Low Plant Growth Research Articles

Effect of Soil Available Phosphorus Levels on Chickpea (Cicer arietinum L.) - Rhizobia Symbiotic Association

Background: Growing chickpea (Cicer arietinum) plants is affected by several environmental constraints as osmotic stress and nutrients deficiency particularly phosphorus (P). For other legume species, it was confirmed that P deficiency affects negatively their rhizobial symbiosis. The purpose of this study was to assess the effect of soil available P level on chickpea-rhizobia symbiosis under field conditions at Oualidia region of Morocco.Methods: Ten farmers’ fields with different soil available P levels were considered to carry out this study based on samples of 10 plants per plot. Result: The results showed that the plants from soil 7, with the lowest pH and the highest available P level (23.52ppm), presented high shoot dry weight (38.3 g/plant). Meanwhile the soil 5 with the lowest available P content showed low plant growth. The shoot P content was positively linked to soil P level but nodule biomass showed an irregular variation with soil available P level. Furthermore, it was confirmed that adequate plant P nutrition results in high chickpea yield and it was the case for plants from soil 7 presenting a mean yield of 62 seeds per plant). Finally, strong correlation was noted between yield and phosphorus concentration in soil (r=0.94).

Phytostabilization of arsenic and manganese in mine tailings using Pennisetum purpureum cv. Mott supplemented with cow manure and acacia wood-derived biochar

The purpose of this research was to investigate the effects of cow manure and acacia wood-derived biochar on the immobilization of arsenic (As) and manganese (Mn) in contaminated mine tailings using Mott dwarf Napier grass (Pennisetum purpureum cv. Mott). Cow manure or acacia wood-derived biochar was separately mixed with mine tailings at rates of 1, 3, and 5% (w/w). Samples of mine tailings and plants were collected every 30 d during the 120-d period. The total As and Mn accumulation amounts in the plants were analyzed in both the underground (roots) and aboveground (stems and leaves) parts of the plants. The results revealed that cow manure and acacia wood-derived biochar can reduce the mobilization of As and Mn in mine tailings and thus reduce their uptake and accumulation in P. purpureum. Acacia wood-derived biochar was able to stabilize and immobilize As and Mn in mine tailings, allowing the metals to be taken up for plant utilization despite the lower plant growth (biomass and relative growth rates) than that obtained with added cow manure. The accumulation amounts of As in the aboveground and underground parts of P. purpureum grown in mine tailings with 5% BC application were 0.52 ± 0.05 mg kg−1 and 1.57 ± 0.1 mg kg−1, respectively, while the accumulation amounts of As in the aboveground and underground parts were 31 ± 1.08 mg kg−1 and 73.05 ± 2.60 mg kg−1, respectively. In other words, the percentage reductions in As and Mn uptake and accumulation in the aboveground and underground parts were 78.6% and 63.9% for As and 72.5% and 69.3% for Mn, respectively. The results of this study can be applied for the remediation of heavy metal-contaminated areas, especially gold mines and surrounding areas, as well as in other areas.

Arbuscular mycorrhizal fungus inocula from coastal sand dunes arrest olive cutting growth under salinity stress.

Cultivation of olive trees covers large coastal areas of land in Mediterranean regions, many of them characterized by low soil fertility and exposed to salinity and seasonal drought. In this frame, we developed mixed community inocula of arbuscular mycorrhizal fungi (AMF) derived from the extreme, seasonally arid environments of six Mediterranean sand dunes and evaluated their effects, in the form of community inocula, on rooted semi-woody olive tree cuttings (Olea europaea cv. Koroneiki). The plantlets were grown in the greenhouse for 10 months under 50 mM and 100 mM concentrations of NaCl, successively applied to induce osmotic stress. Inoculation had a positive effect on plant growth and nutrient uptake. However, the three best-performing inocula in early colonization and in plant growth enhancement also resulted in high plant sensitivity to high salinity, which was not observed for the other three inocula. This was expressed by decreased nutrient uptake and drastically lower plant growth, plant photosynthesis, and stomatal conductance (generally an over 50% reduction compared to no salinity application). Amplicon sequencing analysis of the olive plants under salinity stress showed that the AMF communities in the roots were clearly differentiated by inoculation treatment. We could not, however, consistently associate the plant responses observed under high salinity with specific shared AMF community membership or assembly attributes. The observed physiological overreaction to osmotic stress may be an adaptation trait, potentially brought about by host selection coupled to abiotic environmental filtering, in the harsh conditions from which the AMF inocula were derived. The overreaction may, however, be undesirable if conveyed to allochthonous plants at an agronomic level.

Changes in Growing Season Phenology Following Wildfires in Alaska

Trends and geographic patterns of change in vegetation phenology metrics and snowmelt timing from the MODerate resolution Imaging Spectroradiometer (MODIS) satellite data sets were analyzed across the state of Alaska for all wildfires that burned during the years 2004 and 2005. Phenology metric patterns (over the period 2000 to 2018) derived from the normalized difference vegetation index (NDVI) time-series at 250-m resolution tracked changes in the growing season length and integrated greenness cover over the past two decades. NDVI metrics showed that end of the growing season timing (EOST) and integrated greenness increased significantly in the majority of severely burned areas in Interior Alaska over the past decade particularly in low elevation zones below 500 m. In years with relatively early snowmelt dates (3 to 10 days earlier than the long-term mean), lower plant growth was observed over the ensuing growing season, potentially due to lower snow water inputs that can maintain available soil moisture levels for plant growth into the mid- and late-summer months. Statewide trends in MODIS phenology metrics indicate that the predominant vegetation cover type in most regrowing burned areas of Interior Alaska a decade post-fire is still deciduous shrub and young tree cover. Several large fires of special interest were identified to monitor with remote sensing and continue to track long-term recovery patterns and rates.

Effect of Cattle Slurry on the Growth of Spinach Plants in Cd-contaminated Soil

ABSTRACT In this work the effect of the addition of different amounts of cattle slurry (CS) to a Cd contaminated soil, was studied regarding its effect in spinach plants. Two levels of Cd contamination (2 and 10 mg/kg) and three levels of CS addition were evaluated (2.5, 5 and 10 g CS/100 g soil). Spinach was shown to be a tolerant species, able to accumulate relatively high amounts of Cd (up to 367.7 mg/kg in the leaves), exceeding the limits established by European regulations for leaf vegetables. The addition of 2.5 and 5 g CS/100 g to soil containing 2 mg/kg Cd did not reduce the uptake of this metal but allowed the plants to grow as much as the control. The addition of 10 g CS/100 g lead to a reduced Cd uptake but also to a lower plant growth compared to the lower CS levels. The combined effects of Cd and CS changed element content in the plant, but without causing severe toxicity or deficiency effects.

Evaluation of the Agronomic Performance of Organic Processing Tomato as Affected by Different Cover Crop Residues Management

No-till practices reduce soil erosion, conserve soil organic carbon, and enhance soil fertility. Yet, many factors could limit their adoption in organic farming. The present study investigated the effects of tillage and cover cropping on weed biomass, plant growth, yield, and fruit quality of an organic processing tomato (Solanum lycopersicon L. var. Elba F1) over two seasons (2015–2017). We compared systems where processing tomato was transplanted on i) tilled soil following or not a winter cover crop (Trifolium squarrosum L.) and with/without a biodegradable plastic mulch; and ii) no-till where clover was used, after rolling and flaming, as dead mulch. Tomato in no-till suffered from high weed competition and low soil nitrogen availability leading to lower plant growth, N uptake, and yield components with respect to tilled systems. The total yield in no-till declined to 6.8 and 18.3 t ha−1 in 2016 and 2017, respectively, with at least a 65% decrease compared to tilled clover-based systems. No evidence of growth-limiting soil compaction was noticed but a slightly higher soil resistance was in the no-till topsoil. Tillage and cover crop residues did not significantly change tomato quality (pH, total soluble solids, firmness). The incorporation of clover as green manure was generally more advantageous over no-till. This was partly due to the low performance of the cover crop where improvement may limit the obstacles (i.e., N supply and weed infestation) and enable the implementation of no-till in organic vegetable systems.

Morpho-physiological effect of selenium on salinity-stressed wheat (Triticum aestivum L.)

Wheat (Triticum aestivum) is an important grains plant that can sustain food security and holds high nutritional values to the benefit of mankind. Activities of salinity in arid and semi-arid region have drastically reduced the production of wheat grains. Selenium (Se) is a micronutrient required by plants in small concentration to aid their growth. This study was aimed at identifying impact of Se on salinity-stressed wheat plants. Wheat seeds were soaked for eight hours in 0, 50, 100 and 150 mg/L Selenite concentrations and five sterilize-treated seeds were sown in 5 kg quantity of soil. This was subjected to 0, 100 and 200 mM of Sodium chloride (NaCl) concentration, respectively. The study revealed that Se increased production/expression of superoxide dismutase and catalase enzymes under salinity stress, thus growth of wheat plants was improved. Although the effects of Se on the wheat plants were concentration-based, nevertheless low lipid peroxidation and plant growth at 150 mg/L of Se were observed. Toxicity of Se to wheat plant could occur when there is no salinity stress. Therefore, farmers are encouraged to prime wheat seeds with 150 mg/L Se when cultivating saline soils.

Efficacy of different temperate pasture species to reduce nitrogen leaching from cattle urine applied in different seasons: A soil lysimeter study

AbstractA soil lysimeter field study assessed the efficacy of different pasture species to reduce nitrogen (N) leaching loss from cow urine deposited in different seasons. A single application of cow urine (15N‐labelled; equivalent to 622 kg N ha−1) was applied in three different seasons (summer, autumn or winter) to three pasture species monocultures (perennial ryegrass, plantain or lucerne) on a free‐draining volcanic soil and monitored over 362 days. Leachate analyses revealed consistently large leaching losses of inorganic‐N from lucerne (>200 kg N ha−1) across different urine application times due to the relatively low plant growth rates during winter (<15 kg DM ha−1 day−1) that led to low total recovery of urine‐N by lucerne plants (<20% of the applied urine‐15N). Conversely, plant uptake of the urine‐N was higher by plantain (ranging from 30% to 45% of that applied) driven by moderately higher winter plant growth rates (30 to 60 kg DM ha−1 day−1). Plantain exhibited large seasonal variation in its efficacy to reduce urine‐N leaching relative to ryegrass (ranging from 15% to 50% reduction for summer or winter urine applications, respectively) with an overall reduction of 39% in the total amount of inorganic‐N leached across the three seasons (53 vs. 87 kg N ha−1 leached relative to ryegrass). This study has demonstrated the potential benefit of using plantain to reduce N leaching losses from urine deposited in the summer to winter grazing period. However, further research is required to quantify the effects of plantain on annual N leaching losses from grazed pastoral systems.

Physiological, Biochemical and Chlorophyll Fluorescence Parameters of Physalis Peruviana L. Seedlings Exposed to Different Short-Term Waterlogging Periods and Fusarium Wilt Infection

Cape gooseberry has coped with abiotic and biotic stresses such as prolonged waterlogging periods and vascular wilt in recent years. The aim of this study was to evaluate the influence of four waterlogging periods on stomatal conductance (gs), leaf water potential (Ψwf), plant growth, leaf photosynthetic pigments, malondialdehyde (MDA) production, proline content and chlorophyll fluorescence parameters in cape gooseberry plants infected with Fusarium oxysporum f. sp. physali (Foph). Two-month-old ecotype “Colombia” plants were arranged in a completely randomized factorial design in eight treatments: plants without waterlogging (control), plants with waterlogging for 4, 6 and 8 d with and without Foph, respectively. The area under the disease progress curve was higher in inoculated plants subjected to 6 and 8 d of waterlogging (55.25 and 64.25) compared to inoculated plants but without waterlogging (45.25). The results also showed a lower plant growth, gs, Ψwf, leaf photosynthetic pigments and chlorophyll fluorescence parameters (Fv/Fm, electron transport rate (ETR), Y (II) and qP) as waterlogging periods in plants with Foph increased. However, this group of plants showed a greater proline and malondialdehyde (MDA) accumulation and a higher NPQ. In conclusion, cape gooseberry shows a low acclimation to waterlogging conditions of more than 6 d in soils with Foph.

Spatially Explicit Soil Compaction Risk Assessment of Arable Soils at Regional Scale: The SaSCiA-Model

Soil compaction caused by field traffic is one of the main threats to agricultural landscapes. Compacted soils have a reduced hydraulic conductivity, lower plant growth and increased surface runoff resulting in numerous environmental issues such as increased nutrient leaching and flood risk. Mitigating soil compaction, therefore, is a major goal for a sustainable agriculture and environmental protection. To prevent undesirable effects of field traffic, it is essential to know where and when soil compaction may occur. This study developed a model for soil compaction risk assessment of arable soils at regional scale. A combination of (i) soil, weather, crop type and machinery information; (ii) a soil moisture model and (iii) soil compaction models forms the SaSCiA-model (Spatially explicit Soil Compaction risk Assessment). The SaSCiA-model computes daily maps of soil compaction risk and associated area statistics for varying depths at actual field conditions and for entire regions. Applications with open access data in two different study areas in northern Germany demonstrated the model’s applicability. Soil compaction risks strongly varied in space and time throughout the year. SaSCiA allows a detailed spatio-temporal analysis of soil compaction risk at the regional scale, which exceed those of currently available models. Applying SaSCiA may support farmers, stakeholders and consultants in making decision for a more sustainable agriculture.

Effects of rhizosphere interactions of grass interspecies on the soil microbial properties during the natural succession in the Loess Plateau

Natural vegetation succession is a process of interactions between plants and various environmental factors. The dynamics of soil microbes during successional stages have been intensively explored in the past two decades. The effect of rhizosphere interactions of interspecies on microbial properties, however, has received less attention. During the early stage of succession on a Loess Plateau soil from China, we investigated microbial properties in the rhizospheres of three dominant grass species: Artemisia capillaris, Artemisia sacrorum and Stipa bungeana. Experiments with monocultured and polycultured potted plants were designed to determine the effects of rhizosphere interactions on plant growth and soil microbial properties. The results showed that root biomass, shoot biomass, plant height, microbial biomass carbon (C), microbial biomass nitrogen (N), invertase and urease activities, Gram-negative and Gram-positive bacteria were significantly higher for A. capillaris than for A. sacrorum and S. bungeana in both monocultures and polycultures. Lower root biomass, shoot biomass, plant height, microbial biomass C, microbial biomass N, invertase and alkaline phosphatase activities, and levels of microbial phospholipid-derived fatty acids in polycultures relative to the monocultures indicated that rhizosphere interactions led to lower plant growth and soil microbial activities. Our study suggests that rhizosphere interactions had a significant effect on the microbial properties of plant rhizospheres. The advantage of A. capillaris over A. sacrorum and S. bungeana in growth characteristics and rhizosphere microbial conditions is likely responsible for the dominance of A. capillaris in the early stage of succession in abandoned cropland on the Loess Plateau.

Sustainable growing media based on green waste compost and other organic recycled materials: indicators for potential biodegradation and N immobilization

Composts and lignocellulosic materials allow for reducing or completely replacing peat in growing media. However, these materials may vary in their decomposition rate (as affected by biochemical composition) and interaction with nitrogen, thus affecting the quality of growing media. We identified, characterized and assessed different organic recycled materials that potentially can be combined with green waste compost, known as a qualitative sustainable recycled material for growing media. For better characterization of feedstock materials and growing media mixtures, we tested an indicator for biochemical composition based on the crude fibre analysis, and an indicator for N immobilization based on a 7-day incubation trial. Based in the biochemical composition, potential biodegradation was calculated as the holocellulose/lignin ratio. The materials were tested for immobilization of mineral N by adding 350 mg N L-1 substrate as KNO3 followed by one week of incubation at 37°C and comparing the actual mineral N concentration with the theorethical concentration. Selected raw materials were combined in different ratios. Most raw materials had high pH and/or EC values, limiting their share in the growing media. Based on feedstock selection, green waste compost with sufficiently low EC and pH could be produced. Mixtures complying with the Belgian Federal Legislation (pH-range from 4.5 to 7.0 and EC below 750 µS cm-1) were selected for greenhouse experiments with potted plants. The effect of the mixtures on plant quality was assessed. This resulted in a selection of the five most suitable mixtures. Growing media including materials with high N immobilization resulted in lower plant growth. We conclude that quality of composts and lignocellulosic materials for use in growing media could be successfully assessed based on these indicators. Compost was found to be an important source of P and K, while N could be a limiting factor, especially in mixtures based on organic recycled materials with strong N immobilization such as used coffee grit.

Selecting raw materials for sustainable growing media: a protocol to assess the risk for N immobilization

Several materials to be used in growing media were tested for immobilization of mineral N by adding 350 mg N L-1 substrate as KNO3 followed by one week of incubation at 37°C. Based on the difference between the theoretical and actual mineral N content after incubation, the % N immobilization was calculated. The robustness and reproducibility of the protocol was tested by changing incubation circumstances, the applied N sources and the amount of N added. The relevance of the indicator was tested (a) for a range of green waste composts, (b) during the composting of four mixtures, and (c) in pot trials with growing media including different composts and lignocellulosic materials. Higher microbial activity in green waste composts (indicated by higher oxygen consumption) and thus a lower compost stability resulted in higher N immobilization. N immobilization decreased due to stabilization during the composting process, with a distinct effect of the specific feedstock composition. The protocol was tested for woody materials and for Miscanthus straw, spent coffee grounds and chopped reed straw. The applied source of mineral N in the test affected the pH of the material, and may thus also affect the microbial activity and thus the related N immobilisation. Growing media including materials with high N immobilization resulted in lower plant growth. We conclude that quality of composts and lignocellulosic materials for use in growing media could be successfully assessed based on this protocol.

A practical approach for assessing the efficiency of coated urea on controlling nitrogen availability

ABSTRACT We propose an approach for assessing the efficiency of coating materials on controlling nitrogen (N) availability to plants. It is based on the use of coated and soluble urea (UR) applied to corn over 3 growing cycles, as follows: coated UR with longevity of 2 (UR-2m) or 4 months (UR-4m) with application of 900 mg N∙pot−1 at the beginning of the experiment, soluble UR with a split application of 900 mg N∙pot−1 (300 mg N∙pot−1 per growing cycle, UR-3x), soluble UR with a sole application of 900 mg N∙pot−1 at the beginning of the experiment (UR-1x), and a control treatment. At the end of each growing cycle, shoots were harvested to estimate N provision by the UR by quantifying dry matter (DM) and N uptake. In the first cycle, UR-2m and UR-4m promoted lower plant growth and N accumulation in shoots than UR-1x. However, in the third cycle, higher shoot N uptake and DM production was recorded in UR-4m than in UR-1x. Furthermore, fertilizer contribution for shoot N uptake in UR-4m plants was higher than those in UR-1x and UR-2m at the end of the experiment. Accordingly, consecutive growing cycles combined with forms of soluble UR application were able to characterize the pattern of N release from coated fertilizers, being, thus, a suitable method to evaluate the efficiency of such products. We argue that our practical approach could be used by the industry in fertilizer quality programs and to register fertilizer coating materials by regulatory agencies.

Ornamental flowers in new light: Artificial lighting shapes the microbial phyllosphere community structure of greenhouse grown sunflowers (Helianthus annuus L.)

Artificial assimilation lighting is a common practice in greenhouse horticulture in the circumpolar region to compensate for natural low light conditions. To modulate plant architecture, regulate flowering of photoperiodic crops, increase plant performance per energy input and consequently profitability, light emitting diodes (LEDs) have been suggested as a powerful tool for ornamental growers in complementary or replacement of conventional lighting such as incandescent, fluorescent and high pressure sodium (HPS) lamps. As LED light differs from HPS lamps with regard to spectral output, light distribution as well as heat emission, the microclimate within the crop stand is affected. In two independent experiments conducted in fall and winter, we therefore compared the effect of two types of LED light (red 660nm+blue 460nm LED, 80:20 RB-LED; white LED, W-LED) with HPS lighting on ornamental sunflowers (Helianthus annuus cv. ‘Teddy Bear’). Depending of the solar radiation (fall vs winter experiments), a same PPFD of 70–120μmolm−2s−1 of artificial lighting (photoperiod of 16h) was given at the top of the plants. Plant growth performance and biomass, leaf temperature, photobiological parameters (photosynthetic activity, stomatal conductance, chlorophyll fluorescence) as well as the leaf associated microbiome, assessed using culture dependent and independent methods on apical, directly exposed to the light treatments, and basal leaves, were studied. As expected, significant differences were obtained for plant related parameters between the two repetitions of the experiment due to difference in solar radiation. Light treatments influenced plant growth performance which was lower for all parameters in sunflowers exposed to LEDs than HPS. However, no differences were found with respect to photobiological parameters. Top leaf temperature was higher in the presence of HPS than LEDs, which explained the lower plant growth performance observed under LED regimes. Colony-forming units representing culturable fungi and fluorescent pseudomonads were higher on basal leaves than on apical ones, but did not vary with respect to light treatments. On the other hand, biodiversity estimated with respect to species abundance and evenness (Shannon-H index) and species richness (Chao1) revealed different patterns for the fungal and bacterial microbiome. Regardless of the leaf position, light treatments affected fungal species abundance and evenness, which was highest on leaves exposed to HPS, but not species richness. The fungal microbiome was more diverse on apical than on basal leaves. For the bacterial microbiome, biodiversity estimates differed between the repetitions. Interactions between leaf temperature and bacterial genera were found for several of the dominant genera in the sunflower phyllosphere (Pseudomonas, Staphylococcus, Enhydrobacter) while other decisive bacterial and fungal genera were correlated to photobiological parameters, e.g. Bradyrhizobium, Sphingomonas, Brevibatericum, Bacillus, Hypotrachyna, Aureobasidium. The use of “new light” in greenhouse ornamentals is not only a technological change modifying plant morphology and development, but also affects the microbial ecology on plant surfaces, implying consequences on plant protection issues and biological control strategies.

English

The growth of tree legumes in degraded areas must be preceded by assessments of nodulation ability of naturally established rhizobia populations since such information contributes to defining the species which can be planted for recovering disturbed areas. The aim of this study was to evaluate the growth and natural nodulation of “sabia” (Mimosa caesalpiniifolia Benth.) and leucaena (Leucaena leucocephala (Lam.) de Wit.) in soils of the Brazilian semiarid area under different systems of land use: native vegetation (locally called caatinga) and areas with different agricultural systems (a monocrop system and an intercropping with various species). For each species, a greenhouse experiment in randomized block design was realized, using soils of different types (Luvisol and Ultisol), with 4 replicates. The results evidentiate significant differences in the evaluated growth characteristics (height, leaflet number and shoot diameter) of M. caesalpiniifolia, that have displayed lower plant growth when cultivated in the Luvisol under conventional system. Plant growth, nodulation and total N accumulation in both seedling tree legumes increased in Ultisol under the different systems of land use. L. leucocephala showed higher potential of biological nitrogen fixation and nodulation effectiveness promoted by indigenous rhizobia. Key words: Biological nitrogen fixation, indigenous rhizobia, symbiosis, sustainable agriculture.

Plant nutrition, growth and polygodial production ofTasmannia lanceolata

Rapid growth of some native Australian plant species can be achieved by targeted applications of selected nutrients. The aim of this study was to examine the influence of nutrient levels on early establishment of Tasmannia lanceolata (Winteraceae) for potential plantation production of polygodial extract from leaves. Treatments of a comprehensive fertiliser on a single clone of T. lanceolata were imposed in a pot trial with a factorial design. Measurements of plant height, leaf number and stem diameter were made over a 40-week period to evaluate plant growth performance. Leaf mineral nutrient composition and plant extract quantity and quality were measured. Greatest change in plant height of 553.1 mm was achieved at the highest fertiliser rate of 12 g pot-1 but not greatest leaf number or stem width. The lowest fertiliser rate produced a significantly higher extract yield on a dry matter basis than higher fertiliser treatments, but significantly lower plant growth. Polygodial yield as a proportion of oil yield was unaffected by fertiliser rate. The outcomes of this trial will inform field nutrition requirements to optimise the balance between gross production and polygodial concentration.

Anaerobic co‐digestion of perennials: Methane potential and digestate nitrogen fertilizer value

AbstractCo‐digestion of crop biomass improves the traditional manure‐based biogas yield due to an increased content of easily degradable carbon compounds. In this study, the methane potential of three perennials (grass, legumes, and grass+legume) was determined using various amounts together with animal manure. The nitrogen (N) mineralization dynamics in soil and the N‐fertilizer value of the derived digestates were subsequently tested in both a soil incubation study and a pot experiment with spring barley. Digestion of all tested perennials together with a manure‐based inoculum increased the cumulative methane yield four to five times compared to digestion of the inoculum alone, with the highest increases observed with pure grass. However, the methane potential decreased along with increasing grass biomass concentration. In the plant pot experiment, all tested digestates increased barley shoot biomass by 40–170%, to an extent statistically comparable to mineral N fertilizer. However, the application of the digestate originating from fermentation with pure grass resulted in lower plant growth and a more fluctuating soil mineral N content throughout the incubation study compared to the other digestates. Considering the high dry matter and methane yield ha−1, the possibility to substitute mineral N fertilizer inputs by leguminous biological N2 fixation capacity, and the digestate fertilizer value, the integration of grass–legume mixtures or sole legumes into anaerobic digestion systems as co‐substrate for manure seems to be promising. This could furthermore contribute to the diversification of cropping systems for bioenergy production.

Forest wildfire and grassland prescribed fire effects on soil biogeochemical processes and microbial communities: Two case studies in the semi-arid Southwest

Fire is a natural disturbance that shapes many ecosystems. In semi-arid regions, where high temperatures and low soil moisture limit nutrient cycling and plant growth, fire is critical to supply nutrients and drive vegetation composition. We examined soil chemical and biological properties to assess the short-term impacts of wildfire and prescribed fires on soil functioning in semi-arid regions of Texas. Better understanding of soil organic matter transformation and nutrient cycling processes will aid land managers in predicting ecosystem recovery response post-fire. Soil samples were collected following both prescribed grassland fires in June of 2009 in Lubbock, TX and the April 2012 Livermore Ranch Complex Fire located in the Davis Mountains, TX. Prescribed fire samples (0–2.5cm) were collected within six h prior to burning and again at 0.5, 24, 48, and 168h post-fire to experimentally examine short-term influences of fire and fire frequency (1× vs. 2×) on soil carbon dynamics, inorganic nitrogen, and microbial community composition. Wildfire samples (0–5cm) were collected two and six months following the wildfire. We evaluated the effects of three burn severity levels and sampled under three tree species (Juniperus deppeana, Pinus cembroides, and Quercus grisea). Within 0.5h of the prescribed fire, CO2 flux, NH4+-N concentration and total microbial biomass (as estimated by total fatty acid methyl esters) increased. A shift in the microbial community from a predominance of fungi to Gram positive bacteria occurred immediately following the fire. Chemical shifts were short lived (decreased within 24h), but the biotic shift to a dominance of Gram negative bacteria and actinomycetes was measured in samples collected after 168h. Soil pH and NH4+-N concentration increased at two and six months following the wildfire. In contrast, soil organic matter content decreased at two months post wildfire which, in combination of abiotic conditions such as low moisture content (<3.3%), resulted in reduced soil microbial biomass and enzyme activity. Increased soil moisture six months post fire created more favorable conditions for nitrification resulting in increased NO3−-N concentration (0.8 to 36.1mgNO3−-Nkg−1soil), particularly following high severity fire. Prescribed fire did not have lasting impacts on soil nutrients, but both prescribed and wildfire resulted in increased NH4+-N, shifts in microbial community structure and decreased in microbial biomass. While the increase in nitrogen maybe be beneficial to the plant growth and revegetation, the loss of microbial biomass may have far reaching implications to the overall sustainability of the soils in these systems.

Effects of pruning and plant growth regulators on branching and growth of azalea

Many woody plants do not branch well during nursery container production. Various plant growth regulators (PGRs) have been used to promote branching. The objective of this study was to evaluate the effects of dikegulac sodium (Atrimmec) and cyclanalide (Tiberon 2.8SC) in combination with or without pruning on branching and growth of two cultivars of azalea (Rhododendron sp.). For azalea 'Midnight Flare', Atrimmec at 3100 mg L-1 applied twice and Tiberon 2.8SC at 100 mg L-1 applied twice or 200 mg L-1 applied once significantly increased branching in 8 weeks after the initial treatment (WAIT), regardless of pruning treatment. However, by 20 and 30 WAIT, there were no significant differences on the number of shoots per plant among all the treatments. For azalea 'Katherine Alison', at 8 and 20 WAIT, plants which received pruning and were treated with two applications of Atrimmec at 3100 mg L-1 had significantly more shoots than plants that did not receive pruning but were treated with one application of Atrimmec at 3100 mg L-1. By 30 WAIT, there were no significant differences between the number of shoots per plant among all the treatments. No phytotoxicity was observed. For both azalea cultivars, at 8 WAIT, plants which received pruning had a significantly lower plant growth index (PGI) than plants that did not receive pruning. At 20 and 30 WAIT, pruning generally did not have a significant effect on PGI.