Modelling facilitation or competition within a root system: importance of the overlap of root depletion and accumulation zones

Background and aims

Relevant soil properties and nutrient distributions influencing crop root growth might be different under no-till (NT) and mouldboard plough (MP) management. The possible different root systems within different managements might have key impact on crop nutrient uptake and consequently crop production. Our objective was to assess the long-term combined effects of tillage and phosphorus (P) fertilization on corn (Zea mays L.) root distribution and morphology.

Methods

Corn root and soil samples were collected during the silking stage at five depths (0–5, 5–10, 10–20, 20–30 and 30–40 cm) and three horizontal distances perpendicular to the corn row (5, 15 and 25 cm) under MP and NT with three P fertilizations (0, 17.5, and 35 kg P ha^?1) for a long-term (22 years) experiment in eastern Canada. Root morphology and soil properties were determined.

Results

NT practice decreased corn root biomass by ?26 % compared to MP, mainly by decreasing the primary and secondary roots. Additionally, corn roots in NT tend to be more expansive on the surface layer with higher root length and surface densities for the depth of 0–5 cm at two sampling distances of 15 and 25 cm. The 35 kg P ha^?1 rate increased the root biomass by 26 and 41 % compared to the 0 and 17.5 kg P ha^?1 rates.

Conclusions

No-tillage practice and low rates of P fertilization reduce corn roots. This is probably caused by the weed competition in NT and the continued downward P status with low P rates over 22 years.

     

Effects of beech (Fagus sylvatica), ash (Fraxinus excelsior) and lime (Tilia spec.) on soil chemical properties in a mixed deciduous forest

Background and aims

We investigated the genetic diversity of arbuscular mycorrhizal fungi (AMF) in soils and the roots of Phalaris aquatica L., Trifolium subterraneum L., and Hordeum leporinum Link growing in limed and unlimed soil, the influence of lime application on AMF colonization and the relationship between AMF diversity and soil chemical properties.

Methods

The sampling was conducted on a long-term liming experimental site, established in 1992, in which lime was applied every 6 years to maintain soil pH (in CaCl₂) at 5.5 in the 0–10 cm soil depth. Polymerase chain reaction, cloning and sequencing techniques were used to investigate the diversity of AMF.

Results

Altogether, 438 AMF sequences from a total of 480 clones were obtained. Sequences of phylotypes Aca/Scu were detected exclusively in soil, while Glomus sp. (GlGr Ab) and an uncultured Glomus (UnGlGr A) were detected only in plant roots. Glomus mosseae (GlGr Aa) was the dominant AMF in the pastures examined; however, the proportion of G. mosseae was negatively correlated with soil pH, exchangeable Ca and available P. Generally, diversity of the AMF phylotypes was greater in the bulk unlimed soil and plants from this treatment when compared to the limed treatments.

Conclusions

Long-term lime application changed soil nutrient availability and increased AMF colonization, but decreased AMF phylotype diversity, implying that soil chemistry may determine the distribution of AMF in acid soils. Future studies are required to explore the functions of these AMF groups and select the most efficient AMF for sustainable farming in acid soils.     

Interaction between root growth allocation and mycorrhizal fungi in soil with patchy P distribution

Aims and Background

Many plants preferentially grow roots into P-enriched soil patches, but little is known about how the presence of arbuscular mycorrhizal fungi (AMF) affects this response.

Methods

Lotus japonicus (L.) was grown in a low-P soil with (a) no additional P, (b) homogeneous P (28 mg pot^?1), (c) low heterogeneous P (9.3 mg pot^?1), and (d) high heterogeneous P (28 mg pot^?1). Each P treatment was combined with one of three mycorrhiza treatments: no mycorrhizae, Glomus intraradices, indigenous AMF. Real-time PCR was used to assess the abundance of G. intraradices and the indigeneous AMF G. mosseae and G. claroideum.

Results

Mycorrhization and P fertilization strongly increased plant growth. Homogeneous P supply enhanced growth in both mycorrhizal treatments, while heterogeneous P fertilization increased biomass production only in treatments with indigenous AMF inoculation. Preferential root allocation into P-enriched soil was significant only in absence of AMF. The abundance of AMF species was similar in P-enriched and unfertilized soil patches.

Conclusion

Mycorrhization may completely override preferential root growth responses of plants to P- patchiness in soil. The advantage of this effect for the plants is to give roots more freedom to forage for other resources in demand for growth and to adapt to variable soil conditions.     

Response of soil nematodes to elevated temperature in conventional and no-tillage cropland systems

Aims

Nematodes are sensitive to environmental changes and are strongly affected by tillage practices. However, it remains unclear whether an increase in soil temperature in conventional tillage (CT) and no-tillage (NT) cropland systems would have a significant effect on nematode communities. The response of soil nematodes to increases in temperature will provide valuable information about probable changes in soil ecology under global warming.

Methods

A field experiment using infrared heaters to simulate climate warming was performed in North China. The impacts of predicted warming on the nematode community in CT and NT systems were measured during the growing season of maize.

Results

The results showed that the diversity of nematodes responded positively to warming in both tillage systems early in the maize growing season, though the diversity in NT declined due to warming late in the growing season. However, no significant warming effects were found on the total nematode density, individual feeding group density or functional indices. Compared to CT, NT presented a rather different nematode community that was characterized by a large nematode diversity, low fungal feeder density due to a strong decrease in Aphelenchoides, and high maturity indices.

Conclusions

Tillage is an important factor that influences the soil properties and nematode community. It is proposed that future global warming with soil temperature increasing approximately 1 °C will have only small effects on soil nematodes in the two tillage systems.     

Soil carbon dioxide and methane fluxes as affected by tillage and N fertilization in dryland conditions

Background and aims

The effects of tillage and N fertilization on CO₂ and CH₄ emissions are a cause for concern worldwide. This paper quantifies these effects in a Mediterranean dryland area.

Methods

CO₂ and CH₄ fluxes were measured in two field experiments. A long-term experiment compared two types of tillage (NT, no-tillage, and CT, conventional intensive tillage) and three N fertilization rates (0, 60 and 120 kg N ha^?1). A short-term experiment compared NT and CT, three N fertilization doses (0, 75 and 150 kg N ha^?1) and two types of fertilizer (mineral N and organic N with pig slurry). Aboveground and root biomass C inputs, soil organic carbon stocks and grain yield were also quantified.

Results

The NT treatment showed a greater mean CO₂ flux than the CT treatment in both experiments. In the long-term experiment CH₄ oxidation was greater under NT, whereas in the short-term experiment it was greater under CT. The fertilization treatments also affected CO₂ emissions in the short-term experiment, with the greatest fluxes when 75 and 150 kg organic N ha^?1 was applied. Overall, the amount of CO₂ emitted ranged between 0.47 and 6.0 kg CO₂?equivalent kg grain^?1. NT lowered yield-scaled emissions in both experiments, but these treatment effects were largely driven by an increase in grain yield.

Conclusions

In dryland Mediterranean agroecosystems the combination of NT and medium rates of either mineral or organic N fertilization can be an appropriate strategy for optimizing CO₂ and CH₄ emissions and grain yield.     

Mechanical properties and soil stability affected by fertilizer treatments for an Ultisol in subtropical China

Background and aims

Soil mechanical properties are crucial for plant growth, soil erosion, tillage and traffic. The soil mechanical properties and stability of an Ultisol were determined in a 13-year fertilization experiment in subtropical China. The effect of organic matter on soil structure was also evaluated.

Methods

The treatments include: unfertilized, mineral fertilized, mineral mixed with straw, and animal manure. Bulk soil strengths (shear strength and penetration resistance) were tested in field. Aggregate strengths (penetration resistance and tensile strength), water stability, organic carbon (OC), hot-water-extractable carbohydrate (HWEC) and some related factors were determined in laboratory.

Results

Fertilizer increases aggregate penetration resistance, tensile strength, water stability and organic matter content in cultivated horizon (0–15 cm depth), especially at the 0–5 cm layer. OC and HWEC showed significantly regression relationships with aggregate water stability, porosity and water repellency for the whole soil profile (0–40 cm). Aggregate strengths also increased with OC and HWEC in cultivated horizon.

Conclusions

Animal manure is most effective in improving soil structure while aggregate water stability is the most sensitive index of fertilizer management. Soil organic matter is a strong determinant of soil structure. Both OC and HWEC are good indicators of surface aggregate strengths and stability, and thus, soil quality in this region.     

Field inoculation with arbuscular-mycorrhizal fungi overcomes phosphorus and zinc deficiencies of linseed (Linum usitatissimum) in a vertisol subject to long-fallow disorder

Background and aims

Long-fallow disorder is expressed as exacerbated deficiencies of phosphorus (P) and/or zinc (Zn) in field crops growing after long periods of weed-free fallow. The hypothesis that arbuscular-mycorrhizal fungi (AMF) improve the P and Zn nutrition, and thereby biomass production and seed yield of linseed (Linum usitatissimum) was tested in a field experiment.

Methods

A factorial combination of treatments consisting of ± fumigation, ±AMF inoculation with Glomus spp., ±P and ±Zn fertilisers was used on a long-fallowed vertisol. The use of such methods allowed an absolute comparison of plants growing with and without AMF in the field for the first time in a soil disposed to long-fallow disorder.

Results

Plant biomass, height, P and Zn concentrations and contents, boll number and final seed yield were (a) least in fumigated soil with negligible AMF colonisation of the roots, (b) low initially in long-fallow soil but increased with time as AMF colonisation of the roots developed, and (c) greatest in soil inoculated with AMF cultures. The results showed for the first time in the field that inflows of both P and Zn into linseed roots were highly dependent on %AMF-colonisation (R²?=?0.95 for P and 0.85 for Zn, P?<?0.001) in a soil disposed to long-fallow disorder. Relative field mycorrhizal dependencies without and with P+Zn fertiliser were 85 % and 86 % for biomass and 68 % and 52 % for seed yield respectively.

Conclusions

This research showed in the field that AMF greatly improved the P and Zn nutrition, biomass production and seed yield of linseed growing in a soil disposed to long-fallow disorder. The level of mycorrhizal colonisation of plants suffering from long-fallow disorder can increase during the growing season resulting in improved plant growth and residual AMF inoculum in the soil, and thus it is important for growers to recognise the cause and not terminate a poor crop prematurely in order to sow another. Other positive management options to reduce long fallows and foster AMF include adoption of conservation tillage and opportunity cropping.     

Relation of fine root distribution to soil C in a Cunninghamia lanceolata plantation in subtropical China

Background and aims

Growth and distribution of fine roots closely depend on soil resource availability and affect soil C distribution in return. Understanding of relationships between fine root distribution and soil C can help to predict the contribution of fine root turnover to soil C accumulation.

Methods

A study was conducted in a subtropical Cunninghamia lanceolata plantation to assess the fine root mass density (FRMD), fine root C density (FRCD) of different fine root groups as well as their relations with soil C.

Results

The FRMD and FRCD of short-lived roots, dead roots and herb roots peaked in the 0–10 cm soil layer and decreased with soil depth, while FRMD, FRCD of long-lived roots peaked in the 10–20 cm soil layer. Soil C was positively related to FRMD and FRCD of total fine roots (across all three soil layers), dead roots (0–10 cm) and herb roots (10–20 cm) as well as FRCD of short-lived roots (20–40 cm) (P <0.05).

Conclusions

Soil C was mainly affected by herb roots in upper soil layers and by woody plant roots in deeper soil layers.     

Liebig’s law of the minimum applied to a greenhouse gas: alleviation of P-limitation reduces soil N2O emission

Background and aims

Emission of the greenhouse gas (GHG) nitrous oxide (N₂O) are strongly affected by nitrogen (N) fertilizer application rates. However, the role of other nutrients through stoichiometric relations with N has hardly been studied. We tested whether phosphorus (P) availability affects N₂O emission. We hypothesized that alleviation of plant P-limitation reduces N₂O emission through lowering soil mineral N concentrations.

Methods

We tested our hypothesis in a pot experiment with maize (Zea mays L.) growing on a P-limiting soil/sand mixture. Treatment factors included P and N fertilization and inoculation with Arbuscular Mycorrhizal Fungi (AMF; which can increase P uptake).

Results

Both N and P fertilization, as well as their interaction significantly (P?<?0.01) affected N₂O emission. Highest N₂O emissions (2.38 kg N₂O-N ha^?1) were measured at highest N application rates without P fertilization or AMF. At the highest N application rate, N₂O fluxes were lowest (0.71 kg N₂O-N ha^?1) with both P fertilization and AMF. The N₂O emission factors decreased with 50 % when P fertilization was applied.

Conclusions

Our results illustrate the importance of the judicious use of all nutrients to minimize N₂O emission, and thereby further underline the intimate link between sound agronomic practice and prudent soil GHG management.     

Conventional tillage versus cover crops in relation to carbon fixation in Mediterranean olive cultivation

Background and Aims

For croplands, controversy persists concerning the adequacy of the soil use and the management of environmental problems such as soil erosion and fertility in a context of climate change. In this study, we used the RothC model to evaluate the capacity of carbon fixation by the soil in a Mediterranean olive grove for two different scenarios: the land-use change from native vegetation (NV) to conventional tillage (T) in the olive grove, and for the change in soil management from conventional tillage to cover crop (CC).

Methods

In three experimental olive groves in Andalusia (S Spain) two soil-management systems were sampled: T and CC. Areas of NV adjacent to the grove were also sampled as indicative of the initial state of the soil without olive trees. We measured the aboveground biomass production of the cover and the clay content, bulk density, and soil organic carbon (SOC) for 0–5, 5–15 and 15–30 cm depth.

Results

The removal of NV to implement T resulted in a significantly loss of SOC that depended mainly on the relief of the terrain. However, the use of CC increased the SOC because of greater inputs (above-and belowground plant inputs) to the soil. The final concentration at each location was related to the carbon inputs and the clay content. The CC resulted in carbon storage during the first year of 4.02?±?1.65 Mg C ha^?1, and a total carbon fixation by the soil of 5.91?±?2.06 Mg C ha^?1.

Conclusion

The use of cover crops in Mediterranean olive groves proved to be a suitable strategy to increase the carbon storage into the soil and then to decrease the CO₂ concentration in the atmosphere.     

Restoration of high altitude forests in an area affected by a wildfire: Polylepis australis Bitt. seedlings performance after soil inoculation

Key message

Outplanted Polylepis australis seedling growth, survival and mycorrhizal response were not influenced by inoculation with soil from different vegetation types. Seedling inoculation would not be essential for reforestation practices.

Abstract

Polylepis forests are one of the most endangered high mountain ecosystems of South America and reforestation with native Polylepis species has been recommended. To determine whether native soil inoculation could help in reforestation success, a field trial was set up to evaluate the response of outplanted P. australis seedlings to the inoculation with soils from three vegetation types (a grassland, a mature forest and a degraded forest) and a sterile soil, used as control. We evaluated seedlings performance: growth and survival for 18 months, root/shoot ratio, phosphorous content and arbuscular mycorrhizal fungal (AMF) colonization. To interpret performance patterns we evaluated the colonization potential of the three inoculum soils and the changes of the AMF community composition of the seedlings rhizosphere in relation to inoculation treatment and season. Our main results showed no significant differences in seedlings survival and growth between treatments. The colonization potential of grassland and degraded forest soils was ~25 times greater than mature forest soil and specific spore density of some morphospecies varied with season. However, AMF spore community of seedlings rhizosphere became homogenized after outplanting and was similar between treatments after 12 months. Therefore, we conclude that soil inoculation is not essential for outplanted P. australis survival and increase in height, and thus all the tested soils could be used as inocula, including grassland soils which in practice are the easiest to collect.     

Effects of long-term fertilization on AM fungal community structure and Glomalin-related soil protein in the Loess Plateau of China

Arbuscular mycorrhizal fungi (AMF) are crucial for ecosystem functioning, and thus have potential use for sustainable agriculture. In this study, we investigated the impact of organic and mineral fertilizers on the AMF community composition and content of Glomalin-related soil protein (GRSP) in a field experimental station which was established in 1979, in the Loess Plateau of China. Roots and soils were sampled three times during the growing period of winter wheat in 2008. The treatments including: N (inorganic N), NP (inorganic N and P), SNP (straw, inorganic N and P), M (farmyard manure), MNP (farmyard manure, inorganic N and P), and CK (no fertilization). AMF communities of root and soil samples were analyzed using PCR-DGGE, cloning and sequencing techniques; and GRSP content was determined by Bradford assay. Our results indicated that spore density, GRSP, and AMF community varied significantly in soils of long-term fertilization plots at three different wheat growing stages. The effects of wheat growing period on AMF community in roots were much more evident than fertilization regimes. However, the diversity of AMF was low in our study field. Up to five AMF phylotypes appeared in each sample, with the overwhelming dominance of a Glomus-like phylotype affiliated to G. mosseae. GRSP content was correlated positively with organic carbon, total phosphorus, available phosphorus, soil pH, and spore densities, but correlated negatively with soil C/N (P?<?0.05). The results of our study highlight that the richness of AMF in Loess Plateau agricultural region is low, and long-term fertilization, especially amendments with manure and straw, has beneficial effects on accumulation of soil organic carbon, spore density, GRSP content, and AMF diversity. Host phenology, edaphic factors (influenced by long-term fertilization), and habitats interacted to affect the AMF community and agoecosystem functioning. Additionally, soil moisture and pH make a greater contribution than other determined soil parameters to the AMF community dynamics in such a special semi-arid agroecosystem where crops rely greatly on rainfall.     

Availability of residual fertilizer 15 N from forest floor and mineral soil to Douglas-fir seedlings ten years after fertilization

Background and aims

As low initial uptake and essentially zero later uptake limit efficacy of N fertilization for temperate conifers, we investigated factors limiting long-term tree uptake of residual ¹⁵?N-labeled fertilizer.

Methods

We used a pot bioassay to assess availability of ¹⁵?N from soil sampled 10 years after fertilization of a Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stand with ¹⁵?N-urea (200 kg N ha^?1). Douglas-fir seedlings were grown for 2 years in organic (designated LFH) and mineral soil (0–10 cm) layers reconstructed from control and fertilized plots; residual fertilizer N amounted to 10 % of LHF and 5 % of MIN N.

Results

Percentage recovery of residual ¹⁵?N in seedlings was not affected by the original season of fertilization (spring vs. fall), but differed by the source of ¹⁵?N excess. LFH was a better source of residual ¹⁵?N; 12.4 % of residual LFH ¹⁵?N was taken up by seedlings and 7.6 % transferred to soil, whereas mineral soil yielded only 8.3 % of residual ¹⁵?N to seedling uptake and 2.4 % to LFH. Extractable inorganic N was 2–3 orders of magnitude higher in fallow pots.

Conclusions

Ten-year residual fertilizer ¹⁵?N was clearly cycling between LFH and mineral soil and available to seedlings, indicating that other factors such as denitrification, leaching, and asynchrony of soil N mineralization and tree uptake limit long-term residual N fertilizer uptake in the field.     

Do arbuscular mycorrhizas or heterotrophic soil microbes contribute toward plant acquisition of a pulse of mineral phosphate?

Aims

We investigated the role of arbuscular mycorrhizal fungi (AMF) and heterotrophic soil microbes in the uptake of phosphorus (P) by Trifolium subterraneum from a pulse.

Methods

Plants were grown in sterilised pasture field soil with a realistic level of available P. There were five treatments, two of which involved AMF: 1) unsterilised field soil containing a community of AMF and heterotrophic organisms; 2) Scutellospora calospora inoculum (AMF); 3) microbes added as filtrate from the field soil; 4) microbes added as filtrate from the S. calospora inoculum; 5) no additions, i.e. sterilised field soil. After 11 weeks, plants were harvested: 1 day before (day 0), 1 day after (day 2) and 7 days after (day 8) the pulse of P (10 mg kg^?1).

Results

There was no difference among treatments in shoot and root dry weight, which increased from day 0 to day 8. At day 0, shoots and roots of plants in the colonised treatments had higher P and lower Mn concentrations. After the pulse, the rate of increase in P concentration in the shoots was slower for the colonised plants, and the root Mn concentration declined by up to 50 % by day 2.

Conclusions

Plants colonised by AMF had a lower rate of increase in shoot P concentration after a pulse, perhaps because intraradical hyphae accumulated P and thus reduced its transport to the shoots.     

Fertilization enhancing carbon sequestration as carbonate in arid cropland: assessments of long-term experiments in northern China

Aims

Soil inorganic carbon (SIC), primarily calcium carbonate, is a major reservoir of carbon in arid lands. This study was designed to test the hypothesis that carbonate might be enhanced in arid cropland, in association with soil fertility improvement via organic amendments.

Methods

We obtained two sets (65 each) of archived soil samples collected in the early and late 2000’s from three long-term experiment sites under wheat-corn cropping with various fertilization treatments in northern China. Soil organic (SOC), SIC and their Stable ¹³C compositions were determined over the range 0–100 cm.

Results

All sites showed an overall increase of SIC content in soil profiles over time. Particularly, fertilizations led to large SIC accumulation with a range of 101–202 g C m^?2 y^?1 in the 0–100 cm. Accumulation of pedogenic carbonate under fertilization varied from 60 to 179 g C m^?2 y^?1 in the 0–100 cm. Organic amendments significantly enhanced carbonate accumulation, in particular in the subsoil.

Conclusions

More carbon was sequestrated in the form of carbonate than as SOC in the arid cropland in northern China. Increasing SOC stock through long-term straw incorporation and manure application in the arid and semi-arid regions also enhanced carbonate accumulation in soil profiles.     

Glomeromycotan mycorrhizal fungi from tropical Australia III. Measuring diversity in natural and disturbed habitats

Aims and Background

The aim was to investigate the diversity and distribution of Glomeromycotan fungi forming arbuscular mycorrhizal associations (AMF) in undisturbed and disturbed habitats in the vicinity of Kakadu National Park in tropical Australia. This is a tropical region with a 7–9 month dry season and a monsoonal wet season. Complimentary methods of fungus detection were used to investigate the diversity and relative dominance of AMF at a regional scale.

Methods

Soils were sampled from 32 sites, representing eucalypt savanna woodlands, wetlands, sandstone escarpment, rainforest, and disturbed mine waste rock dumps (overburden or spoil). Populations of AMF were identified and quantified using spores from soil. Morphology patterns of fungi colonising bait plant roots were examined and isolates were obtained by four complimentary pot-culturing methods.

Results

Different methods of detecting fungi produced different answers about which AMF were most important in the tested soils. In particular, spore surveys apparently underestimated the importance of Glomus species and overestimated the activity of Acaulospora species with numerous small spores, while calculated spore biovolumes overestimated the importance of Scutellospora and Gigaspora species with large spores, relative to inoculum levels of these fungus categories measured in bioassays. Spore surveys revealed 15 species of fungi and 8 additional fungi were recovered from the same soil samples using pot-culture isolation methods. Pot-cultures were especially important for detecting Glomus species that had high inoculum levels, but rarely produced spores in soils. Spores of AMF increased in abundance as vegetation developed in mine habitats reaching a peak that was higher than in undisturbed plant communities. Spore numbers (but not biovolumes) were well correlated with bioassay measurements of inoculum levels.

Conclusions

Most AMF species were widespread, but several were restricted to disturbed habitats or wetland soils. Undisturbed sites had a substantially higher diversity of AMF than partially vegetated mine waste rock dumps. It is recommended that AMF population surveys should not be based entirely on spore occurrence data, to avoid overlooking important fungi that sporulate infrequently. These fungi could be detected by bioassays or pot culture isolation from soil. Major variations in the detectability of AMF correspond to different life history strategies and can mask variations in their abundance.     

Assessment of carbon sustainability under different tillage systems in a double rice cropping system in Southern China

Purpose

Adoption of the carbon (C)-friendly and cleaner technology is an effective solution to offset some of the anthropogenic emissions. Conservation tillage is widely considered as an important sustainable technology and for the development of conservation agriculture (CA). Thus, the objective of this study was to assess the C sustainability of different tillage systems in a double rice (Oryza sativa L.) cropping system in southern China.

Methods

The experiment was established with no-till (NT), rotary tillage (RT), and conventional tillage (CT) treatments since 2005. Emission of greenhouse gasses (GHG), C footprint (CF), and ecosystem service through C sequestration in different tillage systems were compared.

Result and discussion

Emission of GHG from agricultural inputs (Mg CO₂-eq ha^?1 year^?1) ranged from 1.81 to 1.97 for the early rice, 1.82 to 1.98 for the late rice, and 3.63 to 3.95 for the whole growing season, respectively. The CF (kg CO₂-eq kg^?1 of rice year^?1) in the whole growing seasons were 1.27, 1.85, and 1.40 [excluding soil organic carbon (SOC) storage] and 0.54, 1.20, and 0.72 (including SOC storage) for NT, RT, and CT, respectively. The value of ecosystem services on C sequestration for the whole growing seasons ranged from ¥3,353 to 4,948 ha^?1 year^?1 and followed the order of NT > CT > RT. The C sustainability under NT was better than that under RT for the late, but reversed for the early rice. However, NT system had better C sustainability for the whole cropping system compared with CT.

Conclusions

Therefore, NT is a preferred technology to reduce GHG emissions, increase ecosystem service functions of C sequestration, and improve C sustainability in a double rice cropping region of Southern China.     

The effect of soil water status on fertiliser, topsoil and subsoil phosphorus utilisation by wheat

Background and aims

Crop phosphorus (P) content is controlled by P uptake from both banded P fertiliser and from P throughout the soil profile. These P supply factors are in turn controlled by soil, climatic and plant factors. The aim of this experiment was to measure the contribution of fertiliser, topsoil and subsoil P to wheat plants under wet and dry growing season conditions.

Methods

An isotopic tracer technique was used to measure P uptake from fertiliser at seven agricultural field sites under wet and dry growing season conditions. At three of these sites a dual isotopic technique was used to distinguish between wheat uptake of P from fertiliser, topsoil (0–15 cm) and subsoil (below 15 cm).

Results

The amount of P fertiliser used by wheat was in the order of 3–30% of the P applied and increased with increasing rainfall. Topsoil P was the most important P source, but when sufficient P was present in the subsoil, P fertiliser addition stimulated the use of subsoil P.

Conclusions

Most crop P uptake was from the topsoil, however P fertiliser banded below the seed increased plant P uptake and stimulated the use of subsoil P in one soil type in a decile 7 (above average rainfall) growing season.     

N-P fertilization did not reduce AMF abundance or diversity but alter AMF composition in an alpine grassland infested by a root hemiparasitic plant

Fertilization has been shown to have suppressive effects on arbuscular mycorrhizal fungi (AMF) and root hemiparasites separately in numerous investigations, but its effects on AMF in the presence of root hemiparasites remain untested. In view of the contrasting nutritional effects of AMF and root hemiparasites on host plants, we tested the hypothesis that fertilization may not show strong suppressive effects on AMF when a plant community was infested by abundant hemiparasitic plants. Plants and soil samples were collected from experimental field plots in Bayanbulak Grassland, where N and P fertilizers had been applied for three continuous years for control against a spreading root hemiparasite, Pedicularis kansuensis. Shoot and root biomass of each plant functional group were determined. Root AMF colonization levels, soil spore abundance, and extraradical hyphae length density were measured for three soil depths (0-10 cm, 10-20 cm, 20-30 cm). Partial 18S rRNA gene sequencing was used to detect AMF diversity and community composition. In addition, we analyzed the relationship between relative abundance of different AMF genera and environmental factors using Spearman's correlation method. In contrast to suppressive effects reported by many previous studies, fertilization showed no significant effects on AMF root colonization or AMF species diversity in the soil. Instead, a marked increase in soil spore abundance and extraradical hyphae length density were observed. However, fertilization altered relative abundance and AMF composition in the soil. Our results support the hypothesis that fertilization does not significantly influence the abundance and diversity of AMF in a plant community infested by P. kansuensis.     

Increased plant density of winter wheat can enhance nitrogen–uptake from deep soil

Background and Aims

Increased plant density improves grain yield and nitrogen (N)–use efficiency in winter wheat (Triticum aestivum L.) by increasing the root length density (RLD) in the soil and aboveground N–uptake (AGN) at maturity. However, how the root distribution and N–uptake at different soil depths is affected by plant density is largely unknown.

Methods

A 2–year field study using the winter wheat cultivar Tainong 18 was conducted by injecting ¹⁵?N–labeled urea into soil at depths of 0.2, 0.6, and 1.0 m under four plant densities of 135 m^?2, 270 m^?2,405 m^?2, and 540 m^?2.

Results

We observed significant RLD and ¹⁵?N–uptake increases at each soil depth as the plant density increased from 135 to 405 m^?2. ¹⁵?N–uptake increased with plant density as the soil depth increased, although the corresponding RLD value fell with depth. The ¹⁵?N–uptake at each soil depth was positively related to the RLD at the same depth. The total AGN was positively related to RLD in deep soil, especially at 0.8–1.2 m.

Conclusions

Increasing the plant density from 135 m^?2 to the optimum increases AGN primarily by increasing the RLD in deep soil and therefore increasing the plant density of winter wheat can be used to efficiently recover N leached to deep soil. Moreover, the total root numbers per unit area and RLD still increased at supraoptimal density while shoot number and N uptake stagnated.