Compost,Manure and Synthetic Fertilizer Influences Crop Yields,Soil Properties,Nitrate Leaching and Crop Nutrient Content

From 1993 to 2001, a maize-vegetable-wheat rotation was compared using either 1) composts, 2) manure, or 3) synthetic fertilizer for nitrogen nutrient input. From 1993 to 1998, red clover (Trifolium pratense L.) and crimson clover (Trifolium incarnatum L.) were used as an annual winter legume cover crop prior to maize production. From 1999 to 2001, hairy vetch (Vicia villosa Roth.) served as the legume green manure nitrogen (N) source for maize. In this rotation, wheat depended entirely on residual N that remained in the soil after maize and vegetable (pepper and potato) production. Vegetables received either compost, manure, or fertilizer N inputs. Raw dairy manure stimulated the highest overall maize yields of 7,395 kg/ha (approximately 140 bushels per acre). This exceeded the Berks County mean yield of about 107 bushels per acre from 1994 to 2001. When hairy vetch replaced clover as the winter green manure cover crop, maize yields rose in three of the four treatments (approximately 500-1,300 kg/ha, or 10-24 bu/a). Hairy vetch cover cropping also resulted in a 9-25 % increase in wheat yields in the compost treatments compared to clover cover cropping. Hairy vetch cover crops increased both maize and wheat grain protein contents about 16 to 20% compared to the clover cover crop. Compost was superior to conventional synthetic fertilizer and raw dairy manure in 1) building soil nutrient levels, 2) providing residual nutrient support to wheat production, and 3) reducing nutrient losses to ground and surface waters. After 9 years, soil carbon (C) and soil N remained unchanged or declined slightly in the synthetic fertilizer treatment, but increased with use of compost amendments by 16-27% for C and by 13-16% for N. However, with hairy vetch cover crops, N leaching increased 4 times when compared to clover cover crops. September was the highest month for nitrate leaching, combining high rainfall with a lack of active cash crop or cover crop growth to use residual N. Broiler litter leaf compost (BLLC) showed the lowest nitrate leaching of all the nutrient amendments tested (P= 0.05).     

Improving soil structure by promoting fungal abundance with organic soil amendments

Building soil structure in agroecosystems is important because it governs soil functions such as air and water movement, soil C stabilization, nutrient availability, and root system development. This study examined, under laboratory conditions, effects of organic amendments comprised of differing proportions of labile and semi-labile C on microbial community structure and macroaggregate formation in three variously textured soils where native structure was destroyed. Three amendment treatments were imposed (in order of increasing C lability): vegetable compost, dairy manure, hairy vetch (Vicia villosa Roth). Formation of water stable macroaggregates and changes in microbial community structure were evaluated over 82 days. Regardless of soil type, formation of large macroaggregates (LMA, >2000 μm diameter) was highest in soils amended with vetch, followed by manure, non-amended control, and compost. Vetch and manure had greater microbially available C and caused an increase in fungal biomarkers in all soils. Regression analysis indicated that LMA formation was most strongly related to the relative abundance of the fungal fatty acid methyl ester (FAME) 18:2ω6c (r = 0.55, p < 0.001), fungal ergosterol (r = 0.58, p < 0.001), and microbial biomass (r = 0.57, p < 0.001). Non-metric multidimensional scaling (NMS) ordination of FAME profiles revealed that vetch and manure drove shifts toward fungal-dominated soil microbial communities and greater LMA formation in these soils. This study demonstrated that, due to their greater amounts of microbially available C, vetch or manure inputs can be used to promote fungal proliferation in order to maintain or improve soil structure.     

Factors affecting soil microbial community structure in tomato cropping systems

Soil and rhizosphere microbial communities in agroecosystems may be affected by soil, climate, plant species, and management. The management and environmental factors controlling microbial biomass and community structure were identified in a three-year field experiment. The experiment consisted of a tomato production agroecosystem with the following nine treatments: bare soil, black polyethylene mulch, white polyethylene mulch, vetch cover crop, vetch roots only, vetch shoots only, rye cover crop, rye roots only, and rye shoots only. The following hypotheses were tested: (1) Temperature and moisture differences between polyethylene-covered and cover-cropped treatments are partly responsible for treatment effects on soil microbial community composition, and (2) Different species of cover crops have unique root and shoot effects on soil microbial community composition. Microbial biomass and community composition were measured by phospholipid fatty acid analysis. Microbial biomass was increased by all cover crop treatments, including root only and shoot only. Cover cropping increased the absolute amount of all microbial groups, but Gram-positive bacteria decreased in proportion under cover crops. We attribute this decrease to increased readily available carbon under cover-cropped treatments, which favored other groups over Gram-positive bacteria. Higher soil temperatures under certain treatments also increased the proportion of Gram-positive bacteria. Vetch shoots increased the amount and proportion of Gram-negative bacteria, fungi, and arbuscular mycorrhizal fungi in the rhizosphere of tomato plants. The imposed treatments were much more significant than soil temperature, moisture, pH, and texture in controlling microbial biomass and community structure.     

苏南稻田4种冬绿肥养分特性及对翻压前土壤无机氮的影响

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

Arable weeds,cover crops,and tillage drive soil microbial community composition in organic cropping systems

Cover crops have traditionally been used to reduce soil erosion and build soil quality, but more recently cover crops are being used as an effective tool in organic weed management. Many studies have demonstrated microbial community response to individual cover crop species, but the effects of mixed species cover crop communities have received less attention. Moreover, the relationship between arable weeds and soil microbial communities is not well understood. The objective of this study was to determine the relative influence of cover crop diversity, early-season weed communities, and tillage on soil microbial community structure in an organic cropping system through the extraction of fatty acid methyl esters (FAMEs). A field experiment was conducted between 2009 and 2011 near Mead, NE where spring-sown mixtures of zero (control), two, and eight cover crop species were included in a sunflower–soybean–corn crop rotation. A mixture of four weed species was planted in all experimental units (excluding the no-cover control), and also included as an individual treatment. Cover crops and weeds were planted in late-March, then terminated in late-May using a field disk or sweep plow undercutter, and main crops were planted within one week of termination. Three (2009) or four (2010–11) soil cores were taken to a depth of 20 cm in all experimental units at 45, 32, and 25 days following cover crop termination in 2009, 2010, and 2011, respectively. Total FAMEs pooled across 2009 and 2010 were greatest in the two species mixture–undercutter treatment combination (140.8 ± 3.9 nmol g⁻¹) followed by the eight species mixture–undercutter treatment combination (132.4 ± 3.9 nmol g⁻¹). Abundance of five (2009 and 2010) and seventeen (2011) FAME biomarkers was reduced in the weedy treatment relative to both cover-cropped treatments and the no-cover control. In 2009 and 2010, termination with the undercutter reduced abundance of most actinomycete biomarkers while termination with the field disk reduced abundance of C18:1(cis11) and iC16:0. Canonical discriminant analysis of the microbial community successfully segregated most cover crop mixture by termination method treatment combinations in 2009 and 2010. Microbial communities were most strongly influenced by the presence and type of early-spring plant communities, as weeds exerted a strong negative influence on abundance of many key microbial biomarkers, including the AMF markers C16:1(cis11) and C18:1(cis11). Weeds may alter soil microbial community structure as a means of increasing competitive success in arable soils, but this relationship requires further investigation.     

Microbial community structure and abundance in the rhizosphere and bulk soil of a tomato cropping system that includes cover crops

Understanding microbial responses to crop rotation and legacy of cropping history can assist in determining how land use management impacts microbially mediated soil processes. In the literature, one finds mixed results when attempting to determine the major environmental and biological controls on soil microbial structure and functionality. The objectives of this research were to: (1) Qualitatively and quantitatively measure seasonal and antecedent soil management effects on the soil microbial community structure in the rhizosphere of a subsequent tomato crop (Solanum lycopersicum) and (2) Determine phylum scale differences between the rhizosphere and bulk soil microbial community as influenced by the antecedent hairy vetch (Vicia villosa), cereal rye (Secale cereale), or black plastic mulch treatments. In this report, we use terminal restriction fragment length polymorphisms in the 16s rDNA gene to characterize changes in microbial community structure in soil samples from a field replicated tomato production system experiment at USDA-ARS Beltsville Agricultural Research Center, Beltsville, MD, USA. We found season of the year had the strongest influence on the soil microbial community structure of some of the major microbial phyla. Although we monitored just a few of the major microbial phyla (four Eubacteria and Archaea), we found that the effects of the tomato plant on the structural composition of these phyla in the rhizosphere differed dependent on the antecedent cover crop. Increased understanding of how agricultural factors influence the soil microbial community structure under field conditions is critical information for farmers and land managers to make decisions when targeting soil ecosystem services that are microbially driven.     

Combining Legumes and Compost: A Viable Alternative for Farmers in Conversion to Organic Agriculture

Soil nitrogen (N) availability and crop performance of broccoli (Brassica oleracea var. orion) were observed in a field plot study under different organic amendments addition and chemical fertilizer. The treatments consisted on no amendment; poultry manure based compost, woollypod vetch (Vicia dasycarpa var. lana), a combination of compost with Lana vetch and ammonium sulphate. For almost all sampling dates, the soils treated with vetch (3.6 Mg/ha) combined with compost (9.0 Mg/ha) showed a good performance in replenishing the inorganic N taken up by plants and soil microbes. High yields were achieved with the combination of vetch and compost and moderately high yields were achieved with vetch only and compost only. Yields appeared to be related to quality and N levels in the amendments, and size of existing soil nitrogen pools susceptible to the priming effect.     

Soil microbial biomass,crop yields,and bacterial community structure as affected by long-term fertilizer treatments under wheat-rice cropping

Soil microbial biomass carbon (SMBC) and nitrogen (SMBN), soil microbial community structure, and crop yields were studied in a long-term (1982–2004) fertilization experiment carried out in Suining, Sichuan province of PR China. Eight treatments included three chemical fertilizer (CF) treatments (N, NP, NPK), three CF + farmyard manure (M) treatments (NM, NPM, NPKM), M alone and no fertilizer (CK) as control. The results showed that the soil microbial biomass was higher in soil treated with CFM than in soil treated with CF alone, and that NPKM gave the highest rice and wheat yields. The SMBC and SMBN were higher after rice than those after wheat cropping. SMBC correlated closely with soil organic matter. Average yields of wheat and rice for 22 years were higher and more stable in the fertilized plots than in control plots. Bacterial community structure was analyzed by PCR-DGGE targeting eubacterial 16S rRNA genes. A higher diversity of the soil bacterial community was found in soil amended with CFM than in other fertilizer treatments. Some specific band emerged in the soil amended with M. The highest diversity of bacterial communities was found in the NPKM treated soil. The bacterial community structures differed in rice and wheat plots. Sequencing of PCR products separated in DGGE showed that some of the common and dominant bands were closely related to Aquicella lusitana and to Acidobacteria. This study demonstrated that mixed application of N, P, and K with additional M amendment increased soil microbial biomass, diversified the bacterial communities and maintained the crop production in the Calcareous Purplish Paddy soil.     

Integration of cover crops and vermicompost tea for soil and plant health management in a short-term vegetable cropping system

Short-term vegetable crop production often involves frequent tillage and other farm activities that results in disturbed soil food web communities. A less disturbed soil community would have a more structured soil food web which contains soil fauna higher up in the food web hierarchy, thus higher integrity in soil nutrient cycling. The objective of this study is to examine if strip-till cover cropping and drenching soil with vermicompost tea could improve soil food web structure in a short-term agroecosystem. Two field trials were conducted in Waialua, HI, USA to evaluate the effect of strip-till planting of sunn hemp (SH, Crotalaria juncea) or crimson clover (Trifolium incarnatum) cover crops in a zucchini (Cucurbita pepo) cropping system. At zucchini planting, each cover crop plot was split to receive four soil treatments: fertilizer (F, chicken pellet), compost tea (CT), fertilizer plus compost tea (F + CT), and none. Compost tea was prepared from chicken manure based vermicompost aerated overnight in water at 1:10 (v:v). Planting of SH increased bacterivorous nematodes and suppressed plant-parasitic nematodes throughout both zucchini cropping cycles, but did not enhance the numbers of omnivorous or predatory nematodes. Crimson clover did not enhance beneficial nematodes nor suppress plant-parasitic nematodes. Adding CT to F suppressed the key plant-parasitic nematodes only at the initial stage of the zucchini growth, increased percentage of predatory or omnivorous nematodes only toward the end of zucchini crops, and increased the structure index at harvest in the first trial. Zucchini yield was increased by planting of SH but not by drenching of CT. Despite the benefits of CT in improving the soil food web structure, a correlation analysis revealed that zucchini yields were correlated to the reduction in the percentage of fungivorous nematodes at planting, an increase in the percentage of bacterivorous nematodes at harvest, and to reduction in the percentage of plant-parasitic nematodes at harvest.     

Identifying indicators of C and N cycling in a clayey Ultisol under different tillage and uses in winter

Although tropical and subtropical environments permit two cropping cycles per year, maintaining adequate mulching on the soil surface remains a challenge. In some cases, leaving soils fallow during the winter as an agricultural practice to control pathogens contributes to reduce soil mulching. The aim of this study was to assess attributes associated with C and N cycling in a soil under conventional and no-tillage management, with contrasting uses in winter: black oats (Avena strigosa Schreb) as cover crop or fallow. No-tillage increased total C and N, irrespective the winter crop. Cropping black oats under no-tillage resulted in more microbial biomass C and N, and glutaminase activity (15.2%, 65.2%, and 24%, respectively) than no-tillage under fallow. Under conventional tillage, winter cropping did not affect the attributes under study. Available P was higher in the no-tillage system (9.2–12.3 mg kg⁻¹), especially when cropped with black oats, than in the conventional tillage system (4.8–6.6 mg kg⁻¹). A multivariate analysis showed strong relationships between soil microbiological and chemical attributes in the no-tillage system, especially when cropped with black oats. Soil pH, dehydrogenase and acid phosphatase activities were the most effective at separating the soil use in winter. Microbial N, total N, microbial to total N ratio, available P, metabolic quotient (qCO₂), and glutaminase activity were more effective at separating soil management regimes. The no-tillage system in association with winter oat cropping stimulated the soil microbial community, carbon and nutrient cycling, thereby helping to improve the sustainability of the cropping system.     

Soil enzyme activities,microbial community composition and function after 47 years of continuous green manuring

Green manuring practices can influence soil microbial community composition and function and there is a need to investigate the influence compared with other types of organic amendment. This study reports long-term effects of green manure amendments on soil microbial properties, based on a field experiment started in 1956. In the experiment, various organic amendments, including green manure, have been applied at a rate of 4 t C ha⁻¹ every second year. Phospholipid fatty acid analysis (PLFA) indicated that the biomass of bacteria, fungi and total microbial biomass, but not arbuscular mycorrhizal (AM) fungi, generally increased due to green manuring compared with soils receiving no organic amendments. Some differences in abundance of different microbial groups were also found compared with other organic amendments (farmyard manure and sawdust) such as a higher fungal biomass and consequently a higher fungal/bacterial ratio compared with amendment with farmyard manure. The microbial community composition (PLFA profile) in the green manure treatment differed from the other treatments, but there was no effect on microbial substrate-utilization potential, determined using the Biolog EcoPlate. Protease and arylsulphatase activities in the green manure treatment were comparable to a mineral fertilized treatment receiving no additional C, whereas acid phosphatase activity increased. It can be concluded that green manuring had a beneficial impact on soil microbial properties, but differed in some aspects to other organic amendments which might be attributed to differences in quality of the amendments.     

Responses of soil nematode community structure to soil carbon changes due to different tillage and cover crop management practices over a nine-year period in Kanto,Japan

The response of the soil food web structure to soil quality changes during long-term anthropogenic disturbance due to farming practices has not been well studied. We evaluated the effects of three tillage systems: moldboard plow/rotary harrow (MP), rotary cultivator (RC), and no-tillage (NT), three winter cover-crop types (fallow, FL; rye, RY; and hairy vetch, HV), and two nitrogen fertilization rates (0 and 100 kg N ha⁻¹ for upland rice, and 0 and 20 kg N ha⁻¹ for soybean production) on changes in nematode community structure. Sixty-nine taxa were counted, total nematode abundance (ALL), bacterial feeders (BAC), predators (PRD), omnivores (OMN), and obligatory root feeders (ORF) were more abundant in NT than in MP and RC, but fungal feeders and facultative root feeders (FFR) were more abundant in RC than in NT and MP. Cover crop also influenced nematode community structure; rye and hairy vetch were always higher in ALL, BAC, FFR, ORF, and OMN than fallow. Seasonal changes in nematode community structure were also significant; in particular, as soil carbon increased, nematode abundance also increased. The relationship between nematode indices and soil carbon was significant only in NT, but not in MP and RC. In NT, with increasing soil carbon, enrichment index and structure index (SI) were positive and significant and channel index was negative. Bulk density was significantly negatively correlated with FFR and ORF. Seasonal difference in nematode community between summer and autumn was larger in an upland rice rotation than in a soybean rotation. Over the nine-year experiment, SI increased not only in NT but also in MP and RC, suggesting that repeated similar tillage inversions in agroecosystems may develop nematode community structures adapted to specific soil environmental conditions. Because NT showed the highest values of both SI and soil carbon, the increase of soil carbon in NT is expected to have a great impact on developing a more diverse nematode community structure.     

Hairy Vetch Incorporated as Green Manure Inhibits Sulfathiazole Uptake by Lettuce in Soil

Veterinary antibiotics like sulfonamides are frequently detected in arable lands and they can potentially contaminate food crops. It is thus of great importance to identify strategies to reduce food crops’ uptake of antibiotics. For the first time, using a pot culture experiment, sulfathiazole (STZ) uptake by lettuce (Lactuca sativa L.) grown in antibiotic-contaminated soils (10 and 100 mg STZ kg^?1 soil) and treated with (in)organic amendments, namely chemical fertilizer (NPK), compost, and hairy vetch, was investigated. Subsequent enhanced plant growth was witnessed when using hairy vetch treatment. The amount of antibiotic uptake was significantly reduced to 5 and 33% with hairy vetch application compared to compost or NPK application at 10 and 100 mg kg^?1 STZ, respectively. The total amounts of accumulated STZ in plant parts increased as the levels of STZ contaminated in soils were increased. STZ was much more abundant in the roots than the leaves. Within 30 days, the extractable STZ in the treated soils—especially with hairy vetch—diminished considerably to concentrations that are frequently detected in arable soils. We conclude that utilization of green manure (cover crop—hairy vetch) is a viable strategy for safer crop production in antibiotic-contaminated soils.     

Spatial patterns of microbial denitrification genes change in response to poultry litter placement and cover crop species in an agricultural soil

Subsurface-banding manure and winter cover cropping are farming techniques designed to reduce N loss. Little is known, however, about the effects of these management tools on denitrifying microbial communities and the greenhouse gases they produce. Abundances of bacterial (16S), fungal (ITS), and denitrification genes (nirK, nirS, nosZ-I, and nosZ-II) were measured in soil samples collected from a field experiment testing the combination of cereal rye and hairy vetch cover cropping with either surface-broadcasted or subsurface-banded poultry litter. The spatial distribution of genes was mapped to identify potential denitrifier hotspots. Spatial distribution maps showed increased 16S rRNA genes around the manure band, but no denitrifier hotspots. Soil depth and nitrate concentration were the strongest drivers of gene abundance, but bacterial gene abundance also differed by gene, soil characteristics, and management methods. Gene copy number of nirK was higher under cereal rye than hairy vetch and positively associated with soil moisture, while nirS gene copies did not differ between cover crop species. The nirS gene copies increased when manure was surface broadcasted compared to subsurface banded and was positively associated with pH. Soil moisture and pH were positively correlated to nosZ-II but not to nosZ-I gene copy numbers. We observed stronger correlations between nosZ-I and nirS, and nosZ-II and nirK gene copies compared to the reverse pairings. Agricultural management practices differentially affect spatial distributions of genes coding for denitrification enzymes, leading to changes in the composition of the denitrifying community.     

Influence of organic Crotalaria juncea hay and ammonium nitrate fertilizers on soil nematode communities

Comparisons of organic and inorganic fertilizer effects on nematode communities depend on the specific organic fertilizer used. Field experiments were conducted during 2001 and 2002 in a squash (Cucurbita pepo) agroecosystem to determine if applying sunn hemp (Crotalaria juncea) hay as an organic fertilizer improved nematode communities involved in soil nutrient cycling compared to an equivalent N rate (100 kg N/ha) of ammonium nitrate. Fertilizer source had minimal effect on nematode communities in 2001 when treatments were applied after a winter cover crop of oats (Avena sativa), but differences (P ≤ 0.05) between the fertilizer sources occurred in 2002 when no winter cover cropping preceded squash. Fertilization with sunn hemp hay increased abundance of the bacterivore guilds Ba₁ and Ba₂, and increased fungivores at the end of the experiment. Compared to ammonium nitrate, fertilization with sunn hemp hay resulted in a community with lower maturity index, higher enrichment index, and lower channel index, consistent with a disturbed and nutrient-enriched soil food web undergoing bacterial decomposition. Sunn hemp hay occasionally stimulated omnivorous nematodes, but suppressed plant-parasitic nematodes relative to ammonium nitrate fertilizer. Increasing the sunn hemp hay rate to 200 kg N/ha increased the abundance of bacterivores, fungivores, and predatory nematodes, and total nematode abundance compared to hay at 100 kg N/ha. Fertilization with ammonium nitrate increased the percentage of herbivores, but reduced percentage and abundance of omnivores. In conclusion, sunn hemp fertilizer maintained greater numbers of nematodes involved in nutrient cycling as compared to ammonium nitrate.     

Soil microbial community responses to dairy manure or ammonium nitrate applications

Soil management practices that result in increased soil C also impact soil microbial biomass and community structure. In this study, the effects of dairy manure applications and inorganic N fertilizer on microbial biomass and microbial community composition were determined. Treatments examined were a control with no nutrient additions (CT), ammonium nitrate at 218 kg N ha⁻¹ (AN), and manure N rates of 252 kg manure-N ha⁻¹ (LM) and 504 kg manure-N ha⁻¹ (HM). All plots were no-till cropped to silage corn (Zea mays, L. Merr) followed by a Crimson clover (Trifolium incarnatum, L.)/annual ryegrass (Lolium multiflorum, Lam.) winter cover crop. Treatments were applied yearly, with two-thirds of the N applied in late April or early May, and the remainder applied in September. Soil samples (0–5, 5–10, and 10–15 cm) were taken in March 1996, prior to the spring nutrient application. Polar lipid fatty acid (PLFA) analysis was used to assess changes in microbial biomass and community structure. Significantly greater soil C, N and microbial biomass in the 0–5 cm depth were observed under both manure treatments than in the CT and AN treatments. There was also a definable shift in the microbial community composition of the surface soils (0–5cm). Typical Gram-negative bacteria PLFA biomarkers were 15 and 27% higher in the LM and HM treatments than in the control. The AN treatment resulted in a 15% decrease in these PLFA compared with the control. Factor analysis of the polar lipid fatty acid profiles from all treatments revealed that the two manure amendments were correlated and could be described by a single factor comprised of typical Gram-negative bacterial biomarkers. The AN treatments from all three depths were also correlated and were described by a second factor comprised of typical Gram-positive bacterial biomarkers. These results demonstrate that soil management practices, such as manuring, that result in accumulations of organic carbon will result in increased microbial biomass and changes in community structure.     

The impact of exogenous organic matter on SOM contents and microbial soil quality

Eight fertilization strategies were compared in a field trial on Alfisol in Belgium (humid temperate climate): cattle slurry (CSL); farmyard manure (FYM); vegetable, fruit and garden waste compost (VFG); high C/N farm compost (FCP1); low C/N farm compost (FCP2); exclusively mineral fertilizer (MIN N); no fertilization (NF+), no fertilization and no crop (NF?). After five growing seasons, VFG resulted in the highest soil organic C (1.46% SOC) and total N contents (0.117%TN). SOC and TN contents of the MIN N plots, on the other hand, remained unchanged and were even similar to those of NF+ plots, despite greater biomass production on the MIN N plots than on the NF+ plots. Application of organic matter mostly increased dehydrogenase, β-glucosidase and β-glucosaminidase activity, but only FYM raised the activity of all three enzymes significantly compared to MIN N. Of the five organic amendments tested, only VFG suppressed Rhizoctonia solani (65% suppressiveness). Plots treated with FCP1, on the other hand, were highly conducive to R. solani (28.3% suppressiveness). Suppressiveness against R. solani probably depended on the maturity and cellulose content of the organic amendments. Highest microbial biomass C contents were found in the VFG plots. PLFA 16:1ω5c contents sensitively reacted to the different treatments and were significantly higher in VFG than in MIN N plots (3.84 and 2.20 nmol g^?1 dry soil, respectively). Finally, a soil quality index was developed using stepwise canonical discriminant analysis. β-glucosaminidase and β-glucosidase activity, and TN content were the most important parameters of the index. According to this index, FYM resulted in a significantly higher soil quality than the other treatments. We conclude that farmyard manure seems to be the preferred organic amendment for maintaining soil quality in arable fields under temperate climatic conditions.     

Surface soil responses to silage cropping intensity on a Typic Kanhapludult in the piedmont of North Carolina

Although reduced tillage itself is beneficial to soil quality and farm economics, the amount of crop residues returned to the soil will likely alter the success of a particular conservation tillage system within a farm operation. We investigated the impact of three cropping systems (a gradient in silage cropping intensity) on selected soil physical, chemical, and biological properties in the Piedmont of North Carolina, USA. Cropping systems were: (1) maize (Zea mays L.) silage/barley (Hordeum vulgare L.) silage (high silage intensity), (2) maize silage/winter cover crop (medium silage intensity), and (3) maize silage/barley grain—summer cover crop/winter cover crop (low silage intensity). There was an inverse relationship between silage intensity and the quantity of surface residue C and N contents. With time, soil bulk density at a depth of 0–3 cm became lower and total and particulate C and N fractions, and stability of macroaggregates became higher with lower silage intensity as a result of greater crop residue returned to soil. Soil bulk density at 0–3 cm depth was initially 0.88 Mg m⁻³ and increased to 1.08 Mg m⁻³ at the end of 7 years under high silage intensity. Total organic C at 0–20 cm depth was initially 11.7 g kg⁻¹ and increased to 14.3 g kg⁻¹ at the end of 7 years under low silage intensity. Stability of macroaggregates at 0–3 cm depth at the end of 7 years was 99% under low silage intensity, 96% under medium silage intensity, and 89% under high silage intensity. Soil microbial biomass C at 0–3 cm depth at the end of 7 years was greater with low silage intensity (1910 mg kg⁻¹) than with high silage intensity (1172 mg kg⁻¹). Less intensive silage cropping (i.e., greater quantities of crop residue returned to soil) had a multitude of positive effects on soil properties, even in continuous no-tillage crop production systems. An optimum balance between short-term economic returns and longer-term investments in improved soil quality for more sustainable production can be achieved in no-tillage silage cropping systems.     

Can using a strip-tilled cover cropping system followed by surface mulch practice enhance organisms higher up in the soil food web hierarchy?

Field trials were conducted in 2008 and 2009 to evaluate the potential of using sunn hemp (SH), Crotalaria juncea, and marigold (MG), Tagetes patula, in a strip till cover cropping system (STCC) followed by clipping SH and MG to provide surface mulch (SM). The overall objective was to examine if the STCC + SM could improve the structure of the soil food web compared to bare ground (BG) system where weeds were maintained at minimum level prior to planting. Cucumber (Cucumis sativus) and winter gourd (Benincasa hispida) were planted as cash crops in 2008 and 2009, respectively. Both the SH and MG in STCC + SM system suppressed herbivorous nematodes through the end of 2008 and up to mid-term crop cycle in 2009. The abundance of bacterivorous and fungivorous nematodes were consistently greater in SH plots during both trials. The structure index was significantly greater in SH treatment plots in 2009, indicating a more structured soil food web than BG treatment. SH and MG plots resulted in higher (P < 0.05) abundances of collembolans and predatory mites, respectively. Although crop yields were similar among treatments in 2008, winter gourd yield was significantly higher in SH during 2009. Possible mechanisms of why using the SH STCC + SM system resulted in improved soil food web structure in a relatively short time frame is discussed.     

Soil nematode community,organic matter,microbial biomass and nitrogen dynamics in field plots transitioning from conventional to organic management

Dynamics of soil bulk density, organic matter, microbial biomass, nitrogen, and nematode communities were assessed for a period of 4 years in field plots transitioning from conventional to organic farming practices. A rotation of soybeans, corn, oats and hay was used as an organic transitioning strategy and the conventional farming system had a corn and soybean rotation for comparison. Organic corn received raw straw pack beef manure and poultry compost at the rate of 27 and 28 Mg/h, respectively, and organic oats received raw straw pack beef manure and poultry compost at the rate of 18 and 1.8 Mg/h, respectively, while conventional plots received synthetic fertilizers. All crops in the organic system received primary tillage (chisel plow, disked and tined) whereas only corn received primary tillage in the conventional system but soybeans were no-till. Weed control was mechanical (twice diskings, rotary hoeings and row cultivation) in the organic system whereas herbicides were used in the conventional system. Soil bulk density did not differ in the two systems over a 4-year period but organic farming had slightly higher organic matter, mineral associated organic matter and particulate organic matter. Conventional system had more N in the mineral pools as indicated by higher NO₃⁻-N whereas organic system had higher N in the microbial biomass indicating shifts in nitrogen pools between the two systems. Bacterivore nematodes were more abundant in the organic than the conventional system for most of the study period. In contrast, the conventional system had significantly higher populations of the root lesion nematode, Pratylenchus crenatus, than the organic system after completion of the rotation cycle (transition period) in spring 2004. The organic hay plots had the lowest populations of P. crenatus compared to corn, soybeans and oats. Nematode faunal profile estimates showed that the food webs were highly enriched and moderately to highly structured and the decomposition channels were bacterial in both systems. The lack of differences in structure index between the organic and conventional systems is probably due to the excessive tillage in the organic farming system, which may have prevented the build up of tillage-sensitive omnivorous and predatory nematodes that contribute to the structure index. We conclude that transition from conventional to organic farming can increase soil microbial biomass-N and populations of beneficial bacterivore nematodes while simultaneously reducing the populations of predominant plant-parasitic nematode, P. crenatus. Our findings also underscore the potential benefits of reducing tillage for the development of a more mature soil food web.