soil mycotlora were investigated in a Pinus contorta forest in Alberta, where it was found that species of Trichoderma and Penicillium were reduced in the burned plot, whereas Gelasinospora sp occurred only in the burned plot: Cylindrocarpon destructans appeared not to be affected by fire.The response of fungi to aqueous extracts of burned and unburned litter, measured as linear growth on agar, showed that, of the isolates tested, all but C. destructans were inhibited by the burned litter extract; C. destructans grew better on the burned litter extract. An examination of spore germination rates and growth in liquid culture showed that Trichoderma polysporum and Penicillium janthinellum were both inhibited by burned litter extracts whereas C. destructans was not. Gelasinospora sp did not grow in liquid culture, nor did it produce spores after being kept in culture for some time.It was concluded that species of Trichoderma and Penicillium were killed by the heat of the fire, and subsequently unable to rccolonize the upper layers of the soil, due to an inhibition of spore germination and growth by the chemical products of burning. C. destructans on the other hand may have been able to recolonize quickly as it appeared to be stimulated in its linear growth rate by the chemical products of burning, and its spore germination rate was only marginally lowered. The occurrence of Gelasinospora sp following fire is possibly explained by its extremely rapid growth rate, and the possibility of its ascospores being more able to withstand high temperatures in the soil.In the light of recent reports, indicating that some species of Trichoderma and Penicillium are actively antagonistic to other fungi, it is suggested that their absence after fire, in the area studied, may permit a high inoculum of C. destructans to develop in the soil, which could possibly result in a high incidence of disease in developing pine seedlings     

Land-use/cover change effects and carbon controls on volcanic soil profiles in highland temperate forests

The stabilization of SOM by Al–humus complexes and non-crystalline minerals is a key issue to explain the soil-C variability and the biogeochemical processes that determine the fate of soil C following land-use/cover change (LUCC) in volcanic landscapes. In an altitudinal gradient of volcanic soils (2550–3500 masl), we quantified the total soil C (C_T) concentrations and stocks in soil pits sampled by genetic horizons. We performed analyses at landscape and local scales in order to identify and integrate the underlying environmental controls on C_T and the effects of LUCC. We selected four sites, two on the upper piedmont, one on the lower mountain slope and one on the middle mountain slope at Cofre de Perote volcano (eastern central Mexico) where temperate forests are the natural vegetation. At each site we selected three to five units of use/cover as a chronosequence of the LUCC pathways. In each soil horizon chemical characteristics (i.e. N, C/N ratio, pH, exchangeable bases) were determined and mineralogical properties were estimated from selective Al, Fe and Si oxalate and pyrophosphate extractions (i.e. the Alp/Alo ratio, the active Al related to non-crystalline minerals as Al_o ? Al_p, the allophane concentration, and the non-crystalline Al and Fe minerals as Al_o + 1/2Fe_o). At landscape scale, the Al–humus complexes were strongly related to the C_T concentration in topsoil (A horizons) but this relationship decreased with depth. In turn, the non-crystalline minerals and the C/N ratio explained the variability of the C_T concentrations in C horizons. At local scale, C_T concentrations and stocks were depleted after conversion of forest to agriculture in Vitric Andosols at the upper piedmont but this was not observed in Silandic Andosols. However, in Vitric Andosols the reduction of the C_T stocks is partially recovered throughout the regeneration/reforestation processes. The results suggest that the lower vulnerability of Silandic Andosols than Vitric Andosols to changes in the C_T after LUCC is due to the higher levels of SOM stabilized by Al–humus complexes and non-crystalline minerals in the Silandic soils. Furthermore, the importance of the allophane to explain the C_T stocks in the Silandic Andosols of the middle slopes suggests that the C_T stabilized by this mineral fraction in the subsoil adds an important fraction of the C_T to the estimates of the stocks.     

Vinasse irrigation: effects on soil fertility and arbuscular mycorrhizal fungi population

Purpose

The aim of this research was to determine the vinasse irrigation effects on the arbuscular mycorrhizal fungi (AMF) population (total spore abundance (TSA), richness, relative abundance, and diversity indices) and soil parameters and nutrients at high doses. The irrigation of soil with vinasses derived from sugarcane, beet, or alcohol production is a common practice around the world. Little is known about how this affects the AMF community and soil nutrients.

Materials and methods

The spider plant (Chlorophytum comosum, (Thunb.) Jacques), a mycorrhizable plant, was used to investigate the effect of 4 months of frequent vinasse irrigation (0, 25, 50, 75, and 100% vinasse concentration) on AMF and soil characteristics, e.g., electrical conductivity (EC), pH, mineral N, available P, Na⁺, K⁺, Ca²⁺, and Mg²⁺.

Results and discussion

The vinasse irrigation decreased the TSA, AMF richness and diversity after 4 months, regardless of vinasse concentration. The vinasse irrigation did not acidify the soil, but the EC, mineral N and available P increased. The biomass of C. comosum decreased (77–81%) after vinasse irrigation for 4 months.

Conclusions

Frequent irrigation with vinasse at concentrations ≥50% increases EC, K⁺, Na⁺, Mg²⁺, Ca²⁺ and available P in the soil, and decreases the amount of AMF spores, richness and diversity, which is not desirable in agricultural soils.

     

基于土壤肥力质量综合指数评价化肥与有机肥配施对红壤稻田肥力的提升作用

[目的]准确评价有机肥料提高农田土壤肥力的效果,是正确选择土壤培肥措施的基础.通过比较两种土壤肥力质量综合指数的计算方法评价有机肥培肥效果的可行性.[方法]3年田间定位试验(2015—2017)在长江中下游的红壤双季稻田进行.共设7个处理:不施肥(CK),等氮磷钾投入量下的单施化肥(CF)和一半化肥氮配施一半的牛粪(+...     

长期不同施肥下红壤性水稻土综合肥力评价及其效应

以江西进贤红壤性水稻土长期试验为基础,运用模糊数学及统计学方法进行土壤肥力综合评价及其效应研究,以期达到土壤培肥的目的.结果表明,有机质、速效氮、速效磷、速效钾、物理性粘粒、团聚度和团聚体稳定率为研究区土壤肥力评价最小数据集,由其所得评价结果具有高度代表性和科学性.NPKM的SFI值最大且与其他处理均呈显著差异.NPKM、2NPK、NPK各处理SFI值分别高出对照(CK) 31.3％、13.0％和10.1％.SFI值的时间演变为NPKM处理先增后降,临界年限在第12年,N和CK处理缓降,其它处理缓增.一定范围内,二次曲线较直线更能揭示作物产量与SFI的关系,进一步拟合发现,SFI和作物相对产量间符合“S”型波尔兹曼生长曲线,SFI增至0.60时,相对产量增幅趋零,NPKM处理(SFI=0.688)已属于此;模拟可知,作物产量趋稳时相应施肥年限表现为NPKM (2a) ＜2NPK (8a) ＜NPK (9a) ＜NP (11a) ＜K、NK (13a)＜P(14a)处理.综上,长期平衡施肥(NPKM、2NPK和NPK)明显提高土壤综合肥力,NPKM更为显著,但其现状对作物增产已无效,应减施或不施若干年;长期偏施肥对土壤肥力贡献不力,尤其是长期单施氮反使土壤肥力下降.     

Land-use effects on organic matter and physical properties of soil in a southern Mediterranean highland of Turkey

Forest and grassland soils in highlands of southern Mediterranean Turkey are being seriously degraded and destructed due to extensive agricultural activities. This study investigated the effects of changes in land-use type on some soil properties in a Mediterranean plateau. Three adjacent land-use types included the cultivated lands, which have been converted from pastures for 12 years, fragmented forests, and unaltered pastures lands. Disturbed and undisturbed soil samples were collected from four sites at each of the three different land-use types from depths of 0–10 cm and 10–20 cm in Typic Haploxeroll soils with an elevation of about 1400 m. When the pasture was converted into cultivation, soil organic matter (SOM) pool of cultivated lands for a depth of 0–20 cm were significantly reduced by, on average 49% relative to SOM content of the pasture lands. There was no significant difference in SOM between the depths in each land-use type, and SOM values of the forest and pasture lands were almost similar. There was also a significant change in soil bulk density (BD) among cultivation (1.33 Mg m⁻³), pasture (1.19 Mg m⁻³), and forest (1.25 Mg m⁻³) soils at depth of 0–20 cm. Only for the pasture, BD of the depth of 0–10 cm was significantly different from that of 10–20 cm. Depending upon the increases in BD and disruption of pores by cultivation, total porosity decreased accordingly. Cultivation of the unaltered pasture obviously increased the soil erodibility measured by USLE-K factor for each soil depth, and USLE-K factor was approximately two times greater in the cultivated land than in the pasture indicating the vulnerability of the cultivated land to water erosion. The mean weight diameter (MWD) and water-stable aggregation (WSA) were greater in the pasture and forest soils compared to the cultivated soils, and didn’t change with the depth for each land-use type. Aggregates of >4.0 mm size were dominant in the pasture and forest soils, whereas the cultivated soils comprised aggregates of the size ≤0.5 mm. I found that samples collected from cultivated land gave the lowest saturated hydraulic conductivity values regardless of soil depths, whereas the highest values were measured on samples from forest soils. In conclusion, the results showed that the cultivation of the pastures degraded the soil physical properties, leaving soils more susceptible to the erosion. This suggests that land disturbances should be strictly avoided in the pastures with the limited soil depth in the southern Mediterranean highlands.     

Integrated soil fertility management enhances population and effectiveness of indigenous cowpea rhizobia in semi-arid eastern Kenya

Legume biological nitrogen fixation is an environmentally friendly and economical means that can reduce low resource farmer dependence on expensive chemical nitrogen (N) fertilizers. We investigated the effect of two cowpea (Vigna unguiculata (L.) Walp) varieties (IT95K-52-34, an international variety from IITA and Kang’au, a local variety) under an integrated soil fertility management trial on indigenous symbiotic rhizobia in a semi-arid farmer's field in eastern Kenya. The ox-ploughed field trial had the following treatments: an unamended control, manure applied at 2.5 t ha⁻¹, triple superphosphate (TSP as (P₂O₅, 0:46:0) at 15 kg ha⁻¹; and a combination of manure and TSP applied at the single rates. Soil samples were collected from each treatment during planting and harvesting of the cowpea crop and used in most probable number (MPN) plant infection assays with the two cowpea varieties as traphosts in Leonard jar growth systems and grown under glasshouse conditions. Generally, soil amendments enhanced cowpea rhizobial populations which varied from 4.89 × 10² rhizobia g⁻¹ soil to 1.074 × 10³ rhizobia g⁻¹ soil. The highest shoot biomass accumulation occurred on cowpea variety IT95K-52-34 plants inoculated with soils from the manure applied plots. We isolated 150 fast- and slow-growing cowpea rhizobia. Contrary to most previous studies, the bulk (97%) of the isolates was fast growing which grouped into 9 types on the growth characteristics on yeast extract agar (YEMA). The study indicated that ISFM was important for rhizobia population build up over a cowpea-growing season.     

The contribution of rabbits (Oryctolagus cuniculus L.) to soil fertility in semi-arid Spain

 Degradation of land in vulnerable areas can be significantly reduced by the maintenance or establishment of plant cover and diversity. Animals can facilitate plant diversity by grazing, by dispersing seeds or by contributing, through excreta, to the heterogeneous distribution of nutrients in soil. We investigated the latter property by examining the effects of rabbit (Oryctolagus cuniculus L.) dung deposition on soil properties in three adjacent plant communities at a semi-arid site in south-east Spain. Rabbit faecal pellets had concentrations of total N and P comparable to dung of stock animals, with K and Mg somewhat lower, although decomposition rates at this site are evidently very low. There was no significant difference in pH, but conductivity and concentrations of organic C, N (as NH₄ ⁺ and NO₃ ^–), K, P and Mg in soils from rabbit latrines were significantly greater relative to controls in each community. Barley plants grown as a bioassay of soil fertility had significantly greater total biomass, and lower root : shoot ratios in latrine compared to control soils. There were differences among communities in conductivity and concentrations of N, P and organic C under latrines which were reflected in the bioassay. Although latrines only comprised approximately 0.1% of the ground surface area in each community, they make significant localised contributions to soil fertility and may therefore be important in establishing and maintaining plant cover. Received: 11 May 1999     

Biomonitoring ozone phytotoxicity in eastern Spain

High ozone (O₃) levels have been recorded in eastern Spain. A project was developed to identify the areas of elevated O₃ and determine if these levels were above critical concentrations for plant damage. Thus, a network of bioindicators was established in two Autonomous Communities of Spain: Catalunya (31.930 km²) and Valencia (23.305 km²) to assess O₃ phytotoxicity. Three tobacco cultivars, (Bel-W3, Bel-C and Bel-B) were used during the 1994 growing season in both Regions. In Catalunya the highest O₃ phytotoxicity was recorded in coastal areas, while the phytotoxicity decreased as plants were grown further in-land. A lower O₃ phytotoxicity was observed in coastal sites of the Valencia Autonomous Community, compared to Catalunya, although the O₃ injury was observed downwind from Valencia city in the most resistant cultivar Bel-B. The results in the Valencian Community were difficult to interpret, since plant viruses were widely distributed, not only in indicator plants, but also in commercial crops grown in the area. The analysis of O₃ concentrations, meteorological parameters and visible injury at the Catalan sites showed that high relative humidity levels could favour O₃ phytotoxicity. Therefore, the interactions between O₃ exposure and environmental conditions on plant response should be further studied for the establishment of sound critical levels.     

红壤旱地长期试验肥力演变及玉米效应研究

采用长期定位试验研究方法,探讨高原旱地红壤施N、NP、NM、NPM和NPK对红壤肥力演变、养分供给能力及玉米的效应。结果表明,N处理8年玉米绝收;NP处理前期比施N增产,长期施用不稳产,至23年绝收;NPM处理玉米产量由试验前10年的4628 kg/hm2,增加到后10年的6875 kg/hm2,增产2247 kg/hm2;在NP基础上施K2O 112.5 kg/hm2的NP+K处理,比施NP增产2264 kg/hm2。说明配施增产效果明显,但长期只施NP会导致其它元素失衡不能稳产。有机肥和NP配施,显著增加土壤有机质含量,红壤28年不施有机肥,有机质含量不下降,年施有机肥30000 kg/hm2,不施化学钾肥,也能维持钾素平衡。长期不施化学钾或有机肥导致钾素枯竭。红壤磷素自然供给能力极低,仅为3.6～15.7%,施磷显著增加速效磷含量,施磷或有机肥提高磷素自然供给能力。NP处理11年不施钾,钾素自然供给能力由35%～68%降低为11.09%～23.2%。     

Ecological effects of rice-duck integrated farming on soil fertility and weed and pest control

Purpose

This paper aims to study the ecological effects of rice-duck integrated farming on soil fertility and weed and pest control.

Materials and methods

A field experiment was carried out in the suburb of Shanghai in 2014, which included a rice-duck integrated treatment and non-duck treatment (CK) under organic management. Each treatment was in triplicate, and the experiment included six plots in total, with each plot 667 m² in area.

Results and discussion

(1) The number of weeds in the plots with the duck treatment was significantly lower than that with CK (p?<?0.01). (2) The incidence of stem borers (Chilo suppressalis) with the duck treatment was significantly lower than that with CK (p?<?0.05). The incidences of rice leaf rollers (Cnaphalocrocis medinalis), rice sheath blight (Rhizoctonia solani), and planthoppers with the duck treatment were extremely significantly lower than those with CK (p?<?0.01). (3) The contents of NH₄ ⁺-N, alkali-hydrolyzable N, available P, and available K in the soils with the duck treatment were higher than those with CK, and the activities of urease, phosphatase, sucrase, and catalase in the soils with the duck treatment were also much higher than those with CK. The grain yield with the duck treatment was 1.9 times that with CK. (4) The number of soil nematodes with the duck treatment was significantly higher than that with CK in the late rice growing stage (p?<?0.01).

Conclusions

Raising ducks in the paddy fields not only showed a potential of controlling weed hazards and reducing rice pests and diseases but also raised soil fertility, improved soil biodiversity, and increased grain yield effectively. Implementing the rice-duck integrated farming could highly reduce the amount of pesticides and herbicides and was beneficial to develop the organic rice farming in the suburbs of Shanghai, Southeast China.

     

Long-term effects of crop rotation and different fertilization systems on soil fertility and productivity

The effects of crop rotation and fertilization systems on yield and soil fertility parameters have been investigated in a long-term field trial established in southeast Norway in 1953. The results indicate the small differences between crop rotations and different fertilization systems in yield and soil fertility parameters; the decreasing trend in soil organic carbon (SOC) (from 3.8 to 3.7%) and increasing trend of N with time (from 0.32 to 0.36%) and, as a result, the decreasing trend in C/N ratio (from 12 to 10).     

Land-use effects on phosphorus fractions in Cerrado oxisols

 Differently managed oxisols from Central Brazil were studied using a sequential P fractionation procedure because the effects of land use on the distribution of P forms in these soils are barely known. Therefore levels of labile and recalcitrant P forms in the natural Cerrado savanna were compared with those of crop, pasture and reforestation sites on differently textured oxisols. Under natural conditions of strong P deficiency, >60% of labile P was organic P (P_o), reflecting the high contribution of P_o to plant nutrition. Fertilisation after land-use change only increased levels of inorganic P (P_i) forms, the increase being most accentuated in the labile P_i fraction. At the crop and the pasture sites P tended to accumulate as recalcitrant P forms in the clayey soils, while in the loamy soils there was only a minor enrichment, probably due to the lower amounts of Fe- and Al-(hydr)oxides. In the reforestation sites, labile P was maintained at high levels, most likely through efficient recycling of the litter. The P fractionation procedure was also applied to particle-size fractions which reflected P transformations along an organic and mineralogical gradient. The clay fraction corresponded to 69–87% of total P and appeared to be both a sink for highly recalcitrant P and a source for labile P, especially labile P_o. The sequential P fractionation procedure was also an effective method with which to detect the presence of fertiliser-P residues in the coarse-silt fraction. Received: 18 June 1999