Above-ground Herbage Research Articles

Effect of magnetic field on growth and protein concentration in aboveground herbage of field pea (Pisum sativum L.) cultivars

Research of the exposure of young pea (Pisum sativum L.) plants of two cultivars (Gold and Uran) to magnetic field (MF) of different flux densities (250 and 350 mT) was conducted in controlled conditions during 20 days. Pea plants were continuously exposed to magnetic field of neodymium magnets. Upon the statistical analysis there were revealed significant effects of MF treatments (P 0.01) on root freshweight, aboveground herbage freshweight and total plant freshweight. Cultivars differed in root (P 0.05), stem (P 0.01) and total plant length (P 0.05). There was also revealed significant Treatment × Cultivar interaction for all the tested traits.

Evaluation of forage resources under poorly drained soils for dairy systems

Alfalfa is crucial for dairy farms, but its potential production and persistence can be hindered by waterlogging, poorly drained soils, and high-water tables. The objectives of this study were (a) to evaluate herbage mas and quality of different forage species on poorly drained soils, and (b) to evaluate root biomass accumulation and their impacts on soil physical properties. The study was conducted in Santa Fe, Argentina, on an Aquic Argiudoll. Four treatments were established in March 2017: Alfalfa (control), Fescue, Annual (Ryegrass and Sorghum rotation regime), and Mixture (a mixture of Brome, Chicory, Red clover, and White clover). Aboveground herbage mass and nutritive quality were analyzed frequently, while roots and soil samples were collected after 2 years for further analysis. Root biomass was significantly higher (p < 0.05) in Annual and Mixture pastures compared to Alfalfa and Fescue. Lower root biomass in Alfalfa was attributed to temporary waterlogging and low plant density. Fescue exhibited reduced root biomass due to higher bulk density and lower soil porosity. Soil bulk density was lowest in Mixture, and no significant differences in soil penetration resistance were found among treatments (p > 0.05). There are alternatives to alfalfa with high production and quality that ensure a good economic return to farmers. The choice of forages for its root biomass accumulation has effects on the physics of the soil that ultimately modify the water dynamics. These findings have implications for sustainable forage management strategies, particularly in areas prone to waterlogging and poorly drained soils.

Distribution of Non-Structural Carbohydrates and Root Structure of Plantago lanceolata L. under Different Defoliation Frequencies and Intensities.

Plantago lanceolata L. (plantain) increases herbage dry matter (DM) production and quality during warm and dry conditions due to its deep roots and drought tolerance and reduces nitrogen losses in grazing systems compared to traditional pastures. However, plantain density usually declines after the third growing season, mainly due to defoliation management. The effects of defoliation frequency and intensity on water-soluble carbohydrate (WSC) reserves and below-ground plant responses need further research to optimize grazing strategies for improved productivity and sustainability of grazing systems. Our study investigated the effects of defoliation frequencies (15, 25, and 35 cm of extended leaf length, ELL) and intensities (5 and 8 cm of residual heights) on morphological traits and WSC concentrations in plantain biomass under controlled environmental conditions. Defoliation frequency significantly influenced morphological and chemical characteristics and biomass distribution more than residual height. Less frequent defoliations promoted above-ground herbage DM production, reproductive stems, and root biomass. Root architecture showed adaptations in response to defoliation frequency, optimizing resource acquisition efficiency. Frequent defoliation reduced high molecular weight WSC concentrations in leaves, affecting regrowth capacity and DM mass. A defoliation frequency of 25 cm ELL (~15 days) balances herbage production and root development, promoting long-term pasture sustainability.

An inventory of grassland use on horse farms

Horses can contribute to the maintenance of grassland. To determine the potential contribution of grassland to horse nutrition, we investigated the seasonal variation of herbage on offer and its nutritional quality in an inventory on six practical horse farms in Central Germany during 2019. On all horse-grazed pastures compressed sward height (CSH) was measured monthly and converted into aboveground herbage (AGH) to allocated short and tall grass sward areas (area-specific) via calibration cuts. In addition, four focus pastures were selected for monthly obtained area-specific herbage quality samples. The farm-specific management was monitored using questionnaires and grazing diaries to determine underlying factors influencing herbage biomass and quality. The proportion of short grass sward areas increased during the grazing season (p=0.0010), which was related to high stocking intensity in terms of livestock unit grazing days (LUGD, p <.0001). On most farms, LUGD were constant throughout the growing season and not adjusted to changing grass growth. Herbage crude protein (CP, p=0.0038), metabolizable energy (ME, p <.0001) concentrations and acid detergent fibre in the organic matter (ADF, p <.0001) differed among the grass sward areas. The results suggest that sufficient ME (4.2 ± 0.32 – 8.4 ± 0.15 MJ ME kg−1 DM) for maintenance and pre-caecal digestible CP (pcdCP) (37.0 ± 3.86 – 77.4 ± 4.44 g kg−1 DM) could be provided during the grazing season. The study highlights the need to incentivise grassland management for herbage provision among horse owners to exploit the potential of grassland during the grazing season.

White clover population effects on the productivity and yield stability of mixtures with perennial ryegrass and chicory

Due to complementary resource use of the components, grass-clover mixtures are usually higher yielding compared to unfertilized pure grass stands. The number and identity of species in a mixture are known as important factors for the mixture’s productivity. How intraspecific variability of component species affects the productivity of mixtures has received less attention. We established an experiment to investigate how and to what extent different populations of white clover (Trifolium repens L.) affect mixture performance. Eight novel populations of white clover and one variety of perennial ryegrass (Lolium perenne L.) and chicory (Cichorium intybus L.) were grown as monocultures and in two- and three-species mixtures at two sites differing in soil fertility. Aboveground herbage was cut twice in the establishing year and four times in each of the three following years. The accumulated dry matter yield was calculated as the sum of the four annual dry matter yields. There was no significant interaction between white clover population and crop stand (i.e., white clover monoculture or mixtures with partner species) on dry matter yield accumulated over four years; the white clover population that performed well in monoculture also did so in mixtures. At both sites, the binary mixtures of white clover and chicory produced significantly higher dry matter yields than the white clover monocultures and other mixtures. Inclusion of chicory in mixtures significantly increased the stability of yield production as well. Site conditions strongly affected the performance of the forage species mixtures. We found that the benefit of mixtures over monocultures was more related to the identity of species in mixture than to the white clover population.

Herbage biomass and its relationship to soil carbon under long-term grazing in northern temperate grasslands

While northern temperate grasslands are important for supporting beef production, it remains unclear how grassland above- and belowground biomass responds to long-term cattle grazing. Here, we use a comprehensive dataset from 73 grasslands distributed across a broad agro-climatic gradient to quantify grassland shoot, litter, and shallow (top 30 cm) root biomass in areas with and without grazing. Additionally, we relate biomass to soil carbon (C) concentrations. Forb biomass was greater (p &lt; 0.05) in grazed areas, particularly those receiving more rainfall. In contrast, grass and total aboveground herbage biomass did not differ with grazing (total: 2320 kg ha−1 for grazed vs. 2210 kg ha−1 for non-grazed; p &gt; 0.05). Forb crude protein concentrations were lower (p &lt; 0.05) in grazed communities compared with those that were non-grazed. Grasslands subjected to grazing had 56% less litter mass. Root biomass down to 30 cm remained similar between areas with (9090 kg ha−1) and without (7130 kg ha−1) grazing (p &gt; 0.05). Surface mineral soil C concentrations were positively related to peak grassland biomass, particularly total (above + belowground) biomass, and with increasing forb biomass in grazed areas. Finally, total aboveground shoot biomass and soil C concentrations in the top 15 cm of soil were both positively related to the proportion of introduced plant diversity in grazed and non-grazed grasslands. Overall, cattle grazing at moderate stocking rates had minimal impact on peak grassland biomass, including above- and belowground, and a positive contribution exists from introduced plant species to maintaining herbage productivity and soil C.

The interrelations of herbage productivity with mouse-like rodents and forest litter in linden and ash flood oak grove of Prysamar'ya

The relationships between the productivity of herbage as one of the structural elements of forest biogeocenosis with the nature of the formation and chemical composition of the forest litter and the activity of mouse-like rodents in linden and ash flood oak grove of Prysamar’ya were investigated. It was found that leaf-litter affects to the species composition and the degree of development of grass of investigated biogeocenose. It was revealed that the trophic removal of herbage phytomass by mouse-like rodents in the initial period of vegetation promotes its products. As a result, the above-ground herbage on rodent habitats increases by 1.2 times. The alienation of above-ground herbal phitomass in natural conditions under the influence of mouse-like rodents in the middle of the vegetation season increases in areas devoid of rodents’ influence by 1.05 times. It was found that in the final vegetation season, the above-ground herbage at the rodents’ exposure sites decreases by 1.3 times. It was investigated that the above-ground herbage for the whole vegetation season in the natural conditions of the flood oak grove was 115.4 g/m2, and in experimental areas, devoid of rodents’ exposure was 124.0 g/m2. Thus in the study biogeocenosis the value of herbage productivity was under the influence of mouse-like rodents and it reduced to 1.07 times during the whole growing period. In turn, the grass contributes to the increase in stocks of leaf-litter, ash elements including trace elements in forest litter. The quantitative proportion of herbaceous plants in leaf-litter and the chemical composition of grass in two synusias (wild chervil and starwort) were studied. It was revealed that the air-dry weight of the above-ground parts of herbage in synusia of wild chervil was higher than in synusia of starwort. It was determined that the accumulation degree of individual trace elements varies in different species of herbaceous plants. The maximum content of Mn, Pb and Cu more at wild chervil and Ti, Mo, V, Ni and Cr maximum contents were marked at starwort.

The intake of lead and associated metals by sheep grazing mining-contaminated floodplain pastures in mid-Wales, UK: I. Soil ingestion, soil–metal partitioning and potential availability to pasture herbage and livestock

This paper first evaluates the relative importance of the soil–plant–animal and soil–animal pathways of Zn, Cu and (especially) Pb investigated over a 15-month study period at 12 floodplain sites located within and downstream of the mineralised and historic mining area of mid-Wales, and secondly considers the implications of a sequential extraction procedure (SEP) undertaken on soils of varying particle size sampled from the study locations. Generally, very good agreement was found between the chemical partitioning of the three metals for each of the physical soil fractions subjected to the SEP. The availability of Pb to pasture vegetation, especially at the contaminated sites, is indicated with its associations with the more soluble (i.e. exchangeable and Fe/Mn oxide) soil phases, yet soil and/or plant barriers effectively restrict above-ground herbage concentrations of this metal. Consequently, with sheep ingesting soil at rates varying according to season from 0.1% to 44% or more of dry matter intake, the soil–animal pathway accounts for the majority of Pb consumption through most of the year, and at moderately and highly contaminated sites significant quantities of relatively soluble soil–Pb can be ingested at rates exceeding safety threshold limits.

Modelling above-ground herbage mass for a wide range of grassland community types

Whereas it is recognized that management of plant diversity can be the key to reconciling production and environmental aims, most grassland models are tailored for high-value grass species. We proposed to adapt a mono-specific grass model to take into account specific features of species-rich permanent grasslands, especially over the reproductive phase. To this end, we used the concept of plant functional type (PFT), i.e. the grouping of plant species according to plant traits determined by the response of plant species to different management practices (land use and fertilization) and characterizing of agronomic properties of the corresponding species. In the model, weather and nutrient availability act upon rates of biophysical processes (radiation capture and use, plant senescence). These rates are modified over times due to PFT-specific parameters determined experimentally which represent the different strategies of plant species regarding growth. The integration of these parameters into the model made it possible to predict herbage biomass accumulation rate under different management practices for a wide range of plant communities differing in their PFT composition. The model was evaluated in two steps, first by analyzing separately the effects of PFT and an indicator of nutrient availability on herbage accumulation and then by conducting a sensitivity analysis. It was validated using two independent datasets; a cutting experiment running over the whole growing season to examine the consistency of the model outputs under different cutting regimes, and a monitoring of meadows and pastures in spring over a whole growth cycle to assess the model’s ability to reproduce growth curves. Although a good fit was observed between the simulated and observed data, the few discrepancies noticed between field data and predicted values were attributed mainly to the potential presence of non-grass species. More specifically, we noticed that nutrient (mainly nitrogen) availability is the main driver of plant growth rate, and that PFT determines the times at which this rate changes in relation to the phenological characteristics of species present. We concluded that integration of the PFT concept into the initial mono-specific growth model is especially suited to evaluating the consequences of management practices on species-rich permanent grasslands to meet feed production targets.

Assimilation of SPOT/VEGETATION NDVI data into a sahelian vegetation dynamics model

This paper presents a method to monitor the dynamics of herbaceous vegetation in the Sahel. The approach is based on the assimilation of Normalized Difference Vegetation Index (NDVI) data acquired by the VEGETATION instrument on board SPOT 4/5 into a simple sahelian vegetation dynamics model. The study region is located in the Gourma region of Mali. The vegetation dynamics model is coupled with a radiative transfer model (the SAIL model). First, it is checked that the coupled models allow for a realistic simulation of the seasonal and interannual variability of NDVI over three sampling sites from 1999 to 2004. The data assimilation scheme relies on a parameter identification technique based on an Evolution Strategies algorithm. The simulated above-ground herbage mass resulting from NDVI assimilation is then compared to ground measurements performed over 13 study sites during the period 1999–2004. The assimilation scheme performs well with 404 kg DM/ha of average error ( n = 126 points) and a correlation coefficient of r = 0.80 (to be compared to the 463 kg DM/ha and r = 0.60 of the model performance without data assimilation). Finally, the sensitivity of the herbage mass model estimates to the quality of the meteorological forcing (rainfall and net radiation) is analyzed thanks to a stochastic approach.

(133) Growth and Development of Introduced Leuzea in the Rose Valley, Bulgaria

Leuzea, or Maralroot, is a perennial medicinal plant originating from Siberia, and is characterized with significant metabolic and tonic effects. A 3-year study was conducted at the Research Institute for Roses, Aromatic and Medicinal Plants Kazanluk, Bulgaria, on the introduction of various genotypes of Leuzea (Rhaponticum carthamoides Willd/Iljin.) from the Altai region, Russia. Phenological observations, and up to 11 morphological indices were characterized for 1-, 2-, and 3-year-old plants. Generally, it was found that the climatic and soil conditions in the region were not very favorable for the growth and development of Leuzea. Also, for the tested region, Leuzea should be grown only under irrigation. Yields of Leuzea roots and rhizomes reached 7.19 t/ha in the 2nd year, and up to 8.62 t/ha in the 3rd year. Yields of aboveground herbage were up to 8.73 t/ha when plants were harvested at the beginning of blossoming. Second cut of the above-ground herbage of Leuzea was not satisfactory under the climatic conditions of the region. When grown for seed production, seed yields during the 3rd year were up to 128 kg/ha. Leuzea may have a potential as a cash crop for the region if grown for seed production.

Increased Quantity and Quality of Coarse Soil Organic Matter Fraction at Elevated CO2 in a Grazed Grassland are a Consequence of Enhanced Root Growth Rate and Turnover

The aims of this study were to determine whether elevated atmospheric CO2 concentration modifies plant organic matter (OM) fluxes to the soil and whether any change in the fluxes can modify soil OM accumulation. Measurements were made in a grazed temperate grassland after almost 4 years exposure to elevated atmospheric CO2 (475 μl l-1) using a Free Air CO2 Enrichment (FACE) facility located in the North Island of New Zealand. Aboveground herbage biomass and leaf litter production were not altered by elevated CO2 but root growth rate, as measured with the ingrowth core method, and root turnover were strongly stimulated by elevated CO2 particularly at low soil moisture contents during summer. Consequently, significantly more plant material was returned to the soil under elevated CO2 leading to an accumulation of coarse (> 1 mm) particulate organic matter (POM) but not of finer POM fractions. The accumulating POM exhibited a lower C/N ratio, which was attributed to the higher proportion of legumes in the pasture under elevated CO2. Only small changes were detected in the size and activity of the soil microbial biomass in response to the POM accumulation, suggesting that higher organic substrate availability did not stimulate microbial growth and activity despite the apparent lower C/N ratio of accumulating POM. As a result, elevated CO2 may well lead to an accumulation of OM in grazed grassland soil in the long term.

An empirical model for quantification of symbiotic nitrogen fixation in grass-clover mixtures

Symbiotically fixed dinitrogen (N 2) is an important nitrogen (N) source in many agricultural systems. In spite of this fact, the input of symbiotically fixed N to a particular cropping system is usually not known and exact measurements are costly and laborious. Consequently, there is a demand for an uncomplicated and reliable tool to estimate symbiotic N 2 fixation (SNF) in leguminous crops. A simple empirical model is proposed for quantification of SNF in forage legumes under low external input conditions. The model estimates SNF using dry matter yield as input and parameters for (i) N concentration in dry matter and the (ii) proportion of the N in the legume that is derived from the atmosphere. Further, the model includes fixed N not included in the estimate of SNF in aboveground herbage. Thus the model operates with parameters for (iii) the ratio of fixed N in below-ground plant tissue, (iv) the ratio of fixed N transferred below-ground to the grass, (v) the ratio of fixed N transferred to the grass through the grazing animals, and (vi) the ratio of fixed N immobilised to the soil organic pool by rhizodeposition. A general value for each parameter is suggested although the need for site-specific parameterisation is underlined.

Nitrogen mineralisation and plant nitrogen acquisition in a nitrogen-limited calcareous grassland

A field study measured the rate of soil mineral N supply and its effects on plant biomass and N accumulation in a 13-year-old, naturally regenerating, calcareous grassland. Gross rates of N mineralisation (2 μg g −1 day −1, i.e. 0.69 kg ha −1 day −1), assessed using 15N pool dilution, were at the lower end of the range previously reported for grasslands. Weekly additions of liquid N fertiliser ([NH 4] 2SO 4, NH 4NO 3 or KNO 3) and, to a lesser extent the addition of water, increased plant growth substantially, demonstrating that the primary constraint to plant growth was low N availability. In plants that had received NO 3 −, the activity of the inducible enzyme nitrate reductase in shoots initially increased in proportion to the amount of NO 3 − supplied. However, as above-ground herbage accumulated, nitrate reductase activity declined to similar low levels in all treatments, despite the continuance of the constant NO 3 − additions. The decline in NR specific activity reflected declining tissue NO 3 − concentrations, although total plant NRA may have remained constant during the period of study. The study has shown that plant growth is limited by low N mineralisation rates and indeed the soil is a sink for much added N. Low water availability provides an additional constraint on N mineralisation in this calcareous grassland soil. Any disturbances in the N cycle which increase the availability of mineral N will result in a substantial increase in plant growth within this ecosystem.

Patterns of aboveground herbage production and nutritional quality structure on semiar1d grasslands

Abstract Botanical composition, aboveground biomass, protein, fibre content, and dry matter digestibility (DMD) were used as tools for studying the production and nutritional quality in semiarid grasslands. The study was carried out in herbaceous communities from Central‐West of Spain over a period of five consecutive years (1986–1990). The grassland typologies were mainly related to their positions in topographical gradients (slopes) which characterize the regional landscape. The mean values for the production of aboveground biomass in the communities range between 126 and 304 g/m2 which seem fitted with the possibilities of those areas. The botanical composition is different in the two zones of the slope (upper and lower) and it responds to a defined pattern. Vegetation in the lower zones is dominated by grasses and in the upper zones by forbs. The correlation between production and botanical fractions considered (grasses, legumes and forbs) is significant for the grass group. The results show also that...

Competition for nitrogen between Pinusradiata and pasture. I. Recovery of 15N after one growing season

As part of a monthly N fertilizer application program, 15N-labelled fertilizers were applied on one occasion, in spring, to 4-year-old Pinusradiata D. Don growing under different levels of competition. The three competition levels were removal of pasture, simulated grazing, and rank ryegrass–cocksfoot–clover pasture. Pinusradiata assimilated similar quantities of 15N when it was supplied as 15NO3− or 15NH4+ in the simulated-grazing treatment. Removing pasture competition doubled tree 15N, but total uptake into above and belowground components did not exceed 15.4% of the 15N applied. Pasture uptake of 15NO3− and 15NH4+ was not significantly different when recovery in pasture stubble and roots at the final harvest was included with the recovery from all pasture harvests. However, 15NO3− recovery was 40% greater than 15NH4+ in aboveground herbage. Uptake by rank pasture was less than half that of the simulated-grazing treatment. Uptake by artificially grazed pasture did not reduce 15N movement into the P. radiata canopy to the same extent as uptake by rank pasture. However, there was little evidence that the simulated-grazing treatment provided any benefit to tree growth through increased cycling of N or reduced pasture root growth. There were no significant differences in 15N recovery between treatments in the 0–20 cm depth of soil; on average this was 49% of the N applied. Total system recovery was 107, 92, 76, and 71% for the 15NO3−-treated, 15NH4+-treated simulated-grazing, 15NH4+-treated rank-pasture, and no-pasture treatments, respectively. The loss of 15N from the system could not be accounted for by leaching to depths of 60 cm. Hence, in the no-pasture treatment, where the loss of 15N was greatest, 15N loss may have been due to denitrification.

The role of the legume in the nitrogen cycle of productive and sustainable pastures

AbstractThe role of the legume in the nitrogen (N) cycle was examined in grazed pastures receiving no N fertilizer of both temperate and tropical regions by simulating the fluxes of N through different processes of the cycle. The amounts of legume‐fixed N required to balance the cycle without invoking a drain on soil organic N reserves (i.e. no net N mineralization) was estimated to vary from 38 to 53% of the above‐ground herbage N or from 20 to 31% on a dry matter (DM) basis for tropical pasture systems with a range of pasture utilization of 10–40%. At higher pasture utilization levels of 50‐70%, more typical of intensively grazed temperate pastures, the N input requirement in the absence of fertilizer N would be 57‐67% of the aboveground herbage N or 35‐45% DM. An examination of the role of each contributory process of recycling (viz. excreta returns, internal cycling or remobilization from senescing tissues, litter decomposition) suggests that variations in the amounts of internally cycled N would have the greatest impact on the requirement for biologically fixed N at low levels of pasture utilization (10‐40%), while at high pasture utilization levels of 70%, variations in the recovery of excreta‐N would have a major effect on the requirement for fixed‐N to balance the cycle.The amounts of biologically fixed N required to sustain a range of herbage DM yields of 3‐22 t DM ha −1 yr−1 would range from 15 to 158 kg N ha−1 yr−1 for tropical pastures. For intensively managed temperate pastures producing 6‐15 t DM ha−1 yr−1 with a N content of 3·5%, a range of fixation of 120‐352 kg N ha−1 yr−1 is required. These simulations indicate how legume contents of 20‐45% of herbage DM could contribute to productive and sustainable (in terms of N) pasture systems of both temperate and tropical regions

A Technique for Quantifying Fire Behavior in Grassland Fire Ecology Studies

A Technique for Quantifying Fire Behavior in Grassland Fire Ecology Studies

Western Wheatgrass Responses to Simulated Grazing

To evaluate responses of range grasses to herbage removal, removal patterns should simulate those under grazing. We compared responses of western wheatgrass (Agropyron smithii Rydb.) in mixed-grass range to no clipping, conventional clipping, and clipping which simulated continuous grazing. Two years of simulated grazing did not affect herbage production or tiller numbers, but both declined under conventional clipping. Belowground phytomass decreased as herbage removal increased. Total nonstructural carbohydrate concentration in rhizomes decreased when utilization exceeded about 40930, but that of roots and crowns decreased only when utilization exceeded 60-70%. Most clipping studies of range grasses make little effort to simulate herbage removal patterns which occur under grazing. Clipping studies usually include clipping at uniform heights, not random heights as occurs under grazing (Jameson 1963), and more severe defoliation than occurs under grazing (Heady 1961). Harris (1976) indicated that frequency, intensity, and timing of defoliation all influence plant responses. Lack of knowledge of these parameters has inhibited design of realistic clipping experiments. Hart and Balla (1982) photographed western wheatgrass (Agropyron smithii Rydb.) tillers at intervals during the grazing season and determined frequency, intensity, and timing of herbage removal. We used this information to design a clipping experiment ‘which simulated grazing more closely than ever before, and compared response of western wheatgrass under simulated grazing to that under conventional clipping and no clipping. Our objective was to provide better guides to grazing management than could be provided from responses to conventional clipping. thread (Stipa comata Trin. & Rupr.). Soils underlying the study plots were a fine-loamy Aridic Argiustoll of the Altvan Series. Stevenson et al. (1984) have given a more complete description of the range sites and vegetation of the research station. Twenty-four plots (25 X 40 cm) were established on an area of native range ungrazed since 1978 and containing450-600 tillers/m* of western wheatgrass. Each plot was bordered by aluminum lawn edging placed into the ground approximately 20 cm to eliminate rhizome spread between plots and between the plots and adjacent native range. Four replications of 6 treatments, in a randomized complete block design, were applied to the 24 plots. The 6 treatments included an unclipped control, clipping western wheatgrass to 2.5 cm 4 times during the summer, and 4 clipping treatments simulating 4 levels of continuous grazing of western wheatgrass. Frequency under simulated continuous grazing was defined as the percentage of tillers clipped 0, I, 2,3, or 4 times, while intensity was the percentage of clipping events at which I / 3,2/ 3, or all the aboveground herbage was removed from a tiller. Two frequencies (Table 1) times 2 intensities (Table 2) gave us 4 simulated grazing treatments.

Recovery of Nitrogen and Phosphorus after 17 Years from Various Fertilizer Materials Applied to Crested Wheatgrass1

AbstractInformation is limited regarding duration of residual effects from different N fertilizer sources upon herbage production and N and P recovery. A field experiment was conducted for 17 years on a Temvik silt loam (fine‐silty, mixed Typic Haploborolls) at Mandan, N.D., to study the effects of 5 years of N and P fertilization upon the production of crested wheatgrass [Agropyron desertorum (Fisch. ex Link), Schult.) and upon N and P recovery during and after fertilization. Fertilizer rates were 0, 90, and 180 kg N/ha from ammonium nitrate, ammonium sulfate, calcium nitrate, or urea, and 19 or 39 kg P/ha. Dry matter production and fertilizer N recovery in aboveground herbage production were least for urea, especially at 180 kg N/ha with P, but there was little difference between the other N sources. Cumulative 17‐year dry matter production was increased about 15 Mg/ha with 90 kg N/ha, and 20 to 25 Mg/ha with 180 kg N/ha. Residual effects from calcium nitrate persisted a few years longer than from other N sources and averaged 58 % recovery of N compared to 48 % for urea. Fertilizer P recovery varied from 26.8 % when P was applied with calcium nitrate to 18.2 % with ammonium sulfate. Cumulative dry matter production was increased 4 to 5 Mg/ha in 17 years by P fertilization. Fertilization with N doubled recovery of fertilizer P. Soil pH in the surface 150 mm of soil, 5 years after fertilization ceased, varied from 6.5 with calcium nitrate to 5.5 with ammonium sulfate. Fertilizer N recovered after fertilization ceased could largely be accounted for by depletion of inorganic soil N pools that had accumulated during the fertilization period. While ammonium sulfate was being applied, inorganic N accumulated primarily as exchangeable ammonium in the surface 0.3 m. Little inorganic soil N accumulated from urea application, suggesting that much N was lost by volatilization. From all sources, 70 to 160 kg fertilizer N/ha was still immobilized in the root biomass, 5 years after fertilization ceased.