Tillage Regimes Research Articles

Community Profiling of Fusarium in Combination with Other Plant-Associated Fungi in Different Crop Species Using SMRT Sequencing.

Fusarium head blight, caused by fungi from the genus Fusarium, is one of the most harmful cereal diseases, resulting not only in severe yield losses but also in mycotoxin contaminated and health-threatening grains. Fusarium head blight is caused by a diverse set of species that have different host ranges, mycotoxin profiles and responses to agricultural practices. Thus, understanding the composition of Fusarium communities in the field is crucial for estimating their impact and also for the development of effective control measures. Up to now, most molecular tools that monitor Fusarium communities on plants are limited to certain species and do not distinguish other plant associated fungi. To close these gaps, we developed a sequencing-based community profiling methodology for crop-associated fungi with a focus on the genus Fusarium. By analyzing a 1600 bp long amplicon spanning the highly variable segments ITS and D1–D3 of the ribosomal operon by PacBio SMRT sequencing, we were able to robustly quantify Fusarium down to species level through clustering against reference sequences. The newly developed methodology was successfully validated in mock communities and provided similar results as the culture-based assessment of Fusarium communities by seed health tests in grain samples from different crop species. Finally, we exemplified the newly developed methodology in a field experiment with a wheat-maize crop sequence under different cover crop and tillage regimes. We analyzed wheat straw residues, cover crop shoots and maize grains and we could reveal that the cover crop hairy vetch (Vicia villosa) acts as a potent alternative host for Fusarium (OTU F.ave/tri) showing an eightfold higher relative abundance compared with other cover crop treatments. Moreover, as the newly developed methodology also allows to trace other crop-associated fungi, we found that vetch and green fallow hosted further fungal plant pathogens including Zymoseptoria tritici. Thus, besides their beneficial traits, cover crops can also entail phytopathological risks by acting as alternative hosts for Fusarium and other noxious plant pathogens. The newly developed sequencing based methodology is a powerful diagnostic tool to trace Fusarium in combination with other fungi associated to different crop species.

Influence of reduced tillage and fertilisation regime on soil quality indicators in an organic potato production system

The aim of this study was to assess the short-term effects of tillage practice (reduced tillage – RT; standard tillage – ST) and fertilisation regime (solid cattle manure – SCM; lucerne pellets – LP; grass/clover silage – GCS) on soil quality indicators in an organic potato (Solanum tuberosum L.) production system. Use of RT enhanced the biomass and number of earthworms compared with ST. Concentrations of soil mineral N ( and ) showed similar decreasing patterns over time across both tillage systems during the potato production period. However, soil mineral N was overall higher in the 0–15 cm soil layer for RT and in the 15–30 cm layer for ST. Soil bulk density was higher for RT than ST at 1, 4 and 7 weeks after planting, while a linear reverse correlation was found between soil bulk density and tuber yield. Although both soil temperature and soil moisture content were not found to be greatly affected by tillage practice, net soil N mineralisation was estimated to be 65 kg N ha−1 greater under ST than RT for the potato production period. The application of LP and GCS resulted in higher mid- and end-season soil mineral N concentrations and crop N accumulation at harvest compared to SCM. During initial adaptation to reduced tillage practices in organic potato systems, farmers need to carefully weigh potential conflicts between initial yield reductions and soil conservation goals.

The impact of tillage regime and row cover use on insect pests and yield in organic cucurbit production

AbstractControl of cucurbit pests, such as striped cucumber beetle (Acalymma vittatum), spotted cucumber beetle (Diabrotica undecimpunctata howardi) and squash bug (Anasa tristis), in organic systems is difficult due to a lack of effective insecticide options. This has led to the development of many integrated pest management techniques, such as use of row covers, crop rotation and cover crops. This study explored the novel use of strip tillage and row covers to reduce pest pressure in summer squash (Cucurbita pepe) and muskmelon (Cucumis melo) production systems. Results showed that although strip tillage reduced striped cucumber beetle and squash bug numbers, there was a yield reduction in both crops compared with the plasticulture system. Row cover increased marketable yield in both systems, with the highest yield being in the plasticulture system. Unmarketable fruit directly attributed to insect damage was higher in the plasticulture systems, but was not significantly different when compared with the strip tillage system. Although there are many documented positive attributes of strip tillage, results from this study indicate that a combination of plasticulture and row cover may be a superior system for organic cucurbit production.

Nitrogen Effects on Productivity and Soil Properties in Conventional and Zero Tilled Wheat with Different Residue Management

Changes in tillage regime from conventional tillage to zero tillage (ZT) call for efficient weed and N management. Nitrogen is subject to immobilization/mineralization under residue-laden ZT system and increasing N-use efficiency through scheduling/rationalization of N is a researchable issue. The authors investigated the N and weed management options for wheat under ZT with or without residue. Results showed that ZT + residue retention (R) + 75% N + GreenSeeker™ (GS)-aided N management (ZT + R+75N + GS) recorded significantly higher wheat yield (5.11 t ha−1) over CT − R + 100N (4.48 t ha−1). The ZT + R+75N + GS improved macro-aggregates by 25.3% and decreased micro-aggregates by 6.8% in surface soil than CT − R + 100N. Treatment ZT + R+75N + GS had highest labile C (~ 3.63 g C kg−1 soil), which was 24.7% higher than CT − R + 100N (2.91 g C kg−1 soil). This treatment resulted in highest microbial biomass C (148.6 µg g−1 soil). It showed a significant increment in fluorescein diacetate (by 30.9%), total phosphatase (by 63.2%) and urease (by 31.6%) activities in surface soil over CT − R + 100N. Optical sensor-based N management saved N to the tune of 15–20 kg ha−1 over CT − R + 100 N. The ZT with residue retention and GS-aided N management has greater potential to secure sustainable yield, better soil aggregation, labile C and soil micro-flora than CT without/with residue incorporation.

Split application of glyphosate in herbicide-tolerant maize provides efficient weed control and favors beneficial epigeic arthropods

Wide deployment of genetically modified herbicide-tolerant (GMHT) maize may affect the efficiency of weed control methods and impair ecosystem functioning. We examined these potential threats using glyphosate-tolerant maize NK603 (Monsanto Technology LLC, St. Louis, MO, USA) planted in 54 randomly distributed plots in 2013 and 2014. Maize was grown in three herbicide treatments combined with six tillage regimes. Conventional, single post-emergence application of a selective herbicide MaisTer (Bayer CropScience GmbH, Frankfurt am Main, Germany; hereafter as MT) was compared with two herbicide strategies used in the glyphosate-tolerant crops: split application of Roundup Rapid (Monsanto Europe S.A./N.V., Brussels, Belgium; hereafter as RRRR) and application of this herbicide mixed with the soil residual herbicide Guardian Extra (Monsanto Europe S.A./N.V.; hereafter as RRGE). MT proved unreliable, whereas RRRR and especially RRGE provided efficient weed control and affected weed performance during the season. RRRR permitted restoration of weed cover during the latter half of the cultivation season. Conventional, reduced, and conservation (mulching with Hordeum vulgare, Phacelia tanacetifolia, Sinapis alba, and Trifolium incarnatum) tillage had minor effect on the weed performance. Carabids, staphylinids, and spiders were monitored to assess environmental impact of tested weed management practices. Carabid communities were not affected by the type of tillage but responded to the herbicide treatments. The plots treated with MT harbored the highest carabid activity abundance and species richness, followed by RRRR, and then by RRGE. RRRR and RRGE treatments also reduced the rise of staphylinid abundance and species richness after harvest, while conventional tillage negatively affected staphylinids at the start of the cultivation season. Spider and carabid activity abundance was similar, but spider species richness was highest in the RRRR plots. Neither herbicides nor tillage strongly affected arthropod species evenness. Multivariate analysis showed that weed species richness was significantly correlated with the species activity abundance of all three arthropod groups; weed coverage had a similar but smaller effect but the effect of herbicides and tillage was negligible. We concluded that herbicide treatments curbed weed performance which consequently influenced associated arthropods.The RRRR herbicide treatment adequately regulates weeds and exerts restoration of weed cover later in growing season that is beneficial to the arthropods. Thus, GMHT crops have a potential to combine economic and environmental advantages for agroecosystem sustainability and can be recommended for implementation in European crop production systems.

Interactive effects of straw incorporation and tillage on crop yield and greenhouse gas emissions in double rice cropping system

Great efforts have been made on the assessment of the effects of straw managements or tillage practices on rice yield and greenhouse gas (GHG) emissions. However, their interactive effects were not well documented. Based on a seven-year field experiment under a double rice system, we tested the effects of rotary tillage (RT) vs. plough tillage (PT) on rice yield, methane (CH4) and nitrous oxide (N2O) emissions with or without straw incorporation. As compared to straw removal, straw incorporation increased rice yield by 12.7% and 1.3% under the PT and the RT, respectively. Straw incorporation significantly stimulated CH4 emissions under both tillage regimes in the late rice season, while no significant effect occurred in the early rice season. Compared to the RT, PT significantly decreased DOC concentrations and methanogen abundances, resulting in a reduction in CH4 emission. The PT decreased yield-scaled global warming potential (GWP) with or without straw incorporation by 31.0% and 15.5%, respectively, as compared to the RT. Together, our results indicate that straw incorporation with plough tillage benefits rice production for higher-yield with less GHG emissions in double rice cropping areas.

Reducing tillage intensity affects the cumulative emergence dynamics of annual grass weeds in winter cereals

SummaryAnnual grass weeds such as Apera spica‐venti and Vulpia myuros are promoted in non‐inversion tillage systems and winter cereal‐based crop rotations. Unsatisfactory weed control in these conditions is often associated with a poor understanding of the emergence pattern of these weed species. The aim of this study was to investigate, understand and model the cumulative emergence patterns of A. spica‐venti, V. myuros and Poa annua in winter cereals grown in three primary tillage regimes: (i) mouldboard ploughing, (ii) pre‐sowing tine cultivation to 8–10 cm soil depth and (iii) direct drilling. Direct drilling delayed the cumulative emergence of A. spica‐venti and V. myuros (counted together) in contrast with ploughing, while the emergence pattern of P. annua was unaffected by the type of tillage system. The total density of emerged weed seedlings varied between the tillage systems and years with a higher total emergence seen under direct drilling, followed by pre‐sowing tine cultivation and ploughing. The emergence patterns of all species were differently influenced by the tillage systems, suggesting that under direct drilling, in which these species occur simultaneously, management interventions should first and foremost consider that A. spica‐venti and V. myuros emerge over a longer period to avoid control failures.

Fungal Communities in Rhizosphere Soil under Conservation Tillage Shift in Response to Plant Growth.

Conservation tillage is an extensively used agricultural practice in northern China that alters soil texture and nutrient conditions, causing changes in the soil microbial community. However, how conservation tillage affects rhizosphere and bulk soil fungal communities during plant growth remains unclear. The present study investigated the effect of long-term (6 years) conservation (chisel plow, zero) and conventional (plow) tillage during wheat growth on the rhizosphere fungal community, using high-throughput sequencing of the internal transcribed spacer (ITS) gene and quantitative PCR. During tillering, fungal alpha diversity in both rhizosphere and bulk soil were significantly higher under zero tillage compared to other methods. Although tillage had no significant effect during the flowering stage, fungal alpha diversity at this stage was significantly different between rhizosphere and bulk soils, with bulk soil presenting the highest diversity. This was also reflected in the phylogenetic structure of the communities, as rhizosphere soil communities underwent a greater shift from tillering to flowering compared to bulk soil communities. In general, less variation in community structure was observed under zero tillage compared to plow and chisel plow treatments. Changes in the relative abundance of the fungal orders Capnodiales, Pleosporales, and Xylariales contributed the highest to the dissimilarities observed. Structural equation models revealed that the soil fungal communities under the three tillage regimes were likely influenced by the changes in soil properties associated with plant growth. This study suggested that: (1) differences in nutrient resources between rhizosphere and bulk soils can select for different types of fungi thereby increasing community variation during plant growth; (2) tillage can alter fungal communities' variability, with zero tillage promoting more stable communities. This work suggests that long-term changes in tillage regimes may result in unique soil fungal ecology, which might influence other aspects of soil functioning (e.g., decomposition).

Temporal Dynamics of Soil Microbial Communities below the Seedbed under Two Contrasting Tillage Regimes.

Agricultural productivity relies on a wide range of ecosystem services provided by the soil biota. Plowing is a fundamental component of conventional farming, but long-term detrimental effects such as soil erosion and loss of soil organic matter have been recognized. Moving towards more sustainable management practices such as reduced tillage or crop residue retention can reduce these detrimental effects, but will also influence structure and function of the soil microbiota with direct consequences for the associated ecosystem services. Although there is increasing evidence that different tillage regimes alter the soil microbiome, we have a limited understanding of the temporal dynamics of these effects. Here, we used high-throughput sequencing of bacterial and fungal ribosomal markers to explore changes in soil microbial community structure under two contrasting tillage regimes (conventional and reduced tillage) either with or without crop residue retention. Soil samples were collected over the growing season of two crops (Vicia faba and Triticum aestivum) below the seedbed (15–20 cm). Tillage, crop and growing stage were significant determinants of microbial community structure, but the impact of tillage showed only moderate temporal dependency. Whereas the tillage effect on soil bacteria showed some temporal dependency and became less strong at later growing stages, the tillage effect on soil fungi was more consistent over time. Crop residue retention had only a minor influence on the community. Six years after the conversion from conventional to reduced tillage, soil moisture contents and nutrient levels were significantly lower under reduced than under conventional tillage. These changes in edaphic properties were related to specific shifts in microbial community structure. Notably, bacterial groups featuring copiotrophic lifestyles or potentially carrying the ability to degrade more recalcitrant compounds were favored under conventional tillage, whereas taxa featuring more oligotrophic lifestyles were more abundant under reduced tillage. Our study found that, under the specific edaphic and climatic context of central Belgium, different tillage regimes created different ecological niches that select for different microbial lifestyles with potential consequences for the ecosystem services provided to the plants and their environment.

Climate Change Predicted to Negatively Influence Surface Soil Organic Matter of Dryland Cropping Systems in the Inland Pacific Northwest, USA

Soil organic matter (SOM) is a key indicator of agricultural productivity and overall soil health. Currently, dryland cropping systems of the inland Pacific Northwest (iPNW) span a large gradient in mean annual temperature (MAT) and precipitation (MAP). These climatic drivers are major determinants of surface soil organic matter dynamics and storage characteristics. Future climate change projections through 2070 indicate significant shifts in MAT and MAP for the iPNW. We assessed surface (0 to 10 cm) soil organic C and N as well as active and recalcitrant fractions of SOM within long-term experiments representing different tillage regimes and cropping intensities across the current climatic gradient of the iPNW. We discovered that current levels of soil C and N as well as various SOM fractions were positively correlated with MAP and negatively correlated with MAT. Furthermore, these climatic drivers were more influential than either tillage regime or cropping intensity in determining SOM levels and characteristics. Soil organic C and total N as well as the hydrolyzable and non-hydrolyzable fractions were negatively correlated with the current ratio of MAT to MAP, called the climate ratio. Future climate projections (2030 and 2070) forecast an increase of the climate ratio, thus predicting declines in surface SOM and associated soil health across the iPNW.

MODELING NO-TILL ADOPTION BY CORN AND SOYBEAN PRODUCERS: INSIGHTS INTO SUSTAINED ADOPTION

AbstractNo-till acreage has increased in recent years, but many farmers alternate no-till with other tillage practices, limiting public and private benefits from sustained no-till adoption. Revealed preference data are used in an ordered logit regression analysis to determine the effect of soil characteristics, climate, regions, farm characteristics, and producer demographics on producers’ choices to use continuous tillage, alternate no-till systems with tillage systems, or continuously use no-till. The model provides insight into the characteristics and conditions that are conducive to each tillage regime. The attributes found to significantly affect continuous no-till use are erodibility classification, drainage, farm size, and climate.

Diversified cropping systems support greater microbial cycling and retention of carbon and nitrogen

Diversifying biologically simple cropping systems often entails altering other management practices, such as tillage regime or nitrogen (N) source. We hypothesized that the interaction of crop rotation, N source, and tillage in diversified cropping systems would promote microbially-mediated soil C and N cycling while attenuating inorganic N pools. We studied a cropping systems trial in its 10th year in Iowa, USA, which tested a 2-yr cropping system of corn (Zea mays L.)/soybean [Glycine max (L.) Merr.] managed with conventional fertilizer N inputs and conservation tillage, a 3-yr cropping system of corn/soybean/small grain+red clover (Trifolium pratense L.), and a 4-yr cropping system of corn/soybean/small grain+alfalfa (Medicago sativa L.)/alfalfa. Three year and 4-yr cropping systems were managed with composted manure, reduced N fertilizer inputs, and periodic moldboard ploughing. We assayed soil microbial biomass carbon (MBC) and N (MBN), soil extractable NH4 and NO3, gross proteolytic activity of native soil, and potential activity of six hydrolytic enzymes eight times during the growing season. At the 0–20cm depth, native protease activity in the 4-yr cropping system was greater than in the 2-yr cropping system by a factor of 7.9, whereas dissolved inorganic N pools did not differ between cropping systems (P=0.292). At the 0–20cm depth, MBC and MBN the 4-yr cropping system exceeded those in the 2-yr cropping system by factors of 1.51 and 1.57. Our findings suggest that diversified crop cropping systems, even when periodically moldboard ploughed, support higher levels of microbial biomass, greater production of bioavailable N from SOM, and a deeper microbially active layer than less diverse cropping systems.

Impact of Management Practices on Water Extractable Organic Carbon and Nitrogen from 12-Year Poultry Litter Amended Soils

Water extractable organic carbon (WEOC) and nitrogen (WEON) are two key parameters of soil water extractable organic matter (WEOM). Proper management of manure application rate in combination with tillage and cropping management could maintain appropriate WEOC and WEON concentrations in soils while decreasing the risk of their runoff from cropland and pastures. The objective of this research was to determine the effect of poultry litter (PL) application on WEOC and WEON in soils under different crops, tillage regimes, and grazing strategies. From 2001 to 2012, PL was applied at multiple rates to cultivated fields in a corn-oat/wheat-hay rotation or to pastures grazed by cattle or ungrazed. Soil samples (0 - 15 cm) were analyzed for KCl-extractable mineral N, and WEOC, and WEON contents. In addition, Ultraviolet-visible (UV-vis) and fluorescence spectroscopies were used to characterize WEOC stability. Organic N levels were higher at the high PL application rates. The soil C:N ratio narrowed as the PL application rate increased. However, the soil from pastures which received PL tended to have a wider range of C:N ratios than soil from the cultivated fields, despite identical PL application rates. The spectral analyses indicated that WEOC properties were responsive to management and PL application rate; therefore, this parameter may be used as a guide to provide best management strategy for manure application.

Assessing the farm-scale impacts of cover crops and non-inversion tillage regimes on nutrient losses from an arable catchment

The efficacy of cover crops and non-inversion tillage regimes at minimising farm-scale nutrient losses were assessed across a large, commercial arable farm in Norfolk, UK. The trial area, covering 143ha, was split into three blocks: winter fallow with mouldboard ploughing (BlockJ); shallow non-inversion tillage with a winter oilseed radish (Raphanus sativus) cover crop (Block P); and direct drilling with a winter oilseed radish cover crop (Block L). Soil, water and vegetation chemistry across the trial area were monitored over the 2012/13 (pre-trial), 2013/14 (cover crops and non-inversion tillage) and 2014/15 (non-inversion tillage only) farm years. Results revealed oilseed radish reduced nitrate (NO3-N) leaching losses in soil water by 75–97% relative to the fallow block, but had no impact upon phosphorus (P) losses. Corresponding reductions in riverine NO3-N concentrations were not observed, despite the trial area covering 20% of the catchment. Mean soil NO3-N concentrations were reduced by ∼77% at 60–90cm depth beneath the cover crop, highlighting the ability of deep rooting oilseed radish to scavenge nutrients from deep within the soil profile. Alone, direct drilling and shallow non-inversion tillage were ineffective at reducing soil water NO3-N and P concentrations relative to conventional ploughing. Applying starter fertiliser to the cover crop increased radish biomass and nitrogen (N) uptake, but resulted in net N accumulation within the soil. There was negligible difference between the gross margins of direct drilling (£731ha−1) and shallow non-inversion tillage (£758ha−1) with a cover crop and conventional ploughing with fallow (£745ha−1), demonstrating farm productivity can be maintained whilst mitigating diffuse pollution. The results presented here support the wider adoption of winter oilseed radish cover crops to reduce NO3-N leaching losses in arable systems, but caution that it may take several years before catchment-scale impacts downstream are detected.

Ecological intensification and arbuscular mycorrhizas: a meta‐analysis of tillage and cover crop effects

Summary Reliance on ecosystem services instead of synthetic, non‐renewable inputs is increasingly seen as key to achieving food security in an environmentally sustainable way. This process, known as ecological intensification, will depend in large part on enhancing below‐ground biological interactions that facilitate resource use efficiency. Arbuscular mycorrhizas (AM), associations formed between the roots of most terrestrial plant species and a specialized group of soil fungi, provide valuable ecosystem services, but the full magnitude of these services may not be fully realized under conventional intensively managed annual agricultural systems. Here, we use meta‐analysis to assess how reducing soil disturbance and periods without roots in agricultural systems affect the formation of AM and the diversity and community composition of arbuscular mycorrhizal fungi (AMF). We compiled data from 54 field studies across five continents that measured effects of tillage and/or cover cropping on AMF colonization and/or communities and assessed effects of management and environmental factors on these responses. Less intensive tillage and winter cover cropping similarly increased AMF colonization of summer annual cash crop roots by ∼30%. The key variables influencing the change in AMF colonization were the type of cover crop or the type of alternative tillage, suggesting that farmers can optimize combinations of tillage and cover crops that most enhance AM formation, particularly with no‐till systems and legume cover crops. Richness of AMF taxa increased by 11% in low‐intensity vs. conventional tillage regimes. Several studies showed changes in diversity and community composition of AMF with cover cropping, but these responses were not consistent. Synthesis and applications. This meta‐analysis indicates that less intensive tillage and cover cropping are both viable strategies for enhancing root colonization from indigenous arbuscular mycorrhizal fungi (AMF) across a wide range of soil types and cash crop species, and possibly also shifting AMF community structure, which could in turn increase biologically based resource use in agricultural systems.

Residue cover, soil structure, weed infestation and spring cereal yields as affected by tillage and straw management on three soils in Norway

ABSTRACTFour field trials (spring wheat and oats) were conducted (one on clay soil, one on loam soil and two on silt soil) for three years in important cereal growing districts, to investigate the influence of tillage regimes (ploughing versus reduced tillage in either autumn or spring) and straw management (removed and retained) on plant residue amounts, weed populations, soil structural parameters and cereal yields. The effect of tillage on soil structure varied, mainly due to the short trial period. In general, the amount of small soil aggregates increased with tillage intensity. Reduced soil tillage, and in some cases spring ploughing, gave significantly higher aggregate stability than autumn ploughing, thus providing protection against erosion. However, decreasing tillage intensity increased the amounts of weeds, particularly of Poa annua on silt soil. Straw treatment only slightly affected yields, while effects of tillage varied between both year and location. Reduced tillage, compared to ploughing, gave only small yield differences on loam soil, while it was superior on clay soil and inferior on silt soil. Our results suggest that shallow spring ploughing is a good alternative to autumn ploughing, since it gave comparable yields, better protection against erosion and was nearly as effective against weeds.

Exploring the relationships between soil fauna, different tillage regimes and CO2 and N2O emissions from black soil in China

Recent studies have shown that soil fauna can significantly affect greenhouse gas emissions. However, different functional groups and different soils can influence soil CO2 and N2O emissions to different extents. To date, little attention has been paid to whether soil fauna interactions with each other and their predators play a significant role in CO2 and N2O emissions under different tillage systems. Therefore, we studied how the interactions between soil fauna and their predators affect soil CO2 and N2O emissions from black soil following 13 years of conservation tillage (no-till) (NT) and conventional tillage (CT). We conducted a 35-day microcosm experiment with black arable soil and hay residue. The results indicated that the presence of earthworms and predator mites (EP) significantly increased the soil CO2 and N2O emissions in both NT and CT systems (P < 0.05). However, the addition of predator mites to microcosms with earthworms and Collembola treatments (ESP) did not significantly increase the soil CO2 (900.7 mg CO2-C kg−1 soil in NT, 991.0 mg CO2-C kg−1 soil in CT) or N2O (75.9 μg N2O-N kg−1 soil in NT, 79.0 μg N2O-N kg−1 soil in CT) emissions compared to earthworms and springtail (ES) treatments (CO2: 924.7 mg CO2-C kg−1 soil in NT, 914.4 mg CO2-C kg−1 soil in CT; N2O: 72.5 μg N2O-N kg−1 soil in NT, 251.4 μg N2O-N kg−1 soil in CT). Therefore, adding predators does not always increase the CO2 and N2O emissions, and the different body lengths of predators and the effect of predator-prey interactions on soil physicochemical properties should be considered. We found much higher dissolved organic carbon and nitrate availability in the E, ES and EP treatments at the time of high gas emissions on day 18, indicating that the major increase in CO2 and N2O emissions in these treatments may be due to enhanced denitrification. Our study indicates that under different tillage regimes, the interaction between soil fauna functional groups on the availability of C and N can decrease or increase soil CO2 and N2O emissions. Compared with CT soils, CO2 and N2O emissions from NT soils were lower, which demonstrates that long-term conservation tillage can reduce CO2 and N2O emissions from soil. The findings indicate that a more stable soil environment and food web with more intact functional groups are built in NT and may be more conducive to carbon and nitrogen sequestration for reducing soil CO2 and N2O emissions in the black soil region of Northeast China.

Tillage effects on soil microbial biomass, SOM mineralization and enzyme activity in a semi-arid Calcixerepts

Soil microbial properties are considered important indicators for assessing and comparing soil quality and degradation under tillage systems due to their early responses to environmental changes. The main objective of this study was to determine the medium-term (6 years) influence of tillage practices on soil microbial attributes in a semi-arid Calcixerepts from Central Iran with a similar plant residue input rate. The experiment was organized as a randomized complete block design with three replicates of each tillage regime. Tillage treatments consisted of moldboard and disk plows as conventional tillage (CT), and chisel and rotary plows as reduced tillage (RT) regimes over a period of six years (2005–2011). Soil microbial biomass carbon C (MBC) and nitrogen (MBN) contents, C (CMR) and N (NMR) mineralization rates; and urease, alkaline phosphatase (ALP) and catalase activities at the 0–20cm depth were determined only in 2008, 2009 and 2011. Less disturbed soils by both chisel and rotary plows under RT had higher MBC (25–43%), MBN (7–13%), MBC/MBN (17%) and enzyme activities (urease 2.0-fold, ALP 31–53% and catalase 18–59%) when compared with more disturbed soils by moldboard and disk plows under CT. In contrast, RT soils had lower microbial turnover rate (9–17%), metabolic quotient (qCO2, 37%), CMR (17–30%) and NMR (24–28%) than CT soils. However, the magnitude of the changes in soil MBC, MBN, CMR, NMR and catalase activity due to tillage effect were more greater during the later years of tillage implementation. The positive effect of RT practices on soil microbial biomass and enzyme activity was most likely due to improved environmental conditions, since soil organic matter (SOM) content was unaffected by tillage treatments. Soils under RT systems were characterized by a higher microbial biomass and enzyme activity, but development of less metabolically active microorganisms; most probably as a result of changes in the microbial community composition and lower microbial turnover rate. Furthermore, increased microbial enzyme production and biomass size with RT does not necessarily lead to higher microbial activity and SOM mineralization rate. It is suggested that the reduced SOM mineralization under RT is largely controlled by changes in the composition of microbial community and microbial turnover. In conclusion, microbial attributes were improved under RT after six years, and hence are regarded as early and sensitive indicators of changes in soil quality induced by tillage systems in this semi-arid environment.

INTEGRATIVE IMPACTS OF SOIL TILLAGE ON CROP YIELD, N USE EFFICIENCY AND GREENHOUSE GAS EMISSION IN WHEAT-CORN CROPPING SYSTEM

Wheat-corn cropping system is one of the most important grain production systems in the world. However, the integrative impacts of soil tillage on crop yield, N use efficiency (NUE) and greenhouse gases (GHGS) emissions are not well documented in this system. Thus, a twoyear field experiment was carried out in a typical wheat-corn cropping system with four tillage regimes during the wheat season, including no-tillage (NT), rotary tillage (RT), sub-soiling tillage (ST) and sub-soiling with rotary tillage (SRT) in a randomized block design with three replicates. No-tillage was conducted for all treatments during corn season. Over the two years, the highest yields of wheat, corn and annual were found in the SRT treatment, while the lowest annual yield was found in the NT treatment averagely. Two-year average annual yield in the SRT was 19643.9 kg ha -1 , which was 4.8, 5.9 and 7.7% higher than that in the ST, RT and NT treatments, respectively (P<0.05). SRT also stimulated plant N uptake with a higher N harvest index and higher partial factor productivity (PFP) than those under the other tillage practices (P<0.05). Although SRT stimulated N2O emission in wheat season, it significantly reduced the emission in corn season compared with the NT (P<0.05). Thus, no significant differences in total GHGS emissions, area-scaled and yield-scaled global warming potential (GWP) were found among the tillage practices. Our results indicate that sub-soiling with rotary tillage might benefit crop production for high yield and N use efficiency with less GHGS emissions for wheat-corn cropping system in North China Plain.

Effects of 30 Years of Crop Rotation and Tillage on Bacterial and Archaeal Ammonia Oxidizers.

Ammonia-oxidizing bacteria (AOB) and archaea (AOA) both mediate soil nitrification and may have specialized niches in the soil. Little is understood of how these microorganisms are affected by long-term crop rotation and tillage practices. In this study, we assessed abundance and gene expression of AOB and AOA under two contrasting crop rotations and tillage regimes at a 30-yr-old long-term experiment on a Canadian silt loam soil. Continuous corn ( L.) (CC) was compared with a corn-corn-soybean [ (L.) Merr.]-winter wheat ( L.) rotation under-seeded with red clover ( L.) (RC), with conventional tillage (CT) and no-till (NT) as subplot treatments. Soil sampling was performed during the first corn year at four time points throughout the 2010 season and at three discrete depths (0-5, 5-15, and 15-30 cm). Overall, AOA abundance was found to be more than 10 times that of AOB, although AOA transcriptional activity was below detectable levels across all treatments. Crop rotation had a marginally significant effect on AOB abundance, with 1.3 times as many gene copies under the simpler CC rotation than under the more diverse RC rotation. More pronounced effects of depth on AOB abundance and gene expression were observed under NT versus CT management, and NT supported higher abundances of total archaea and AOA than CT across the growing season. We suggest that AOB may be more functionally important than AOA in this high-input agricultural soil but that NT management can promote enhanced soil archaeal populations.