Continuous Maize Research Articles

Risk Assessment and Area-Wide Crop Rotation to Keep Western Corn Rootworm below Damage Thresholds and Avoid Insecticide Use in European Maize Production.

Simple SummaryDiabrotica virgifera virgifera LeConte, the Western corn rootworm (WCR), is a maize-specific pest that has been a serious threat in Europe since the mid-1990s. To properly implement integrated pest management, it is necessary to identify the key factors associated with risks of crop damage from WCR and to evaluate the effectiveness of area-wide strategies based on agronomic measures, such as crop rotation, in reducing those risks. In Italy and Croatia, a survey of agronomic and cultural factors in fields damaged by WCR allowed us to determine that the beetle population size accounts for most of the risk of maize damage from WCR. Crop rotation (without insecticide use), both structural and flexible, was the most effective strategy for keeping WCR populations below the damage threshold. This indicates that WCR management can be carried out in accordance with European Union regulations to limit or avoid insecticide treatments and reduce environmental impacts.The Western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, has been a serious quarantine pest to maize in Europe since the mid-1990s. The integrated pest management of WCR requires an accurate knowledge of the factors that contribute most to risks of crop damage, as well as knowledge of effective area-wide strategies based on agronomic measures, such as crop rotation. In Italy and Croatia, agronomic and cultural factors in fields damaged by WCR were evaluated through a long-term survey. Based on the survey results, high-WCR densities contribute most to risks of damage to maize. Extensive field research in north-eastern Italy compared large areas of continuous maize production with areas under different crop rotation systems (i.e., a structural one with one-time maize planting in a three-year rotation and a flexible one with continuous maize planting interrupted when beetle populations exceed the threshold). The objective was to evaluate the effectiveness of different rotation regimes as possible best practices for WCR management. Captures of beetles in yellow sticky traps, root damage, larval densities, and damage to maize plants (e.g., lodging) were assessed at the center of each area. The results demonstrated the both structural and flexible crop rotation systems were effective strategies for maintaining WCR below damage threshold densities without the need for insecticides.

Orychophragmus violaceus-maize rotation increases maize productivity by improving soil chemical properties and plant nutrient uptake

Appropriate use of cover crops and crop rotation in agriculture can contribute to food security and sustainable production. However, the impacts of Orychophragmus violaceus ( O. violaceus ) as rotation cover crop in maize on soil physicochemical properties and crop nutrient uptake have rarely been verified and quantified via field studies. With a conventional wheat ( Triticum aestivum L.)-maize ( Zea mays L.) rotation used as a control, a field experiment was conducted on the North China Plain in 2017–2018 and 2018–2019 to evaluate the dynamic variations in soil chemical properties and maize agronomic indexes and the impacts on maize nutrient uptake and yield under continuous maize and O. violaceus -maize rotation. We observed that rotation of O. violaceus with maize positively impacts soil chemical properties and subsequent maize productivity. Compared to those in the wheat-maize rotation, the mean contents of soil organic matter (SOM), soil alkali–hydrolyzable nitrogen (SAN), soil available phosphorus (SAP), and soil available potassium (SAK) in the O. violaceus -maize rotation increased by 8%, 11%, 13% and 18%, respectively, within the 0–60 cm soil layer, thereby increasing the maize N and P uptake and yield at maturity. According to correlation analysis and path model results, the most powerful direct factor affecting the maize yield was plant nutrient uptake rather than biomass accumulation. The O. violaceus -maize rotation was superior to the wheat-maize rotation and continuous maize in term of SOM, SAN, plant agronomic indexes, and maize nutrient uptake and yield. Overall, O. violaceus -maize is a reasonable rotation system for use on the North China Plain and provides new insight into the mechanisms and processes underlying crop yield and nutrient uptake. • O. violaceus -maize greatly increased soil organic matter and soil available nitrogen. • The maize nutrients uptake was increased at maturity in O. violaceus -maize system. • Replacing wheat or fallow field with O. violaceus increased maize yield by 8%−12%. • The relationship between soil chemical property and maize yield was quantified.

Land use-land cover gradient demonstrates the importance of perennial grasslands with intact soils for building soil carbon in the fertile Mollisols of the North Central US

The impact of land use change and agricultural management on the cycling of soil organic carbon (SOC) is not well understood, limiting our ability to manage for, and accurately model, soil carbon changes at both local and regional scales. To address this issue, we combined long-term soil incubations with acid-hydrolysis and dry combustion to parse total SOC (Ct) into three operationally defined SOC pools (active, slow, and recalcitrant) from 9 long-term sites with varying land uses on current and former tallgrass prairie soil. Land uses represented a gradient of soil disturbance histories including remnant prairie, restored prairie, grazed pasture, annual crop rotations, and continuous maize. Dry combustion was used to estimate total carbon (Ct, physical), while acid hydrolysis of both the active (Ca) and slow (Cs) pools was used to estimate a recalcitrant carbon pool (Cr, chemical). Non-linear modeling of CO2 efflux data from the long-term incubations was then used to estimate Ca, and the decomposition rates of both Ca and Cs (ka and kr, biological). The size of the slow pools Cs was then defined mathematically as Ct-(Ca + Cr). Remnant prairie had the highest Ct, while cool-season pasture and a 35-y-old restored prairie had higher Ct than the other agricultural systems. All agricultural systems, including pasture, had the highest fraction of Ct as Cr (∼50%), whose mean residence time (MRT) in these soils is ≥500 years (Paul et al., 2001a) demonstrating that this fraction persists, while the more labile fractions were lost over the course of a few months (Ca) to a few decades (Cs) as a result of tillage-intensive agriculture. The two- to four-decade MRT time of Cs indicated a pool likely to be more responsive to the 20 to 40 years of land-use practices used at some of the sites. The Cs pool was largest in the remnant- and 35-y-old prairies indicating significant C accrual and stabilization compared to the agricultural ecosystems. Interestingly, the remnant prairie maintained the highest Ca pool as well, demonstrating the strong connection between the quantity of fresh C inputs and the potential for long-term C stabilization and accrual. The accumulation of C in active (≈labile) pools as a first step toward long-term stabilization highlights the tenuous nature of early carbon gains, which can be quickly lost in response to climate change or poor management.

Maize Lethal Necrosis: Impact and Disease Management

The authors summarise and explore maize lethal necrosis (MLN) global impact, its causal viruses, their vectors, and disease management strategies. MLN is a destructive synergistic virus disease of maize caused by maize chlorotic mottle virus (MCMV) in combination with one of several viruses in the Potyviridae family. MLN causes severe chlorosis, necrosis, and eventual plant death, instigating severe yield losses. The causal viruses of MLN are mostly transmitted between plants by arthropod vectors, but they can also be transmitted at low frequency through seed and soil. Effective MLN management approaches include developing and growing maize with improved tolerance, crop rotation, controlling arthropod vector populations, managing disease reservoirs, and reducing disease transmission and spread through seed and soil. Despite the devastating impact of MLN over the past decade, especially in East Africa, tremendous progress has been achieved towards successful disease management. The rapid development and deployment of MLN tolerant maize in East Africa has proven an extremely effective management strategy, despite continuous maize plantings and the extensive presence of "green bridges". Identifying and stacking additional sources of MLN tolerance is desirable for breeding durable resistance. In the U.S., weed and vector management combined with crop rotation has effectively prevented the spread of MLN beyond a few states in the Midwest. However, it is important to consider the potential impact of climate change and the presence of pesticide/Bt resistant MLN insect vectors, which may facilitate greater vector proliferation and virus spread. Continued vigilance geared towards preventing virus or vector introduction to new locations is desirable, especially in tropical climates where multiple growing seasons occur annually. Fortunately, conditions conducive to an MLN epidemic are complex, requiring the presence of multiple maize infecting viruses and their respective vectors. Thus, several combinations of the disease management strategies discussed above are effective at managing the disease.

First Report of Fusarium culmorum Causing Maize Stalk Rot in China.

Maize stalk rot has become one of the most important diseases in maize production in China. From 2017 to 2019, a survey was conducted to determine the population diversity of Fusarium species associated with maize diseases in 18 cities across Henan Province. Maize stalk rot with an incidence of more than 20% that caused yield losses up to 30% was observed on maize variety Zhengdan958, which was grown in two continuous maize fields in Zhumadian City, Henan Province. The stem tissues from the boundary between diseased and healthy pith were chopped into small pieces (3 × 8 mm), disinfected (70% ethanol for 1 min) and then placed onto potato dextrose agar (PDA) amended with L-(+)-Lactic-acid (1 g/L) and incubated at 25°C for 4 days. Colonies on PDA produced fluffy, light yellow aerial mycelium and purple to deep brick red pigment at 25°C (Fig 1A, 1B). On carnation leaf agar (CLA), macroconidia in orange sporodochia formed abundantly, but microconidia were absent. Macroconidia were short and thick-walled, had 3 to 5 septa, a poorly developed foot cell and rounded apical cell (Fig 1C). These characteristics matched the description of Fusarium culmorum (Leslie and Summerell 2006) and isolates DMA268-1-2 and HNZMD-12-7 were selected for further identity confirmation. Species identification was confirmed by partial sequences of three phylogenic loci (EF1-α, RPB1, and RPB2) using the primer pairs EF1/EF2, CULR1F/CULR1R, and CULR2F/CULR2R, respectively (O'Donnell et al., 1998). The consensus sequences from the two isolates were deposited in GenBank (MZ265416 and MZ265417 for TEF, respectively; MZ265412 and MZ265414 for RPB1, respectively; MZ265413 and MZ265415 for RPB2). BLASTn searches indicated that the nucleotide sequences of the three loci of the two isolates revealed 99% to 100% similarity to those of F. culmorum strains deposited in the GenBank, Fusarium-ID, and MLST databases (Supplementary Table 1~3). Pathogenicity test was conducted at the flowering-stage using Zhengdan958 and Xundan20 plants according to previously described method (Zhang et al., 2016; Cao et al., 2021; Zhang et al., 2021). The second or third internodes of thirty flowering plants were drilled to make a wound approximately 8 mm in diameter using an electric drill. Approximately 0.5 mL inoculum (125 mL colonized PDA homogenized with 75 mL sterilized distilled water) was injected into the wound and sealed with Vaseline and Parafilm to maintain moisture and avoid contamination. Sterile PDA slurry was used as a control. Thirty days after inoculation, the dark-brown, soft rot of pith tissues above and below the injection sites were observed, and some plants were severely rotten and lodged (Fig 1D, 1E). These symptoms were similar to those observed in the field. No symptoms were observed on control plants. The same pathogen was re-isolated from the inoculated stalk lesions but not from the control, thereby fulfilling Koch's postulates. To our knowledge, this is the first report of F. culmorum as the causal agent of stalk rot on maize plants in China. Also, this fungus has been reported to cause maize ear rot in China (Duan et al. 2016) and produce mycotoxins such as trichothecenes, nivalenol, and zearalenone that cause toxicosis in animals (Leslie and Summerell 2006). The occurrence of maize stalk rot and ear rot caused by F. culmorum should be monitored due to the potential risk for crop loss and mycotoxin contamination.

Correction to: Continuous maize cropping accelerates loss of soil organic matter in northern Thailand as revealed by natural 13C abundance

Correction to: Continuous maize cropping accelerates loss of soil organic matter in northern Thailand as revealed by natural 13C abundance

Rare microbial populations as sensitive indicators of bacterial community dissimilarity under different agricultural management practices

ABSTRACT Revealing the composition and role of rare and abundant microbial groups is crucial to understand ecosystem processes and function. In 2018, we characterized soil bacterial community, abundant (AMPs) and rare microbial populations (RMPs) with mineral fertilizer and mineral fertilizer combined with straw return under continuous maize (Zea mays L.) and soybean (Glycine max Merr.)-maize rotation systems in a Mollisol in Northeast China. The results showed that the effects of fertilization on total bacterial community, AMPs and RMPs were greater than cropping systems. The cropping systems had a stronger effect on α diversity of bacterial community than fertilization. The RMPs accounted for 50.1% of the relative abundance and contributed 64.3% to the community dissimilarity. The RMPs accounted for 96.7% of the amount of operational taxonomic units (OTUs), thus became the most important contributors to community diversity. The OTUs with lower relative abundance had a narrower niche range, indicating that rare OTUs were more easily affected by habitat uniqueness. The RMPs were important contributors to chemoheterotrophs and were more closely correlated with variations in soil functions than AMPs. Our results provided deep insight into the ecological role of RMPs, which is useful for rational management and improving agricultural ecosystem sustainability.

Irrigation effects on the formation of soil organic matter from aboveground plant litter inputs in semiarid agricultural systems

In semiarid agricultural systems, irrigation may increase soil organic matter (SOM) due to higher biomass production. However, aboveground production tends to increase more than belowground biomass, and in no-till systems SOM responses to irrigation would strongly depend on the fate of crop residues left on the soil surface. Litter decomposition and SOM formation can also be affected by irrigation due to changes in water dynamics, but little is known about the impacts of irrigation on the pathways of SOM formation. We used dual 13C and 15N labeled maize litter to quantify the effect of irrigation on the contribution of aboveground crop residues to SOM formation in semiarid, no-till agricultural systems. We incubated the litter in a continuous maize cropping system with two treatments, dryland and irrigated, and measured litter decomposition and its contribution to different SOM pools. Irrigation had a larger effect on litter C and N losses than on the formation of new SOM. After 13 months the C and N losses from the litter layer were 24% higher under irrigation, but there were no treatment differences in the litter-derived C and N recovered in SOM. Most of the litter-derived organic matter (OM) was found in the mineral associated OM pool (MAOM), but irrigation did not affect the amount of litter-derived OM found as MAOM or as particulate organic matter. Irrigation increased the amount of litter-derived OM found in macroaggregates, and this observation was more related to a higher aggregation than to aggregate enrichment in the irrigated treatment. Our results suggest that a smaller proportion of aboveground crop residues will form SOM in irrigated systems compared to dryland conditions and may help to partially explain why irrigation has a stronger relative effect on crop productivity and C inputs than on SOC stocks in semiarid agricultural systems.

Plant and soil microbial responses to irrigation retirement in semiarid cropping systems

Water scarcity limits irrigated agriculture, and there is an increasing frequency of situations where farmers must transition from irrigated to dryland cropping systems. This transition poses several challenges, and it is necessary to understand the changes in crop productivity and soil health for the design of viable cropping systems. Our objective was to compare the impact of irrigation retirement on crop production and soil microbial dynamics under the two major crops of the semiarid High Plains. In a formerly irrigated field, we installed a transition experiment that consisted of two irrigation managements, irrigated and non-irrigated (retired), under two cropping systems: continuous maize and continuous winter wheat. Lower soil moisture after irrigation retirement decreased plant biomass production in both crops, with a higher effect on maize (2 to 6-fold decrease) than on wheat (20% less aboveground biomass production). In both crops, irrigation retirement affected crop development in the order grain yield > aboveground biomass > belowground biomass. Soil microbial communities were less affected by irrigation retirement than the evaluated crops and changes were concentrated in the maize agroecosystem. After three seasons, the high decrease in maize productivity and soil moisture resulted in 50% less extracellular enzyme activity in the dryland treatment, but without consistent effects on microbial biomass or community composition assessed by phospholipid fatty acids. Winter wheat appears as a viable option not only to sustain crop production but also to minimize the negative impacts of irrigation retirement on soil health. However, root production was lower in wheat than in maize, which may affect the long-term evolution of soil organic carbon.

Analysis of cropping pattern in black soil region of Northeast China based on geo-information Tupu.

Different cropping patterns have their own economic and ecological significance. Developing cropping patterns suitable for local conditions is needed to protect and make good use of black soils. At present, the cropping patterns and their spatial characteristics in the black soil region of Northeast China is poorly understood. Based on the crop classification data in 2017-2019, we used geo-information Tupu methods, distribution index model, and bivariate spatial autocorrelation to examine the cropping patterns. The results showed that: 1) The main cropping patterns in the black soil region of Northeast China were continuous maize cropping, continuous rice cropping, continuous soybean cropping, and maize-soybean rotation, accounting for 38.3%, 18.5%, 10.3% and 26.0%, respectively. The maize-soybean rotation included maize-soybean two-year rotation, maize-maize-soybean three-year rotation, and soybean-soybean-maize three-year rotation, accounting for 44.1%, 34.5% and 21.4% of the rotation area, respectively. 2) Various cropping patterns had obviously horizontal differentiation. For instance, continuous maize cropping had very obvious gradient differentiation characteristics in temperature and humidity, but soybean continuous cropping and maize-soybean rotation showed no gradient differentiation, while continuous rice cropping had gradient differentiation only in humidity. 3) Various cropping patterns had obviously spatial clustering characteristics. They had spatial transition characteristics from soybean continuous cropping, soybean-soybean-maize three-year rotation, maize-soybean two-year rotation, maize-maize-soybean three-year rotation, to continuous maize cropping. The cropping pattern in black soil region of Northeast China was dominated by continuous cropping. Understanding its distribution pattern can provide a basis for future spatial optimization of crop rotation.

Continuous maize cropping accelerates loss of soil organic matter in northern Thailand as revealed by natural 13C abundance

AimsThe loss of soil organic matter (SOM) has widely been reported in the tropics after changing land use from shifting cultivation to continuous cropping. We tested whether continuous maize cultivation accelerates SOM loss compared to upland rice and forest fallow.MethodsBecause litter sources include C4 plants (maize in maize fields and Imperata grass in upland rice fields) in Thailand, C3-derived and C4-derived SOM can be traced using the differences in natural 13C abundance (δ13C) between C3 and C4 plants. We analyzed the effects of land use history (cultivation or forest fallow period) on C stocks in the surface soil. Soil C stocks decreased with the cultivation period in both upland rice and maize fields.ResultsThe rate of soil organic carbon loss was higher in maize fields than in upland rice fields. The decomposition rate constant (first order kinetics) of C3-plant-derived SOM was higher in the maize fields than in the upland rice fields and the C4-plant-derived SOM in the forest fallow. Soil surface exposure and low input of root-derived C in the maize fields are considered to accelerate SOM loss. Soil C stocks increased with the forest fallow period, consistent with the slow decomposition of C4-plant-derived SOM in the forest fallows.ConclusionsContinuous maize cultivation accelerates SOM loss, while forest fallow and upland rice cultivation could mitigate the SOM loss caused by continuous maize cultivation.

Persistent soil carbon enhanced in Mollisols by well-managed grasslands but not annual grain or dairy forage cropping systems

Intensive crop production on grassland-derived Mollisols has liberated massive amounts of carbon (C) to the atmosphere. Whether minimizing soil disturbance, diversifying crop rotations, or re-establishing perennial grasslands and integrating livestock can slow or reverse this trend remains highly uncertain. We investigated how these management practices affected soil organic carbon (SOC) accrual and distribution between particulate (POM) and mineral-associated (MAOM) organic matter in a 29-y-old field experiment in the North Central United States and assessed how soil microbial traits were related to these changes. Compared to conventional continuous maize monocropping with annual tillage, systems with reduced tillage, diversified crop rotations with cover crops and legumes, or manure addition did not increase total SOC storage or MAOM-C, whereas perennial pastures managed with rotational grazing accumulated more SOC and MAOM-C (18 to 29% higher) than all annual cropping systems after 29 y of management. These results align with a meta-analysis of data from published studies comparing the efficacy of soil health management practices in annual cropping systems on Mollisols worldwide. Incorporating legumes and manure into annual cropping systems enhanced POM-C, microbial biomass, and microbial C-use efficiency but did not significantly increase microbial necromass accumulation, MAOM-C, or total SOC storage. Diverse, rotationally grazed pasture management has the potential to increase persistent soil C on Mollisols, highlighting the key role of well-managed grasslands in climate-smart agriculture.

Integrating Crop-Livestock System Practices in Forage and Grain-Based Rotations in Northern Germany: Potentials for Soil Carbon Sequestration

Integrating leys, cover crops, and animal manures constitute promising avenues to reach annual soil organic carbon changes (ΔSOC) >0.4% in forage and grain-based crop rotations, rates required to offset the increasing C emissions from fossil fuels (“4 per mille” initiative). How these practices and rotations perform in reaching this aim was object of analysis in this paper. Five cropping systems (CS), including three three-year forage and grain-based crop rotations containing annual grass-clover leys (FR and MR) or cover crops (GR), and two contrasting controls (continuous silage maize (CM), and permanent grassland (PG)) were compared for their impact on SOC stocks over eight years (2010–2018). The CS were unfertilized (N0) or fertilized using cattle slurry (N1) at a rate of 240 kg N ha−1 yr−1 applied in the non-leguminous crops. The ΔSOC of the top 30 cm soil layer and the annual carbon inputs (Cin) from slurry applications and plant residues were estimated, their relationship established, and the slurry-induced C retention coefficient was determined. The FR and MR SOC stocks remained stable at N1, while the GR and CM SOC decreased over time by tendency even at N1. Only the PG reached ΔSOC >0.4%. Differences in ΔSOC between CS and N rates were highly associated with the system-specific increase in belowground Cin, induced by slurry applications. Slurry-induced C retention coefficients differed strongly between CS: CM (3%) followed by GR (12%), and by FR and MR (20–15%), and lastly by PG (24%). Promoting belowground carbon inputs was identified as an efficient way to reach significant increases in ΔSOC. We conclude that a ley in only one out of three years is not sufficient to significantly increase SOC stocks in arable crop rotations of the study region.

Exploring long-term impacts of different crop rotation systems on sustainable use of groundwater resources using DSSAT model

Groundwater depletion has been a global concern due to unreasonable agricultural water managements. Identifying long-term impacts of crop rotation systems on hydrological parameters and crop yields can help to alleviate groundwater depletion. The Decision Support System for Agro-technology Transfer model was applied to simulate impacts of nine crop rotation systems (H1: continuous spring maize; H2: continuous potato; H3: continuous spring wheat; H4:potato-maize rotation; H5:maize-wheat rotation; H6: wheat-potato rotation; H7: two year fallow-maize rotation; H8: two year fallow-potato rotation; H9: two year fallow-wheat rotation) on crop evapotranspiration, percolation, yields, water use efficiency, net water use and groundwater table depth changes in Zhangjiakou, China from 1985 to 2018. The results showed DSSAT model performed well in simulating crop ET, yields (R2>0.9, RMSE<500 kg ha−1) and soil water content (R2>0.9 and RMSE<10.1 mm). The long-term two year fallow with one single crop rotation systems (H7 to H9) had lower total accumulative groundwater table depth changes (2.8–14.4 m) than others (12.7–52.3 m) from 1985 to 2018. Also, cropping rotation systems H7 to H9 obtained the lower annual average net water use (14–70 mm) compared to other cropping rotation systems (62–253 mm). The significant difference of net water use, crop yields, water use efficiency and accumulative groundwater table depth changes of nine different cropping systems indicated H4 and H8 is suitable in the study region. Our results is useful for selecting suitable cropping systems based on the water use for local farmers.

Soil Management and Crop Practice Effect on Soil Water Infiltration and Soil Water Storage in the Humid Lowlands of Beles Sub-Basin, Ethiopia

To investigate the response of soil management and cropping practice on infiltration, a field experiment was conducted under natural environment on Nitisol of Pawi area. Eight treatments combining two soil management methods (Zero tillage and conventional tillage) and four crop covers (continuous maize, continuous soya bean, rotated maize, and maize soya bean intercrop) were laid out on permanent plots in a randomized complete block design (RCBD) with three replications. The results showed that soil management and crop cover significantly affect both the capacity and rate of infiltration. Relative to conventionally tilled continuous maize, zero tilled maize soya bean intercrop improved infiltration rate and infiltration by 164.6% and 148%, respectively. While maize rotation with zero tillage, maize soya bean intercropping with conventional tillage and maize with zero tillage methods improve infiltration rate by 117.8%, 105.8%, 108%, respectively. The soil management and crop cover practices such as maize with zero tillage, maize soya bean intercrop with zero tillage, rotated maize with conventional tillage, maize soya bean intercrop with conventional tillage, soya bean with zero tillage and rotated maize with zero tillage increased soil water storage in the order of 65mm, 41mm, 41mm, 35mm, 15mm and 13mm. Generally, zero tillage with greater cover is an appropriate method to improve infiltration and soil water storage.

Evidence of western corn rootworm (Diabrotica virgifera virgifera LeConte) field-evolved resistance to Cry3Bb1 + Cry34/35Ab1 maize in Nebraska.

Western corn rootworm (WCR; Diabrotica virgifera virgifera) field-evolved resistance to transgenic maize expressing the Cry3Bb1 protein derived from Bacillus thuringiensis (Bt) has been confirmed across the United States Corn Belt. Although use of pyramided hybrids expressing Cry3Bb1 + Cry34/35Ab1 has increased in recent years to mitigate existing WCR Bt resistance, susceptibility of Nebraska WCR populations to this rootworm-Bt pyramid has not been assessed. Plant-based bioassays were used to characterize the susceptibility of WCR populations to Cry3Bb1 and Cry3Bb1 + Cry34/35Ab1 maize. Populations were collected from areas of northeastern Nebraska with a history of planting Bt maize that expressed Cry3Bb1 and Cry34/35Ab1. Significant differences in mean corrected survival among populations within Bt hybrids indicated a mosaic of WCR susceptibility to Cry3Bb1 + Cry34/35Ab1 and Cry3Bb1 maize occurred in the landscape. All field populations exhibited some level of resistance to one or both Bt hybrids when compared to susceptible laboratory control populations in bioassays. Most WCR populations exhibited incomplete resistance to Cry3Bb1 + Cry34/35Ab1 maize (92%) and complete resistance to Cry3Bb1 maize (79%). The present study confirms the first cases of field-evolved resistance to Cry3Bb1 + Cry34/35Ab1 maize in Nebraska and documents a landscape-wide WCR Cry3Bb1 resistance pattern in areas characterized by long-term continuous maize production and associated planting of Cry3Bb1 hybrids. Use of a multi-tactic integrated pest management approach is needed in areas of continuous maize production to slow or mitigate resistance evolution to Bt maize. © 2021 Society of Chemical Industry.

In-season split nitrogen application and cover cropping effects on nitrous oxide emissions in rainfed maize

Cover crops and in-season nitrogen (N) management are promoted as key conservation practices for reducing nitrate leaching losses from agricultural fields. However, their combined effects on soil nitrous oxide (N2O) emissions per unit of crop productivity remains uncertain. These practices might contribute to high N2O emissions by providing N and C substrates for microbial denitrification activity, especially when in-season N application coincides with cover crop decomposition. The objective of this study was to evaluate the effects of N application timing and cereal rye (CR, Secale cereale L) cover crops on area- and yield-scaled soil N2O emissions in continuous maize (Zea mays L.) over 3-yr (2018–2020). Treatments were: Pre-Season-N: 224 kg N ha-1 split-applied in fall + pre-plant in 2018, or as single pre-plant applications in 2019 and 2020; In-Season-N: pre-plant + side-dress (growth stage V6-V7); In-Season-N + CR: ; and a zero N plot as the Control. We found that shifting from pre-season to in-season split N application did not significantly affect area- or yield-scaled N2O emissions in any year. Despite high N2O spikes for the In-Season-N + CR following side-dress N application in all years, this did not translate to consistently higher cumulative N2O emissions. Compared with Pre-Season-N and In-Season-N, In-Season-N + CR significantly increased area- and yield-scaled N2O emissions by approximately 50% in 1 of 3 years. These results suggest the combination of high soil N supply, warm and wet soil conditions, and cover crop decomposition contributes to elevated N2O emissions, but the cumulative effects of side-dress N application with a CR cover crop are variable across years. With increasing adoption of these practices to reduce nitrate leaching losses from croplands, future work should simultaneously assess effects on N2O emissions and crop yield to account for potential tradeoffs in N loss pathways.

Simulation of soil water balance and crop productivity of long-term continuous maize cropping under high planting density in rainfed agroecosystems

Increasing planting density is one of the main management practices contributing to maize grain yield improvements across the world, but the soil water sustainability after long-term continuous high-density under rainfed farming systems is not clear. Crop simulation models may help explore suitable management systems for increasing crop productivity and economic benefits. The present study calibrated and validated the DSSAT-CERES-Maize model in a four-year field experiment, which coupled four densities from 52,500 to 97,500 plant ha−1 and two cultivars under rainfed conditions. The calibrated CERES-Maize model performed fairly well in simulating the phenological dates, and the average root mean-squared error (RMSE) ranged from 0.7 to 2.8 d for anthesis and 0 to 2.8 d for maturity date. The normalized root mean squared errors (nRMSE) for biomass and grain yield were 17.5% and 12.4%, respectively. The average nRMSE for soil water dynamics in the 0–200 cm soil layers was 15.6% among the different growth stages. The calibrated model was subsequently used to evaluate the soil water regime and crop productivity in response to planting density under 38 years of meteorological data. The results showed that maize water productivity and evapotranspiration (ET) fluctuated with seasonal rainfall, and normal and wet years were significantly higher than dry years. Although ET during the growing season tended to increase with increasing density, the long-term continuous high planting density did not cause excessive soil water consumption. Grain yield and water use efficiency (WUE) tended to exhibit a parabolic relationship with planting density during the long-term simulated seasons between different experimental sites. No significant differences were detected between different cultivars in water productivity under long-term simulation. However, the simulation results suggested that the optimal planting density was often related to variability in climate conditions between sites and years. The scenario simulation results suggest that the optimal density should not exceed 67,500 plant ha−1 when the annual precipitation is less than 500 mm, but it should not exceed 82,500 plant ha−1 in areas where the rainfall is greater than 500 mm. Therefore, this study suggests that moderate planting density has the potential to realize sustainable maize development in dryland farming systems on the Loess Plateau and similar areas.

Sustainable irrigation based on co-regulation of soil water supply and atmospheric evaporative demand

Irrigation is an important adaptation to reduce crop yield loss due to water stress from both soil water deficit (low soil moisture) and atmospheric aridity (high vapor pressure deficit, VPD). Traditionally, irrigation has primarily focused on soil water deficit. Observational evidence demonstrates that stomatal conductance is co-regulated by soil moisture and VPD from water supply and demand aspects. Here we use a validated hydraulically-driven ecosystem model to reproduce the co-regulation pattern. Specifically, we propose a plant-centric irrigation scheme considering water supply-demand dynamics (SDD), and compare it with soil-moisture-based irrigation scheme (management allowable depletion, MAD) for continuous maize cropping systems in Nebraska, United States. We find that, under current climate conditions, the plant-centric SDD irrigation scheme combining soil moisture and VPD, could significantly reduce irrigation water use (−24.0%) while maintaining crop yields, and increase economic profits (+11.2%) and irrigation water productivity (+25.2%) compared with MAD, thus SDD could significantly improve water sustainability.

Effects of Long-Term Bare Fallow During the Winter-Wheat Growth Season on the Soil Chemical Properties, Fungal Community Composition, and the Occurrence of Maize Fungal Diseases in North China.

On the North China Plain, one of the most water-deficient regions in China, bare fallow has been implemented over a large-scale area to conserve water during the growth season of water-intensive winter wheat since 2015. However, the effects of this bare fallow on fungal community and the occurrence of crop diseases are poorly understood. Here we measured soil chemical properties, fungal community composition, and the occurrence of crop diseases after 15 years of long-term fallow (continuous maize or soybean) and non-fallow (maize-wheat rotation; soybean-wheat rotation) cropping systems. Bare fallow during the winter-wheat growth season significantly decreased soil organic matter, available nitrogen, and phosphorus. It also changed the composition of soil fungal communities, i.e., increased relative abundances of some potentially pathogenic species of Lectera, Fusarium, and Volutella but decreased beneficial Cladorrhium and Schizothecium. Meanwhile, the epidemic tendency of maize diseases changed correspondingly: the disease index of southern corn leaf blight and maize brown spot increased, but the incidence of stalk rot decreased compared with the non-fallow system. Soybean diseases were very mild regardless of the cropping system during the total experimental period. Network analysis demonstrated that the soil fungal diversity associated with maize diseases was affected by the decreased soil organic matter and available nitrogen and phosphorus. Our results suggest that bare fallow in the winter-wheat season affected the soil chemical properties, fungal community, and the occurrence of maize fungal diseases.