Continuous Monoculture Research Articles

Long-Term Monoculture Negatively Regulates Fungal Community Composition and Abundance of Tea Orchards

Continuous cropping frequently leads to soil acidification and major soil-borne diseases in tea plants, resulting in low tea yield. We have limited knowledge about the effects of continuous tea monoculture on soil properties and the fungal community. Here, we selected three replanted tea fields with 2, 15, and 30 years of monoculture history to assess the influence of continuous cropping on fungal communities and soil physiochemical attributes. The results showed that continuous tea monoculture significantly reduced soil pH and tea yield. Alpha diversity analysis showed that species richness declined significantly as the tea planting years increased and the results based on diversity indicated inconsistency. Principal coordinate analysis (PCoA) revealed that monoculture duration had the highest loading in structuring fungal communities. The relative abundance of Ascomycota, Glomeromycota, and Chytridiomycota decreased and Zygomycota and Basidiomycota increased with increasing cropping time. Continuous tea cropping not only decreased some beneficial fungal species such as Mortierella alpina and Mortierella elongatula, but also promoted potentially pathogenic fungal species such as Fusarium oxysporum, Fusarium solani, and Microidium phyllanthi over time. Overall, continuous tea cropping decreased soil pH and potentially beneficial microbes and increased soil pathogenic microbes, which could be the reason for reducing tea yield. Thus, developing sustainable tea farming to improve soil pH, microbial activity, and enhanced beneficial soil microbes under a continuous cropping system is vital for tea production.

Remote Sensing Study on Improving Rice Yield by Cotton-Rice Rotation

From 2001 to 2002, an observation experiment based on satellite remote sensing was conducted in Xinghua City to study the difference between continuous rice monoculture and cotton-rice rotation rice in the rice ratio vegetation indexes or rice yields. This paper introduces the analysis method of rice yield difference developed for this experiment, and demonstrates it with the rice vegetation index. The results show that the average rice vegetation index or yield of cotton-rice and rice-rice modes is different. We have found enough experiment data to come to conclusion that rice yield under cotton-rice mode is higher than that under continuous rice monoculture.

Quantity and quality of water percolating below the root zone of three biofuel feedstock crop systems

Biofuel demand is on the rise, yet there is limited information available about the likely implications of increased planting of cellulosic biofuel crops on water and nutrient fluxes. To help address this gap, this study quantifies subsurface water, nitrate, and dissolved phosphorus fluxes below feedstock crops managed for biofuel production on naturally well drained soils in southern Wisconsin. Automated equilibrium tension lysimeters were used to measure subsurface (below root zone) fluxes of water and nutrients below continuous corn (CC), monoculture switchgrass (SG), and hybrid poplar (HP) cropping systems for three years. Average water fluxes below SG were nearly double those below CC and HP. Most of this difference can be linked to seasonal events, particularly during late winter and early spring when subsurface water fluxes and increased soil moisture were observed below SG plots, likely due to enhanced macropore flow. Nitrate fluxes were approximately 14 times higher below CC than the 37.4 kg NO3-N/ha three year annual average observed for SG; the nitrate fluxes were negligible below HP despite similar nitrogen application rates. The high flux in one of the two CC plots is likely due to excessive manure applications prior to the study period; however, the nitrate loss potential from CC is much higher than the perennial crops. Dissolved reactive phosphorus (DRP) concentrations were very low below all three cropping systems (average of 0.076, 0.083, 0.034 mg/L in SG, CC, and HP respectively). For the cropping systems evaluated, nitrate fluxes were driven by concentration differences in leachate and not influenced by nominal differences in N fertilizer inputs, whereas DRP fluxes were mainly driven by water fluxes and therefore independent of phosphorus inputs and soil test phosphorus. The data in this paper provide a foundation to better understand differences in fluxes below different biofuel cropping systems.

Characterizing differences in microbial community composition and function between Fusarium wilt diseased and healthy soils under watermelon cultivation

Continuous cropping of watermelon is known to result in the disruption of the rhizospheric bacteria and fungi that contribute to the occurrence of Fusarium wilt disease. However, the underlying changes in microbial composition and function as a response to mono-cropping are less studied. In this study, differences in composition and potential function of the microbiome between healthy and diseased soils were investigated using MiSeq targeted sequencing and the functional GeoChip array, respectively. Twenty years of continuous watermelon monoculture was found to significantly alter the soil microbial communities by increasing bacterial diversity but decreasing fungal diversity. Compare to bacterial network, fungal co-occurrence networks were less robust and less connected in the monoculture diseased soil. Identified keystone species, belonging to the Proteobacteria, Bacteroidetesand Acidobacteria, were present in both the diseased and healthy soils. Key fungal species from the healthy soil belonged solely within the Ascomycete, while in the diseased soil Basidiomycota were dominant. As such, overall variations in the composition of the soil microbiome are accompanied by changes in the identities of the keystone species when comparing healthy versus diseased soils, further suggesting that soil function may also be altered. Relative abundances of genes associated with the degradation of hemicelluloses and chitin, the Calvin circle, ammonification, stress responses, iron uptake, and nitrogen fixation were significantly higher under long-term monoculture. Particularly, Fusarium spp. relative abundance was positively correlated with the relative abundances of genes involved in adherence, cellular metabolism, and immune evasion which may facilitate pathogen infection of plant roots. In conclusion, these results highlight the significant compositional and functional differences in microbial communities between Fusarium wilt diseased soils and healthy soils under watermelon cultivation. This provides insight into the complex array of microorganisms in soils that suffer from Fusarium disease and illustrates potential directions towards the manipulation of the soil microbiome for suppression of this disease.

Changes in soil organic carbon and total nitrogen stocks in response to walnut plantation in the southern region of the Loess Plateau, China

Afforestation of croplands has been widely adopted on the semi-arid Loess Plateau in recent decades. However, knowledge of soil carbon and nitrogen changes after afforestation is still limited because of the complexity of afforestation approaches. Therefore, an experiment was conducted on two dominant arable soils (tableland soil and terrace soil) on the southern Loess Plateau to evaluate the impact of two afforestation approaches (walnut monocultures and walnut-based agroforestry) on the soil organic carbon (SOC) and soil total nitrogen (STN) content within 2 m soil profiles. In the tableland soil, compared with the continuous crop monoculture (135.90 t C ha−1), SOC stocks in the agroforestry and walnut monoculture system increased by 7.91% and 1.91%, respectively. While in the terrace soil, compared with crop monoculture (102.95 t C ha−1), SOC stocks in the agroforestry and walnut monoculture system decreased by 3.86% and 0.20%, respectively. The STN stock was lower in the tree monocultures and SOC content was significantly correlated with STN. Afforestation increased the SOC and STN stocks in the 0–10 cm soils, but decreased them in the 10–60 cm soils. In the deep soil layers (60–200 cm), SOC content increase was only found in agroforestry in the tableland soil, and no significant differences were found in the terrace soil. Converting cropland to agroforestry has advantages in terms of soil carbon sequestration.

Integrated Soil-Crop System Management Increases Phosphorus Concentrations and Bioavailability in a Primosol

In recent years, integrated soil-crop system management (ISSM), i.e., using crop modeling and advanced nutrient management to redesign the cropping system, has been successfully used to improve crop yield and nutrient-use efficiency in China. However, the effects of ISSM on the properties of soils are not yet clear. Based on a seven-year (2009–2016) field plot trial with continuous corn monoculture, this study compared the effects of ISSM with improved practice (IP), high-yield practice (HY), and current farming practice (FP) on phosphorus (P) forms in an Alluvic Primosol of Northeast China by using chemical and spectroscopic (31P NMR) analyses. The concentrations of total P and Olsen P were in the order FP < IP < HY < ISSM; the order for inorganic and organic P fractions obtained by chemical analysis was also the same except for Ca10-P that showed an opposite order. 31P NMR spectroscopy showed that inorganic orthophosphate, pyrophosphate, orthophosphate monoesters, and orthophosphate diesters were all higher in the surface soil in ISSM treatment than in HY, IP, and FP treatments. Our results suggest that ISSM has a positive effect on the availability of P in soil.

Variation in soil fungal community structure during successive rotations of Casuarina equisetifolia plantations as determined by high-throughput sequencing analysis

Regeneration failure and productivity decline, which is collectively known as consecutive monoculture problem (CMP), were observed during long-term monoculture Casuarina equisetifolia plantations. In this study, the high-throughput sequencing method was applied to determine whether the rhizospheric microbial community composition would be significantly degenerated by consecutive monoculture in C. equisetifolia plantations. The results showed that the soil fungal community structure exhibited obvious differences among the first rotation plantation (FCP), the second rotation plantation (SCP), and the third rotation plantation (TCP). Both the Shannon and Simpson diversity indices of the soil fungal community in the FCP were significantly higher than in the SCP (P < 0.05). Additionally, the relative abundance of Fusarium, Thelephora, Hortaea and Penicillium were significantly higher in the SCP and TCP soils than in the FCP soils, suggesting that certain fungi gradually became predominant in the continuous monoculture plantation soils. Conversely, the relative abundance of Tolypocladium and Trichoderma were significantly lower in the SCP and TCP soils than in the FCP soils, suggesting that some microbes gradually decreased in the continuous monoculture plantation soils. Overall, the results demonstrated that the long-term pure plantation pattern exacerbated the microecological imbalance in rhizospheric soils of C. equisetifolia and markedly decreased soil microbial community diversity.

Fungal Endophyte Phomopsis liquidambari Improves Iron and Molybdenum Nutrition Uptake of Peanut in Consecutive Monoculture Soil

Iron (Fe) and molybdenum (Mo) are essential trace elements for plants, especially for peanut. However, peanut planted in consecutive monoculture soil usually suffers from malnutrition. Thus, the objective of this study was to investigate the effects of the fungal endophyte Phomopsis liquidambari on Fe and Mo nutrition uptake of peanut in consecutive monoculture soil. Plant growth parameters, physiological parameters, the accumulation of Fe and Mo elements, gene expression related to absorption and transformation of Fe and Mo in planta, and the low-molecular-weight organic acids (LMWOAs) concentration in rhizosphere soil were analyzed by greenhouse pot experiments. The results showed that the application of P. liquidambari improved growth parameters, chlorophyll content, nitrate reductase (NR) activity, and Fe and Mo nutrition of peanut. Furthermore, LMWOAs in peanut rhizosphere soil and the expression levels of AhFRO1, AhIRT1, and AhMOT1 were significantly changed by the application of fungal endophyte. These findings indicated that the improvement of Fe and Mo nutrition in peanut was mostly derived from the promoting growth function of P. liquidambari and the regulation of peanut-P. liquidambari symbiosis with rhizosphere LMWOAs and Fe- and Mo-related gene expression in continuous monoculture soil.

Continuous Monoculture Shapes Root and Rhizosphere Fungal Communities of Corn and Soybean in Soybean Cyst Nematode-Infested Soil

The rhizosphere effect shapes microbial communities around and within plant roots and may lead to the enrichment of fungi involved in both positive and negative plant-soil feedbacks. We used internal transcribed spacer 1 amplicon sequencing to investigate how continuous monoculture affects the fungal communities in the corn and soybean rhizosphere, rhizoplane, and root endosphere in a long-term crop rotation experiment where soils were infested with a major soybean pathogen, the soybean cyst nematode (SCN, Heterodera glycines). Community-level statistical analyses showed evidence of selective filtering and enrichment of fungi in and around corn and soybean roots and in SCN cysts. Patterns of relatedness between fungal communities in various agroecosystem compartments suggested that SCN cysts are colonized by soybean root endophytic fungi and that colonization of roots and cysts may aid proliferation of these fungi in the bulk soil agroecosystem compartment over time. Natural antagonists of the SCN such as nematode-trapping fungi and nematode endoparasites increased in relative abundance in the rhizosphere and root endosphere, respectively, over continuous soybean monoculture. In contrast, arbuscular mycorrhizal and plant-pathogenic fungi, several of which were negatively correlated with corn yield, increased in relative abundance over continuous corn monoculture. These results suggest the possibility of positive plant-soil feedbacks involving nematophagous fungi over continuous soybean monoculture and negative plant-soil feedbacks involving plant pathogens and some nonbeneficial arbuscular mycorrhizal fungi over continuous corn monoculture.

Cover Crops Impacts on Louisiana Corn Production and Soil Properties

Core Ideas Combination of cover crops with conservation tillage increased soil C. Cover crops significantly reduced nitrate‐N levels during the fallow season. Legume cover crops reduced N requirements when compared with non‐legumes. Conventionally managed, continuous monoculture row‐crop production has depleted the soil of nutrients, organic matter, and overall productivity. This has increased the need for external inputs, specifically N, to meet crop demand. Despite the growing interest in conservation practices, including minimal tillage and cover crops, little work has been reported in the Mid‐South region. Cereal rye (Secale cereal L.), forage radish (Raphanus sativus var. longipinnatus L.), berseem clover (Trifolium alexandrinum L.), crimson clover (Trifolium incarnatum L), winter pea (Pisium sativum L), hairy vetch (Vicia villosa Roth), and a cereal rye–forage radish mix were seeded in discrete blocks in October 2014, 2015, and 2016 along with a non‐cover fallow. Each block was divided into 16 sub‐plots to which one of four N fertilizer rates (0, 235, 268, and 302 kg N ha−1) were applied. Corn (Zea mays L.) grain yields increased with additions of N fertilizer; however, no difference was observed between the three fertilizer rates in 2 of 3 yr. Cover crops aided in the uptake and recycling of inorganic N, potentially reducing losses and providing N for subsequent cash crops. Following legume cover crops, corn grain yields were maximized with the addition of 235 kg N ha−1. Inclusion of grass and brassicas with no additional N input reduced corn grain yield, which remained lower than yield measured following legumes up to the 302 kg N ha−1 rate. Secondary benefits of cover crops included increased soil C (36%) and N (22%), and N cycling over a 2‐yr period.

Impact of conservation tillage and intensifying crop rotations in enhancing soil carbon, microbial cycling and aggregation in semiarid agro-eco systems: A review

Tillage influenced SOC and microbial cycling but most effects were observed at 0–5 cm rather than 5–15 cm. Reduced tillage (RT) in a continuous monoculture increased SOC by 24% compared to conventional tillage (CT) at 0–5 cm, but tillage had no effect at 5–15 cm. Crop rotation increased soil C contents compared to continuous monocropping rotation under CT increased SOC by 28% at 0–5 cm compared to CT continuous monocropping. Reduced tillage increased soil microbial biomass C (MBC) by an average of 11 and 18% compared to CT continuous monocropping and the adoption of crop rotation, respectively, while microbial biomass N (MBN) for RT was 62% greater than for CT. NT (no-till with residue) and RTW (rotary tillage with residue) treatments significantly increased the proportion of macroaggregate fractions (>2000 and 250-2000 im) compared with the MP-R (moldboard plow without residue) and MP+R (moldboard plow with residue) treatments. Averaged across all depths, mean weight diameters of aggregates (MWD) in NT and RT were 47 and 20% higher than that in MP+R. Aggregate stability in continuous rotations was about twice that in wheat-fallow rotations. Fungal biomass was three times greater in continuous rotations than wheat fallow, but was not significantly different from mid-intensity rotations.

Rhizosphere responses to environmental conditions in Radix pseudostellariae under continuous monoculture regimes

The root exudates of Radix pseudostellariae, working as a rhizospheric intermediary between plants and microbes, can deteriorate the microbial community in the rhizosphere in a consecutive monoculture system. We assessed the effects of artificially applied R. pseudostellariae root exudates on R. pseudostellariae seedling growth, rhizosphere soil microbial communities, and soil physicochemical properties. We found that phenolic acids and organic acids acted as a driver of changes in the microbial community. High-throughput sequencing and qRT-PCR analysis demonstrated that treatment with phenolic acids significantly decreased the relative abundance of Trichoderma, Penicillium, Pseudomonadales, Xanthomonadales, and Streptomycetales. Organic acids had a significant negative effect on the relative abundance of Pseudomonadales and Streptomycetales and significantly increased the abundance of Fusarium, Xanthomonadales, Micrococcales, and Gemmatimonadales. Analysis based on the noninvasive microtest technique indicated that root exudates increased H+ efflux and plasma membrane H+-ATPase activity in the pathogenic fungi and decreased them in the beneficial fungi. These phenomena created an acidic environment for the inhibition of beneficial bacteria and accumulation of specialized plant pathogens. This study explains the mechanisms underlying the shift in microflora and structural disorder caused by root exudates in continuously monocultured R. pseudostellariae rhizosphere soil through responses to environmental conditions.

Effects of soil improvement technology on soil quality in solar greenhouse.

Currently, cucumber cultivation is mainly through monoculture, as continuous culture leads to the decrease of crop yield and soil quality. In order to improve soil quality to achieve continuous monocultures, soil physicochemical properties, microbial biomass, content of phenolic compounds, and the size of bacterial, fungal, ammonia-oxidizing bacteria (AOB), and Fusarium oxysporum were first evaluated in cucumber monoculture solar greenhouse. Soil improvement technology, including catch wheat (CW), calcium cyanamide disinfection (LN), and straw reactor technology (SR) during summer fallow period, was compared with conventional fallow (CK). Results showed that CW, LN, and SR all significantly increased soil pH, and LN and SR increased soil electrical conductivity (EC); however, CW decreased soil EC. Meanwhile, LN increased soil available N content significantly and SR increased available P content significantly. CW had negative effect on the accumulation of soil available nutrients, conversely, CW and SR had positive effect on the accumulation of microbial biomass carbon (MBC). All the treatments increased the total phenol content in the soil compared with CK. While CW increased the size of bacteria, AOB in the soil inhibited fungal and wilt pathogen size. LN also increased the size of soil bacteria and reduced the size of fungi. The comprehensive evaluation of all treatments showed that CW could control soil nutrient loss and improve the continuous cropping soil, making the soil transform from fungi to bacteria type. All the treatments accelerate the accumulation of phenolic compound, while whether or not developing autotoxicity requires further investigation.

Microbial communities in soil profile are more responsive to legacy effects of wheat-cover crop rotations than tillage systems

Declining trends in soil health under continuous monoculture systems of winter wheat are a concern for sustainable production in the Southern Great Plains of the US. This study was conducted to evaluate the long-term implementation of conservation tillage in combination with nitrogen treatments and summer cover crop (cowpeas) rotations with winter wheat, for their legacy effects on soil health attributes of microbial communities and soil organic carbon (SOC). Microbial biomass and composition were estimated, along with soil physico-chemical parameters in the soil profile during the annual rotation cycle of wheat and cover crops. Positive legacy effects of cover crop rotations were evident, as arbuscular mycorrhizal fungi (AMF) biomass during the wheat-growing season was significantly higher in cover crop treatments (by around 30-70%) compared to summer fallow treatment. Some dominant taxons such as Acidobacteria, Actinobacteria, Proteobacteria (>70% of prokaryotic relative abundance) and Ascomycota (>50% of fungal relative abundance) were detected in all experimental treatments. Microbial composition did not significantly change at phylum level, although some reorganization at OTU level was evident throughout the soil profile, mostly because of nitrogen treatments. Several Glomeromycota OTUs were significantly altered by soil depth and by nitrogen fertilization suggest distinct mycorhizosphere interactions in subsurface soil than the surface soil. Tillage treatment did not significantly alter the microbial abundance and their diversity. Differences in microbial biomass-C concentration among experimental treatments did not result in a change in SOC concentrations within the soil profile. Results of this study demonstrated that summer cowpea appeared to be an effective cover crop for enhancing beneficial microbial biomass and expansion of the mycorrhizosphere to deeper soil layers. Cover crop rotations appeared to be a suitable option for rapidly enhancing soil health in winter wheat production systems.

Nitrogen balances of innovative cropping systems for feedstock production to future biorefineries

Future biorefineries will prefer crops with high biomass yields, thus may precipitate fundamental changes to the agricultural landscape and the biomass production systems. Understanding the fate of nitrogen (N) in novel agricultural land uses is vital for product optimisation and environmental protection. This work reports and investigates the first multi-annual N balances for novel cropping systems optimised for high biomass production compared to traditional systems under North European climate and soil conditions.In a three-year study, two types of novel systems, i) a rotation of annual crops optimised for maximum biomass production (maize, beet, hemp/oat, triticale as main crops, and winter rye and winter oilseed rape as “second” - cover crops), and ii) perennial grasses (intensively fertilised (festulolium, reed canary grass, tall fescue and cocksfoot), low-fertilised (miscanthus) and unfertilised (grass-legume mixtures)), were compared with iii) traditional systems (continuous maize or triticale, and a cereal crop rotation) at two sites in Denmark varying in temperature, rainfall and soil type (sandy loam and coarse sand). Harvested biomass N and soil nitrate dynamics, as well as model-supported nitrate leaching and field surface N balance (input minus output) of the systems were compared.At each study site, the fertilised perennial grasses outperformed all other systems by doubling biomass N and reducing nitrate leaching by 70–80% compared to the traditional systems. Compared to continuous maize monoculture, the optimised rotation supplied 70% more biomass N and 40% less nitrate leaching on coarse sandy soil, whereas on sandy loam soil it yielded about 10% less biomass N with 50% less nitrate leaching. Field surface N balances were overall neutral/positive, except for festulolium and continuous maize monoculture that slightly mined the soil for N. When N losses by leaching, denitrification and volatilisation were included, soil total N stocks were estimated to decline for the majority of the systems at both sites.

A Review: Suppressive Soils and its Importance

Microbial communities play a vital role in functioning of plants in respect to their growth and development. The activity of rhizospheric microbial community is higher than the surrounding environment. Microorganisms are colonizing near the plant roots thus affecting their growth and development either by promoting growth or developing diseases. Soil borne pathogens are commonly associated with causing diseases in the plant. Naturally occurring beneficial microbes may inhibit their growth and retention in soil. These beneficial microbes may serve as an agent to suppress these diseases in that particular soil. Therefore, greater emphasis has been laid on manipulation of cropping system to manage native beneficial microorganisms as a means to suppress soil borne plant pathogens. The mechanism following this suppressiveness might be due to various biological attributes like production of antibiotics, competition for nutrients and space, parasitism and predation. Natural biological suppression of soil-borne diseases is a function of the activity and composition of soil microbial communities. Many soils possess similarities with regard to microorganisms involved in disease suppression, while other attributes are unique to specific pathogen-suppressive soil systems. For example, non pathogenic Fusarium spp. and fluorescent Pseudomonas spp. play a critical role in naturally occurring soils that are suppressive to Fusarium wilt. Suppression of take-all of wheat, caused by Gaeumannomyces graminis var. tritici, is induced in soil after continuous wheat monoculture due to presence of fluorescent Pseudomonads with capacity to produce the antibiotic 2,4-diacetylphloroglucinol. Rhizoctonia root rot caused by Rhizoctonia solani may be suppressed by specific fluorescent Pseudomonad genotypes with antagonistic activity toward this pathogen. The enhancement of soil suppressiveness using organic amendments has also been widely described, especially for soil-borne diseases. However, there is great variability in the effectiveness of suppression depending on the nature of the amendment, the crop, the pathogen, and the environmental conditions. Moreover managing soil physico-chemical properties also suppresses certain pathogen thus improving soil health and quality. Managing soil parameters and microbial communities also proved to be suppressing weeds. Methods that transform resident microbial communities along with improving soil health and quality in a manner which induces natural soil suppressiveness have potential as a component in environmentally sustainable systems for management of soilborne plant pathogens.

Comparative effects of different organic materials on nematode community in continuous soybean monoculture soil

Plant parasitic nematodes are the most devastating pest in continuous soybean monoculture, which have been managed mainly by chemical nematicides. However, safe and alternative methods need to be developed. A variety of organic materials are used for this purpose, but the control efficiency of different organic materials for nematodes has not been assessed in a comparative manner. Therefore, based on a 7-year experiment of continuous soybean monoculture, we directly compared the effects of different organic materials (maize straw combined with chemical fertilizer (F + S), poplar leaf combined with chemical fertilizer (F + L), cow manure combined with chemical fertilizer (F + C) and only fertilizer as CK) on nematode trophic groups and functional guilds under the same condition. Despite the lack of total nematode density differences, organic materials altered the soil nematode community in a soybean monoculture system. The relative abundance of plant parasites was highest in F + L treatment, followed by F + S treatment, while lowest in F + C and CK treatments. Meanwhile, bacterivores and fungivores had a higher relative abundance in CK and F + C treatments and a lower relative abundance in F + L and F + S treatments. Furthermore, significant treatment effects were also observed on the relative abundance of different functional guilds, except colonizer-persister (c-p) 5 plant parasites. The relative abundance of c-p 2 bacterivores was significantly higher in CK and F + C treatments than in F + S and F + L treatments, while the relative abundance of c-p 3 omnivore-carnivores was significantly higher in F + S and F + L treatments than in CK and F + C treatments. Organic materials treatments had a significant effect on Shannon index (H’), plant parasite index (PPI), structure index (SI) and enrichment index (EI) (P < .05), and the significant effects varied among different organic materials treatments. The results of this study suggest that the influence on the soil nematode community of organic materials is associated with their chemical composition, and so is its efficacy of controlling plant parasitic nematodes.

Long-term effects of residue and water management practices on plant parasitic nematode abundance and soybean root infection

Soil-borne, plant parasitic nematodes are potentially agronomically and economically damaging in the wheat (Triticum aestivum L.)-soybean (Glycine max L.), double-crop production system that is common in the mid-southern United States. Double-crop field studies with at least five years of consistent management are rare, but can provide a valuable setting to assess long-term, and potentially cumulative, management practice effects on nematode abundance and root damage. The objective of this study was to evaluate the effects of a combination of management practices including residue burning (burned and no burn)-irrigation (irrigated and non-irrigated), wheat residue level (high and low), and tillage (conventional tillage and no-tillage) practices on plant parasitic nematode soil abundance and reproduction on soybean 34 and 70 days after planting following 14 complete cropping cycles in a wheat-soybean, double-crop production system on a silt-loam soil in eastern Arkansas. Stunt and total nematode abundances were at least 8.2 and 4.2 times greater (P < 0.05), respectively, under the burn-non-irrigated-no-tillage than under the other three burn-irrigation-tillage treatment combinations 34 and 70 days after planting. Root-associated soybean cyst nematode egg concentrations were 16.2 and 4.5 times greater under the burn-non-irrigated-low-residue than under the no-burn-irrigated-low-residue and burn-non-irrigated-high-residue treatment combinations, respectively, which did not differ, 34 days after planting, but were unaffected by any field treatment 70 days after planting. Producers may consider avoiding the combination of residue burning, no-tillage, and dryland soybean production to help keep the parasitic nematode population low. Results of this long-term field support the notion that properly managed crop rotations contribute enough diversity of inputs and processes to limit the known negative effects of continuous monoculture.

Evaluating water conservation effects due to cropping system optimization on the Beijing-Tianjin-Hebei plain, China

Irrigation of the conventional double cropping system of winter wheat and summer maize has caused serious problems regarding water resources and the environment on the Beijing-Tianjin-Hebei plain (HP), China. Reducing or replacing high water consumption crops (such as winter wheat) is the most impactful way to effectively save water in the HP region. In this study, crop coefficient and vegetation remote sensing data were used to estimate evapotranspiration (ETa) for winter wheat and summer maize on the HP from 2009 to 2013. For early maize, ETa and yield were based on the results from the APSIM (Agricultural Production System Simulator) crop model, which had been calibrated and validated using field experimental data. The effects on groundwater conservation and grain yield were estimated at the regional scale for the conventional winter wheat (WW) and summer maize (SM) double cropping system (Y1M2) and three alternative cropping systems: three harvests in two years system (Y2M3, 1st year: WW-SM; 2nd year: early maize), four harvests in three years system (Y3M4, 1st year: WW-SM; the next two years: early maize), as well as a continuous early maize monoculture system (Y1M1). The results showed that: (1) Relative to Y1M2, the water savings in each alternative cropping system exceeded 50% of the groundwater overdraft on the HP. The evapotranspirations of Y2M3, Y3M4 and Y1M1 decreased by 14%, 19% and 29% over that of Y1M2 (740mm), respectively. The economic water use efficiencies (WUEe) of the alternative cropping systems were 7% –16% greater than that of Y1M2. The groundwater drop by Y1M2 (0.59myear−1) was higher than that by Y2M3 (0.20myear−1) and Y3M4 (0.07myear−1), and the drop by Y1M1 was negative, indicating a groundwater rise of 0.20m. The groundwater overdraft in Y1M2 was 160mm (3.83billionm3), and the alternative cropping systems were more sustainable, with groundwater overdrafts that were less than the recharge value of 128mm on the HP. (2) In comparison with Y1M2, the total yield was reduced by 2.28, 3.04 and 4.56billionkga−1 (or 7.7%, 10.2% and 15.3%) for Y2M3, Y3M4 and Y1M1, respectively, which accounted for <15% of the regional total or <1% of the national total. It is important to note that the yield loss of the alternative cropping systems was below the net grain export amount in Hebei province, so the grain supply and demand could be roughly balanced. (3) In summary, Y2M3 is a preferred alternative cropping system over Y1M2 in the near future because of the advantages of high WUEe, economic return, mitigated groundwater level decline and balance between wheat supply and demand on the HP. Y1M1, which had the least water use and highest WUEe and economic return, is an option for the most serious groundwater overdraft area despite a contradiction between the traditional dietary habit and complete abandonment of wheat. Y3M4 is recommended as the transitional cropping system between Y2M3 and Y1M1. The method in this study is applicable to relevant regional research, and the results can be of use to the government when formulating policies on cropping systems and groundwater management.

Long-term impact of no-till conservation agriculture on abundance and order diversity of soil macrofauna in continuous maize monocropping system

ABSTRACTUnsuitable soil management in agriculture is known to results in the deterioration of soil health and the decline of biodiversity. The experiment tested whether no-tillage with mulch (NT), could boost biological activity of soil macrofauna population in continuous maize monocropping system compared with rotational tillage with mulch (RT) and conventional tillage (CT). Soil macrofauna was sampled at the end of the 2014/2015 growing season using 25 × 25 × 25 cm steel monoliths. The mean density of individual orders was higher (p < 0.001) under NT (46%) and RT (38%) compared with CT (16%). However, the Shannon-Weaver index revealed that the diversity and evenness of orders were similar for all treatments. Macrofauna patterns revealed that NT and RT contained higher (p < 0.001) population of Isoptera and Diplopoda. Isoptera was 51% and 17% higher in NT than CT and RT, while in Diplopoda, NT was 39% and 2% higher than CT and RT, respectively. It was concluded that NT and RT systems favoured the development of macrofauna communities in the studied maize continuous monoculture cropping system but did not favour order diversity of macrofauna. This suggests the importance of crop rotation for the development of the more diverse macrofaunal population.