Effects of weed control and fertilization at early establishment on tree nitrogen and water use in an exotic F1 hybrid pine of subtropical Australia

Purpose

We investigated the effects of weed control and fertilization at early establishment on foliar stable carbon (δ¹³C) and nitrogen (N) isotope (δ¹⁵N) compositions, foliar N concentration, tree growth and biomass, relative weed cover and other physiological traits in a 2-year old F₁ hybrid (Pinus elliottii var. elliottii (Engelm) × Pinus caribaea var. hondurensis (Barr. ex Golf.)) plantation grown on a yellow earth in southeast Queensland of subtropical Australia.

Materials and methods

Treatments included routine weed control, luxury weed control, intermediate weed control, mechanical weed control, nil weed control, and routine and luxury fertilization in a randomised complete block design. Initial soil nutrition and soil fertility parameters included (hot water extractable organic carbon (C) and total nitrogen (N), total C and N, C/N ratio, labile N pools (nitrate (NO₃ ^?) and ammonium (NH₄ ⁺)), extractable potassium (K⁺)), soil δ¹⁵N and δ¹³C. Relative weed cover, foliar N concentrations, tree growth rate and physiological parameters including photosynthesis, stomatal conductance, photosynthetic nitrogen use efficiency, foliar δ¹⁵N and foliar δ¹³C were also measured at early establishment.

Results and discussion

Foliar N concentration at 1.25 years was significantly different amongst the weed control treatments and was negatively correlated to the relative weed cover at 1.1 years. Foliar N concentration was also positively correlated to foliar δ¹⁵N and foliar δ¹³C, tree height, height growth rates and tree biomass. Foliar δ¹⁵N was negatively correlated to the relative weed cover at 0.8 and 1.1 years. The physiological measurements indicated that luxury fertilization and increasing weed competition on these soils decreased leaf xylem pressure potential (Ψ_xpp) when compared to the other treatments.

Conclusions

These results indicate how increasing N resources and weed competition have implications for tree N and water use at establishment in F₁ hybrid plantations of southeast Queensland, Australia. These results suggest the desirability of weed control, in the inter-planting row, in the first year to maximise site N and water resources available for seedling growth. It also showed the need to avoid over-fertilisation, which interfered with the balance between available N and water on these soils.     

Assessing the potential of using biochar in mine rehabilitation under elevated atmospheric CO<Subscript>2</Subscript> concentration

Purpose

Re-establishment of soil nitrogen (N) capital is a priority in mine rehabilitation. We aimed to evaluate the effects of biochar addition on improving mine spoil N pools and the influence of elevated CO₂ concentration on mine rehabilitation.

Materials and methods

We assessed the effects of pinewood biochar, produced at three temperatures (650, 750 and 850 °C, referred as B₆₅₀, B₇₅₀ and B₈₅₀, respectively), on mine spoil total N concentrations with five different plant species, including a tree species (Eucalyptus crebra), N-fixing shrubs (Acacia floribunda and Allocasuarina littoralis) and C₃ and C₄ grasses (Austrodanthonia tenuior and Themeda australis) incubated at ambient (400 μL L^?1) and elevated (700 μL L^?1) atmospheric CO₂ concentrations, as well as the effects of elevated CO₂ on mine rehabilitation.

Results and discussion

Soil total N significantly improved following biochar incorporation under all plant species (P < 0.05) except for T. Australis. E. crebra had the highest soil total N (0.197%, 0.198% and 0.212% for B₆₅₀, B₇₅₀ and B₈₅₀, respectively). Different from the negligible influence of elevated CO₂ on soil properties under the grasses and the N-fixing shrubs, elevated CO₂ significantly increased soil water and hot water extractable organic C (WEOC and HWEOC, respectively) and decreased total C under E. crebra, indicating that the nutrient demands were not met.

Conclusions

Biochar addition showed the potential in mine rehabilitation in terms of improving soil N pool, especially with E. crebra. However, it would be more difficulty to rehabilitate mine spoils in future with the rising atmospheric CO₂ concentration.

     

Increases in soil CO<Subscript>2</Subscript> and N<Subscript>2</Subscript>O emissions with warming depend on plant species in restored alpine meadows of Wugong Mountain,China

Purpose

Ecosystem restorations can impact carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions which are important greenhouse gasses. Alpine meadows are degraded worldwide, but restorations are increasing. Because their soils represent large carbon (C) and nitrogen (N) pools, they may produce significant amounts of CO₂ and N₂O depending on the plant species used in restorations. In addition, warming and N deposition may impact soil CO₂ and N₂O emissions from restored meadows.

Materials and methods

We collected soils from degraded meadows and plots restored using three different plant species at Wugong Mountain (Jiangxi, China). We measured CO₂ and N₂O emissions when soils were incubated at different temperatures (15, 25 or 35 °C) and levels of N addition (control vs. 4 g m^?2) to understand their responses to warming and N deposition.

Results and discussion

Dissolved organic C was higher in restored plots (especially with Fimbristylis dichotoma) compared to non-restored bare soils, and their soil inorganic N was lower. CO₂ emission rates were increased by vegetation restorations, decreased by N deposition, and increased by warming. CO₂ emission rates were similar for the three grass species at 15 and 25 °C, but they were lower with Miscanthus floridulus at 35 °C. Soils from F. dichotoma and Carex chinensis plots had higher N₂O emissions than degraded or M. floridulus plots, especially at 25 °C.

Conclusions

These results show that the effects of restorations on soil greenhouse gas emissions depended on plant species. In addition, these differences varied with temperature suggesting that future climate should be considered when choosing plant species in restorations to predict soil CO₂ and N₂O emissions and global warming potential.

     

Changes in CH<Subscript>4</Subscript> production during different stages of litter decomposition under inundation and N addition

Purpose

Our aim was to examine linkages between mass loss, chemical transformation and CH₄ production during decomposition of leaf litters submerged under water. We hypothesised that (i) labile leaf litters would fuel a rapid, high rate of methane (CH₄) production and that recalcitrant litters would fuel long-lasting but lower emissions, (ii) leaf litters experiencing a greater alteration to chemical properties would stimulate increased CH₄ production and (iii) nitrogen (N) addition would increase CH₄ emissions.

Materials and methods

Litters from six plant species were collected from a riparian ecosystem adjacent to Wyaralong Dam, located in Queensland, Australia, i.e., Lophostemon confertus, Cynodon dactylon, Heteropogon contortus, Chamaecrista rotundifolia, Chrysocephalum apiculatum and Imperata cylindrica. We evaluated the rate of mass loss and CH₄ emissions for 122 days of incubation in inundated microcosms with and without N addition. We quantified the chemical changes in the decomposing litters with ¹³ C-cross polarization and magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectrum.

Results and discussion

The inundation treatment of plant litters significantly affected decomposition rates. All litters decomposed in either inundated or aerobic microcosms were quite distinct with regard to the NMR spectra of their initial litters. N addition altered the NMR spectra under both inundation and aerobic conditions. The N treatment only marginally influenced the decomposition rates of I. cylindrica and C. apiculatum litters. The diurnal patterns of CH₄ production in the H. contortus, C. rotundifolia and C. apiculatum litters under inundation incubation could be expressed as one-humped curves, with the peak value dependent on litter species and N treatment. N addition stimulated CH₄ emission by C. rotundifolia and C. apiculatum litters and inhibited CH₄ emission from microcosms containing the litters of the three gramineous species, i.e., I. cylindrica, C. dactylon and H. contortus.

Conclusions

Our results provide evidence that labile leaf litters could fuel a rapid, high rate of CH₄ production and that recalcitrant litters fuelled a lower CH₄ emission. We did not find that leaf litters with altered chemical properties stimulated increased CH₄ production. We also found that N addition was able to increase CH₄ emissions, but this effect was dependent on the litter species.

     

Contrasting response of two grassland soils to N addition and moisture levels: N<Subscript>2</Subscript>O emission and functional gene abundance

Purpose

Nitrification and denitrification processes dominate nitrous oxide (N₂O) emission in grassland ecosystems, but their relative contribution as well as the abiotic factors are still not well understood.

Materials and methods

Two grassland soils from Duolun in Inner Mongolia, China, and Canterbury in New Zealand were used to quantitatively compare N₂O production and the abundance of bacterial and archaeal amoA, denitrifying nirK and nirS genes in response to N additions (0 and 100 μg NH₄ ⁺–N g^?1 dry soil) and two soil moisture levels (40 and 80 % water holding capacity) using microcosms.

Results and discussion

Soil moisture rather than N availability significantly increased the nitrification rate in the Duolun soil but not in the Canterbury soil. Moreover, N addition promoted denitrification enzyme activities in the Canterbury soil but not in the Duolun soil. The abundance of bacterial and archaeal amoA genes significantly increased as soil moisture increased in the Duolun soil, whereas in the Canterbury soil, only the abundance of bacterial amoA gene increased. The increase in N₂O flux induced by N addition was significantly greater in the Duolun soil than in the Canterbury soil, suggesting that nitrification may have a dominant role in N₂O emission for the Duolun soil, while denitrification for the Canterbury soil.

Conclusions

Microbial processes controlling N₂O emission differed in grassland soils, thus providing important baseline data in terms of global change.

     

Nitrogen transformation rates and N<Subscript>2</Subscript>O producing pathways in two pasture soils

Purpose

Better understanding of N transformations and the regulation of N₂O-related N transformation processes in pasture soil contributes significantly to N fertilizer management and development of targeted mitigation strategies.

Materials and methods

¹⁵N tracer technique combined with acetylene (C₂H₂) method was used to measure gross N transformation rates and to distinguish pathways of N₂O production in two Australian pasture soils. The soils were collected from Glenormiston (GN) and Terang (TR), Victoria, Australia, and incubated at a soil moisture content of 60% water-filled pore space (WFPS) and at temperature of 20 °C.

Results and discussion

Two tested pasture soils were characterized by high mineralization and immobilization turnover. The average gross N nitrification rate (n_tot) was 7.28 mg N kg^?1 day^?1 in TR soil () and 5.79 mg N kg^?1 day^?1 in GN soil. Heterotrophic nitrification rates (n_h), which accounting for 50.8 and 41.9% of n_tot, and 23.4 and 30.1% of N₂O emissions in GN and TR soils, respectively, played a role similar with autotrophic nitrification in total nitrification and N₂O emission. Denitrification rates in two pasture soils were as low as 0.003–0.004 mg N kg^?1 day^?1 under selected conditions but contributed more than 30% of N₂O emissions.

Conclusions

Results demonstrated that two tested pasture soils were characterized by fast N transformation rates of mineralization, immobilization, and nitrification. Heterotrophic nitrification could be an important NO₃^?–N production transformation process in studied pasture soils. Except for autotrophic nitrification, roles of heterotrophic nitrification and denitrification in N₂O emission in two pasture soils should be considered when developing mitigation strategies.

     

Interactive effects of biochar addition and elevated carbon dioxide concentration on soil carbon and nitrogen pools in mine spoil

Purpose

This study aimed to assess the effects of biochar on improving nitrogen (N) pools in mine spoil and examine the effects of elevated CO₂ on soil carbon (C) storage.

Materials and methods

The experiment consisted of three plant species (Austrostipa ramossissima, Dichelachne micrantha, and Lomandra longifolia) planted in the N-poor mine spoil with application of biochar produced at three temperatures (650, 750, and 850 °C) under both ambient (400 μL L^?1) and elevated (700 μL L^?1) CO₂. We assessed mine spoil total C and N concentrations and stable C and N isotope compositions (δ¹³C and δ¹⁵N), as well as hot water extractable organic C (HWEOC) and total N (HWETN) concentrations.

Results and discussion

Soil total N significantly increased following biochar application across all species. Elevated CO₂ induced soil C loss for A. ramossissima and D. micrantha without biochar application and D. micrantha with the application of biochar produced at 750 °C. In contrast, elevated CO₂ exhibited no significant effect on soil total C for A. littoralis, D. micrantha, or L. longifolia under any other biochar treatments.

Conclusions

Biochar application is a promising means to improve N retention and thus, reduce environmentally harmful N fluxes in mine spoil. However, elevated CO₂ exhibited no significant effects on increasing soil total C, which indicated that mine spoil has limited potential to store rising atmospheric CO₂.

     

The foliar spray of <Emphasis Type="Italic">Rhodopseudomonas palustris</Emphasis> grown under <Emphasis Type="Italic">Stevia</Emphasis> residue extract promotes plant growth via changing soil microbial community

Purpose

The extract of Stevia residue is an ideal substitute for cultivation of the purple nonsulfur bacterium, like Rhodopseudomonas palustris (R. palustris). But the influence of R. palustris grown under residue extract on its downstream application is still not well-characterized. The objective of this study was to assess the effect of foliar spray of R. palustris grown under Stevia residue extract on the plant growth and soil microbial properties.

Materials and methods

A pot experiment was carried out under the greenhouse condition, consisting of four treatments varying in the sprayed substances: sterilized water (control), R. palustris grown under the chemical medium supplemented with L-tryptophan (SyT), R. palustris grown under Stevia residue extract supplemented with L-tryptophan (ExT), and R. palustris grown under Stevia residue extract supplemented with NH₄Cl (ExT). The net photosynthesis rate of the uppermost leaves was measured with a portable photosynthesis system. Soil microbial activity was analyzed by microcalorimetry. Soil bacterial community components were determined by real-time quantitative PCR (qPCR) and high-throughput sequencing techniques.

Results and discussion

Compared with SyT, the R. palustris grown under Stevia residue extract not only improved the plant biomass and the net photosynthetic rate to a large extent, but also increased soil microbial metabolic activity and altered community compositions as well. The treatments receiving R. palustris, especially ExT and ExN, increased the relative abundances of some functional guilds involved in C turnover and nutrient cycling in soil, including Acidobacteria, Actinobacteria, Proteobacteria, Gemmatimonadaetes, Nitrospirae, and Planctomycetes.

Conclusions

R. palustris grown under the Stevia residue extract showed advantages over that under the chemical medium on both plant growth and soil microbial properties. One of the possible reasons could result from the increases in microbial activity and several bacterial keystone guilds involved into C and nutrient cycling, both of which potentially contribute to the improved plant growth. The results would be conducive to the downstream application of R. palustris in an economical way.

     

Ecological effects of rice-duck integrated farming on soil fertility and weed and pest control

Purpose

This paper aims to study the ecological effects of rice-duck integrated farming on soil fertility and weed and pest control.

Materials and methods

A field experiment was carried out in the suburb of Shanghai in 2014, which included a rice-duck integrated treatment and non-duck treatment (CK) under organic management. Each treatment was in triplicate, and the experiment included six plots in total, with each plot 667 m² in area.

Results and discussion

(1) The number of weeds in the plots with the duck treatment was significantly lower than that with CK (p?<?0.01). (2) The incidence of stem borers (Chilo suppressalis) with the duck treatment was significantly lower than that with CK (p?<?0.05). The incidences of rice leaf rollers (Cnaphalocrocis medinalis), rice sheath blight (Rhizoctonia solani), and planthoppers with the duck treatment were extremely significantly lower than those with CK (p?<?0.01). (3) The contents of NH₄ ⁺-N, alkali-hydrolyzable N, available P, and available K in the soils with the duck treatment were higher than those with CK, and the activities of urease, phosphatase, sucrase, and catalase in the soils with the duck treatment were also much higher than those with CK. The grain yield with the duck treatment was 1.9 times that with CK. (4) The number of soil nematodes with the duck treatment was significantly higher than that with CK in the late rice growing stage (p?<?0.01).

Conclusions

Raising ducks in the paddy fields not only showed a potential of controlling weed hazards and reducing rice pests and diseases but also raised soil fertility, improved soil biodiversity, and increased grain yield effectively. Implementing the rice-duck integrated farming could highly reduce the amount of pesticides and herbicides and was beneficial to develop the organic rice farming in the suburbs of Shanghai, Southeast China.

     

Combined biochar and nitrogen fertilizer reduces soil acidity and promotes nutrient use efficiency by soybean crop

Purpose

Soil acidification is universal in soybean-growing fields. The aim of our research was to evaluate the effects of soil additives (N fertilizers and biochar) on crop performance and soil quality with specific emphasis on ameliorating soil acidity.

Materials and methods

Four nitrogen treatments were applied as follows: no nitrogen (N0), urea (N1), potassium nitrate (N2), and ammonium sulfate (N3), each providing 30 kg N ha^?1. Half plot area of the N1, N2, and N3 treatments was also treated with biochar (19.5 t ha^?1) to form N-biochar treatments (N1C, N2C, N3C). Both bulk and rhizosphere soils were sampled separately for the following analyses: pH, exchangeable base cations (EBC), exchangeable acidity (EA), total inorganic N (IN), total N (TN), and microbial phospholipid fatty acids (PLFAs). Soybean biomass and nutrient contents were also determined. Correlation analysis was applied to analyze the relationships between soil chemical properties and soybean plant parameters.

Results and discussion

With N-biochar additions (N1C, N2C, N3C), soil chemical properties changed as follows: pH increased by 0.6–1.2 units, EBC, IN, and TN increased by 175–419, 38.5–54.7, and 136–452 mg kg^?1, respectively, and PLFAs increased by 23.6–40.9 nmol g^?1 compared to the N0 in the rhizosphere. Microbial PLFAs had positive correlations with soil pH; EBC; exchangeable K, Ca, Na, and Mg; TN; IN; NH₄ ⁺; and NO₃ ^? (r?=?0.66–0.84, p?<?0.01). There were negative correlations between PLFAs and EA or exchangeable Al (r?=??0.64, ?0.66, p?<?0.01), which indicated that the additives increased microbial biomass by providing a suitable environment with less acid stress and more nutrients. The additives increased soil NH₄ ⁺ and NO₃ ^? by promoting soil organic N mineralization and reducing NH₄ ⁺ and NO₃ ^? leaching. Moreover, the soybean seed biomass and the nutrient contents in seeds increased with N-biochar additions, especially in the N3C treatment.

Conclusions

N-biochar additions were effective in ameliorating soil acidity, which improved the microenvironment for more microbial survival. N-biochars influenced N transformations at the plant–soil interface by increasing organic N mineralization, reducing N leaching, and promoting N uptake by soybeans. The soil additive ammonium and biochar (N3C) were best in promoting soybean growth.

     

Response of CaCl<Subscript>2</Subscript>-extractable heavy metals,polychlorinated biphenyls,and microbial communities to biochar amendment in naturally contaminated soils

Purpose

Biochar can be used to reduce the bioavailability and leachability of heavy metals, as well as organic pollutants in soils through adsorption and other physicochemical reactions. The objective of the study was to determine the response of microbial communities to biochar amendment and its influence on heavy metal mobility and PCBs (PCB52, 44, 101, 149, 118, 153, 138, 180, 170, and 194) concentration in application of biochar as soil amendment.

Materials and methods

A pot (macrocosm) incubation experiment was carried out with different biochar amendment (0, 3, and 6 % w/w) for 112 days. The CaCl₂-extractable concentration of metals, microbial activities, and bacterial community were evaluated during the incubation period.

Results and discussion

The concentrations of 0.01 M CaCl₂-extractable metals decreased (p?>?0.05) by 12.7 and 20.5 % for Cu, 5.0 and 15.6 % for Zn, 0.2 and 0.5 % for Pb, and 1.1 and 8.9 % for Cd, in the presence of 3 and 6 % of biochar, respectively, following 1 day of incubation. Meanwhile, the total PCB concentrations decreased from 1.23 mg kg^?1 at 1 day to 0.24 mg kg^?1 at 112 days after 6 % biochar addition, representing a more than 60 % decrease relative to untreated soil. It was also found out that biochar addition increased the biological activities of catalase, phosphatase, and urease activity as compared with the controls at the same time point. Importantly, the Shannon diversity index of bacteria in control soils was 3.41, whereas it was 3.69 and 3.88 in soils treated with 3 and 6 % biochar soil. In particular, an increase in the number of populations with the putative ability to absorb PCB was noted in the biochar-amended soils.

Conclusions

The application of biochar to contaminated soils decreased the concentrations of heavy metals and PCBs. Application of biochar stimulated Proteobacteria and Bacteroides, which may function to absorb soil PCB and alleviate their toxicity.

     

High Zn concentration does not impair biomass,cutting radial growth,and photosynthetic activity traits in <Emphasis Type="Italic">Populus alba</Emphasis> L.

Purpose

Evaluate the efficiency of Populus alba clone Villafranca in the uptake and translocation of Zn from contaminated soils.

Materials and methods

The effects of 48 days of zinc treatment (Zn _t ) on the growth and the photosynthetic activities of P. alba L. clone Villafranca were studied using ZnSO₄ (375 ppm per unit of soil dry weight) added in sand and peat moss substrate at the beginning of the treatment (T ₀) and again after 30 days (T ₁) in order to reach a target Zn concentration of 375 ppm at T ₀ and 750 ppm at T ₁ per unit of soil dry weight.

Results and discussion

Zn uptake in the different organs was analyzed after 30 (T ₁) and 48 days (T ₂) from the beginning of treatment, showing the following order: root ? leaves ≥ woody cutting = stem. The leaf area increased by 12 % in comparison to control plants at the end of second treatment (48 days). Cutting radial growth showed a high synchronicity in the growth rate fluctuation among control and Zn _t plants, but a higher increase in radial diameter of Zn _t cutting was observed starting from day 38 (after 8 days of second Zn _t ) reaching after 48 days 38 % higher than control plants.

Conclusions

Although our data of leaf Zn concentration were in the range usually reported as toxic for plants, Villafranca clone in Zn _t substrate were unaffected in terms of net CO₂ assimilation and stomatal conductance to water vapor.

     

Biochar nutrient availability rather than its water holding capacity governs the growth of both C3 and C4 plants

Purpose

Biochar has been suggested as a soil conditioner to improve soil fertility and crop productivity while simultaneously mitigate global climate change by storing carbon in the soil. This study investigated the effect of pine (Pinus radiata) biochar application on soil water availability, nitrogen (N) and carbon (C) pools and growth of C3 and C4 plants.

Materials and methods

In a glasshouse pot trial, a pine biochar (untreated) and nutrient-enriched pine biochar were applied to a market garden soil with C3 (Spinacia oleracea L.) and C4 (Amaranthus paniculatus L.) plants at rates of 0, 1.0, 2.0, and 4.0 % (w/w). Plant biomass, soil pH, moisture content, water holding capacity (WHC), hot water extractable organic C (HWEOC), and total N (HWETN), total C and N, and their isotope compositions (δ ¹³C and δ ¹⁵N) of soils and plants were measured at the end of the experimentation.

Results and discussion

The soil moisture content increased while plant biomass decreased with increasing untreated biochar application rates. The addition of nutrient-enriched biochar significantly improved plant biomass in comparison to the untreated biochar addition at most application rates. Biochar application also increased the levels of labile organic C and N pools as indicated by HWEOC and HWETN.

Conclusions

The results suggested that the addition of pine biochar significantly improved soil water availability but not plant growth. The application of nutrient-enriched pine biochar demonstrated that the growth of C3 and C4 plants was governed by biochar nutrient availability rather than its water holding capacity under the pot trial condition.

     

Effect of <Emphasis Type="Italic">Bacillus subtilis</Emphasis> QST713 and <Emphasis Type="Italic">Trichoderma asperellum</Emphasis> T34 on P uptake by wheat and how it is modulated by soil properties

Purpose

The effect on P uptake by plants after inoculation with P-mobilizing microorganisms may be modulated by soil properties, including natural microbiota. However, to put this theory into practical use, research is needed to shed new light on the soil factors which affect the capability of improving P nutrition in plants. The aim of this study was to assess how two P-mobilizing microorganisms, Trichoderma asperellum T34 and Bacillus subtilis QST713, influence P uptake by wheat plants in different soils; this will allow us to identify the soil properties which affect the efficiency of P nutrition in plants.

Materials and methods

In a completely randomized experiment, wheat was grown in pots in a growing chamber in soils with Olsen P values ranging from 4.8 to 8.7 mg kg^?1. The plants were inoculated with three treatments: T34, B. subtilis, and a non-inoculated control.

Results and discussion

Overall, B. subtilis was more effective in increasing plant P uptake and in mobilizing soil P (measured as Olsen P values) than T34. In some soils, B. subtilis was the only treatment which increased Olsen P in the rhizosphere after cultivation. However, the effect of both microorganisms differed depending on the soil. For B. subtilis, phytase hydrolysable P, Olsen P, carbonates, the Fe_ca/Fe_cbd ratio, and citrate-soluble P accounted for 92% of the variation in P uptake in inoculated plants (compared with the non-inoculated control). Most of these soil properties also accounted for 87% of the variation in the levels of shoot dry matter (DM) in B. subtilis-inoculated plants compared with shoot DM in the control plants. In addition, Olsen P, the Fe_ca/Fe_cbd ratio, and phytase hydrolysable P in the NaOH extracts accounted for 82 and 74% of the variation in the effect of T34 on P uptake and shoot DM, respectively. Overall, the lower the initial Olsen P in the soil, the higher the P uptake caused by microorganisms.

Conclusions

The initial availability of P and organic P in soil, in addition to other properties affecting P dynamics in the soil, may explain the triggering and efficiency of the P-mobilizing mechanisms in microorganisms. These are crucial in explaining the potential benefits to crops and, as a result, their practical use as a bio-fertilizer.

     

The potential of using alternative pastures,forage crops and gibberellic acid to mitigate nitrous oxide emissions

Purpose

In grazed pastures, nitrous oxide (N₂O), a powerful greenhouse gas and an ozone depletion substance, is mostly emitted from animal excreta, particularly animal urine-N returned to the soil during grazing. We conducted a series of four field lysimeter and plot experiments to assess the potential of using gibberellic acid (GA) and/or alternative pastures or forage crops to mitigate N₂O emissions from outdoor dairy farming systems.

Materials and methods

Pasture and forage plants assessed in the experiments included Italian ryegrass (Lolium multiflorum L.), lucerne (Medicago sativa L.), diverse pastures (including plantain (Plantago lanceolata L.), chicory (Cichorium intybus L.), perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.)), fodder beet (Beta vulgaris L.), kale (Brassica oleracea L.), as well as the standard perennial ryegrass and white clover (RG/WC) pastures. N₂O was determined using a standard static chamber method in the field either on top of lysimeters or field plots.

Results and discussion

The results showed that the application of GA to urine-treated lysimeters with Italian ryegrass, lucerne or RG/WC pastures did not result in lower N₂O emissions. However, the use of diverse pastures which included plantain with a lower urine-N loading rate at about 500 kg N ha^?1 significantly decreased N₂O emissions by 46 % compared with standard RG/WC with a urine-N loading rate at 700 kg N ha^?1. However, when urine-N was applied at the same rates (at 500 or 700 kg N ha^?1), the N₂O emissions were similar between the diverse and the standard RG/WC pastures. This would indicate that it is the N-loading rate in the urine from the different pastures that determines the N₂O emissions from different pastures or forages, rather than the plants per se. The N₂O emissions from cow urine from fodder beet were 39 % lower than from kale with the same urine-N application rate (300 kg N ha^?1).

Conclusions

These results suggest that N₂O emissions can potentially be reduced by incorporating diverse pastures and fodder beet into the grazed pasture farm system. Further studies on possible mechanisms for the lower N₂O emissions from the different pastures or forages would be useful.

     

Predicting soil loss in central and south Italy with a single USLE-MM model

Purpose

The USLE-MM estimates event normalized plot soil loss, A_e,N, by an erosivity term given by the runoff coefficient, Q_R, times the single-storm erosion index, EI₃₀, raised to an exponent b₁?>?1. This modeling scheme is based on an expected power relationship, with an exponent greater than one, between event sediment concentration, C_e, and the EI₃₀/P_e (P_e = rainfall depth) term. In this investigation, carried out at the three experimental sites of Bagnara, Masse, and Sparacia, in Italy; the soundness of the USLE-MM scheme was tested.

Materials and methods

A total of 1192 (A_e,N, Q_REI₃₀) data pairs were used to parameterize the model both locally and considering all sites simultaneously. The performances of the fitted models were established by considering all erosive events and also by distinguishing between events of different severity.

Results and discussion

The b₁ exponent varied widely among the three sites (1.05–1.44) but using a common exponent (1.18) for these sites was possible. The A_e,N prediction accuracy increased in the passage from the smallest erosion events (A_e,N?≤?1 Mg ha^?1, median error =?3.35) to the largest ones (A_e,N?>?10 Mg ha^?1, median error =?1.72). The Q_REI₃₀ term was found to be usable to predict both A_e,N and the expected maximum uncertainty of this prediction. Soil erodibility was found to be mainly controlled by the largest erosion events.

Conclusions

Development of a single USLE-MM model appears possible. Sampling other sites is advisable to develop a single USLE-MM model for a general use.

     

Impacts of continuous excessive fertilization on soil potential nitrification activity and nitrifying microbial community dynamics in greenhouse system

Purpose

Sampling and analysis of greenhouse soils were conducted in Shouguang, China, to study continuous excessive fertilization effect on nitrifying microbial community dynamics in greenhouse environment.

Materials and methods

Potential nitrification activity (PNA), abundance, and structure of nitrifying microbial communities as well as the correlations with soil properties were investigated.

Results and discussion

Short-term excessive fertilization increased soil nutrient contents and the diversity of nitrifying microbial communities under greenhouse cultivation. However, the abundance and diversity of nitrifying communities decreased greatly due to the increase of soil acidity and salinity after 14 years of high fertilization in greenhouse. There was a significant positive correlation between soil PNA and the abundance of ammonia-oxidizing bacteria (AOB) but not that of ammonia-oxidizing archaea (AOA) in topsoil (0–20 cm) when pH ≥7. Soil PNA and AOB were strongly influenced by soil pH. The groups of Nitrososphaeraceae, Nitrosomonadaceae, and Nitrospiraceae were predominant in the AOA, AOB, and nitrite-oxidizing bacteria (NOB) communities, respectively. Nitrifying community structure was significantly correlated with soil electrical salinity (EC), organic carbon (OC), and nitrate nitrogen (NO₃ ^?–N) content by redundancy analysis (RDA).

Conclusions

Nitrification was predominated by AOB in greenhouse topsoil with high fertilizer loads. Soil salinity, OC, NO₃ ^?–N content, and pH affected by continuous excessive fertilization were the major edaphic factors in shaping nitrifying community structure in greenhouse soils.

     

Effects of saline water irrigation and fertilization regimes on soil microbial metabolic activity

Purpose

Irrigation and fertilization can change soil environment, which thereby influence soil microbial metabolic activity (MMA). How to alleviate the adverse effects by taking judicious saline water irrigation and fertilization regimes is mainly concerned in this research.

Materials and methods

Here, we conducted a field orthogonal designed test under different saline water irrigation amount, water salinity, and nitrogen fertilizer application. The metabolic profiles of soil microbial communities were analyzed by using the Biolog method.

Results and discussion

The results demonstrated that irrigation amount and fertilizer application could significantly change MMA while irrigation water salinity had no significant effect on it. Medium irrigation amount (30 mm), least (50 kg ha^?1) or medium (350 kg ha^?1) N fertilizer application, and whatever irrigation water salinity could obtain the optimal MMA. Different utilization rates of carbohydrates, amino acids, carboxylic acids, and polymers by soil microbial communities caused the differences of the effects, and D-galactonic acid γ-lactone, L-arginine, L-asparagine, D-glucosaminic acid, Tween 80, L-threonine, and D-galacturonic acid were the indicator for distinguishing the effects.

Conclusions

The results presented here demonstrated that by regulating irrigation water amount and fertilizer application, the effects of irrigation salinity on MMA could be alleviated, which offered an efficient approach for guiding saline water irrigation.

     

Short-term effects of organo-mineral biochar and organic fertilisers on nitrogen cycling,plant photosynthesis,and nitrogen use efficiency

Purpose

Organo-mineral biochar fertiliser has the potential to replace conventional biochar and organic fertiliser to improve soil quality and increase plant photosynthesis. This study explored mechanisms involved in nitrogen (N) cycling in both soil and ginger plants (Zingiber officinale: Zingiberaceae) following different treatments including organic fertiliser, commercial bamboo biochar fertiliser, and organo-mineral biochar fertiliser.

Materials and methods

Soil received four treatments including (1) commercial organic fertiliser (5 t ha^?1) as the control, (2) commercial bamboo biochar fertiliser (5 t ha^?1), (3) organo-mineral biochar fertiliser at a low rate (3 t ha^?1), and (4) organo-mineral biochar fertiliser at a high rate (7.5 t ha^?1). C and N fractions of soil and plant, and gas exchange measurements were analysed.

Results and discussion

Initially, organo-mineral biochar fertiliser applied at the low rate increased leaf N. Organo-mineral biochar fertiliser applied at the high rate significantly increased N use efficiency (NUE) of the aboveground biomass compared with other treatments and improved photosynthesis compared with the control. There was N fractionation during plant N uptake and assimilation since the ¹⁵N enrichment between the root, leaf, and stem were significantly different from zero; however, treatments did not affect this N fractionation.

Conclusions

Organo-mineral biochar fertiliser has agronomic advantages over inorganic and raw organic (manure-based) N fertiliser because it allows farmer to put high concentrations of nutrients into soil without restricting N availability, N uptake, and plant photosynthesis. We recommend applying the low rate of organo-mineral biochar fertiliser as a substitute for commercial organic fertiliser.