Autumn Nitrogen Research Articles

Autumn nitrogen enrichment destabilizes ecosystem biomass production in a semiarid grassland.

Nitrogen (N) deposition decreases the temporal stability of ecosystem aboveground biomass production (ecosystem stability). However, little is known about how the responses of ecosystem stability differ based on seasonal N enrichment. By adding N in autumn, winter, or growing season, from October 2014 to May 2020, in a temperate grassland in northern China, we found that only N addition in autumn resulted in a significantly positive correlation between ecosystem mean aboveground net primary productivity (ANPP) and its standard deviation and significantly reduced ecosystem stability. Autumn N-induced reduction in ecosystem stability was associated with the vanished negative effect of community-wide species asynchrony (asynchronous dynamics among populations to environmental perturbations) on the standard deviation of ecosystem ANPP in combination with the emerged positive effect of dominance (Simpson's dominance index that indicates the relative weight of dominant species in a community). Our findings indicate that autumn N addition might overestimate the negative effect of annual atmospheric N deposition on ecosystem stability, suggesting that to better evaluate the influence of N deposition in temperate grasslands, both field experiments and global modeling should consider not only the annual N load but also its seasonal dynamics. Moreover, further studies should pay more attention to the alteration in the ecosystem temporal deviations, which might be more sensitive to human-induced environmental changes.

Performance and bacterial community analysis of a two-stage A/O-MBBR system with multiple chambers for biological nitrogen removal.

A two-stage anoxic/oxic (A/O)-moving bed biofilm reactor (MBBR) system with multiple chambers was established for municipal wastewater treatment. At the total hydraulic retention time (HRT) of 11.2h and nitrate recycling ratio of 1, the removal efficiencies reached 83.8%, 82.5%, and 77.8% for soluble chemical oxygen demand (SCOD), 98.0%, 97.5%, and 94.9% for ammonia nitrogen (NH4+-N), and 91.8%, 92.0%, and 87.7% for total inorganic nitrogen (TIN) in summer, autumn and winter, respectively. Biofilms with functional bacterial populations were formed in the pre-anoxic reactors, the pre-oxic reactors, the post-anoxic reactors and the post-oxic reactors of the two-stage A/O-MBBR system. The highest nitrification potential was found in the last oxic reactor of the first A/O-MBBR subsystem with the highest relative abundances of the functional genes including [EC:1.14.99.39] and [EC:1.7.2.6]). The highest denitrification potential was found in the post-anoxic reactors with the highest relative abundances of the functional genes including [EC:1.7.2.1], [EC:1.7.2.5] and [EC:1.7.2.4]. This work constructed an efficient municipal biological nitrogen removal technology to achieve high effluent nitrogen standards in winter, and investigated its working mechanism to provide a basis for its design and optimization.

Fertilization of oilseed rape with and without autumn nitrogen dose

Investigation of the effect of autumn nitrogen dose, in comparison to nitrogen fertilization without autumn dose, on rapeseed yield, oil content and oil production was the main aim of the experiment. The plot scale experiment was conducted during three experimental years 2013 – 2016 in terms of agricultural cooperative in Mojmírovce. The experiment consisted of three treatments of nitrogen fertilization. The block method of experimental plot size of 600 m2 was used in this experiment. It was tested in triplicate. The total dose of nitrogen was 240 kg ha-1. Both treatments were fertilized during spring in phonological growth stages BBCH 20, 30 and 51. There was applied autumn nitrogen dose in BBCH 15 at treatment 2. Considering the weather conditions of the previous year, a significant effect of autumn nitrogen dose was not expected in this experiment. Results were predictably, significantly influenced by different weather conditions. The experimental year 2013/2014 was wetter and warmer than the other two experimental years. The highest average yield of seed, 3.63 t ha-1 was reached at treatment 3 without any autumn nitrogen application. The average oil content fluctuated from 44.36 % to 45.09 %. The highest average oil content 46.72 % was observed in weather more favourable the experimental year 2013/2014. Although the highest average oil production of treatment 3 reached 1625.04 kg ha-1, the difference in oil production between treatments with and without an autumn dose of nitrogen was not statistically significant, similarly as yield. The highest average oil production was statistically significant in the experimental year 2013/2014. Keywords: oilseed rape, the yield of seed, oil content, oil production, autumn nitrogen dose

Winter crop choice and body condition loss change the eco-efficiency of sheep flocks

Lamb survival (ewe reproductive performance) and lamb growth are key levers to changing eco-efficiency, particularly in hill country systems. New research has highlighted reproduction losses when feeding some winter crop options such as fodder beet. Current research findings are used to understand the impact of changes in reproductive performance of sheep flocks caused by body condition change and winter forage crop choices on whole farm eco-efficiency. Eight farms were anonymously selected from an existing database, four with ‘low rainfall’ and four with ‘high rainfall’, averaging 590 and 1090 mm/annum respectively to represent the cool temperate climates of southern New Zealand. Ewe and lamb survival, and lamb liveweight gain to weaning were altered to reflect the impacts of either losing or retaining body condition in late gestation, either on a fodder beet or brassica diet in mid-late gestation. Ewes retaining body condition with fodder beet scenarios were fed a supplement added to ensure adequate protein nutrition using a combination of Lucerne hay, soy meal, and urea. General adjustments made to maintain pasture use similar to the original farms included adjusting lamb sales date, supplement making, stocking rate and autumn nitrogen use. Eco-efficiency was reduced using fodder beet as a winter forage as greenhouse gas emissions were increased per unit of product. The loss of condition score during mid to late pregnancy also led to a reduction in eco-efficiency, though this was more severe when feeding fodder beet. The impacts of fodder beet were mitigated if the diet was balanced for protein. Nitrogen and phosphorus loss from soil was low, and reduced under fodder beet feeding conditions, due to the smaller area of cropping than traditional brassicas.

Seasonal variations of nutrient concentrations and their ratios in the central Bohai Sea

The Bohai Sea is a typical semi-enclosed sea in the northwest Pacific, which is subject to serious eutrophication due to human activities. Similar to hydrographic variables such as water temperature and salinity, the nutrient concentrations and ratios in the Bohai Sea also exhibit seasonal variations. However, the effects of external inputs, biological processes, and benthic processes on these seasonal variations have not been quantified to date. To address this issue, a physical–biological coupled model was developed to capture the seasonal nutrient cycling in the central Bohai Sea. The simulation results revealed apparent seasonal variations in the concentrations of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silicate (DSi). The N/P ratio (as the molar ratio of DIN/DIP) also exhibited an apparent seasonal variation, with the maximum and minimum values in surface water occurring in summer (>100) and winter (<30), respectively. The Si/N ratio (as the molar ratio of DSi/DIN) was slightly higher in summer than in other seasons. The budget for three types of nutrient indicated that the biological processes determined the seasonal variations in nutrient concentrations and the N/P ratio. The external inputs of nutrients via river input, atmospheric deposition, and sediment release were probably important in summer when they could alleviate the reduced nutrient concentrations due to biological processes. To maintain a reasonable nitrogen budget, it was necessary to include benthic nitrogen loss, which removed a large amount of inorganic nitrogen in summer and autumn. In addition, the variation of N/P ratio of phytoplankton uptake can reduce the ratio of DIN to DIP in surface water by ~20 in summer as compared to the calculation with a fixed N/P ratio (16:1) in phytoplankton uptake.

EFFECT OF SOWING METHOD AND N APPLICATION ON SEED YIELD AND N USE EFFICIENCY OFWINTER OILSEED RAPE

In the conditions of the Right-Bank Forest-Steppe, the cultivation of winter rapeseed crops after winter wheat usually leads to a delay in sowing the latter and deterioration of autumn plant development. Based on data from a field experiment conducted in 2016/2017, 2017/2018 and 2018/2019, the aim of this study was to investigate how sowing delay affects seed yield, nitrogen uptake by seeds and significant efficiency of nitrogen use by winter rape plants; to check the ability of autumn and spring application of nitrogen fertilizers to compensate for the negative impact of delays in sowing crops; and estimate the minimum autumn development for optimal seed yield. To solve the set tasks, a combination of four sowing dates (from the first week of August to the third week of September) and four autumn nitrogen applications (0, 30, 60 and 90 kg / ha per year) was fixed. In each of these 16 variants, nitrogen application was performed 5 times in the spring (0/0, 40/40, 80/80, 120/120, 140/140 kg / ha, etc.) in order to estimate the individual nitrogen reaction curves. Nitrogen accumulation by aboveground mass of plants in autumn, seed yield and nitrogen uptake by seeds were determined. It was found that sowing the crop after mid-September significantly reduced yields. Application of nitrogen fertilizers in autumn in the amount of at least 30 kg / ha per year increased the yield and absorption of nitrogen seeds without any significant interaction with the sowing period and spring application of nitrogen fertilizers. Increasing the dose of spring fertilizer application to 130 kg / ha increased seed yield. Nitrogen utilization efficiency decreased with increasing application rate when winter oilseed rape plants used nitrogen applied in the fall to a lesser extent than in the spring. In order to achieve high yields, it was necessary for the above-ground mass of plants to absorb nitrogen at the level of at least 10-15 kg / ha at the end of the autumn vegetation. From an ecological point of view, the optimal autumn development of plants should be achieved by choosing an adequate sowing date, rather than using additional nitrogen in autumn.

Arbuscular Mycorrhizas Traits and Yield of Winter Wheat Profiled by Mineral Fertilization

Our aim is to evaluate the changes in arbuscular mycorrhiza characteristics of winter wheat in a three-year experiment. Study results show that fertilizers produce strong variations in arbuscular mycorrhiza extension, with colonization frequency values within 76–98%. The intensity of colonization is only 12% when phosphorus (P) exceeds nitrogen (N) in autumn, but reaches 38% when the N:P ratio is equal. Root colonization shows no consistency from one experimental year to another, with the largest fluctuations recorded in colonization intensity (22–65%) and arbuscules abundance (0–5%). Arbuscules are maintained below 1% by fertilizer with more P than N. Colonization forecasting models indicate P as a factor for the reduction of symbiosis. Each kg of applied P can reduce the colonization frequency by 0.28% and intensity by 0.37%. The maximum of the colonization degree is 61% due to the synergy of equal N and P doses in autumn and ammonium nitrate applied in spring. The application of multiple moderate doses acts as a stimulant for the development of a large root-fungal interface.

Autumn flooding disrupts seasonal nitrogen storage and impacts spring growth in Quercus texana seedlings

Autumn flooding reduced nitrogen uptake and fine root mass. Leaf nitrogen resorption increased, but overall autumn nitrogen accumulation was negligible in flooded seedlings. Subsequently, spring survival and growth were decreased. Since nitrogen (N) is often limiting in terrestrial ecosystems, N is conserved in trees by resorption before leaf senescence. Bottomland forests are prone to flooding, which could reduce N uptake, and may decrease phloem transport, which is essential for N resorption. Therefore, we hypothesized that autumn flooding may diminish both N uptake and N resorption in trees, and this would reduce spring growth. Two-year-old Quercus texana seedlings either had no flood or had their complete root system flooded during dormancy induction, the period in autumn when trees prepare metabolically and physiologically for winter dormancy. We measured seedling growth and nutrient contents before flooding and after leaf fall and determined impacts of autumn flooding on growth during the subsequent spring. Autumn flooding resulted in a small increase in N resorption from leaves. In non-flooded seedlings, much more N accumulated in stems and roots than the amount resorbed from leaves, suggesting that there was substantial N uptake during the autumn dormancy induction period. However, flooding severely reduced accumulation of N in roots and stems during autumn, probably by directly reducing uptake and by increasing fine root mortality. Winter survival was reduced 50% by autumn flooding. Autumn-flooded seedlings that survived winter had greater new root growth in spring than non-flooded seedlings, but substantially decreased stem diameter growth. Our results indicate that Q. texana seedlings which are flooded during dormancy induction may be less competitive the following spring due to fine root mortality and reduced nutrient storage, which negatively impact spring growth.

Windstorm disturbance triggers multiple species invasion in an urban Mediterranean forest

Plant invasion in forest ecosystems is a serious ecological and economic issue, deserving attention by researchers, managers and policy-makers worldwide. Many invasive plants have been reported as early successional species able to colonize disturbed areas following abrupt changes in microhabitat and resource availability. We investigated disturbance effects of a severe windstorm generated by a wet microburst (hail and rain at 160 mm h-1) remarkably affecting the canopy cover of an old-growth Quercus ilex urban forest in Southern Italy. This stand-replacing disturbance produced a mosaic of 103 gaps, 5.6 to 1632 m2 in size, over an area of 1.53 ha, uprooting 76% of the trees and decreasing thereby 85% of the standing above-ground dry biomass into the gaps. By intensive monitoring we compared above- and below-ground microclimate, soil moisture and mineral N availability in paired disturbed and control areas of the study forest. Within newly formed gaps we observed a seasonally consistent 70% higher content of nitrate nitrogen, 29% and 47% decreases of ammonia nitrogen in summer and autumn, respectively, and a higher moisture in topsoil, in addition to different above- and below-ground microclimatic conditions, with canopy cover mitigating extreme temperatures. One year after the windstorm, the microhabitat shift promoted the establishment in gaps of 15 native and 10 alien taxa previously absent in both disturbed and control plots. In such conditions, the rarefaction of the dominant Q. ilex canopy cover and the occurrence of empty niches prone to invasion could dramatically affect the local community structure and diversity. Our data indicate that stand-replacing windstorm can transiently transform the studied urban evergreen forest to an early allogenic successional community dominated, in the medium and large gaps, by annual and perennial non-native species. This is particularly relevant under a perspective of possible increasing frequency of windstorm events in the Mediterranean region in the near future.

Above- and belowground nitrogen uptake of winter catch crops sown after silage maize as affected by sowing date

Abstract Regions in north-western Europe characterized by high density of livestock/biogas plants and extensive silage maize production are facing major environmental challenges due to excessive residual soil mineral nitrogen (N) in autumn and hence nitrate leaching. Winter catch crops (CC) have potential to accumulate residual N; however, the N uptake potential after maize harvest in autumn and spring remains unclear. Therefore, a two-year field trial (April 2012–April 2014) was conducted at three sites, to quantify the combined effects of four consecutive CC sowing dates (10 Sep; 20 Sep; 30 Sep and 15 Oct) and two CC species (rye, Secale cereale. L. and Italian ryegrass, Lolium multiflorum Lam.) on DM accumulation and N uptake of CC above- and belowground in autumn and spring, and to derive functional relationships. The results clearly showed that rye was more effective in accumulating biomass and nitrogen than Italian ryegrass. The better performance of rye was related to increased growth intensity of roots and shoot, a different allocation pattern and higher N uptake efficiency. An exponential function of temperature sum (Tsum) produced a reliable prediction of above- and belowground biomass and N. To achieve an agronomically relevant N uptake of 20 kg N ha−1, rye required 278 °Cd Tsum, which corresponds to a sowing date latest in the second decade of September. Under favourable growing conditions, a biomass accumulation of up to 5 Mg DM ha−1, corresponding to 83 kg N ha−1 above- and belowground, seems achievable under the given environmental conditions. In continuous maize grown under the environmental conditions of Northern Germany, however, catch crops will not reach a relevant N uptake on the long-term average.

Straw management and optimal N fertilization in seed production of timothy (Phleum Pratense L.) and Meadow Fescue (Festuca Pratensis Huds.)

ABSTRACTThe market for herbage seed straw has diminished in many seed-production areas due to less livestock. Seed growers are therefore looking for alternatives to straw removal, which up to now has been the most common practice. During 2000–2006, different alternative straw chopping methods, both at the back of the combiner and with a tractor-mounted flail-chopper, and field burning strategies were evaluated in seed crops of timothy (Phleum pratense) and meadow fescue (Festuca pratensis) in southeast Norway. The requirement for an extra N input in autumn (30–40 kg ha-1) when practising straw chopping was also examined. Compared to straw removal, straw chopping at the back of the combiner during seed harvest did not reduce seed yield in the following year as long as stubble height was low (<10 cm in timothy) and the straw spread uniformly in the field. On average, seed yield was 1–4% and 1–9% higher compared to straw removal in timothy and meadow fescue, respectively. If the chopped straw was spread unevenly, or long stubble was left at combining, it is recommended to use a tractor-mounted flail-chopper after harvest. The experiments did not provide any support for an extra input of nitrogen in autumn, either in timothy or meadow fescue, when the straw was chopped rather than removed. Burning of stubble and straw soon after seed harvest was another efficient clean-up method after harvest, which increased seed yield 9–15% and 17–20% compared to straw removal in the two species, respectively. However, as the burning method is risky and causes smoke emissions, it is normally not recommended. It is concluded that for most seed growers, the most effective, least laborious and most environment-friendly alternative to straw removal will be to chop the straw at the back of the combiner during seed harvest.

Diurnal changes in water-soluble carbohydrate concentration in lucerne and tall fescue in autumn and the effects on in vitro fermentation

The aim of the experiment was to study diurnal variation in water-soluble carbohydrate (WSC) concentrations in leaf and stem of tall fescue and lucerne in autumn and to determine the impact of these changes on the rate and the extent of in vitro fermentation. Vegetative herbage of lucerne and tall fescue were sampled at 0900, 1300 and 1700 h, following three consecutive regrowths between April and May. Whole plants, leaf and stem were analysed for chemical composition and in vitro gas production. There was a linear increase in WSC throughout the day for all plants and plant components (P < 0.001). In both fescue and lucerne, this rise resulted in an increased rate of gas production, although this relationship was more pronounced in fescue. Use of time of day to govern grazing management decisions to potentially improve the rumen supply of WSC and nitrogen in autumn can be achieved from tall fescue or lucerne pastures.

A review of the effect of autumn nitrogen fertiliser on pasture nitrogen concentration and an assessment of the potential effects on nitrate leaching risk

The aim was to test the hypothesis that nitrogen (N) fertiliser applied in autumn increases N leaching by increasing pasture N concentration (Nconc) and thus increasing partitioning of excretal N to urine. A review of past data showed that N fertiliser application generally had only a small effect on pasture Nconc, on average. The general effect was ±5% or less for single applications of 50 kg N/ha or less, compared with nil N fertilised pasture, depending on the season. Based on this, we estimated that the increase in pasture Nconc from autumn fertiliser is less important for nitrate leaching risk than the extra forage grown, and the resultant extra N consumed and excreted as a result of the applied fertiliser N. However, if the period between fertiliser application and grazing is short, the elevation in Nconc is likely to be larger with a greater influence on partitioning to urinary N. Keywords: Nitrogen, fertiliser, pasture nitrogen concentration, urine

OPTIMUM DISTRIBUTION BETWEEN AUTUMN-APPLIED AND SPRING-APPLIED NITROGEN IN SEED PRODUCTION OF TALL FESCUE

The effect of different autumn and spring nitrogen (N) application rates on plant establishment, plant development, and seed yield were tested in a field experiment using tall fescue (Festuca arundinacea Schreb.). Results clearly showed that the optimum distribution of N between autumn and spring to achieve the highest seed yield and economical benefit was dependent on the choice of cover crops and location. The economically optimum N application rate was in the range from 44 to 73 kg ha−1 in autumn and 94 to 157 kg ha−1 in spring. The results are discussed in relation to Danish N regulations and plant establishment and development.

The influence of winter oilseed rape (Brassica napusssp.oleiferavar.biennis) canopy size on grass weed growth and grass weed seed return

SUMMARYFour experiments conducted over three seasons (2002–05) at the Crops Research Unit, University of Reading, investigated effects of canopy management of autumn sown oilseed rape (Brassica napusL. ssp.oleiferavar.biennis(DC.) Metzg.) on competition with grass weeds. Emphasis was placed on the effect of the crop on the weeds.Rape canopy size was manipulated using sowing date, seed rate and the application of autumn fertilizer.Lolium multiflorumLam.,L.×boucheanumKunth andAlopecurus myosuroidesHuds. were sown as indicative grass weeds.The effects of sowing date, seed rate and autumn nitrogen on crop competitive ability were correlated with rape biomass and fractional interception of photosynthetically active radiation (PAR) by the rape floral layer, to the extent that by spring there was good evidence of crop: weed replacement.An increase in seed rate up to the highest plant densities tested increased both rape biomass and competitiveness, e.g. in 2002/3,L. multiflorumhead density was reduced from 539 to 245 heads/m2and spikelet density from 13 170 to 5960 spikelets/m2when rape plant density was increased from 16 to 81 plants/m2. Spikelets/head ofLoliumspp. was little affected by rape seed rate, but the length of heads ofA. myosuroideswas reduced by 9% when plant density was increased from 29–51 plants/m2.Autumn nitrogen increased rape biomass and reducedL. multiflorumhead density (415 and 336 heads/m2without and with autumn nitrogen, respectively) and spikelet density (9990 and 8220 spikelets/m2without and with autumn nitrogen, respectively). The number of spikelets/head was not significantly affected by autumn nitrogen.Early sowing could increase biomass and competitiveness, but poor crop establishment sometimes overrode the effect. Where crop and weed establishment was similar for both sowing dates, a 2-week delay (i.e. early September to mid-September) increasedL. multiflorumhead density from 226 to 633 heads/m2and spikelet density from 5780 to 15 060 spikelets/m2.

Effects of early season and autumn nitrogen applications on young ‘Keisie’ canning peach trees on a sandy, infertile soil

The effects of autumn (A) and early season (S) nitrogen (N) applications were investigated in a young ‘Keisie’ canning peach orchard on an infertile sandy soil in the Western Cape Province, South Africa. Over the first four consistent bearing seasons, AN was supplied at four levels, averaging 19.9, 39.8, 59.9 and 119.7 g N tree−1, respectively (treatments AN1, 2, 3, and 4). Early-season N was supplied at three levels, averaging 42.4 (SN1), 82.2 (SN2) and 157.0 (SN3) g N tree−1. Four-year average yields tended to increase as the AN application rate increased from AN2 to AN4 (39.8 to 119.7 g N tree−1), and also tended to increase with increasing SN application rate. At the lowest level of AN (19.9 g tree−1) the yield and growth responses to moderate (82.2 g tree−1) and high (157.0 g tree−1), but not to low (42.4 g tree−1) rates of SN, were large. Thus, whilst yields in AN2, AN3 and AN4 were greater by 4.6% on average in SN2 than in SN1, and by 6.8% in SN3 than SN2, the yields in AN1 were 44.6% greater in SN2 than SN1 and 1.2% greater in SN3 than in SN2. Only in SN1 were progressive yield responses observed with increasing AN. Annual increases in trunk circumference, averaged over the same period, showed the same pattern of response to AN, and to SN, as average yield. Fruit and leaf N concentrations increased with SN at all levels of AN, but fruit diameter and single fruit mass increased with SN only at the lowest level of AN. A high total N rate of 222 g tree−1 (247 kg ha−1), in three applications, was required for a 26.4 t ha−1 yield in the seventh season on this infertile, sandy soil.

Effects of interspecific competition and nitrogen seasonality on the photosynthetic characteristics of C 3 and C 4 grasses

This study examined impacts of interspecific competition and seasonal nitrogen variability on the photosynthetic characteristics of a C 3 ( Leymus chinensis) and a C 4 ( Chloris virgata) grass species. Plants received the same total amount of nitrogen but in three seasonal patterns, i.e., one-peak model (more nitrogen in summer than in spring and autumn), two-peak model (more nitrogen in spring and autumn than in summer) and even model (nitrogen evenly distributed over the growing season). Interspecific competition exerted negative impacts on assimilation rate ( A), quantum efficiency ( Φ PSII), light-saturated assimilation rate ( A sat) of the C 3 species but had no effect on the C 4 species. Nitrogen treatment did not affect A, Φ PSII, A sat or maximum rate of carboxylation ( V c,max) of either the C 3 or C 4 species at any of the measuring dates. The C 3 and C 4 species showed different seasonal dynamics of photosynthetic characteristics over the growing season. The highest photosynthesis in the C 3 species occurred in September and the lowest in July. The opposite seasonal pattern was observed in the C 4 species. There were positive linear relationships between A and nitrogen amount applied in the C 3 species under two-peak model and in the C 4 species under one-peak model treatment. Our observations of no effect of nitrogen treatment on the photosynthetic performance of the C 3 and C 4 species suggest that the temporal differentiation between the C 3 and C 4 species is determined primarily by temperature or other factors rather than the seasonal dynamics of nitrogen availability.

Overlapping resource use in three Great Basin species: implications for community invasibility and vegetation dynamics

Summary In the Great Basin of the western United States of America, the invasive annual grass Bromus tectorum has extensively replaced native shrub and bunchgrass communities, but the native bunchgrass Elymus elymoides has been reported to suppress Bromus. Curlew Valley, a site in Northern Utah, provides a model community to test the effects of particular species on invasion by examining competitive relationships among Elymus, Bromus and the native shrub Artemisia tridentata. The site contains Bromus/Elymus, Elymus/Artemisia and monodominant Elymus stands. Transect data indicate that Elymus suppresses Bromus disproportionately relative to its above‐ground cover. Artemisia seedlings recruit in Elymus stands but rarely in the presence of Bromus. This relationship might be explained by competition between the two grasses involving a different resource or occurring in a different season to that between each grass and Artemisia. Time reflectometry data collected in monodominant patches indicated that in spring, soil moisture use by Bromus is rapid, whereas depletion under Elymus and Artemisia is more moderate. Artemisia seedlings may therefore encounter a similar moisture environment in monodominant or mixed perennial stands. However, efficient autumn soil moisture use by Elymus may help suppress Bromus. In competition plots, target Artemisia grown with Bromus were stunted relative to those grown with Elymus, despite equivalent above‐ground biomass of the two grasses. Competition for nitrogen in spring and autumn, assessed with 15N tracer, appears to be secondary to moisture availability in determining competitive outcomes. Elymus physiology and function appear to play an important role in determining the composition of communities in Curlew Valley, by maintaining zones free of Bromus where Artemisia can recruit.

Nitrate leaching: modifying the loss from mineralized organic matter

SummaryThe impact on nitrate leaching of agronomic practices designed to immobilize nitrogen in autumn and winter was investigated over 4 years. Experimental treatments (reducing tillage depth, incorporating harvest residues, reducing fertilizer N by growing unfertilized grass or by spring‐sown rather than autumn‐sown crops) were compared with a control treatment in which autumn crops were sown after burning harvest residues, mouldboard ploughing and seedbed preparation. Winter cover cropping was also compared with winter fallowing. In the first year, incorporation of harvest residues or reducing tillage depth significantly decreased nitrate leaching compared with the control. Unfertilized grass did not affect leaching in the first winter but significantly decreased it in years 2 and 3. When winter cover crops were grown, nitrate leaching was never less than that under an autumn‐sown cereal, and in the subsequent year leaching could be significantly greater. Winter fallowing caused the most nitrate leaching over the year. In the winter following a spring‐sown crop, leaching under an autumn‐sown crop greatly increased. Summed over 4 years, most leaching occurred with the winter fallow—spring cropping treatment; it was 18% more than where a winter cover crop preceded the spring crop. Reducing tillage depth or incorporating harvest residues did not significantly decrease leaching. Unfertilized grass ley followed by an autumn‐sown cereal in the fourth year was the only treatment that significantly decrease leaching. Unfertilized grass ley followed by an autumn‐sown cereal in the fourth year was the only treatment that significantly reduced leaching loss compared with the control. Incorporating harvest residues resulted in a balance between annual N inputs and outputs. All other treatments required substantial net annual N mineralization to balance annual inputs and outputs.

Spring and autumn nitrogen fertiliser effects, with and without phosphorus, potassium and sulphur, on dairy pastures: Pasture nutritive value and mineral content

Experiments were conducted at three sites to examine effects of applying different nitrogen (N) fertilisers at 45 kg N ha−1, with and without phosphorus (P), potassium (K) and sulphur (S) on dairy pasture nutritive value and mineral content in autumn and spring. Pasture nutritive value was assessed by measures of crude protein (CP), metabolisable energy (ME), water‐soluble carbohydrates (WSC) and neutral detergent fibre (NDF). Pasture mineral content was assessed by estimates of the major minerals phosphorus (P), potassium (K), sulphur (S), sodium (Na), calcium (Ca), and magnesium (Mg), and trace minerals manganese (Mn), iron (Fe), copper (Cu) and zinc (Zn). Apart from some exceptions, applications of N, with and without additional P, K and S generally increased pasture CP and ME content in autumn and CP content in spring. Again with some exceptions, pasture WSC content was unaffected by fertiliser application in autumn, but was decreased by some treatments (containing N and N with P, K and S) in spring. Fertiliser treatments generally had no effect on pasture NDF content at Sites 1 and 3 during autumn and spring. At Site 2, some treatments (containing N and N with P, K and S) reduced pasture NDF content in autumn while during spring some treatments (containing N and N with P, K and S) increased pasture NDF content. Different N fertilisers applied at the same rate, with and without additional P, K and S, generally produced the same effect on pasture nutritive value. The application of P, K and S in the absence of N generally had no effect on pasture nutritive value. Apart from some exceptions, pasture P content was increased by fertiliser treatments including P, K and S, but N on its own did not influence pasture P content. Pasture K content was generally not influenced by treatment. At Site 1 during autumn and spring, and at Site 3 during spring, treatments containing P, K and S increased pasture S content while applications of N had no effect. At Site 2 during autumn, P, K and S increased pasture S content relative N only, while during spring pasture S content was generally increased by all treatments. At Site 3 during autumn, applications of N decreased pasture S content while P, K and S increased pasture S content relative to no fertiliser. Pasture Na and Ca content were generally not influenced by treatment. Pasture Mg content was not influenced by treatment at Sites 2 and 3. At Site 1 during autumn and spring, however, some treatments (containing N and N with P, K and S) increased pasture Mg content. Fertiliser treatments produced no consistent patterns or differences with respect to trace minerals (Mn, Fe, Cu and Zn).