有机栽培和常规栽培水稻体系土壤酶及微生物量的比较研究

本研究探讨了有机栽培与常规栽培体系下水稻土微生物量及脲酶、酸性磷酸酶和过氧化氢酶的动态变化过程,以及有机栽培体系不同肥料调控措施对上述指标的影响.结果表明:与常规栽培水稻体系相比,有机栽培水稻有利于土壤微生物的生长和繁衍;水稻生长不同时期有机栽培方式的土壤微生物生物量碳、脲酶、酸性磷酸酶和过氧化氢酶活性均高于常规栽培体系.就水稻全生育期而言,土壤微生物生物量碳高于常规栽培7.3%～9.1%;脲酶、酸性磷酸酶和过氧化氢酶活性分别高于常规栽培7.3%～14.5%、5.2%～6.5%和12.5%～29.2%;有机水稻栽培体系下配施生态肥,在有机肥施用量减半时,土壤微生物生物量碳含量及土壤脲酶、酸性磷酸酶和过氧化氢酶活性较单施有机肥平均分别提高1.6%、6.8%、1.3%和14.8%,在水稻生长前期和中期该增加作用尤为显著.     

Chemical and biochemical properties in a silty loam soil under conventional and organic management

To improve soil fertility, efforts need to be made to increase soil organic matter content. Conventional farming practice generally leads to a reduction of soil organic matter. This study compared inorganic and organic fertilisers in a crop rotation system over two cultivation cycles: first crop broad bean (Vicia faba L.) and second crop mixed cropped melon-water melon (Cucumis melo-Citrullus vulgaris) under semi-arid conditions. Total organic carbon (TOC), Kjeldahl-N, available-P, microbial biomass C (Cmic), and N (Nmic), soil respiration and enzymatic activities (protease, urease, and alkaline phosphatase) were determined in soils between the fourth and sixth year of management comparison. The metabolic quotient (qCO₂), the Cmic/Nmic ratio, and the Cmic/TOC ratio were also calculated. Organic management resulted in significant increases in TOC and Kjeldahl-N, available-P, soil respiration, microbial biomass, and enzymatic activities compared with those found under conventional management. Crop yield was greater from organic than conventional fertilizer. The qCO₂ showed a progressive increase for both treatments during the study, although qCO₂ was greater with conventional than organic fertilizer. In both treatments, an increase in the Cmic/Nmic ratio from first to second crop cycle was observed, indicating a change in the microbial populations. Biochemical properties were positively correlated (p < 0.01) with TOC and nutrient content. These results indicated that organic management positively affected soil organic matter content, thus improving soil quality and productivity.     

Crop yield and soil fertility response to reduced tillage under organic management

Conservation tillage (no-till and reduced tillage) brings many benefits with respect to soil fertility and energy use, but it also has drawbacks regarding the need for synthetic fertilizers and herbicides. Our objective was to adapt reduced tillage to organic farming by quantifying effects of tillage (plough versus chisel), fertilization (slurry versus manure compost) and biodynamic preparations (with versus without) on soil fertility indicators and crop yield. The experiment was initiated in 2002 on a Stagnic Eutric Cambisol (45% clay content) near Frick (Switzerland) where the average annual precipitation is 1000 mm. This report focuses on the conversion period and examines changes as tillage intensity was reduced. Soil samples were taken from the 0–10 and 10–20 cm depths and analysed for soil organic carbon (C_org), microbial biomass (C_mic), dehydrogenase activity (DHA) and earthworm density and biomass. Among the components tested, only tillage had any influence on these soil fertility indicators. C_org in the 0–10 cm soil layer increased by 7.4% (1.5 g C_org kg⁻¹ soil, p < 0.001) with reduced tillage between 2002 and 2005, but remained constant with conventional tillage. Similarly, C_mic was 28% higher and DHA 27% (p < 0.001) higher with reduced than with conventional tillage in the soil layer 0–10 cm. In the 10–20 cm layer, there were no significant differences for these soil parameters between the tillage treatments. Tillage had no significant effect on total earthworm density and biomass. The abundance of endogeic, horizontally burrowing adult earthworms was 70% higher under reduced than conventional tillage but their biomass was 53% lower with reduced tillage. Wheat (Triticum aestivum L.) and spelt (Triticum spelta L.) yield decreased by 14% (p < 0.001) and 8% (p < 0.05), respectively, with reduced tillage, but sunflower (Helianthus annuus L.) yield was slightly higher with reduced tillage. Slurry fertilization enhanced wheat yield by 5% (p < 0.001) compared to compost fertilization. Overall, C_org, C_mic, and DHA improved and yields showed only a small reduction with reduced tillage under organic management, but long-term effects such as weed competition remain unknown.     

华北地区有机种植和常规种植模式下土壤重金属含量及污染评价

为探讨有机种植与常规种植两种不同种植方式对土壤重金属含量和污染特性的影响,本文在华北5个地区选取典型的有机蔬菜和有机小麦种植基地及附近相似条件的常规种植地块,比较了土壤中Cu、Zn、Pb、Cr、Cd、As共6种重金属含量的差异,并采用不同评价方法对不同种植方式下土壤中重金属的污染程度进行了评价。结果表明:与常规种植相比,有机种植减轻了土壤酸化和盐渍化,提高了土壤有机质含量和阳离子交换量,在一定程度上有利于降低土壤中重金属的生物有效性。与土壤背景值相比,所有调查地区的土壤重金属均有不同程度的增加和积累。与常规种植相比,有机种植模式能有效降低土壤中Cd、Cr含量,有机小麦种植地块因长期施用大量有机肥导致土壤中Cu、Zn、As大量富集;而常规温室菜田同时施用大量的有机肥、化肥及农药,土壤中Cu、Zn、As富集的风险比有机种植模式高;露天蔬菜有机种植地块土壤中Cu、Zn、As含量与常规地块差异不明显。综合污染指数评价结果显示,调查地区土壤均属于轻污染程度,主要贡献因子为Cd、Cu、Zn,有机种植降低了土壤中重金属的综合污染水平;地累积指数法评价结果表明,调查地区处于无污染到中等污染水平,最明显的污染元素是Cd,有机种植降低了土壤中重金属污染的程度和风险;潜在生态危害指数评价结果表明,所调查地块存在轻微潜在生态风险,其中产生较大生态危害的是Cd,表现出轻微生态危害程度。本研究表明,有机种植减轻了土壤中重金属综合污染水平和污染风险,并减轻了土壤重金属的潜在生态危害。     

有机和常规生产模式下菜田土壤酶活性差异研究

通过对露地及温室环境下有机和常规蔬菜栽培土壤采样,测定分析了5种参与土壤碳氮循环的酶活性,及其与土壤相关理化性质之间的关系。结果显示:温室及露地土壤EC值在有机生产中相应低于常规生产12%和16%;有机生产土壤微生物碳氮含量显著高于常规生产;不同生产模式下土壤酶活性差异显著,有机生产土壤中的蛋白酶、脲酶、脱氢酶、β-葡糖苷酶活性高于常规生产,而硝酸还原酶活性较常规生产低;有机与常规栽培对蛋白酶活性影响极显著(P=0.006 8),对脲酶活性影响程度达显著水平(P=0.012 4)。除脱氢酶以外,不同栽培模式环境对土壤中另外4种酶活性均有显著影响,温室栽培环境中的蛋白酶、脲酶和硝酸还原酶活性高于露地。除硝酸还原酶外,其他4种酶活性与可溶性全氮、微生物碳、微生物氮相关系数达到显著水平。分析表明,土壤酶活性受到栽培方式以及环境的影响,并且有机生产能够提高参与土壤碳氮循环的酶活性。土壤蛋白酶、脲酶、脱氢酶和β-葡糖苷酶活性能够作为表征土壤碳氮循环以及微生物活性的指标。     

Decomposition of wheat straw differing in nitrogen content in soils under conventional and organic farming management

An incubation experiment was carried out to investigate the interactions of two straw qualities differing in N content and two soils differently accustomed to straw additions. One soil under conventional farming management (CFM) regularly received straw, the other soil under organic farming management (OFM) only farmyard manure. The soils of the two sites were similar in texture, pH, cation‐exchange capacity, and glucosamine content. The soil from the OFM site had higher contents of organic C, total N, muramic acid, microbial biomass C and N (C_mic and N_mic), but a lower ergosterol content and lower ratios ergosterol to C_mic and fungal C to bacterial C. The straw from the CFM had threefold higher contents of total N, twofold higher contents of ergosterol and glucosamine, a 50% higher content of muramic acid, and a 30% higher fungal C–to–bacterial C ratio. The straw amendments led to significant net increases in C_mic, N_mic, and ergosterol. Microbial biomass C showed on average a 50% higher net increase in the organic than in the CFM soil. In contrast, the net increases in N_mic and ergosterol differed only slightly between the two soils after straw amendment. The CO₂ evolution from the CFM soil always exceeded that from the OFM, by 50% or 200 µg (g soil)^–1 in the nonamended control soil and by 55% or additional 600 µg (g soil)^–1 in the two straw treatments. In both soils, 180 µg g^–1 less was evolved as CO₂‐C from the OFM straw. The metabolic quotient qCO₂ was nearly twice as high in the control and in the straw treatments of the CFM soil compared with that of the OFM. In contrast, the difference in qCO₂ was insignificant between the two straw qualities. Differences in the fungal‐community structure may explain to a large extent the difference in the microbial use of straw in the two soils under different managements.     

Organic matter returns to soils must be higher under organic compared to conventional farming

The aim of this paper is to discuss the demand of fresh organic matter (FOM) supply to maintain soil organic matter (SOM) levels and productivity of arable soils under organic management. The basic question is whether the different frame conditions in organic vs. conventional farming result in a different and system‐specific FOM demand. If this is the case, it would follow that the farming system has to be considered in the calculation of SOM balances. SOM balances are the most common decision support tools in organic matter management. A conversion to organic farming in practice usually leads to an increase of SOM levels as well as soil microbial activity over time. The system‐specific driver of this effect is the indispensable extension of the share of (perennial) legumes in crop rotations at the expense of non‐legumes such as cereals, row crops, and maize. Extended legume cropping is essential for N supply in crop rotations as the import of N fertilizer in total is limited by organic farming regulations and mineral N fertilizer may not be used at all. Based on this characteristic of organic management, we argue that the demand of FOM supply to soils must be higher than in conventional crop production. The most relevant factors are (1) the non‐existence of mineral N fertilizer as an external N source that supports the maintenance of SOM by decreasing the demand for SOM‐N, (2) benefits of increasing SOM stocks and turnover for soil productivity under organic management, and, (3) increased mass‐losses of FOM and easily degradable SOM compartments due to higher microbial activity in soils. These effects have to be quantified and must be considered in SOM balances in order to avoid misleading assessments and erroneous decisions.     

Microbial properties and nitrogen contents of arable soils under different tillage regimes

Attention is being paid to the use of different tillage regimes as a means of retaining soil organic carbon (SOC) and sequestering more SOC. Alongside earlier measurements of total SOC stocks under different tillage regimes, we have examined the distribution of nitrogen (N), microbial activity and the structure of the soil bacterial community from differently tilled plots under continuous barley. The plots were established 5 yr before sampling and have been maintained annually under conventional tillage (CT; moldboard ploughing to 20 cm and disking), deep ploughing (DP; ploughing to 40 cm and disking), minimum tillage (MT; disking to 7 cm) or zero tillage (ZT). Our earlier work showed there was no difference in SOC contents down to 60‐cm depth between the treatments, but now we report that there were significant differences in the total N and active microbial biomass (substrate‐induced respiration) contents of the same soils. The N contents of the CT, DP and MT treatments were not significantly different, but the ZT contained significantly more N, indicating either greater N retention under the ZT treatment or preferential loss from the more intensively tilled treatments, or a combination of both. The microbial biomass content was greater for the CT and DP treatments than for the MT and ZT treatments, indicating greater sensitivity to treatment effects of the microbial biomass pool than the total C pool, consistent with its more dynamic nature. Terminal restriction fragment length polymorphism (T‐RFLP) analyses of the soil bacteria DNA (a method of assessing the bacterial community structure) enabled the samples to be distinguished both according to SOC content, which is to be expected, and to tillage regime with the greatest differences in community structure occurring in the ZT treatment and the least in DP and CT treatments, reflecting the degree of homogenization or disturbance resulting from tillage.     

Phosphorus forms and enzymatic hydrolyzability of organic phosphorus in soils after 30 years of organic and conventional farming

Lower P‐input levels in organic than conventional farming can decrease soil total and available P, which can potentially be resupplied from soil organic P. We studied the effect of 30 y of conventional and organic farming on soil P forms, focussing especially on organic P. Soil samples (0–20 cm) were taken in a field experiment with a nonfertilized control, two organic systems receiving P inputs as animal manure, and two conventional systems receiving only mineral P or mineral P and manure. Soils were analyzed for total, inorganic, organic, and microbial P, by sequential P fractionation and by enzyme additions to alkaline soil extracts. Samples taken prior to starting the experiment were also analyzed. Average annual P balances ranged from –20 to +5 kg ha^–1. For systems with a negative balance, labile and moderately labile inorganic P fractions decreased, while organic and stable inorganic P fractions were hardly affected. Similar quantities and proportions of organic P extracted with NaOH‐EDTA were hydrolyzed in all soils after addition of an acid phosphatase, a nuclease, and a phytase, and enzyme‐stable organic P was also similar among soils. Thus, neither sequential fractionation nor enzyme addition to alkaline soil extracts showed an effect of the type of applied P (manure vs. mineral) on organic P, suggesting that organic P from manure has largely been mineralized. Thus far, we have no indication that the greater microbial activity of the organic systems resulted in a use of stable P forms.     

Nitrogen pools and turnover in arable soils under different durations of organic farming: I: Pool sizes of total soil nitrogen,microbial biomass nitrogen,and potentially mineralizable nitrogen

Soil organic matter contents, soil microbial biomass, potentially mineralizable nitrogen (N) and soil pH values were investigated in the Ap horizons of 14 field plots at 3 sites which had been under organic farming over various periods. The objective was to test how these soil properties change with the duration of organic farming. Site effects were significant for pH values, microbial biomass C and N, and for potentially mineralizable N at 0—10 cm depth. The contents of total organic C, total soil N, and potentially mineralizable N tended to be higher in soils after 41 versus 3 years of organic farming, but the differences were not significant. Microbial biomass C and N contents were higher after 41 years than after 3 years of organic farming at 0—10 cm depth, and the pH values were increased at 10—27 cm depth. Nine years of organic farming were insufficient to affect soil microbial biomass significantly. Increased biomass N contents help improve N storage by soil micro‐organisms in soils under long‐term organic farming.     

Soil microbial biomass and activity in organic tomato farming systems: Effects of organic inputs and straw mulching

Organic farming is rapidly expanding worldwide. Plant growth in organic systems greatly depends on the functions performed by soil microbes, particularly in nutrient supply. However, the linkages between soil microbes and nutrient availability in organically managed soils are not well understood. We conducted a long-term field experiment to examine microbial biomass and activity, and nutrient availability under four management regimes with different organic inputs. The experiment was initiated in 1997 by employing different practices of organic farming in a coastal sandy soil in Clinton, NC, USA. Organic practices were designed by applying organic substrates with different C and N availability, either in the presence or absence of wheat-straw mulch. The organic substrates used included composted cotton gin trash (CGT), animal manure (AM) and rye/vetch green manure (RV). A commercial synthetic fertilizer (SF) was used as a conventional control. Results obtained in both 2001 and 2002 showed that microbial biomass and microbial activity were generally higher in organically than conventionally managed soils with CGT being most effective. The CGT additions increased soil microbial biomass C and activity by 103-151% and 88-170% over a period of two years, respectively, leading to a 182-285% increase in potentially mineralizable N, compared to the SF control. Straw mulching further enhanced microbial biomass, activity, and potential N availability by 42, 64, and 30%, respectively, relative to non-mulched soils, likely via improving C and water availability for soil microbes. The findings that microbial properties and N availability for plants differed under different organic input regimes suggest the need for effective residue managements in organic tomato farming systems.     

集约经营雷竹林土壤微生物的演变

Phyllostachys praecox C. D. Chu et C. S. Chao, a favored bamboo shoot species, has been widely planted in recent years. Four stands with different historical management practices were selected for this study to understand the evolution of soil microbial ecology by determining the effects of a new mulching and heavy fertilization practice on soil quality using microbiological parameters. Compared with the traditional practice (index 1), microbial biomass carbon (MBC) and soil microbial respiration carbon (MRC) with the new management practice significantly decreased (P < 0.01 and P < 0.05, respectively) with 1--2 years of mulching (index 2) and then for continued mulching significantly increased (P < 0.05). The ratios of MBC/TOC (total organic carbon) and MRC/TOC also significantly diminished (P < 0.05) with mulching. The average well color development (AWCD) and Shannon index decreased with mulching time, and the significant decrease (P < 0.05) in Shannon index occurred from index 2 to index 3. The results from a principal components analysis (PCA) showed that the scores of the first principal component for indexes 1 and 2 were significantly larger (P < 0.05) than soils mulched 3--4 years or 5--6 years. Also, the second principal component scores for index 1 were larger than those for index 2, suggesting that the ability of soil microorganisms to utilize soil carbon was decreasing with longer use of the new management practice and causing a deterioration of soil biological properties.     

Soil phosphorus dynamics in cropping systems managed according to conventional and biological agricultural methods

The effects of conventional and biological farming systems on soil P dynamics were studied by measuring some microbiological parameters after 13 years of different cropping systems. The treatments included control, biodynamic, bio-organic, and conventional plots and a mineral fertilizer treatment. The farming systems differed mainly in the form and quantity of nutrients applied and in the plant protection strategies. The results of a sequential fractionation procedure showed that irrespective of the form of P applied, neither 0.5 M NaHCO _inf3 ^sup- nor 0.1 M NaOH-extractable organic P, but only the inorganic fractions, were affected. The residual organic P, not extracted by NaHCO₃ or NaOH was increased in the biodynamic and bio-organic plots. The soil microbial biomass (ATP content) and the activity of acid phosphatase were also higher in both biologically managed systems. These results were attributed to the higher quantity of organic C and organic P applied in these systems, but also to the absence of or severe reduction in chemical plant protection. The relationship between acid soil phosphatase and residual organic P was interpreted as an indication that this fraction might be involved in short-term transformations. The measurement of the intensity, quantity, and capacity factors of available soil P using the ³²P isotopic exchange kinetic method showed that P could not be the factor limiting crop yield in the biological farming systems. The kinetic parameters describing the ability of P ions to leave the soil solid phase, deduced from isotopic exchange, were significantly higher for the biodynamic treatment than for all other treatments. This result, showing a modification of chemical bonds between P ions and the soil matrix, was explained by the higher Ca and organic matter contents in this system.     

Microbiological processes in soil organic phosphorus transformations in conventional and biological cropping systems

We studied microbiological processes in organic P transformations in soils cultivated with conventional and biological farming systems during the 13th and 14th year of different cropping systems. The treatments included control, biodynamic, bioorganic, and conventional plots and a mineral fertilization treatment. Different P fractions were investigated using a sequential fractionation method. Labile organic P, extracted by 0.5 M NaHCO₃, was not affected by the farming systems. However, residual organic P remaining in the soil at the end of the sequential fractionation procedure showed that the biodynamic treatment, in particular, led to a modification of the composition of organic P. Labile organic P, organic P extractable in 0.1 M NaOH, and total residual P all showed temporal fluctuations. As total residual P consists of more than 70% organic P, it can be assumed that residual organic P contributed to these variations. This result indicates that chemically resistant organic P participates in short-term accumulation and mineralization processes. All biological soil parameters tested in this study showed significant temporal fluctuations, mainly attributed to differences in climatic conditions between years, but possibly also related to the growth cycle of the crop. The higher values of the biological soil parameters in the biodynamic and bioorganic treatments were explained by the greater importance of manure and the different plant protection strategies. The level of phosphatase activity and mineralization of organic C indicated a higher turnover of organic substrates, and thus of organic P, in the biodynamic and bioorganic treatments. Biological parameters were shown to be critical for assessing the significance of organic P in the soil P turnover.     

温室菜园土壤氮矿化和微生物群落对水分的响应

Soil drying and wetting impose significant influences on soil nitrogen (N) dynamics and microbial communities. However, effects of drying-wetting cycles, while common in vegetable soils, especially under greenhouse conditions, have not been well studied. In this study, two greenhouse vegetable soils, which were collected from Xinji (XJ) and Hangzhou (HZ), China, were maintained at 30% and 75% water-holding capacity (WHC), or five cycles of 75% WHC followed by a 7-day dry-down to 30% WHC (DW). Soil inorganic N content increased during incubation. Net N mineralization (Nmin), microbial activity, and microbial biomass were significantly higher in the DW treatment than in the 30% and 75% WHC treatments. The higher water content (75% WHC) treatment had higher Nmin, microbial activity, and microbial biomass than the lower water content treatment (30% WHC). Multivariate analyses of community-level physiological profile (CLPP) and phospholipid fatty acid (PLFA) data indicated that soil moisture regime had a significant effect on soil microbial community substrate utilization pattern and microbial community composition. The significant positive correlation between Nmin and microbial substrate utilization or PLFAs suggested that soil N mineralization had a close relationship with microbial community.     

Influence of reduced tillage on earthworm and microbial communities under organic arable farming

Although reduced tillage is an agricultural practice reported to decrease soil erosion and external inputs while enhancing soil fertility, it has still rarely been adopted by European organic farmers. The objective of this study was to assess the long-term interactive effects of tillage (conventional (CT) vs. reduced (RT)) and fertilization (slurry (S) vs. composted manure/slurry (MCS)) on earthworms and microbial communities in a clay soil under spelt in an organic 6-year crop rotation. Earthworm populations (species, density and biomass, cocoons) were investigated by handsorting the soil nine years after initial implementation of the treatments. Soil microbial carbon (C_mic) and nitrogen (N_mic) were measured by chloroform-fumigation extraction and a simplified phospholipid fatty acid (PLFA) analysis was used to separate for populations of bacteria, fungi and protozoa. Significantly increased total earthworm density in RT plots was mainly attributed to increased numbers of juveniles. Moreover, we found five times more cocoons with RT. Species richness was not affected by the treatments, but tillage treatments had differentially affected populations at the species-level. In addition, cluster analysis at the community level revealed two distinct groups of plots in relation to tillage treatments. In RT plots C_mic increased in the 0–10 cm and 10–20 cm soil layers, while PLFA concentrations indicative of Gram-negative bacteria, fungi and protozoa only increased in the topsoil. Lower bacteria-to-fungi ratios in the upper soil layer of RT plots indicated a shift to fungal-based decomposition of organic matter whereas a higher C_mic-to-C_org ratio pointed towards enhanced substrate availability. Slurry application decreased microbial biomass and enhanced density of juvenile anecic earthworms but overall fertilization effect was weak and no interactions with tillage were found. In conclusion, tillage is a major driver in altering communities of earthworms and microorganisms in arable soils. The use of reduced tillage provides an approach for eco-intensification by enhancing inherent soil biota functions under organic arable farming.     

Labile pools of organic matter and microbial biomass in the surface soils under shifting cultivation in northern Thailand

In order to analyze the N mineralization process under shifting cultivation in northern Thailand, labile pools of soil organic matter were studied, which were considered to be the factors contributing to the N mineralization process. Organic C, (organic + NH₄ ⁺)-N, and hexose-C were extracted from fresh soils in the surface 0–5 cm layers with a 0.5 M K₂S₀. solution at 110°C in an autoclave (fraction A) or at room temperature with a reciprocal shaker (fraction B), and analyzed as labile pools of organic matter. In the traditional shifting cultivation system, the content of organic C in fraction A in the fallow fields for 8 to 15 y was 3,710 mg kg^-1 while that in the fallow fields for 1 y and 3 to 5 y was 2,640 and 2,600 mg kg^-1, respectively. A high correlation was observed between the contents of the labile pool in fraction A and total soil organic matter. The ratio of the pool in fraction A to total soil organic matter apparently remained constant through the input-output balance in the pool. The content of the labile pool in fraction B was the highest among the fields cultivated for 1 y after the slash and burn practice and it decreased in the course of the fallow period. The content of organic C was 548 mg kg^-1 in the fields cultivated for 1 y and 235 mg kg^-1 in the fallow fields for 8-15 y, respectively. There was a reverse relation between the contents of the pool in fraction B and microbial biomass. Therefore, the origin of the pool in fraction B was attributed to the microbial debris associated mainly with a decrease in the soil moisture content in the dry season. On the other hand, in the relatively intensive cultivation system, there was no significant difference in the contents of the labile pools both in fractions A and B among the land use stages, suggesting that the preservation mechanism of these pools, which was observed in the traditional cultivation system, did not operate well in the intensive system. In alternative farming systems in future, it will be essential to apply organic materials to soils to supply organic matter and to maintain the microbial biomass.     

Effect of tillage on earthworms over short- and medium-term in conventional and organic farming

Earthworms play an important role in many soil functions and are affected by soil tillage in agricultural soils. However, effects of tillage on earthworms are often studied without considering species and their interactions with soil properties. Furthermore, many field studies are based on one-time samplings that do not allow for characterisation of temporal variation. The current study monitored the short (up to 53 days) and medium term (up to 4 years) effects of soil tillage on earthworms in conventional and organic farming. Earthworm abundances decreased one and three weeks after mouldboard ploughing in both conventional and organic farming, suggesting direct and indirect mechanisms. However, the medium-term study revealed that earthworm populations in mouldboard ploughing systems recovered by spring. The endogeic species Aporrectodea caliginosa strongly dominated the earthworm community (76%), whereas anecic species remained <1% of all earthworms in all tillage and farming systems over the entire study. In conventional farming, mean total earthworm abundance was not significantly different in reduced tillage (153 m⁻²) than mouldboard ploughing (MP; 130 m⁻²). However, reduced tillage in conventional farming significantly increased the epigeic species Lumbricus rubellus from 0.1 m⁻² in mouldboard ploughing to 9 m⁻² averaged over 4 years. Contrastingly, in organic farming mean total earthworm abundance was 45% lower in reduced tillage (297 m⁻²) than MP (430 m⁻²), across all sampling dates over the medium-term study (significant at 3 of 6 sampling dates). Reduced tillage in organic farming decreased A. caliginosa from 304 m⁻² in mouldboard ploughing to 169 m⁻² averaged over 4 years (significant at all sampling dates). Multivariate analysis revealed clear separation between farming and tillage systems. Earthworm species abundances, soil moisture, and soil organic matter were positively correlated, whereas earthworm abundances and penetration resistance where negatively correlated. Variability demonstrated between sampling dates highlights the importance of multiple samplings in time to ascertain management effects on earthworms. Findings indicate that a reduction in tillage intensity in conventional farming affects earthworms differently than in organic farming. Differing earthworm species or ecological group response to interactions between soil tillage, crop, and organic matter management in conventional and organic farming has implications for management to maximise soil ecosystem functions.     

Comparison of glycine uptake by pak choi in organic and conventional soil under different glycine concentrations: A pot study

Many studies have shown that plants can utilize organic N in the form of amino acids. However, it is unclear whether the glycine‐uptake capability responds differently to various farm management systems, and whether the interaction of farm management type with soil glycine concentrations affects the glycine uptake by plants. A pot experiment was conducted in which pak choi (Brassica campestris ssp. chinensis Makino var. communis Tsen et Lee) was grown in soil from organic and conventional agricultural systems for 15 d prior to labeling with 2‐¹³C, ¹⁵N‐glycine in a range of Gly concentrations (0, 0.005, 0.05, 0.5, 5, and 15 μg N g^?1 dry soil). The glycine uptake rate increased with increasing applied N concentrations, whereas the glycine recovery increased initially and then decreased. Regardless of glycine concentration, the glycine uptake rates of whole plants were moderate, but not significantly higher in organic than in conventional soil. The plant glycine recovery in organic soil was significantly higher than in conventional soil. Therefore, we suggest that pak choi glycine uptake differs under organic and conventional management systems. More research efforts should focus on the nutritional function of organic N in organic systems.     

Characteristics of phosphorus accumulation in soils under organic and conventional farming in plastic film houses in Korea

Organic farming (OF) is a fast growing alternative for sustainable agriculture in Korea. However, information on the effects of OF on the soil properties and environmental conservation is limited. In order to determine the effects of OF on the soil properties, 31 fields under OF (hereafter referred to as "OF fields") and 61 fields under conventional farming (CF) (hereafter referred to as "CF fields") in plastic film houses were selected throughout Korea and the soil chemical properties were investigated, including the P distribution characteristics. Average organic matter (OM) content was significantly higher (44 g kg^-1) in the OF fields then in the CF fields (24 g kg^-1). Bray-2 P values were 986 and 935 mg kg^-1 in the OF and CF soils, respectively, markedly exceeding the optimum range. Average total P (T-P) values were 2,973 mg kg^-1 in the OF fields and 1,830 mg kg^-1 in the CF fields. The high T-P values were due to repeated application of manure compost with a low N/P ratio. Inorganic P was the dominant fraction with 62–65% of T-P. The amounts of residual and organic P were significantly lower. The level of OF organic P was significantly higher (453 mg kg^-1) compared to the 106 mg kg^-1 value for the CF fields. Fractionation of soil inorganic P showed that Ca-P predominated with 1,332 mg kg^-1 in the OF fields, which was associated with soil pH values over 6.0. The main inorganic P fraction in the CF soils whose pH values were generally less than 6.0 consisted of Al-/Fe-P. The levels of water-soluble P was significantly higher (65 mg kg^-1) in the OF fields than in the CF fields (24 mg kg^-1). These results indicated that the OF system may lead to a serious degradation of the soil environment due to the accumulation of phosphorus and may be an important source of water pollution compared to the CF systems in Korea.