Autumn Soil Research Articles

Integrating corn nitrogen management strategies and cover crops following winter wheat

Following winter wheat, there can be approximately a 90‐day fallow period with no crop N uptake and autumn soil temperatures >50°F, leading to increased residual soil NO3–N availability. Opportunities exist for incorporation of cover crops to assimilate residual autumn soil N and reduce the potential for N loss. The objective of this study was to quantify daikon radish and forage oat cover crop biomass and N uptake, cover crop impact on soil NO3–N concentration, and corn growth, grain yield, and profitability responses to N placement and timing combinations following cover crops. Earn 1 CEU in Nutrient Management by reading this article and taking the quiz at www.certifiedcropadviser.org/education/classroom/classes/699.

On the hydrological role of the relief in the southern part of the Russian plain

On the example of a southern part of the Russian Plain the surface slope runoff, the runoff from the hydrographic network and snow melt river runoff are considered. Based on the analysis of the data by water balance stations and the correlation of surface slope runoff values from different lands to the zonal river runoff value, the zonal values of the spring surface slope flow from separate lands located on loam and sandy loam soils are determined. Within agricultural lands there are fall plowed fields and non-plowed in autumn (stubble, layland, winter crops, perennial grasses). By the beginning of the spring flood, the soil at autumn-plowed fields is loosened and reduces the runoff, while on the fields that were not plowed in the autumn soil is compacted. In addition, the microtopography created by autumn plowing also contributes to the runoff reduction. The smallest surface slope runoff occurs under the forest. Differences in runoff increase in the direction from the southern part of the forest zone to the steppe areas. Taking into account the land composition and the mechanical composition of the soils, the weighted average values of the surface slope runoff were obtained for the period of the long-time average annual flow calculation (late 19th century and early 1960s). It is shown that subsequently there was a decrease in the spring surface slope runoff, initially as a result of the autumn plowing increase, and more recently, mainly as a result of changes in meteorological conditions, especially during the cold season (air temperature rising, frequent thaws, increased infiltration). In the overall structure of the spring river flood, along with a decrease in the share of surface slope runoff, the share of surface runoff formed in the hydrographic network increases, and especially the flow of infiltration origin (verhovodka and underground runoff). In the steppe zone the structure of river flow has changed most significantly.

Plant community regulates decomposer response to freezing more strongly than the rate or extent of the freezing regime

AbstractArctic tundra ecosystems are warming disproportionately in the winter, including a delayed autumn soil freeze‐up. Because microbial processes are extremely sensitive to change in temperature below freezing, overwinter warming strongly stimulates decomposition and nutrient mineralization and ultimately promotes the conversion of sedge‐dominated tussock tundra into shrub tundra. We characterized the responses of decomposition in shrub tundra and tussock tundra soils to changes in the rate and extent of freezing using laboratory simulations to study a range of active layer freeze‐up scenarios that included variation in time held above 0°C (an acclimation period) and final temperature (−2°C to −20°C). We hypothesized that shrub soil decomposers would be more sensitive to the rate of the freezing process than tussock soil decomposers, but less sensitive to the extent of freezing. Although freezing strongly influenced microbial processes, the effects of freezing tended to not significantly vary across the range freezing regimes tested. Unexpectedly, the tussock‐derived soil decomposer community was more sensitive than shrub‐derived soil to the freezing treatments. Freezing conditions stimulated tussock soil to release more water‐extractable organic carbon (WEOC) that was composed of a greater proportion of microbially derived materials than shrub soil under the same conditions. Freezing‐driven changes in the tussock WEOC pool coincided with reduced microbial decomposer biomass, while the shrub decomposer biomass was relatively insensitive to the freezing treatments. These findings suggest that the microbial community of shrub‐dominated soils is more resistant to the soil freezing process than the tussock‐dominated decomposer community and increases available soil N while reducing labile C release as the soils freeze. Because autumn nutrient dynamics set the stage for overwinter tundra biogeochemical conditions, increasing shrub dominance in tussock tundra may therefore promote both plant N availability and decomposer C limitation during thaw.

Relationship between CO2 emissions and soil properties of differently tilled soils

Different tillage technologies have different effects on CO2 emissions from soil. Unfortunately, little information exists about the impact of different types of tillage as compared with no-tillage, and the main controls. The aim of this research is to determine the relationship between physicomechanical, chemical and biological properties of soil and CO2 emissions from differently tilled soils under the climatic conditions of central Lithuania before and after autumn tillage. The studies were conducted in 2009–2012 and 2014 at the Experimental Station of Aleksandras Stulginskis University in Central Lithuania. Different tillage technologies were applied: deep ploughing at 23–25 cm depth (DP); shallow ploughing at 12–15 cm depth (SP); deep cultivation with a cultivator at 25–27 cm depth (DC); shallow cultivation with a disc harrow at 12–15 cm depth (SC); and no-tillage (NT). The correlation of physicomechanical, chemical and biological soil properties with CO2 emissions was determined. During all the experimental period total CO2 emissions from soil in DP, SP, DC, SC and NT technologies were respectively 6.05, 4.25, 4.97, 4.42, 3.94 μmol m−2 s−1 before autumn soil tillage and 29.88, 22.50, 16.73, 13.72, 10.00 μmol m−2 s−1 after autumn tillage. Negative correlation between soil temperature and CO2 emissions before the autumn tillage from soil was evidenced (r = −0.98). A strong negative correlation between soil respiration and total soil porosity was observed. Correlation between aeration soil porosity and CO2 emissions was strong. After autumn tillage, the strongest correlations were found between soil penetration resistance and respiration in the upper (r = −0.75) and deeper (r = −0.71) layers. In autumn, a significant strong correlation (r = 0.78) between soil respiration and aeration porosity was obtained in the upper soil layer under ploughing or cultivation. This study revealed that CO2 emissions were significantly higher immediately after autumn ploughing technologies compared to deep and shallow cultivation and no-tillage.

Corn Nitrogen Management Following Daikon Radish and Forage Oat Cover Crops

Core Ideas Daikon radish and forage oat cover crops following winter wheat sequestered residual autumn soil NO3–N levels. Nitrogen availability to the ensuing corn crop may be reduced when preceded by radish or oat cover crops. When using radish or oat cover crops, increased 5×5 starter rates (> 45 kg N ha‐1) may be required if full SD is delayed until V11. Radish and oat cover crops preceding corn did not provide a subsequent N fertilizer replacement value but may still be effectively utilized as soil conservation tools. Cover crops (CC) preceding corn (Zea mays L.) may influence subsequent nitrogen (N) availability, but it is not clear whether N strategies require adjustment. Field studies conducted in 2015 to 2016 evaluated the effects of a daikon radish [Raphanus sativus (L.)], forage oat [Avena sativa (L.)], and no CC following winter wheat [Triticum aestivum (L.)] on soil chemical properties, corn growth, grain yield, and profitability. Nitrogen management strategies were equalized to 179 kg N ha–1 and included pre‐plant incorporated (PPI) N, poultry litter (PL) PPI (61 kg N ha–1) plus sidedress (SD) N V11, starter N (45 kg N ha–1) subsurface banded (5 cm below and 5 cm beside the seed, 5×5) followed by V4, V11, or V4 plus V11 SD, and a zero N control. Cover crops reduced autumn soil NO3–N levels 78 to 84% relative to no CC but occasionally reduced N during critical corn uptake periods. Cover crops did not increase soil base cation availability to the ensuing corn crop. When 5×5 starter was followed by full SD at V11, CCs reduced yield 3.2 to 3.9% and profitability 11.8 to 13.2% compared with no CC indicating reduced efficacy and possibly greater 5×5 requirements to maintain yield potential until SD time. In the zero N control, CCs reduced grain yield 11.8 to 14.2% and increased yield response to N 63 to 79% suggesting reduced N availability. Radish and oat CCs provided a trap crop for autumn residual N, but N management strategies may need to account for reduced N availability.

Influence of Fertilization and Environmental Conditions on the Phenological and Morphological Development of Carrot Plants During Seed Production

The main goal of the present study was to establish the influence of different rate of fertilization with nitrogen, phosphorus and potassium and interaction with the environmental conditions and their effect on phenological development of the carrot seed plant. The experiment was carried out in the Experimental fields of the Agricultural University of Plovdiv, Bulgaria with carrot variety Tushon. The plants were grown by conventional technology with steckling. Two way of fertilization was applied. In the first one, the total amounts of fertilizers were put in the autumn soil treatment and in the second one, it was split twice - in autumn the half and the other in spring in stecklings planting. The phenophases of beginning and mass: developed of leave rosette; appearing, flowering, developed and maturity of the seed of central, primary, secondary and tertiary umbels were recorded. Morphological characteristic of seed plant as a high and total vegetative weight was established. The average daily temperature, maximal and minimal temperature, rainfall and the hydrothermal coefficient of vegetation period were calculated. The relations between phenological behaviors and morphological development and elements of climatic conditions were determinated. The significance of the environmental conditions on the phenological development, especially for appearing of the umbels and flowering as well as the maturity of the seeds was established.

Indicators of microbial activity in the assessment of soil condition subjected to several years of reclamation

The investigations were carried out in the form of a field reclamation experiment established in the former “Jeziórko” Sulphur Mine (Poland). For soil reclamation, various combinations of sewage sludge, mineral wool, post-flotation lime and mineral fertilisation were introduced in a single application to the degraded soil. The following parameters were determined in the reclaimed soil in spring and autumn of the 2nd and 3rd year after waste application: number of oligotrophic, cellulolytic and lipolytic bacteria, number of filamentous, cellulolytic and lipolytic fungi, respiratory activity, intensification of cellulose mineralisation, lipase activity and DNA concentration. The applied wastes had a stimulating effect on the growth of the analysed bacterial groups. The growth of fungi was stimulated only in the soil treated with sewage sludge, whereas the values of these parameters in other treatments were usually reduced. The addition of wastes contributed to the intensification of respiration processes and cellulose mineralisation. Lipase activity and DNA concentration fluctuated depending on the type of waste and the time period of investigations; these parameters exhibited the highest values in the soil treated with sewage sludge. In general, the increase in microbiological and biochemical activities was clearly evident in the soil treated with sewage sludge applied separately or in combination with other wastes. The use of sewage sludge together with post-floatation lime, rather than sewage sludge alone, and the application of mineral wool as a 5-cm pad, rather than a mixture of mineral wool and soil, proved to be more beneficial for most of the analysed parameters.The current study is important in the context of safe and effective application of waste for reclamation purposes. In addition, the work raises the innovative aspect of using DNA concentration as an indicator of degraded soil status.

Early‐Season Wind Erosion Influenced by Soil‐Incorporated Green Manure in the Pacific Northwest

Core Ideas Irrigated soils in the Pacific Northwest are highly susceptible to wind erosion. Early‐season wind erosion potential was assessed from soil‐incorporated green manure and no green manure treatments. Soil‐incorporated green manure did not influence wind erosion. Management strategies are sought to minimize wind erosion of irrigated agricultural soils along the Columbia River of the Inland Pacific Northwest (PNW), particularly during the early season (March–April) when high winds coincide with sowing of vegetable crops. Early‐season wind erosion potential from soil‐incorporated green manure (i.e., incorporation of a cover crop of mustard into the soil in autumn) and no green manure treatments was assessed at two locations over 2 yr using a portable wind tunnel. Incorporation of green manure the preceding autumn did not influence wind erosion or soil erodible characteristics the following spring. Soil‐incorporated green manure, however, did influence early‐season crop residue characteristics. Although differences were significant, low residue cover and stem silhouette area suggested relatively small differences in empirical estimates of windblown soil loss between manure treatments. Soil crusting resulting from irrigation and/or rainfall prior to assessing wind erosion may have masked any influence of green manure on wind erosion. Due to the high erosion rates measured from the crusted soils, multiple years of green manure or minimum or reduced tillage may be required to promote aggregation and/or enhance residue cover and thereby reduce wind erosion of irrigated soils.

Влияние технологии возделывания яровой мягкой пшеницы, гороха и рапса на водный режим почвы и урожайность

<p><span lang="EN-US">We performed field research with the purpose of increasing the efficiency of the technology of spring soft wheat, pea and rape cultivation in the GPR “Timiryazevsky” in the Mamontovsky District of the Altai Territory within the framework of the international research project "Kulunda" in 2013-2016. The technological process of crop cultivation in the rotation of wheat-pea-wheat-rape was chosen as an object of research. The subject of the study was the interrelation of technology of cultivation of crops, water regime of soil and yield. Variable factors in the experiment for each culture were the methods of autumn soil cultivation, pre-sowing treatment and sowing aggregates. As a result of the analysis of the data obtained, a tendency has been found to reduce the specific consumption of moisture with a decrease in the intensity of autumn soil cultivation, as well as variants of agricultural technologies with a maximum crop yield of the studied crops has been found.</span></p>

Hydrometeorological conditions preceding wildfire, and the subsequent burning of a fen watershed in Fort McMurray, Alberta, Canada

Abstract. The destructive nature of the ∼ 590 000 ha Horse river wildfire in the Western Boreal Plain (WBP), northern Alberta, in May of 2016 motivated the investigation of the hydrometeorological conditions that preceded the fire. Historical climate and field hydrometeorological data from a moderate-rich fen watershed were used to (a) identify whether the spring 2016 conditions were outside the range of natural variability for WBP climate cycles, (b) explain the observed patterns in burn severity across the watershed, and (c) identify whether fall and winter moisture signals observed in peatlands and lowland forests in the region are indicative of wildfire. Field hydrometeorological data from the fen watershed confirmed the presence of cumulative moisture deficits prior to the fire. Hydrogeological investigations highlighted the susceptibility of fen and upland areas to water table and soil moisture decline over rain-free periods (including winter), due to the watershed's reliance on supply from localized flow systems originating in topographic highs. Subtle changes in topographic position led to large changes in groundwater connectivity, leading to greater organic soil consumption by fire in wetland margins and at high elevations. The 2016 spring moisture conditions measured prior to the ignition of the fen watershed were not illustrated well by the Drought Code (DC) when standard overwintering procedures were applied. However, close agreement was found when default assumptions were replaced with measured duff soil moisture recharge and incorporated into the overwintering DC procedure. We conclude that accumulated moisture deficits dating back to the summer of 2015 led to the dry conditions that preceded the fire. The infrequent coinciding of several hydrometeorological conditions, including low autumn soil moisture, a modest snowpack, lack of spring precipitation, and high spring air temperatures and winds, ultimately led to the Horse river wildfire spreading widely and causing the observed burn patterns. Monitoring soil moisture at different land classes and watersheds would aid management strategies in the production of more accurate overwintered DC calculations, providing fire management agencies early warning signals ahead of severe spring wildfire seasons.

Mechanization and automation of working processes of tillage and seeding

A new layout of the working elements of the chisel cultivator is presented: V-shaped weeps with the chisel rippers on the end and tooth spring harrows allowing to use the chisel cultivator for primary autumn soil tillage after harvesting. With installation of the rippers in the form of the shank together with the V-shaped weeps, it is possible to carry out solid surface tillage, cut the weeds fully, loosen the lower horizon, level the surface of the tilled field, and improve the water-air regime of the soil. A new model of the cultivator tooth is created performing simultaneously cultivation of the soil layer, cutting of the weeds, and para-plowing. The structure of the chisel cultivator permits the reduction of the metal consumption by 20% as compared to the prototype without worsening the quality of the soil tillage. The pneumatic sowing machine was developed proving single-seed, combined, and bunch planting.

Biodiversity of arbuscular mycorrhizal fungi in Amygdalus scoparia Spach plantations and a natural stand

The biodiversity of arbuscular mycorrhizal fungi (AMF) was surveyed in the Kolm region of Iran in three adjacent sites, a natural stand, a 10-year-old and a 15-year-old plantation of Amygdalus scoparia. To date, there have been few studies of AMF biodiversity in Iran, especially in the western forests of the country. For this study, soil and root samples were taken from A. scoparia rhizosphere soil in spring and autumn. Almost half of the root length was colonized by AMF. We identified 13 AMF species belonging to Glomeraceae, Claroideoglomeraceae or Diversisporaceae. The three plantations differed in terms of soil electrical conductivity, organic C and P. Spore density was significant correlated with P concentration. Root length colonization was correlated only with soil Ca. Species diversity and richness were significantly correlated with soil N, P, organic C and spore density. AMF diversity in 15-year-old plantations was more similar to that in the natural stand than in the 10-year-old plantation. We confirmed that a 15-year-old plantation is not similar in terms of AMF colonization to natural stands. We conclude that more than 15 years are required for AMF colonization of plantations to resemble that of natural stands.

Early autumn soil disturbance decreases persistence of volunteer summer‐annual oilseed rape (Brassica napus)

SummaryVolunteer summer‐annual oilseed rape (sOSR; Brassica napus) is an ongoing concern in Canadian crop production. Large harvest seed losses and secondary dormancy in this species generate a persistent volunteer seedbank. Yield loss in subsequent crops, potential sOSR oil profile contamination and herbicide‐resistance trait introgression create a need for effective sOSR seedbank management. This field study evaluated the effects of timing and type of implement of post‐harvest soil disturbance and seeding a winter cereal on volunteer sOSR population persistence and demographic life‐stage transition rates at five locations in Manitoba, Canada. Following sOSR harvest and supplemental seed rain, seedbank densities ranged from 6770 to 15360 and 50 to 2610 seeds m−2 among sites in autumn and spring respectively. In contrast to European research on winter‐annual oilseed rape, early autumn soil disturbance, shortly after sOSR harvest, was the best strategy to decrease volunteer sOSR persistence (3% population persistence from autumn to spring, compared with 6% in zero tillage). Substantial autumn seedling recruitment (38% of the autumn seedbank) and subsequent winterkill contributed to lower population persistence. Soil disturbance in spring stimulated spring seedling recruitment compared with other disturbance timings (11% and 3% of the spring seedbank, respectively). The implement used for soil disturbance and seeding winter wheat (Triticum aestivum) had minimal effect on population persistence. This research showed that timing of post‐harvest soil disturbance should be utilised as an effective tactic to decrease population persistence of volunteer sOSR via stimulation of autumn seedling recruitment and concomitant winterkill.

Airborne basidiospores as an inoculum source of Typhula variabilis and the effect of hilling on the incidence of Typhula winter rot of carrots

Typhula winter rot on overwintering carrots caused by Typhula variabilis is a newly confirmed disease, and no practical control measure is yet available. To develop a control method, here we researched the infection period of T. variabilis and the time that winter rot appeared on carrots. Using spore traps, we found that basidiospore rain occurred from September to November before snowfall in Memuro, Hokkaido. In addition, carrot leaves collected in autumn had already been infected by T. variabilis. These epidemiological investigations revealed that the pathogen releases basidiospores to infect carrot leaves before snow cover, resulting in root decay under snow. An effective control method was then developed to avoid direct contact of basidiospores of T. variabilis with plant tops by covering the plants with soil in autumn. Thus, the percentage of rotted roots was reduced to about half.

Long-term effect of temperature and precipitation on radial growth in a threatened thermo-Mediterranean tree population

Key messageBased on the first dendroclimatological analyses of the thermo-Mediterranean treePyrus bourgaeana, the positive relationship between the growth and climate (i.e., precipitation) has strengthened in recent decades.The combined effect of climate change and habitat destruction and fragmentation threatens many plant populations and even entire communities in Mediterranean ecosystems. The Iberian pear, Pyrus bourgaeana Decne, a characteristic species of Mediterranean ecosystems, is threatened by both habitat and climate changes. We ask whether and how the growth of mature P. bourgaeana in the thermo-Mediterranean zone (i.e., altitude <700 m) has been affected by long-term climate changes during the last century in a fragmented landscape. Dendrochronological methods were used to find growth–climate relationships. We made the first dendroclimatological analyses and constructed a first 103-year tree-ring chronology (1905–2007) of this species. The tree-ring series revealed large growth variability. We found a clear, strong relationship between tree growth and climate, with annual precipitation being the most important climate factor enhancing radial growth. Our results also showed that warm autumns and winters positively affect growth. There was no temporal stability in the relationship between tree growth and climate. The most general trend was in the relationship between annual precipitation and tree growth: the decrease of rainfall in the last decades of the twentieth century was associated with a constant increase of the correlation coefficient. Water accumulated in the soil in autumn and winter proved to be a key factor augmenting tree growth in the following vegetation period. The climate–growth relationship in P. bourgaeana has strengthened in recent decades apparently due to decreased precipitation levels.

O3 dry deposition flux observation and soil resistance modeling over a bare soil in Nanjing area in autumn

In this study, the concentration of O3 and its deposition flux over a bare soil in Nanjing in autumn were observed by using an eddy covariance system with rapid ozone analyzer. We analyzed the correlation of ozone concentration, deposition flux, and meteorological conditions in order to explore the characteristics of the variations in ozone deposition flux and deposition velocity. We also compared flux and velocity by using modeled soil resistance with observations. The results showed that the diurnal variation of ozone concentration exhibited a single peak distribution, and it increased due to radiation enhancement from September 25th to October 28th, 2015. Ozone deposition flux over a bare soil in autumn was mainly affected by its concentration, with diurnal average values varying from -31.4 to -156.8 ng·s-1·m-2(the negative sign indicated that the deposition direction was toward the ground). As a result of non-vegetation over a bare soil, the ozone deposition flux was significantly influenced by environmental factors. Diurnal average of deposition velocities varied in the range of 0.09-0.30 cm·s-1. The turbulence exchange played a major role in the atmosphere transportation of ozone, and underlying surface condition was particularly important to O3 dry deposition over the bare soil. Soil resistance (Rs) increased exponentially with air relative humidity (RH), and the equation was Rs=89.981e0.0246RH. The parameterized ozone deposition velocities and fluxes were in good agreement with the measured values.

Investigation of Strongyloides stercoralis Seroprevalence in Individuals Who Grow Vegetables and Gather Mushroom in Muğla Province in Turkey.

This study aimed to determine the incidence of Strongyloides stercoralis in individuals who live in rural areas in the towns near Mugla and have contact with humid soil and gather saffron milk cap mushroom in autumn, and to obtain epidemiological data in our region. A total of 281 volunteers were included; 192 of them were the individuals who only gather mushroom, only work in the garden, or gather mushroom as well as work in the garden, while 89 had no contact with the soil. Totally, 281 sera were tested for the presence of S. stercoralis-IgG antibodies by ELISA technique, using a commercial kit (DRG® Diagnostics Strongyloides IgG ELISA EIA-4208; Germany). One of 281 volunteers (0.3 %) was found positive for S. stercoralis-IgG antibodies, while the other 280 volunteers (99.7 %) were found negative. Thirty-seven, 33, and 43 of 192 volunteers reported wearing only boots, only gloves, and both boots and gloves, respectively. Seventy-nine of 192 volunteers reported wearing neither boots nor gloves. This preliminary study is the first study that involves the individuals with soil contact in our country, and it was concluded that this study will offer an insight into the other studies on S. stercoralis.

Effects of different mulching materials on nitrate metabolism in soil of apple root-zone in summer and autumn.

This study explored the effects of mulching straw mat, agricultural carpet, transparent-plastic film and horticultural fabric on nitrification-denitrification, nitrate reductase (NR), nitrite reductase (NiR), ammonium, nitrate and nitrite nitrogen in root-zone soil grown with three-year old apple trees (Malus domestica cv. Starkrimson) during summer and autumn. Results showed that the four treatments decreased nitrification intensity in summer soil, NiR activity in summer-autumn soil and the variation coefficient of nitrification-denitrification intensity and NR in both summer and autumn soil. The treatments increased the denitrification intensity, NR activity, ammonium nitrogen contents in summer-autumn soil and ammonium nitrogen contents in autumn soil. Straw mat treatment increased denitrification intensity and nitrate nitrogen contents in both summer and autumn soil and decreased the activity of NR and NiR in summer soil. The coefficient of variation of nitrification-denitrification intensity and NR activity treated by mulching straw mat was lower than those in the other treatments in both summer and autumn soil. Agricultural carpet increased the NR and NiR activity in summer soil, the nitrate nitrogen contents in summer-autumn soil and the denitrification intensity in autumn soil and decreased denitrification intensity in summer soil. Transparent-plastic film increased the nitrite nitrogen contents in summer soil, the contents of nitrate nitrogen in summer-autumn soil, the nitrification intensity and NiR activity in autumn soil, and decreased nitrate nitrogen contents in summer soil. Horticultural fabric increased denitrification intensity in summer soil, nitrification intensity in summer-autumn and autumn soil and the nitrate nitrogen contents in autumn soil. The four mulching treatments all promoted plant growth. In the four mulching treatments, the new shoot and trunk thickening growth were more under straw mat and horticultural fabric treatments. The four mulching treatments had different effects on nitrate metabolism in summer and autumn soil, but they were able to stabilize the soil nitrate metabolism and transformation. Among the treatments, straw mat had the best stable effect.

Carbon and water exchange over a temperate semi-arid shrubland during three years of contrasting precipitation and soil moisture patterns

Water is considered a key factor affecting ecosystem carbon exchange in dryland regions. However, the relationship between inter-annual variations in precipitation and ecosystem productivity remains to be clarified for arid and semi-arid areas. Based on eddy-covariance measurements, we examined how ecosystem production in a shrubland of northern China varied over three years (2012–2014) with contrasting precipitation and soil moisture patterns. Net ecosystem production (NEP) was 77±10 (±standard deviation), −4±10 and −22±5gCm−2 in 2012–2014, respectively, indicating a rapid shift from an annual sink to a source of carbon. Gross ecosystem production (GEP), total ecosystem respiration (TER) and evapotranspiration (ET) also declined over the three years. Annual carbon and water fluxes appeared to be suppressed in years with low spring soil moisture, which declined dramatically from 2012 to 2014. GEP declined more than TER and ET, leading to reduced carbon sequestration capacity and water use efficiency (WUE=GEP/ET). Neither annual nor growing-season precipitation could explain the year-to-year variations in carbon fluxes, whereas at our site ET was a better proxy for water available to ecosystem carbon exchange on an annual basis. Autumn soil moisture levels were carried over winter to the following spring, and, thus, may affect the rates of leafout, plant growth and carbon uptake in the early- to mid-growing season. Our conclusions were drawn from only three years of measurements and are therefore preliminary. Longer timeseries encompassing a wider range of precipitation and soil moisture conditions are needed to confirm or refine these conclusions. Our findings highlight the importance of precipitation timing and soil moisture carry-over in controlling ecosystem productivity. Winter warming and decreases in autumn and winter precipitation may induce spring drought and thus impair the carbon sequestration potential of shrubland and steppe ecosystems in semi-arid and arid Eurasia.

Influence of brassicaceous soil amendments on potentially beneficial and pathogenic soil microorganisms and seedling growth in Douglas-fir nurseries

Fusarium, Cylindrocarpon and Pythium spp. are the major soil-borne pathogens of conifer seedlings. Soil fumigation with methyl bromide and chloropicrin has been the most effective method for reducing the population density and disease pressure of these organisms. Due to safety and environmental concerns, use of methyl bromide as a pre-plant soil fumigant has been abolished in the majority of cropping systems. However, the conifer seedling industry continues to use methyl bromide under a quarantine pre-shipment exemption due to a lack of effective alternatives. Toward identifying alternatives to methyl bromide for management of soil microbial populations, a three-year field study was conducted in northwest USA. The objective of this study was to examine the effects of brassica seed meals and green manures on potentially pathogenic and beneficial microorganisms, soil health, and seedling growth in conifer nursery fields. The study treatments were Brassica juncea seed meal, B. carinata seed meal, Sinapis alba seed meal, B. juncea green manure, methyl bromide/chloropicrin fumigation, and a non-treated control, with four replications in a randomized complete block design. The treatments were incorporated into soil in autumn or early spring, and Douglas-fir (Pseudotsuga menziesii) seedlings were transplanted into plots in late spring. Population densities of Fusarium, Cylindrocarpon, Pythium, actinomycetes, and Trichoderma; mineralizable nitrogen; and dehydrogenase enzyme activity in soil were assessed at pre-transplant, post-transplant, and seedling harvest. The pre-treatment soil pathogen count was similar among study plots. At transplant time, Fusarium spp. densities in soil were generally similar among most brassica treatments but fumigated plots generally had less Fusarium. Treatment with S. alba, however, increased soil densities of Fusarium spp. In 2012, Fusarium spp. density was significantly lower after B. juncea green manure incorporation [1.8 log CFU (colony forming units)] than after chemical fumigation (2.4 log CFU) or in the untreated control (2.6 log CFU); whereas the soil density of potentially antagonist Trichoderma spp. was significantly greater in fumigated plots (3.7 log CFU) followed by B. juncea green manure (3.4 log CFU) and lowest in control (3.2 log CFU). Fumigation produced the largest seedlings but B. juncea green manure also produced significantly larger seedlings than control. Dehydrogenase activity, an indicator of soil microbial activity, was greatest with B. juncea green manure and lowest in fumigated soil. Mineralizable nitrogen in soil followed the same trend. These results suggest that B. juncea green manure may have a suppressive effect on soil-borne pathogens, and maintain or improve soil and seedling health.