Aggregate stability and glomalin in alternative crop rotations for the central Great Plains

 Land productivity, along with improvement or maintenance of soil health, must be evaluated together to achieve sustainable agricultural practices. Winter wheat-fallow (W-F) has been the prevalent cropping system in the central Great Plains for 60 years where moisture is a limitation to crop production. Alternative cropping systems show that producers can crop more frequently if residue management and minimum tillage are used. The impact of different crops, crop rotations and tillage management practices on soil quality was assessed by measuring aggregate stability and glomalin production by arbuscular mycorrhizal (AM) fungi in soil from cropping trials established in 1990. Crops were wheat (W), corn (C), proso millet (M), and sunflower (S). Rotations sampled were W-F, W-C-M, W-C-M-F, W-C-F, and W-S-F. In the same area as the cropping trials, soils were taken from a perennial grass (crested wheatgrass) and from a buffer area that had been planted to Triticale for the past 2 years but prior to that had been extensively plowed for weed control. We found that aggregate stability and glomalin were linearly correlated (r=0.73, n=54, P<0.001) across all treatments sampled. Highest and lowest aggregate stability and glomalin values were seen in perennial grass and Triticale soils, respectively. Aggregate stability in W-S-F was significantly lower than in the other crop rotations (P≤0.03), while W-C-M had significantly higher glomalin than the other rotations (P<0.05). Differences between crop rotations and the perennial grass indicate that selected comparisons should be studied in greater detail to determine ways to manage AM fungi to increase glomalin and aggregate stability in these soils. Received: 16 March 1999     

Differential effects of soil disturbance and plant residue retention on function of arbuscular mycorrhizal (AM) symbiosis are not reflected in colonization of roots or hyphal development in soil

The effects of soil disturbance and residue retention on the functionality of the symbiosis between medic (Medicago truncatula L.) and arbuscular mycorrhizal fungi (AMF) were assessed in a two-stage experiment simulating a crop rotation of wheat (Triticum aestivum L.) followed by medic. Plants were inoculated or not with the AMF, Glomus intraradices and Gigaspora margarita, separately or together. The contribution of the arbuscular mycorrhizal (AM) pathway for P uptake was determined using ³²P-labeled soil in a small hyphal compartment accessible only to hyphae of AMF. In general AM colonization was not affected by soil disturbance or residue application and disturbance did not affect hyphal length densities (HLDs) in soil. At 4 weeks disturbance had a negative effect on growth and phosphorus (P) uptake of plants inoculated with G. margarita, but not G. intraradices. By 7 weeks disturbance reduced growth of plants inoculated with G. margarita or AMF mix and total P uptake in all inoculated plants. With the exception of plants inoculated with G. margarita in disturbed soil at 4 weeks, the AM pathway made a significant contribution to P uptake in all AM plants at both harvests. Inoculation with both AMF together eliminated the negative effects of disturbance on AM P uptake and growth, showing that a fungus insensitive to disturbance can compensate for loss of contribution of a sensitive one. Application of residue increased growth and total P uptake of plants but decreased ³²P in plants inoculated with the AMF mix in disturbed soil, compared with plants receiving no residue. The AMF responded differently to disturbance and G. intraradices, which was insensitive to disturbance, compensated for lack of contribution by the sensitive G. margarita when they were inoculated together. Colonization of roots and HLDs in soil were not good predictors of the outcomes of AM symbioses on plant growth, P uptake or P delivery via the AM pathway.     

杂草利用模式对后茬小麦产量的影响研究

为明确杂草绿肥以及作物秸秆的利用潜力,本试验以山东地区休耕农田中杂草为研究对象,设置6个处理,即未刈割(W0,对照)、刈割1次(W1)、刈割2次(W2)、杂草与玉米共作(W0+M)、杂草与高粱共作(W0+B)以及杂草与大豆共作(W0+S),采取有机管理模式,研究夏季休耕农田不同杂草利用模式对后茬小麦产量的影响。结果表明,杂草与作物共作能提升土壤肥力,显著提高冬小麦籽粒产量,各处理中杂草与大豆共作(W0+S)优势最明显。与对照相比,W0+M、W0+B及W0+S处理2020年土壤有机碳分别提高4.3%、4.7%、11.8%,冬小麦产量分别提高8.8%、11.0%、12.7%;冬小麦籽粒中,N、P、Ca、Fe、Mn含量均以W0+S处理最高。综合土壤理化性质、冬小麦生物学特性以及产量等指标,推荐夏茬休耕模式可适当种植豆科类作物进行养地。本研究为农田杂草资源的合理利用提供了技术支持。     

The inconsistent effect of soil disturbance on colonization of roots by arbuscular mycorrhizal fungi: a test of the inoculum density hypothesis

Reducing the tillage of agricultural soils can increase early-season crop-P uptake. Consistent increases in plant-P have been found in both field- and laboratory-systems with undisturbed (U) compared to disturbed (D) soil. A concomitant stimulatory effect on colonization of roots in U soil by arbuscular mycorrhizal (AM) fungi has been found in some cases, but in others the colonization has been similar in U and D treatments. Disruption of the extraradical mycelium that remains from the previous crop is the mechanism by which soil disturbance restricts mycorrhizally mediated P uptake for the subsequent crop, with a tandem change in colonization not necessary, but sometimes seen. Nonetheless, a complete account of these processes will need an understanding of the conditions under which the extent of colonization is affected. Soil-P does not explain when a difference in colonization will appear. Among ecosystems in Western Australia, high inoculum density in a pasture was reported previously to preclude the appearance of a difference in colonization in response to soil disturbance, whereas for other ecosystems with lower inoculum densities a difference in colonization was seen. Here, we determined if a similar mechanism operates for an agricultural soil collected mid-season during the growth of a maize (Zea mays L.) crop in Ontario, Canada. Blending various proportions of pasteurized and non-pasteurized soil gave a range of inoculum densities. Maize was taken through two 3-week growth cycles in pots, and for the D treatment the soil was passed through a 5 mm sieve between cycles. All plants became colonized with AM fungi. Reducing the inoculum density served to limit colonization to similar low levels in both U and D soils. Stimulation of colonization and of shoot-P uptake in the U-compared with the D-treatment was greater for plants under the higher inoculum conditions tested. We conclude that the inoculum density during crop growth of the soil studied here is moderate, and that this density makes it possible, if other conditions are met, for a reduction of colonization of roots in response to soil disturbance. Whether or not a difference in colonization will appear following disturbance of a soil such as the one studied here probably depends on the interaction between the environment and the plant. Possible interactions are discussed. The high inoculum density of ecosystems such as the pasture studied in Australia likely overrides any effect of soil disturbance and ensures roots of all plants become well-colonized by AM fungi.     

Arbuscular mycorrhizal colonization and spore density across different land‐use types in a hot and arid ecosystem,Southwest China

We investigated the arbuscular mycorrhizal (AM) colonization and spore density in cropped land, fallow land, and an undisturbed savanna ecosystem under hot and arid climatic conditions in a valley of southwest China. Plants surveyed in the three land‐use types showed heavy arbuscular mycorrhizal colonization, indicating a high mycorrhizal dependency of plants in this environment. One‐way analysis of variance (ANOVA) showed that the colonization of different AM structures and the spore density varied greatly among plant species both within and between different land‐use types. The AM colonization and spore density were higher in undisturbed than in fallow or cropped land. No significant correlation between AM colonization and spore density was observed when land‐use types were either considered separately or together. Cluster analysis based on the similarity in AM status with respect to both colonization and spore density showed similarities between fallow land and the undisturbed savanna. The results indicate that continuous cropping reduces AM colonization and spore density. These parameters appear to nearly fully recover when the land has been left to fallow for 4 years.     

Effect of tillage and crop on arbuscular mycorrhiza colonization of winter wheat and triticale under Mediterranean conditions

Large‐scale inoculation with arbuscular mycorrhizal fungi (AMF) is generally impractical in most regions and we have little understanding of the factors that determine inoculation success. Nevertheless, the ability to take full advantage of indigenous AMF for sustainable production needs to be developed within cropping systems. We used part of a long‐term field experiment to understand the influence of tillage and the preceding crop on AMF colonization over the growing season. Arbuscular mycorrhiza colonization rate was more affected by treatment (tillage or the combination of crop and preceding crop) than by the total number of AMF spores in the soil. Conventional tillage (CT) had a statistically significant negative effect (P ≤ 0.05) on spore numbers isolated from the soil, but only in the first year of study. However, the AMF colonization rate was significantly reduced by CT, and the roots of wheat, Triticum aestivum, L, cv. Coa after sunflower, Helianthus annuus L., were less well colonized than were those of triticale, X Triticosecale Wittmack, cv. Alter after wheat, but the affect of tillage was more pronounced than was the effect of crop combination. Under no‐till there was a significant increase in AMF colonization rate throughout the sampling period in both wheat and triticale, indicating that the extraradical mycelium previously produced acted as a source of inoculum. In general, triticale showed greater AMF colonization than wheat, despite the preceding crop being less mycotrophic. Under these experimental conditions, typical of Mediterranean agricultural systems, AMF colonization responded more strongly to tillage practices than to the combination of crop and preceding crop.     

Summer survival of arbuscular mycorrhiza extraradical mycelium and the potential for its management through tillage options in Mediterranean cropping systems

The potential to manage arbuscular mycorrhizal colonization within Mediterranean agricultural systems depends on the summer survival of extraradical mycelium. To investigate this further a three‐stage experiment was undertaken. The first stage was the creation of two contrasting levels of extraradical mycelium development, achieved by two contrasting levels of soil disturbance (typifying full tillage and no‐till). In the second stage, this differential mycelial inoculum was subjected to Mediterranean summer temperature and soil water regimes representing the post‐harvest fallow. During the third stage, corresponding to the next growing season, survival was evaluated without further soil disturbance (typifying no‐till conditions) using wheat as host crop. The results clearly indicate that the extraradical mycelium survived the prevailing summer conditions. The knowledge that extraradical mycelium can survive the Mediterranean summer encourages the use of tillage systems that minimize mechanical disturbance of the soil, such as no‐till. The results from this study suggest that by making the appropriate choice of crops to establish a mycorrhizal‐supportive rotation there can be opportunities for agro‐ecosystem management to benefit from the symbiotic relationship.     

Evaluation and management of acetyl-CoA carboxylase inhibitor resistant littleseed canarygrass (Phalaris minor) in Pakistan

A field survey was conducted for the sampling of Acetyl-CoA carboxylase (ACCase) inhibitor resistance littleseed canarygrass, a major weed of wheat, from Punjab, Pakistan in 2014 for confirmation of resistance. The surveyed regions encompassed four different cropping systems including rice–wheat, maize–wheat, cotton–wheat and mixed cropping. Dose–response assay was conducted for confirmation of resistance. Efficacy of herbicide mixtures including clodinafop–propargyl, metribuzin, pinoxaden and sulfosulfuron at a range of doses was investigated to manage littleseed canarygrass. Results revealed that all populations were resistant to fenoxaprop except PM-BWL-2. The higher level resistance (6.5) was found in populations collected from rice–wheat cropping system. The tested herbicide mixtures at 75% and 100% of the recommended dose of each mixture component provided the effective control of resistant littleseed canarygrass. Mixtures at 50% provided more than 80% control and reduced growth and seed production potential of surviving plants. The confirmation of ACCase inhibitor resistance as the first case of herbicide resistance in Pakistan, leads us to discourage use of ACCase inhibitor herbicides alone. However, herbicide mixtures at 75% and 100% of the recommended dose are suggested to manage this weed for sustainable wheat production in the surveyed cropping systems.     

Precise tillage systems for enhanced non-chemical weed management

Soil and residue manipulation can assist weed management by killing weeds mechanically, interfering in weed lifecycles, facilitating operations and enhancing crop establishment and growth. Current tillage systems often compromise these functions, resulting in heavy reliance on herbicides, particularly in no-till systems. Herbicides are an exhaustible resource, so new approaches to merge soil conservation and non-chemical weed management are needed. This paper broadly reviews various preventive and curative non-chemical weed management tactics. It also demonstrates how innovations can be derived from functional requirements of weed management operations, and from biological processes and weaknesses in weed's lifecycles. Mechanical weeding and enhancement of weed seed mortality are highlighted as examples. Major limitations with mechanical weeding include limited weed control in crop rows at early vulnerable crop stages, weather-dependent effectiveness, and difficulties in handling crop residues. Precise steering and depth control, improved seedbed friability and lighter tractors or controlled traffic could bring considerable improvements. To expose weed seeds to predators, position them for fatal germination, viability loss or low emergence may require completely different soil displacement patterns than those of current implements and systems. Controlled traffic and precise strip tillage offer good opportunities for implementing these weed management strategies in minimum-tillage systems.     

Residue incorporation mitigates tillage‐induced loss of soil carbon in laboratory microcosms

Annual horticultural systems rely on frequent and intensive tillage to prepare beds, manage weeds and control insects. But this practice reduces soil organic carbon (SOC) through accelerated CO₂ emission. Crop residue incorporation could counteract this loss. We investigated whether vegetable systems could be made more resilient by including a high‐residue grain crop such as sweet corn (Zea mays L. var. rugosa), in the rotation through the use of conventional (no residue, no soil sieving) and organic (residue incorporated and soil sieved) soil management scenarios. We evaluated short‐term emission of CO₂‐C and soil C content in incubated Chromosol and Vertosol soils (Australian Classification) with and without sieving (simulated tillage) or the incorporation of ground sweet corn residue. Residue treatment emitted 2.3 times more CO₂‐C compared to the no‐residue treatment, and furthermore, sieved soil emitted 1.5 times more CO₂‐C than the unsieved across the two soil types. The residue incorporation had a greater effect on CO₂‐C flux than simulated tillage, suggesting that C availability and form can be more important than physical disturbance in cropping soils. The organic scenario (with residue and sieved) emitted more CO₂‐C, but had 13% more SOC compared with the conventional scenario (without residue and unsieved), indicating that organic systems may retain more SOC than a conventional system. The SOC lost by soil disturbance was more than offset by the incorporation of residue in the laboratory conditions. Therefore, the possible SOC loss by tillage for weed control under organic management may be offset by organic residue input.     

Effects of tillage systems on soil characteristics, glomalin and mycorrhizal propagules in a Chilean Ultisol

Tillage affects the soil physical and chemical environment in which soil microorganisms live, thereby affecting their number, diversity and activity. However, soil disturbance generally has the greatest impact on biological properties, including both free and symbiotic fungal populations. Interest in more ecologically sustainable agricultural systems is rising with increasing recognition that agricultural intensification can adversely affect environmental quality. This paper discusses the effect of tillage system on some soil characteristics, such as pH, C, N and S levels, total and Olsen-P contents including some P forms associated with organic matter, glomalin contents and arbuscular mycorrhizae (AM) parameters, such as root colonization, spore number and total and active hyphal length. Measurements were in the sixth year of an on-going tillage-rotation experiment conducted on an Ultisol under no-till (NT), reduced tillage (RT) and conventional tillage with stubble mixed into the soil (CTS) or stubble burnt (CTB). Soil was sampled at two dates; after wheat (Triticum aestivum) harvest (autumn) and 6 months after subsequent grassland seeding (spring). Higher C, N, S, total P and fulvic acid-P concentrations and pH occurred under NT and RT than under CTS and CTB after wheat harvest. However, results at the second sampling were not consistent. AM spore number and active hyphal length were highest under NT having the greatest incidence on AM root colonization and P concentration in shoots of the pasture. Glomalin concentration was higher under NT and RT than under CTS and CTB but no differences in calculated glomalin to total C (ca. 5%) were found. It is concluded that a less disruptive effect of NT influences positively all soil characteristics and also increases P acquisition by the following crop in the rotation system.     

Influence of Sesbania Brown Manuring and Rice Residue Mulch on Soil Health,Weeds and System Productivity of Conservation Rice–Wheat Systems

The sustainability of rice–wheat cropping system (RWCS) is threatened by increasing labor, water, and energy crises in the region. Conservation RWCSs offers an ecofriendly alternate option. This study was aimed to evaluate the impact of sesbania brown manuring in direct‐seeded aerobic rice (DSAR) and of rice residue mulch in no‐tilled wheat (NTW) on soil health, weed dynamics and system productivity. The experiment was composed of five RWCS systems: (i) DSAR‐NTW; (ii) DSAR + sesbania brown manuring‐NTW; (iii) DSAR‐NTW + rice residue mulch; (iv) puddled transplanted flooded rice (PudTR)‐NTW; and (v) PudTR‐plow‐tilled wheat. Sesbania brown manuring in direct‐seeded rice decreased the weed density and dry biomass 41–56% and 62–75%, respectively, than the sole direct‐seeded rice crop. At rice harvest, better soil health, in terms of total nitrogen (N), soil organic carbon, soil microbial biomass carbon, and soil microbial biomass nitrogen, was noted with DSAR + sesbania brown manuring‐NTW. Rice residue mulch retention in NTW decreased weed density and dry weight by 60 and 69%, respectively, than those under NTW with no mulch. At wheat harvest, highest total N, soil organic carbon, and soil microbial biomass carbon were recorded with DSAR‐NTW + rice residue mulch, followed by DSAR + sesbania brown manuring‐NTW. Overall, NTW grown after DSAR + sesbania brown manuring produced more grain yield than PudTR‐NTW and PudTR‐plow‐tilled wheat systems. In conclusion, sesbania brown manuring in DSAR and residue mulch retention in NTW may be opted to improve soil properties, suppress weeds, and to harvest better grain yield and achieve higher system productivity in conservation RWCSs. Copyright © 2016 John Wiley & Sons, Ltd.     

Population size and specific potential of P-mineralizing and -solubilizing bacteria under long-term P-deficiency fertilization in a sandy loam soil

The effects of organic manure, mineral fertilizer (NPK), and P-deficiency fertilization (NK) on the individual biomass of young wheat plants, arbuscular mycorrhizal (AM) colonization in wheat root systems, population sizes of soil organic phosphorus mineralizing bacteria (OPMB) and inorganic phosphate solubilizing bacteria (IPSB) as well as soil P-mineralization and -solubilization potential were investigated in a long-term (18-year) fertilizer experiment. The experiment included five treatments: organic manure, an equal mixture of organic manure and mineral fertilizer, fertilizer NPK, fertilizer NK, and the control (without fertilization). Plant biomass, population sizes of soil OPMB and IPSB were greatly increased (P<0.05) by the application of organic manure and slightly increased by the balanced application of mineral fertilizer, while undiminished AM colonization in wheat root system was only observed in the case of the NK treatment. Compared to balanced fertilization, P-deficiency fertilization resulted in a significant increase (P<0.05) of OPMB-specific mineralization potential (soil P-mineralization potential per OPMB cell) and highest IPSB-specific solubilization potential (soil P-solubilization potential per IPSB cell), suggesting that OPMB and IPSB are likely more metabolically active in P-deficiency fertilized soils after long-term fertilizer management, and mycorrhizal plants are more dependent on AM in P-poor soils than in P-fertilized soils. Our results also showed the different effects of mineral fertilizer versus organic manure on soil P-mineralization and -solubilization potentials, as well as specific potentials of OPMB and IPSB in arable soils.     

Temporal and compositional differences of arbuscular mycorrhizal fungal communities in conventional monocropping and tree-based intercropping systems

Previous research has found that conventional agricultural systems adversely affect arbuscular mycorrhizal (AM) fungi. However, there is little information on how more ecologically sustainable agricultural practices such as tree-based intercropping (TBI) influence AM fungal communities. In this study, we investigated whether TBI promotes a more abundant and diverse AM fungal community compared to conventional monocropping (CM). Abundance was estimated by measuring spore abundance and hyphal length in soil, and AM fungal colonization of corn (Zea mays) roots. Overall, AM fungal abundance was similar in both systems as corn roots from the CM and TBI systems were heavily colonized (>50%) by AM fungi throughout the growing season. Additionally, soil samples from the CM and TBI systems contained similar spore densities and hyphal length. Molecular analysis of the AM fungal community was assessed using terminal restriction fragment length polymorphism (T-RFLP) analysis of large subunit rRNA genes amplified from roots in the two cropping systems. A total of fourteen AM fungal phylotypes that belonged to the Glomeraceae were found in the two cropping systems. The TBI system had a higher AM fungal richness and contained several taxa not found in the CM system. Molecular analysis of AM fungal communities also revealed significant temporal and compositional differences between the TBI and CM systems. Within the TBI system, tree species differentially influenced the AM fungal community composition in the alley cropping regions. Future research should focus on determining whether compositional differences among AM fungal communities in CM and TBI systems have a functional effect on crop growth and productivity.     

Spatial and temporal effects of direct drilling on soil structure in the seedling environment

Inherent poor soil fertility is one of the factors responsible for the low productivity of rainfed cotton (Gossypium hirsutum) grown on the vertisols of the Indian sub-continent. A conservation tillage system such as reduced tillage (RT) is one approach to improve soil conditions. Field studies were conducted over 5 years to evaluate RT systems and determine the effects of retaining cotton crop residues on growth and yield of cotton. Results indicated that the RT systems (RT1: two inter-row cultivations and RT2 with no inter-row cultivation) gave significantly greater seed cotton than the conventional tillage (CT) in the first 3 years. In the later 2 years, the differences were not significant. However, yield decline was noticed in RT2 where there was no soil disturbance due to the increased build up of dicot weeds. The effect of crop residue on seed cotton yield was significant in 1998–1999 and 2000–2001. Leaf amended (R1) and leaf+stalk amended (R3) yields were equal to the control (R0). Stalk alone amended (R2) plots had the least seed cotton yield. The RT plots, generally had greater plant dry matter and yield attributes (number of bolls per plant and seed cotton yield per plant) than CT plots during the first 3 years, which contributed to significant yield differences between RT and CT plots. Residue amended plots had significantly greater SOC than the control. Eliminating complete soil disturbance, as in RT2, may not be a viable option, because of increased weed density, especially dicot weeds. The RT1 comprising pre-plant herbicide application and one pass of harrow, and two inter-row cultivation for early season and late season weed control, respectively, is a viable option to cotton growers of the semi-arid tropics of India.     

Effect of reduced tillage on weeds and soil organisms in winter wheat and summer maize cropping on Humic Andosols in Central Japan

Although reduced tillage (RT) may preserve soil biota and improve the productivity and sustainability of arable lands in temperate regions, the extension of RT is limited by difficulties in controlling weeds. We studied the effect of RT without herbicide application on weed communities and soil biota in a 1-year 2-crop rotation system with winter wheat (Triticum aestivum L.) and maize (Zea mays L.) on Andosols in Japan. RT of the surface 3 cm and conventional moldboard plowing (CT) were conducted before seeding twice per year. For the first 3 years, from autumn 1997 to spring 2000, one field was managed with RT and another with CT. For the second 3 years, from autumn 2000 to spring 2003, RT and CT were conducted in two replicated plots in each field. Weed communities and soil biota were studied in the last 2 years. Dominant weed species in winter wheat cropping were Italian ryegrass (Lolium multiflorum Lam.) in 2002 and common vetch (Vicia angustifolia L.) in 2003, and their biomass was high where RT or CT was continuously conducted. Switching of tillage methods, from RT to CT or vice versa, reduced the biomass of winter weeds. In summer maize cropping, several annual and perennial weed species tended to increase under RT in the second 3 years. However, redroot pigweed (Amaranthus retroflexus L.), the most dominant weed in 2002 and 2003, responded to tillage inconsistently and its biomass was not always increased by RT. Species diversity of winter weeds was decreased by CT conducted in the first 3 years, and that of summer weeds was decreased by CT conducted in the second 3 years. The seedbank in the 0–10-cm soil layer under recent RT was large (7200–16 300 seeds m⁻²) compared with that under CT (2900–7300 seeds m⁻²). The microbial substrate-induced respiration (SIR) and the population densities of nematodes and mites were higher under RT in the second 3 years and were not affected by previous tillage practices. Both were highly correlated with soil total nitrogen. The positive effect of RT on these soil organisms was primarily attributable to the accumulation of organic matter in soil, but not to plant cover as a result of incomplete weed control by RT. Occasional adoption of RT in current CT systems may be effective at enriching soil organisms with little risk of weed infestation.     

Reintroduction of a native Glomus to a tropical Ultisol promoted grain yield in maize after fallow and restored the density of arbuscular mycorrhizal fungal spores

Maize (Zea mays L.) is an important crop in central Thailand where fallow is widely practiced and farmers are interested in crop rotation and beneficial soil biota. A pot experiment using a Typic Paleustult (topsoil + subsoil) from the National Corn and Sorghum Research Centre, Nakhonratchasima Province, Thailand was undertaken over three successive crops to evaluate effects of agronomic practices on populations of arbuscular mycorrhizal (AM) fungi and to determine whether reintroduction of a local Glomus was beneficial to maintain maize yield. The three crops and their treatments were: (1) preceding crop: maize grown in all pots; (2) subexperiment 1: agronomic practices [maize, fallow ± soil disturbance, fallow with solarization, non–AM host (cabbage)]; and (3) subexperiment 2: maize ± Glomus sp. 3 at three rates of P fertilization (0, 33, 92 kg P ha^–1). The AM‐fungal community was established under the preceding crop. In subexperiment 1, the three fallow treatments decreased (30%–40%) the total AM spore number in the topsoil whereas there was no change under maize or cabbage. Glomus, the dominant genus, showed sensitivity to fallow. In subexperiment 2, inoculation with Glomus sp. 3 enhanced total AM spore number and root colonization when applied following the three fallow treatments. Furthermore, inoculation promoted grain yield; at nil P following fallow ± soil disturbance, at 33 kg P ha^–1 following fallow without soil disturbance, and following solarization. Two treatments, maize following maize and maize following cabbage, did not respond to inoculation with Glomus sp. 3. Overall, the results suggest that reintroduction of Glomus sp. 3, a local AM fungus in this soil, may overcome negative effects of fallow and promote effectiveness of P fertilizer. Further work is needed to evaluate the benefits of other indigenous AM species that persist under modern fertilization practices.     

丙酯草醚对百合生长的影响及其在鳞茎中的残留

百合田间种植易受杂草危害,为寻求高效低毒、适用于百合生产的新型除草剂及其使用技术,本试验研究了我国创制的新型高效除草剂丙酯草醚对百合田间杂草的控制情况和对其生长的影响规律,同时利用高效液相色谱法检测了其在百合鳞茎中的残留。结果表明,丙酯草醚作为土壤处理剂,于杂草芽前处理,在60 g ai·hm~(-2)用药剂量下能有效防除百合田间禾本科和部分阔叶杂草,杂草鲜重总防效为87.2%;百合田早期喷施丙酯草醚,不仅对百合整个生育期的植株无药害,而且处理组百合在现蕾期、始花期和盛花期的株高、地上部鲜重、花蕾数、花苞数和花朵数均极显著大于对照组,丙酯草醚处理显著促进了百合的生理和生殖生长。高效液相色谱分析结果表明,百合田早期喷施丙酯草醚,在处理组百合鳞茎中未检出丙酯草醚残留(检测限0.001 mg·kg~(-1)FW)。由此可见,丙酯草醚能用于百合田间杂草防除,对百合生长及其食用是安全的。本研究结果为百合田间杂草防除提供了科学依据和技术支持。     

Annual warm-season grasses vary for forage yield,quality, and competitiveness with weeds

Warm-season annual grasses may be suitable as forage crops in integrated weed management systems with reduced herbicide use. A 2-year field study was conducted to determine whether tillage system and nitrogen (N) fertilizer application method influenced crop and weed biomass, water use, water use efficiency (WUE), and forage quality of three warm-season grasses, and seed production by associated weeds. Tillage systems were zero tillage and conventional tillage with a field cultivator. The N fertilization methods were urea broadcast or banded near seed rows at planting. Warm-season grasses seeded were foxtail (Setaria italica L.) and proso (Panicum mileaceum L.) millets, and sorghum–sudangrass (Sorghum bicolor (L.) Moench × Sorghum sudenense Stapf.). Density of early emerging weeds was similar among treatments, averaging 51 m^?2. Millets exhibited higher weed density and weed biomass than sorghum–sudangrass. At harvest, sorghum–sudangrass produced significantly greater biomass and N accumulation than either millet. Water use (157 mm) and WUE (25.1 kg mm^-1 ha^?1) of total biomass did not vary among treatments or grass entries. Weed seed production by redroot pigweed and green foxtail was respectively 93 and 73% less in sorghum–sudangrass than proso millet. Warm-season grasses offer an excellent fit in semiarid cropping systems.     

Interactions between crop residues application and mycorrhizal developments and some soil-root interface properties and mineral acquisition by plants in an acidic soil

The addition of plant residues and the appropriate management of arbuscular mycorrhizal (AM) symbioses have been tested in an acidic soil, an Andisol from Southern Chile, to ascertain whether these agro-technologies help plants to withstand potential mineral deficiency and the toxicities inherent to the low pH conditions. Firstly, the effects of legume (lupine) and non-legume (wheat) crop residues on some key root-soil interface activities (including AM development), on mineral acquisition by the plants, and on the yield of wheat growing in the test Andisol were investigated in a pot experiment under greenhouse conditions. Both lupine and wheat residues were added at a rate equivalent to 300 g m^-2 to the natural soil. These organic amendments increased soil pH (wheat more than lupine), P availability and AM development (lupine more than wheat), plant performance and mineral acquisition (wheat more than lupine). Because of an increase in mycorrhizal activity, which appeared to be involved in the effect of the added crop (particularly lupine) residues, the role of the AM symbiosis was further investigated in a tailored inoculation assay, using a selected AM fungus (Glomus etunicatum), in interaction with lupine and wheat residues. A significant effect of AM inoculation on the reduction of Zn and Cu, and Mn and Al acquisition was demonstrated, which could be of interest in acid soils with regard to potential toxicity problems.