Increased Herbage Production Research Articles

Adjusting nitrogen fertilization to spatial variations in growth conditions in silvopastoral systems for improved nitrogen use efficiency

Grass swards in silvopastoral systems have a lower herbage production near trees than open grassland. This is related to a lower nitrogen (N) uptake in an area close to the tree lines. The N use efficiency for the whole field can then be improved when N input is spatially adjusted and the overall amount reduced. We performed a 2-year field experiment to gain insights into this idea for making savings on N inputs by studying the response of the grass sward to fertilizer N input in relation to the distance from trees. We hypothesized an interaction between N input rate and position to the tree line on grassland herbage production and N uptake and, accordingly, N use efficiency. The field trial was carried out in a silvopastoral system in Germany consisting of the factors year (2019 and 2020), position (2.5, 6.5 and 24.5 m distances to tree line), annual N application rate (0, 15 and 30 g N m−2) and harvest date (four harvests per year). We found significant interactions between position × N rate for all target variables, and usually also in interactions with the harvest date or year. The N application close to trees at a distance < 6.5 m had in most cases no significant influence on herbage production but significantly increased herbage production by up to 35% at positions further away. Omitting the N fertilization in a corridor of 6.5 m near the trees would contribute directly to the saving of fertilizer N without a negative trade-off in herbage production.

Tree cover influences the soil C balance in Mediterranean cork oak-based silvopastoral systems

Mediterranean silvopastoral systems provide a wide range of ecosystem services, among which soil C sequestration is one of the most relevant. Although the role of trees in enhancing soil C content of silvopastoral systems is widely recognized, the impacts of the tree cover on the overall soil C balance and hence the soil C sequestration rates are not clear enough to identify feasible options and effective management pathways. This study aimed to assess the effect of trees on soil C balance in a Mediterranean cork-oak silvopastoral system under contrasting cover classes. A three-year study was conducted in a Long-Term Observatory in Sardinia (Italy). A hierarchical design was used to test the tree effect (below and outside the tree crown projection) and the tree cover (high tree cover – from 39% to 42%; low tree cover – from 15% to 36%) on the soil C balance. The C balance was calculated as the difference between the C input from the herbaceous and tree components of the ecosystem and the C output from soil heterotrophic respiration. The position with respect to the tree stem influenced the C input, the C output, and the overall C balance. The tree class influenced only the C output and C balance. The annual C balance was higher (more gains) in low-covered areas below the tree crown projection (8.30 ± 0.72 Mg ha−1 of C) than in open pasture and high-covered areas. At the field level, the overall weighted C balance was significantly influenced by tree cover; according to this last evidence, the maximum C balance was reached at about 24% tree cover. The results highlight the importance of management practices oriented to increase herbage production, tree cover, and regulating tree distribution, which in turn can provide ecosystem services such as SOC sequestration.

“Summer sowing”: A successful innovation to increase the adoption of key species of annual forage legumes for agriculture in Mediterranean and temperate environments

AbstractThis paper reports on the evaluation of “summer sowing,” an innovative approach to increase the adoption of recently domesticated species of hard seeded annual legumes in Mediterranean and temperate Agriculture. The research revealed that several species of annual legumes whose seed can be readily harvested on‐farm and which possess natural hard seed dormancy, may be sown into dry soil in late summer without additional processing. These studies proved that the hard seed dormancy was broken down sufficiently in the soil over 4–6 weeks to produce robust legume pastures with more than 150 seedlings per m2 following the first winter rains, in replicated field sites established across wide agro‐ecological zones in Western Australia (WA) and New South Wales (NSW). Ornithopus sativus Brot., O. compressus L. and Trifolium spumosum L. were suitable for summer sowing based on both hard seed breakdown patterns and subsequent seedling survival in WA. While in NSW, in addition to these legumes, Biserrula pelecinus L., T. vesiculosum Savi. and T. glanduliferum Boiss. were also suitable for summer sowing. A 1.5‐ to 10‐fold increase in herbage production was achieved relative to conventionally sown T. subterraneum L. This development represents a step change in forage legume development for renovated pastures in these environments. Importantly, the experiments revealed differences in G x E effects on seedling establishment, total herbage production and seed yield in different climatic zones. The summer sowing approach is presented as a revolutionary method for pasture renovation that overcomes significant barriers to adoption.

Assessing and Modeling Pasture Growth under Different Nitrogen Fertilizer and Defoliation Rates in Argentina and the United States

Core Ideas Model‐based approach identified sets of adaptive practices for pasture management across seasons. Suitable combinations of N rate and residual heights can improve the use of N fertilizer and water. The increment in residual pasture mass and N fertilizer may be crucial for more efficient use of water. Pasture growth responses to residual leaf area increased with N fertilization. The objectives of this research were to (i) evaluate the effects of N fertilizer, irrigation, and residual pasture heights on pasture growth, (ii) validate the ability of the SALUS model to predict dynamics of pasture growth, and (iii) evaluate during long‐term period the effects of using different N fertilizer levels and defoliation strategies on pasture growth, N fertilizer use, and water use efficiency (WUE). Eight single‐season experiments were performed at plot scale (8 m2) in Buenos Aires (Argentina, ARG) and Michigan. In ARG different N fertilizer rates (from 0–500 kg N ha−1) were imposed on both rainfed and irrigated tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] pasture during autumn, spring, and summer. In the United States, three residual pasture height treatments (30, 60, and 120 mm) were imposed on both tall fescue and ryegrass (Lolium perenne L.) pasture in the spring and summer. The SALUS was parameterized to simulate tall fescue and ryegrass growth using soil, weather, and different pasture treatments previously tested in ARG and the United States. Results showed that the SALUS accurately represented the response of herbage mass to irrigation and added N in the ARG site (RMSE &lt; 650 kg DM ha−1) and to differences in residual pasture heights in the U.S. experiment (RMSE &lt; 509 kg DM ha−1). Ten‐year simulations (2000–2010) demonstrated that suitable combinations of N fertilizer and residual pasture heights can significantly improve the use of N fertilizer by ∼300% and water by ∼230% through increases in herbage production.

Impact of introducing a herb pasture area into a New Zealand sheep and beef hill country farm system: a modeling analysis

New Zealand is well known for export of meat and dairy products from low cost pastoral systems. These farm systems are continually evolving for increased efficiency, in part through the use of metabolic energy modeling tools by farmers and farm consultants to explore alternative farm system configurations and identify new efficiencies. One recent innovation is the introduction of a herb pasture area, such as plantain. We used metabolic energy modeling to quantify seasonal feed flows in two successive years in a New Zealand hill country farm system, and to analyze the impact of the introduction of an area of plantain. Models employed were a self-built Microsoft Excel spreadsheet and a commercial New Zealand farm systems modeling package, FARMAX. Herbage production, animal performance and financial results for a base farm scenario created from the average of survey data for hill farms in the southern North Island, and the same farm with 10% and 20% of the area in plantain for the years 2010–2011 and 2011–2012 were modeled. The self-built model performed similarly to the commercial model. The system configuration of the base farm stockpiles surplus autumn feed for release to animals in winter and also incorporates flexibility that confers resilience to interannual weather variation through varying dates animals are purchased or sold. The introduction of an area of plantain was predicted to increase herbage production, animal performance and financial returns. The predicted benefit was higher for the year 2010–2011 where a drought occurred in summer than for the following year with higher summer rainfall. This demonstrates the profitability of introducing a plantain area to New Zealand hill farm systems, and suggests plantain will assist to mitigate adverse effects of warmer and drier summer conditions associated with current climate change trends.

Comparative study of soil physico-chemical properties under &lt;i&gt;Acacia senegal&lt;/i&gt; in three different plantations in Maifari, Jigawa state, Nigeria

Acacia senegal is a multipurpose drought-tolerant tree or shrub legume, and is commonly used in agroforestry systems in sub-Saharan Africa for gum arabic production and soil fertility improvement. Despite its relatively wide distribution in Nigeria, there has not been exhaustive evaluation on the effects of the tree/shrub on soil physicochemical properties under its canopy forsustainable utilization of the tree. Accordingly, three sitesin the semi-arid regionof Nigeria representing three plantation ages of 7, 27and 37 years old were selected for assessment. Soil samples were collected under tree canopies and were compared with the soils from the open canopies. Results indicated that there were significant differences in soil physicochemical properties among the three ages (P&lt;0.05 and P&lt; 0.01). Generally, soil nutrients under the canopies were higher than in the open canopies irrespective of the age mainly due to effects of litter accumulation. The tree/shrubhas beneficial effects on soil nutrient status in their natural ecosystems and would most likely improve crop productivity in agroforestry systems such as alley cropping. The resultant improvement in soil nutrients status can increase herbage production in agricultural rangelands thus enhancing animal production in the study area. The tree/shrub growing under different soil types may have an effect on their gum Arabic production and quality.Keywords: Acacia senegal,plantation ages, soil nutrients accumulation, sustainable utilization.

Predicted dairy product yields and deficits of lactose for manufacturing under differing selection and manufacturing scenarios in New Zealand

The New Zealand dairy industry is pasture-based and more than 90% of milk products are exported. The breeding goal of the breeding programme of New Zealand dairy cattle is to improve the capability of the cow to convert feed into farmer profit. The breeding objective rewards yields of protein and fat but penalises milk volume and ignores lactose, despite it being an important component of milk powders. With the industry currently in deficit for lactose, this study investigated the expected response to selection over the next 10 years and its impact on the annual industry production of milk, its components and yields of dairy products based on expected cow performance, number of cows and a fixed area for dairying. After 10 years of selection (with no increase in herbage production), there was a 5% increase in milk production per hectare. Total milk exports increased by 5.9% and the lactose deficit increased by 14% when 60% of milk was processed into whole milk powder.

Applying urine collected from non-lactating dairy cows dosed with dicyandiamide to lysimeters and grass plots: effects on nitrous oxide emissions, nitrate leaching and herbage production

SUMMARYIn agricultural production systems, nitrogen (N) losses to the environment can occur through nitrous oxide (N2O) emissions and nitrate (NO3−) leaching. The objectives of the present study were to evaluate: (1) if urine excreted by non-lactating dairy cows pulse-dosed with dicyandiamide (DCD) and applied to lysimeters reduced N2O-N emissions and NO3−-N leaching on two soil types; and (2) if urine + DCD would increase herbage production over winter. Lysimeters were used to measure N2O emissions and NO3-N leaching. The soils used were a free-draining acid brown earth of sandy loam to loam texture (termed free-draining) and a poorly drained silt loam gley (termed poorly drained). Grass plots were established on the free-draining soil to measure herbage production. The N loading rate of the urine + DCD was 508 kg N/ha and the urine without DCD (urine only) was 451 kg N/ha. Total NO3−-N leaching losses from the free-draining and poorly draining soils were reduced from 100 and 81 kg NO3−-N/ha on the urine-only treatment, respectively, to 9 and 11·6 kg NO3−-N/ha on the urine + DCD treatment, respectively. Total N2O-N emissions from the free-draining and poorly drained soils were reduced significantly from 13·6 and 12·1 kg N2O-N/ha on the urine-only treatment, respectively, to 2·23 and 5·24 kg N2O-N/ha on the urine + DCD treatment, respectively. Applying urine with DCD to pastures inhibited the nitrification process for up to 56 days after treatment application. In the current experiment, there was no significant effect on spring herbage production when urine + DCD was applied to grass plots. Therefore, feeding DCD to dairy cows to apply DCD directly in urine patches was shown to be an effective mitigation strategy to reduce NO3−-N leaching and N2O-N emissions but did not appear to increase spring herbage production.

Nitrogen Application for Spring Growth of Cool‐season Grasses Overseeded in Unimproved Warm‐season Pasture

In the southern Great Plains fall overseeding of annual forages into dormant warm‐season pasture can increase herbage production in spring and early summer of the following year, but production in early spring, when it is most needed, is usually limited and competition between cool‐ and warm‐season components of mixed pasture may result in only small benefit in total annual yield. The effects of early‐producing species, or of stimulation of early growth by nitrogen (N) fertilizer application to the cool‐season crop, on early‐season availability of herbage and on competition within mixed pasture were evaluated in a series of experiments. Rye (Secale cereale L.), oats (Avena sativa L.), or annual ryegrass (Lolium multiflorum Lam.) were overseeded into dormant unimproved warm‐season pasture in fall and provided 22, 45, or 67 lb/acre of N fertilizer in mid‐February of the following year. Neither rye nor annual ryegrass showed significant advance in early‐season growth (up to early April) resulting from increased N application, and herbage dry matter (DM) yield response was &lt;4.0 lb DM/lb N applied over this period. Over uninterrupted spring growth to a mid‐May harvest, DM yield responses to applied N were similar in rye and annual ryegrass and ranged from 9.3 to 32.3 lb DM/lb N. Oats did not tolerate low winter temperatures. Choice of cool‐season annual grass species for overseeding and level of N application in spring had little impact on DM yield of the warm‐season grass component of mixed cool‐ and warm‐season pasture.

Forage Legumes for Grazing and Conserving in Ruminant Production Systems

As a plant group, forage legumes present some unique advantages and disadvantages for ruminant production. When compared to grasses or cereals their main advantages are generally (i) low reliance on fertilizer nitrogen (N) inputs, (ii) high voluntary intake and animal production when feed supply is non-limiting and (iii) high protein content. The main disadvantages of forage legumes are generally (i) lower persistence than grass under grazing, (ii) high risk of livestock bloat and (iii) difficulty to conserve as silage or hay. In comparison to grass or legume monocultures, grass + legume mixtures have particular advantages such as more balanced feeding values, increased resource use efficiency and increased herbage production. However, maintaining the optimum legume contents (40-60% of herbage dry matter) to achieve these benefits remains a major challenge on farms. When compared to ruminant systems based on grass or cereals supplemented with fertilizer N, forage legume based ruminant systems tend to have less negative environmental impact on biodiversity, N losses to water and greenhouse gas emissions. Economically, the primary advantage of forage legumes over other forages is their ability to reduce fertilizer N costs and their main disadvantage is usually lower intensity of animal production per ha of land. Despite the numerous benefits of forage legumes for ruminant farming (to the farmer and wider society), their use is reported as being low or declining relative to other forages in many regions. This is most likely a result of their disadvantages being perceived to outweigh their advantages at farm level. This may change if the price ratio of fertilizer N to product (meat/milk) continues to increase as it has done in some regions in recent years.

Impact of deferred grazing and fertilizer on herbage production, soil seed reserve and nutritive value of native pastures in steep hill country of southern Australia

AbstractDeveloping sustainable grazing management systems based on perennial species is critical to preventing land degradation in marginal land classes. A field study was conducted from 2002 to 2006 to identify the impacts of deferred grazing (no defoliation of pastures for a period generally from spring to autumn) and fertilizer application on herbage accumulation, soil seed reserve and nutritive value in a hill pasture in western Victoria, Australia. Three deferred grazing strategies were used: short‐term deferred grazing (no defoliation between October and January), long‐term deferred grazing (no defoliation from October to the autumn break) and optimized deferred grazing (withholding time from grazing commenced between annual grass stem elongation and seed head emergence and concluded in February/March). These treatments were applied with two fertilizer levels (with or without fertilizer at 50 kg phosphorus ha−1 and 2000 kg lime ha−1 applied in year 1 only) in a factorial arrangement and two additional treatments: continuous grazing (CG) and no grazing (NG) in year 1. The deferred grazing treatments on average produced herbage dry matter of 4773 kg ha−1, the NG produced 4583 kg ha−1 and the CG produced 3183 kg ha−1 in year 4 (2005–06) of the experiment. Deferred grazing treatments with and without fertilizer application produced an average of 5135 and 4411 kg DM ha−1 respectively. Averaged over 4 years, deferred grazing increased the germinable seed pool of perennial grasses by 200% and annual grasses by 50% (except optimized deferred grazing that considerably decreased the annual grass seed pool) compared with the CG. The best of the deferred grazing strategies increased the digestibility of pastures by 7% compared with the CG. The results demonstrated that deferred grazing from spring to autumn followed by rotational grazing could be an effective tool to increase herbage production and soil seed pool and improve the digestibility of native pastures in the steep hill country of southern Australia.

Variation for constitutive flavonols and morphological traits in a new white clover population

Breeding forage legumes combining high levels of stress-protective secondary metabolites and high herbage yield are possible. Previous findings suggested a trade-off between flavonol glycosides and biomass production in white clover (Trifolium repens L.), with population specific evidence indicating that association. The present study used a novel white clover first filial (F1) reciprocal cross (n=130, 3 replications in pots) between the productive cultivar “Kopu II” and the cold- and drought stress-resistant population “Tienshan”. The conditions were non-limiting as the plants were watered at regular intervals as needed, to establish a baseline for both constitutive flavonol glycosides and above-ground biomass production. This study showed that the phenotypic correlation between the traits quercetin glycosides (Q) and shoot dry matter (SDM) although significant (P<0.001) was weak with r2=0.0903 (9%). This suggests the possibility of improving white clover performance by increasing the levels of stress protective metabolites in tandem with selection for high yield. At a genotype level, constitutive quercetin (Q) glycoside accumulation in this white clover line is not a major constraint on DM production in the absence of moisture stress. This indicates that combining high DM yield and high constitutive levels of Q glycosides for abiotic stress protection is possible. This finding is significant to overcoming a key challenge in plant breeding: combining stress tolerance with increased herbage production.

Root distribution and herbage production under different management regimes of mountain grassland

The importance of grassland as providers of an ecosystem service is increasing. Our objective was to determine the effect of land management on the root distribution and herbage production of mountain grassland. A field experiment was conducted on the Haplic Cambisol Dystric soil from 2004 to 2007. The treatments considered the use of separate meadows as follows: one without any fertilizers (MC), one with mineral fertilization (MM), another with organic fertilization (MSM), a sheep-grazed pasture (PP) and an abandoned meadow (MA). Botanical composition, herbage yield and root morphology in terms of root length density, mean root diameter, specific root length and root dry matter were determined. The different land management regimes used in the experiment affected the herbage production. Sheep pens (PP) and all treatments with mineral or organic fertilization (MM and MSM) increased dry matter yields (5.95 t DM ha −1 in average) in comparison with meadow without any fertilization (3.08 t DM ha −1). The highest herbage production was obtained from the meadow with mineral fertilization, which was 6.51 t DM ha −1. The land management treatments also affected the botanical composition. Mineral N fertilization decreased the percentage of legume and small grass species which were replaced by tall grasses such as Festuca pratensis, Poa pratensis and Agropyron repens. Sheep manure decreased the occurrence of Deshampsia ceaspitosa. At the untreated control there was observed the increasing in percentage of Festuca rubra. The treatments applied in the experiment resulted not only in above ground plant yields and botanical composition but also affected root distribution and morphology. The effect of land management on root dry matter distribution was observed only in the upper, 0–5 cm, soil layer. The highest values (above 0.0100 g cm −3) were observed for the MC, PP and MA treatments with respect to 0.0067 g cm −3 from plants with sheep manure fertilization (MSM). The non-fertilized control (MC) had the highest root length (56.27 cm cm −3) but only in the 0–10 cm soil layer, whereas for the other treatments (MM, MSM, PP and MA) it was usually below 40 cm cm −3. Root diameter was greater (0.26 mm in average) in the MM, PP and MA treatments with respect to roots from non-fertilized plots and those receiving sheep manure (0.22 mm in average). We conclude that fertilization will increase herbage production but it will also change botanical composition and decrease the strength of root systems which may be undesirable with regard to preventing soil erosion.

Temperate grassland: key developments in the last century and future perspectives

In temperate regions, grassland provides most of the feed requirements for ruminants. Its management has implications for landscape and environmental quality as well as agricultural production. The present paper reviews the key developments in grassland management, production and utilization during the 20th century, focusing primarily on the UK but drawing on research and practice from other areas. Increased production from grassland has arisen from improved understanding of soil and plant nutrition, plant physiology and cultivar improvement, while improved understanding of feed evaluation, ruminant nutrition, grazing management and silage technology have contributed to increased utilization of grassland under grazing and cutting. Permanent and long-term swards occupied most of the total grassland area at both the beginning and end of the century, but inputs of nitrogen resulted in greatly increased herbage production, particularly from the 1960s; this, combined with reseeding and early cutting for silage, led to reduced botanical diversity with ryegrass dominance in lowland areas. Forage legumes were highly regarded at the beginning of the century, then decreased in many areas, but are again recognized as having a key role in low- and medium-input systems. Recognition of the environmental implications of grassland management has increased since the 1980s. This includes the need to reduce nutrient emissions in grassland agriculture, and also the role of grassland in biodiversity protection, carbon sequestration and landscape quality. Research is increasingly focused on addressing these issues and on integrating agricultural management with environmental protection. Improved nutrient management, legume-based systems and agri-environmental schemes, as well as interest in the food quality attributes of particular systems and grassland communities, are important in the medium term. In the longer term the effects of population increase, competition for other land uses and the impacts of climate change could impact on global food supplies and affect future grassland management in the temperate zones.

The use of a nitrification inhibitor, dicyandiamide (DCD), to decrease nitrate leaching and nitrous oxide emissions in a simulated grazed and irrigated grassland

Abstract. In grazed dairy pasture systems, a major source of NO3– leached and N2O emitted is the N returned in the urine from the grazing animal. The objective of this study was to use lysimeters to measure directly the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO3– leaching and N2O emissions from urine patches in a grazed dairy pasture under irrigation. The soil was a free‐draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). The use of DCD decreased NO3–‐N leaching by 76% for the urine N applied in the autumn, and by 42% for urine N applied in the spring, giving an annual average reduction of 59%. This would reduce the NO3–‐N leaching loss in a grazed paddock from 118 to 46 kg N ha–1 yr–1. The NO3–‐N concentration in the drainage water would be reduced accordingly from 19.7 to 7.7 mg N L–1, with the latter being below the drinking water guideline of 11.3 mg N L–1. Total N2O emissions following two urine applications were reduced from 46 kg N2O‐N ha–1 without DCD to 8.5 kg N2O‐N with DCD, representing an 82% reduction. In addition to the environmental benefits, the use of DCD also increased herbage production by more than 30%, from 11 to 15 t ha–1 yr–1. The use of DCD therefore has the potential to make dairy farming more environmentally sustainable by reducing NO3– leaching and N2O emissions.

Effect of spring grazing management on perennial ryegrass and ryegrass‐white clover pastures

The objective of this study was to investigate the effects of timing and duration of lax spring grazing on tiller dynamics in perennial ryegrass swards, with and without white clover. Two periods of lax grazing—short release (SR) from 26 October to 8 December and long release (LR) from 15 September to 8 December—were compared with a conventional hard grazing—early control (EC). These treatments were applied to swards of perennial ryegrass, with and without white clover, and grazed by sheep. Tiller weight, tiller population density, tiller appearance and death, and stolon population were analysed in a factorial design with three (Experiment 1) and four (Experiment 2) replicates. Tiller weight was increased during the reproductive period, particularly in SR and LR treatments. Also, tiller appearance rate increased in all treatments from September to late January, and was particularly high late in December after grazing of the apices of the main group of reproductive tillers. Lax grazing management increased tiller appearance rate by 53% (P ≤ 0.05) in Experiment 1 and 23% (P ≥ 0.05) in Experiment 2, and tiller loss rate by 40% in Experiment 1 (P ≥ 0.05) and 23% in Experiment 2 (P ≤ 0.05). Over 6 weeks following the return to hard grazing, these effects were reflected in increased tiller population densities of 170, 147, and 115% in LR, SR, and EC treatments respectively in Experiment 1 (P ≥ 0.05), and 97, 110.5, and 36.5% in LR, SR, and EC treatments respectively in Experiment 2 (P ≤ 0.05). It is concluded that the increases in herbage production observed in summer‐autumn following imposition of managements which combined lax spring grazing and hard grazing at the time of anthesis, can be attributed to increased tiller densities. The increase was most marked when the period of lax grazing was longer.

Effect of spring grazing management on perennial ryegrass and ryegrass‐white clover pastures

The aim of this study was to investigate the effects of timing and duration of lax spring grazing on rates of leaf growth, botanical composition, and pasture production in perennial ryegrass swards, with and without white clover. In the first field experiment (September 1992‐March 1993), swards of perennial ryegrass with and without white clover were rotationally grazed by sheep every 21 days to residual heights of 70–100 mm (lax) and every 14 days to 30–50 mm (hard). Two periods of lax grazing—short release (SR) from 26 October to 8 December and long release (LR) from 15 September to 8 December—were compared with conventional hard grazing throughout—early control (EC). All treatments were grazed to 30–50 mm every 14 days from 8 December until the end of March. Swards without white clover received 28 kg nitrogen (N)/ha every 2 weeks as urea. Treatments were arranged in a factorial design with three replicates. Overall, herbage accumulation in the SR and LR treatments was increased by 20 and 30%, respectively, compared to the EC treatment (P ≤ 0.001). Leaf growth in ryegrass and white clover was also increased following lax grazing. In the second field experiment (September 1993‐April 1994) plots were subjected to similar grazing managements, though all spring treatments were imposed at a consistent grazing interval of 21 days and N use on non‐clover swards was reduced to 14 kg/ha every 2 weeks. SR and LR treatments increased herbage production during spring by 24 and 28%, respectively, by increasing tiller weight, and during summer and autumn by 16 and 26% by enhancing tiller population density and leaf growth per tiller and/or stolon. Spring management effects were similar for swards with and without white clover. It is concluded that lax spring grazing management of ryegrass‐white clover swards followed by hard grazing at the time of anthesis enhances pasture production, particularly during the summer—autumn period, by increasing both tiller population density and net leaf growth per tiller. Effects were larger following an extended spell of lax grazing. Contribution of tiller population density differences to these responses is discussed in the second paper in this series (Hernandez et al. 1997, this issue).

Effect of sheep, deer and cattle dung on herbage production and soil nutrient content

AbstractA field experiment compared the effects of sheep, deer and cattle dung on pasture growth and soil nutrient status. Sheep and deer dung pellets degraded rapidly within three to eight weeks, while it was 12 months before all visible cattle dung had gone from the soil surface. The cattle dung initially reduced herbage yield owing to smothering. However, after 40 days, herbage around the edges of the dung patch responded positively to the dung and more dry matter was produced in this patch than in the control patch during the first 12 months. There was no measurable herbage response to sheep dung, but deer dung significantly increased herbage production. While the rate of nutrient application per unit area was similar for sheep and deer dung, the latter was more evenly spread within the patch area. Consequently, a greater percentage of pasture plants in the patch received nutrient additions from the deer dung and a measurable response was recorded. Twelve months after dung application, soil nitrate, phosphate and organic C were higher in dung patches than in the control patches. In cattle dung patches, this response was accompanied by higher microbial biomass C levels, arylsulphatase and arylphosphatase activities. Some residual effect on organic C levels was still evident three years after cattle dung application.

Response of a Mixed Native Warm-Season Grass Planting to Nitrogen Fertilization

Plant available nitrogen limits production of native warm-season grasses on marginal farmland in the Southern Plains. In this western Oklahoma study, N was applied at 0, 35, 70, or 105 kg N ha-1 yr-1 to a mixed stand of blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Griffiths), sideoats grama (B. curtipendula (Michx.) Torr.), little bluestem (Schizachyrium scoparium (Michx.) Nash), sand bluestem (Andropogon hallii Hack.), switchgrass (Panicum virgatum L.) and indian grass (Sorghastrum nutans (L.) Nash). The grass was established on sandy loam soil farmed an estimated 90 years. With near-normal precipitation the first year, production of perennial grasses increased linearly with 26 kg herbage produced kg-1 N applied. In drouth conditions, the second and third years, production averaged 10 kg herbage kg-1 N applied. The fourth and fifth year the stand was not fertilized and residual effects measured. Herbage production increased 10 kg for each kg N applied over the previous 3 years. Blue Grama made up much of this increased herbage production along with warm-season annuals (Panicum capillare L. and Amaranthus retroflexus L.). With increasing N rates the residual N effect increased the proportion of blue grama and decreased the proportion of taller perennial grasses. Thus, N fertilization of mixed native warm-season grass stands established on marginal farmland, typical of stands established on sandier soils under the USDA Conservation Reserve Program, can result in substantial herbage yield increases, however, some of the increased yield may be from weedy species.

Influence of Litter on Herbage Production in the Mixed Prairie

Lifter (dead plant material) increases production in xeric environments but the nature of this effect is uncertain. The purpose of this study was to determine the relationship between liner quantity and herbage production over a 4-year period as well as to determine the effect of repeated removal of lifter on production. The study was made in a Stipa-Bouteloua-Agropyron faciation of the Mixed Prairie association, near Lethbridge, Alberta, Canada. Litter quantity was altered by mechanical removal before spring growth and the residue separated into coarse and fine components. In Experiment 1, the effect of lifter on herbage production was tested by removing lifter at 0, medium, and high levels that resulted in an average residue of coarse liner of 1,171, 787, and 377 kg ha-1. Coarse litter was related to an increase in herbage production (P < 0.05) in 3 of the 4 years studied. The effects of lifter were related to the growing conditions of each year. The linear regression coefficients describing the response (herbage production related to litter) ranged from 0.114 to 0.802 with the smallest effect under either very dry or very wet conditions. In Experiment 2, lifter was removed at high levels in either 0, 1, 2, or 3 successive years. These treatments resulted in an average residue of coarse litter of 1,300, 164, 149, and 188 kg ha-1. Herbage production was not affected by removing litter for more than 1 year but plant height, tiller weight, and herbage yield of some plant species were.