贵州山区生态茶园不同凋落物木质素、纤维素分解特征

采用凋落物分解袋法,以贵州久安生态茶园内云南樟（Cinnamomum glanduliferum）、光皮桦（Betula luminifera）、杉木（Cunninghamia lanceolata）和马尾松（Pinus massoniana）叶凋落物以及茶树（Camellia sinensis）修剪物为研究对象,分析5种单一凋落物类型,以及9种混合凋落物类型（茶树-云南樟、茶树-马尾松、茶树-杉木、茶树-光皮桦、杉木-光皮桦、云南樟-光皮桦、云南樟-马尾松、云南樟-杉木、光皮桦-马尾松）分解速率和木质素、纤维素释放特征及差异性。结果表明,单一凋落物类型中,阔叶树种凋落物分解速率大于针叶树种;阔叶树种凋落物木质素含量总体上呈现增加趋势,而针叶树种总体上则呈现下降趋势;凋落物纤维素含量总体上呈现下降趋势。单一凋落物纤维素释放规律与混合凋落物纤维素释放一致,均为直接释放;单一凋落物木质素释放存在3种规律;混合凋落物木质素释放规律有5种。分析9种混合凋落物分解特征,44.4%的混合凋落物混合分解表现为加和效应,11.2%的混合分解表现为拮抗效应,44.4%的混合分解表现为协同效应;22.2%的混合凋落物木质素的释放表现为促进释放,55.6%的混合凋落物木质素释放表现为促进富集;22.2%的混合凋落物纤维素释放表现为促进释放;11.1%的混合凋落物纤维素释放表现为促进富集。研究结果可为维持茶园肥力提供理论依据。     

Above and belowground litter decomposition of cover crops grazed at different intensities

Grazing cover crops may increase land-use efficiency while promoting sustainability. We investigated how grazing intensity affects cover crop litter quantity, quality, decomposition, and cotton (Gossypium hirsutum L.) N uptake. Cover crops were a mixture of rye (Secale cereale L.) and oat (Avena sativa L.) managed as follows: no grazing +34 kg N ha⁻¹ (NG34), no grazing +90 kg N ha⁻¹ (NG90), heavy grazing (HG), moderate grazing (MG), and light grazing (LG). Grazed treatments received 90 kg N ha⁻¹. After cover crop termination, above- and belowground litter was collected and incubated in situ for 0, 4, 8, 16, 32, 64, and 128 days, with cotton plants sampled on the same days to estimate N recovery and synchrony between N release from litter and uptake by cotton. By Day 128, only 13% of initial NG34 aboveground biomass had disappeared, whereas 42% of HG disappeared. Nitrogen retained in aboveground litter of HG was less than NG90 (27 vs. 60 kg N ha⁻¹), and aboveground final N stock (at Day 128) of HG was less than NG90 and LG (16, 47, and 41 kg N ha⁻¹, respectively). Belowground litter contributed 98 kg N ha⁻¹ versus 46 for aboveground. Belowground N disappearance from litter bags was greater from NG90 than NG34 (39 vs. 21 kg N ha⁻¹). Cotton N uptake by Day 128 was similar across treatments (191 kg N ha⁻¹). Grazing cover crops impact aboveground litter quantity, quality, and decomposition rates, and belowground litter plays an important role on the N cycling.     

Effects of systemic fungal endophytes on the performance of meadow fescue and tall fescue in mixtures with red clover

A symbiosis between grasses and systemic fungal endophytes exists in both natural and agricultural grassland communities. Our objective was to examine the effects of systemic endophytes on the competitive ability of two agronomically important grass species: meadow fescue [Festuca pratensis (Huds.) syn. Schedonorus pratensis (Huds.) P. Beauv] and tall fescue [Festuca arundinacea (Schreb.) syn. Schedonorus phoenix (Scop.)]. Plants of meadow and tall fescue were grown for 48 days in replacement series of interspecific mixture with a legume (red clover, Trifolium pratense L.) in different nutrient environments in a greenhouse. Neither of the grass species gained endophyte‐promoted competitive advantage over red clover in grass–clover mixtures. Endophyte infection increased the growth of meadow fescue monocultures by 89% compared to endophyte‐free monocultures in high‐nutrient soils, but plant competition or the cost of endophyte infection to the meadow fescue decreased the yield in resource‐limited conditions. On average, endophyte‐infected and endophyte‐free meadow fescues produced 0·15 and 0·17 g, and 0·14 and 0·14 g dry biomass per plant in mixtures with red clover in high‐ and low‐nutrient soils respectively. In contrast to meadow fescue, endophyte‐promoted growth of tall fescue monocultures was not detected. Endophyte‐infected and endophyte‐free tall fescue monocultures produced 0·76 and 0·95 g biomass per pot, respectively, in the high‐nutrient environment. Endophyte infection can increase the performance of the host grass, but the positive effects depend on the host species, the species composition and soil nutrient availability.     

Evaluation of forage legumes for introduction into natural pastures of semi‐arid rangelands of Kenya

To address the potential of legumes to contribute to improved quality and quantity of natural pastures in the semi‐arid rangelands of Kenya, five legume species were introduced and evaluated in a small‐plot field experiment over three growing seasons. The investigated species were glycine (Neonotonia wightii), siratro (Macroptilium atropurpureum), dolichos (Lablab purpureus cv. Rongai), velvet bean (Mucuna pruriens) and shrubby stylo (Stylosanthes scabra cv. seca). Treatments included two cutting heights (ground level and 15 cm) and two cutting intervals (at 2 and 4 months). The mean dry matter (DM) yields of glycine and siratro were highest when the legumes were harvested at ground level at 2‐month intervals (10·31 and 7·81 t ha^?1 year^?1 respectively). Mean DM yield of stylo was highest when the legume was harvested at 15 cm after 4 months (3·52 t ha^?1 year^?1). These three legumes also produced high organic matter through litter fall, which contributed to soil fertility. Evidence from a supporting pot experiment showed effective nodulation and potential for N fixation. These legumes also possessed deep tap roots and withstood heavy defoliation. These three legumes were selected for further integration with grasses in natural pastures. The DM yields of dolichos and velvet bean when harvested at 15 cm after 2 or 4 months were low (2·48 and 1·91 t ha^?1 year^?1), and these species were considered inappropriate for further investigation.     

Litter dynamics of Dactylis glomerata and Vicia villosa with respect to climatic and soil characteristics

The rates of litter decomposition, organic matter loss and nutrient release for Dactylis glomerata (Gramineae) and Vicia villosa (Leguminosae) were studied at two sites in north Greece, which differed in soil pH, soil particle distribution and nutrient availability.
Climate, soil characteristics and taxonomic plant differences affected the rates of litter decomposition. Litter loss was higher at site A (neutral soil) than at site B (acid soil). Organic matter loss was generally low. Dry weather affected both parameters. Nitrogen release from litter was higher for both species at site A. The rate of P and K release was higher in the neutral soil than in the acid soil for both species, while that of Ca for both species and of Mg for Vicia was higher in the acid soil. Phosphorus, Ca and Na release from the litter of the leguminous species began earlier than from the graminaceous species. P mineralization from Vicia litter seemed to start just after its incorporation into the soil.     

Leaf litter decomposition and diversity of arthropod decomposers in tropical <Emphasis Type="Italic">Muyong</Emphasis> forest in Banaue,Philippines

The Muyong forest, an indigenous secondary forest in Banaue, Ifugao, Philippines, plays a crucial role in the Muyong–Payoh system, a continuum of secondary forest and rice terrace, of the Banaue rice terraces by providing water and nutrients to the rice plants in the Payoh terraces. In recent decades, the planting of introduced tree species in the Muyong forest has threatened the sustainable provision of ecosystem services such as water balance and nutrient cycling. To further understand nutrient cycling in the Muyong–Payoh systems, this study was conducted in Poitan, Banaue, Ifugao to gather preliminary baseline data on floral diversity, leaf litterfall rate, leaf litter decomposition rate, and diversity and succession of arthropods in decomposing leaf litter in a Muyong forest. Vegetation analysis was done by identifying and describing the trees growing inside the five 10 m × 10 m quadrat sampling plots. Monthly leaf litter fall was collected in 1 m × 1 m litter traps, and the dry weight was determined after oven-drying at 65 °C for 48 h. Leaf litter decomposition experiment was established by laying out 12 nylon mesh bags containing fresh leaf litter in each of the four sites on the forest floor and one bag was retrieved every month to determine the change in dry weight of the leaf litter. Six bulk soil samples were collected from the Muyong forest floor and analyzed for organic matter, pH, available P and exchangeable K. Fresh leaf litter samples were analyzed for total N, P and K contents. Arthropods in the collected decomposing leaf litter were extracted using Berlese funnel and later identified up to families level using arthropod taxonomic key. The diversity of plants in the Muyong forest includes thirty-eight tree species belonging to 19 families dominated by indigenous tree species. Results showed that the monthly leaf litter fall was higher during the dry months of March to May and lower during the wet months. The estimated total leaf litter fall in Muyong forest was comparable to published litter fall from tropical secondary forests. The N, P and K contents of fresh leaf litter range from 1.0 to 1.2, 0.11 and 0.40%, respectively. The first month of decomposition has the fastest rate while the decomposition rate during the next 4 months ranged from 0.125 to 0.251. Complete decomposition or mass lost in the leaf litter in the Muyong forest took place within 5 months. The soil arthropods identified in the decomposing leaf litter were composed of 13 orders and 28 families. Majority of the collected arthropods were insects while other species including mites, spiders, millipedes and sowbugs were also present. Detrivore and fungivore Families were found to be dominant in the decomposing leaf litter. Moreover, the composition and succession of arthropod decomposer community varied in the three sampling methods and with the changing quality of the litter material as decomposition progressed. The wide diversity and succession of leaf litter decomposers consisting of detritivores, predators, fungivore and herbivore coupled with abundant rainfall and warm temperature are the two main factors that contribute to the fast rate of leaf litter decomposition and nutrient turn over in the Muyong forest. Thus, the Muyong forest can sustain the productivity of rice planted in the adjoining downstream Payoh terraces. Hence, the conservation and management of the Muyong forest is critical in maintaining the ecological functions of the Muyong–Payoh continuum.     

Metal uptake by tall fescue (Festuca arundinacea) as affected by poultry litter application

Poultry litter is commonly applied to pastures as an organic fertilizer. However, poultry litter also typically contains numerous heavy metals that may accumulate in soil and can pose an environmental threat when it is applied to pastures. The objective was to ascertain uptake characteristics of heavy metals by tall fescue (Festuca arundinacea Schreb.) from soil with a history of poultry litter additions as affected by subsequent applications of poultry litter. Poultry litter was applied to small plots at rates of 0, 2·2 and 4·5 t dry litter ha^?1. In the 7·5 months following application of litter, cumulative dry‐matter (DM) production of herbage was higher (P < 0·05) in the plots that received poultry litter compared with the control plots where no litter was applied. However, concentrations of Al, Cu, Fe, Mg, Mn, Se and Zn in herbage were unaffected by the rate of application of poultry litter. All metal tissue concentrations, except for Fe, were affected by sampling date. While tall fescue responds to poultry litter with increased DM production, it does not appear to accumulate excessive quantities of micronutrients associated with the application of poultry litter.     

海南岛东南沿海地区不同森林类型林地凋落物现存量和养分特征

为揭示热带沿海地区不同森林类型凋落物现存量及其养分元素储存能力的差异,选取林地相邻、生境条件基本一致的青皮林和木麻黄林为研究对象,设置随机样地,采集未分解层、半分解层、已分解层凋落物样品,测定凋落物层现存量和主要养分元素含量、储量及其释放率。结果表明：（1）木麻黄林凋落物层现存量为29.49 t/hm²,是青皮林的2倍,2种林型不同分解层表现为：已分解层>半分解层>未分解层;（2）2种林型不同分解层养分元素含量基本遵循C>N>Mg>K>P的变化模式,随着凋落物分解,青皮林各养分元素含量逐级降低,木麻黄林则因养分元素不同而异,可能因凋落物C含量流失过多出现损失速率大于分解释放养分速率而造成半分解层N、P、Mg的含量相对增加,但均在已分解层含量最低;（3）木麻黄林凋落物层养分储量值为8448.23 kg/hm²,是青皮林的2倍,各分解层凋落物养分元素的储量依次为C>N>Mg>K>P,与养分元素含量变化规律一致,而养分释放率从未分解层（-1.79%、-0.97%）到半分解层（0.65%、1.23%）呈现增加趋势。总之,同一立地条件下,不同林型的凋落物现存量、养分含量及其储量的差异可能与植物叶片生物学特征、微环境条件、微生物种群及活性不同有关。     

Effect of nitrogen and phosphorus availability on the emergence,growth and over‐wintering of Rumex crispus and Rumex obtusifolius

Rumex crispus and R. obtusifolius are known to be nitrophilous but it is not known whether either or both species require a high N supply at all developmental stages. Furthermore, it is not clear whether both species require a high P supply, attain flowering in the seeding year, or have similar levels of winter resistance. The effect of nutrient availability on the emergence, growth and over‐wintering of both Rumex species was investigated in a pot experiment (ten N, P and K fertilizer treatments) in Prague, Czech Republic. In both species, emergence of seedlings was negatively affected by very high N, but positively affected by increased P availability in the soil. No effect of K supply on the emergence, or subsequent growth, was recorded. High flowering in the seeding season and high winter mortality of R. obtusifolius contrasted with no flowering and no mortality of R. crispus. Over‐wintering was not markedly affected by N, P or K supply. Both Rumex species are sensitive to a very high N supply in early developmental stages but tend to require a high N supply from the fully developed rosette‐stage onwards. In addition to high N requirements during stem growth, flowering and seed ripening, both species also require a high P supply. At least some Central European populations of R. crispus, in contrast to R. obtusifolius, do not flower in the seeding year. In Central Europe, the frequently reported high field winter mortality of R. obtusifolius can be caused by its low frost resistance.     

Long-term effects of poultry litter and conservation tillage on crop yields and soil phosphorus in cotton–cotton–corn rotation

Long-term field experiments are needed to fully realize positive and negative impacts of conservation tillage and poultry litter application. A study was initiated on a Decatur silt loam soil at the Tennessee Valley Research and Extension Center, Belle Mina, AL, USA in 1996 to evaluate cotton (Gossypium hirsutum L.) performance with long-term poultry litter (PL) application under different tillages and to study the build up of phosphorus (P) with application of PL. Treatments include incomplete factorial combinations of three tillage systems [conventional till (CT), mulch till (MT), and no-till (NT)], two cropping systems [cotton-fallow and cotton-winter rye (Secale cereale L.)], and two nitrogen sources and rates [100 kg N ha⁻¹ from ammonium nitrate (AN), and 100 and 200 kg N ha⁻¹ from poultry litter (PL)]. Cotton was rotated with corn (Zea mays L.) every third year. Results from 2003 to 2008 showed that all tillages gave similar cotton lint yields with AN at 100 kg N ha⁻¹. Application of PL at 100 kg N ha⁻¹ in NT plots resulted in 12 and 11% yield reductions compared to that of CT and MT, respectively. However, NT plots with higher quantity of PL (200 kg N ha⁻¹) gave similar yields to CT and MT at 100 kg N ha⁻¹. During corn years, higher residual fertility of PL, in terms of grain yields, was observed in NT plots compared to CT and MT. Long-term PL application (100 kg N ha⁻¹ year⁻¹) helped to maintain original soil pH in CT and MT while AN application decreased soil pH. In NT plots, PL at 100 kg N ha⁻¹ was not sufficient to maintain original soil pH, but 200 kg N ha⁻¹ maintained original pH. Although not-significant, elevated P levels were observed in all tillages compared to original P levels which indicates possibility of P build up in future with further application of PL. Application of PL at double rate (200 kg N ha⁻¹) in NT plots resulted in significant build up of P. Results indicate that NT gives similar yields to CT when received AN, but needs higher rate of PL application to achieve similar yields to CT.     

Residual effect of poultry litter applied to cotton in conservation tillage systems on succeeding rye and corn

The burgeoning poultry industry in the southeastern US is presenting a major environmental problem of safe disposal of poultry litter (PL). In a comprehensive study, we explored ways of PL use in conservation tillage-based cotton (Gossypium hirsutum L.) production systems on a Decatur silt loam soil in north Alabama, from 1996 to 1999. The study reported here-in presents the residual effects of PL applied to cotton in mulch-till (MT) and no-till (NT) conservation tillage systems in 1997 and 1998 cropping seasons on N uptake, growth, and yield of rye (Secale cereale, L.) cover crop and rotational corn (Zea mays L.) in 1999. Rye was grown without additional N, whereas corn was grown at three inorganic N levels (0, 100, and 200 kg N ha⁻¹). Poultry litter was applied to cotton in 1997 and 1998 at 0, 100, and 200 kg N ha⁻¹. Residual N from PL applied to cotton in 1997 and 1998 produced up to 2.0 and 17.3 Mg ha⁻¹, respectively, of rye cover crop and corn biomass (includes 7.1 Mg ha⁻¹ of corn grain yield) without additional fertilizer. Therefore, in addition to supplying crop residues which reduce soil erosion, increase soil organic matter, and conserve soil moisture, the rye cover crop was able to scavenge residual N left by the cotton crop, which would otherwise, be at risk of being leached and pollute groundwater resources. Poultry litter applied to cotton also increased corn grain quality as shown by up to 100% increase in grain N content compared to the 0N treatment. Using PL with a slower rate of N release compared to inorganic fertilizer to meet some of the N requirements of corn, will not only reduce N fertilizer costs for corn, but will also reduce the risk of nitrate N leaching into groundwater. The maximum amount of crop residues added to the cotton based cropping system by residual N from PL and inorganic N was 21.3 Mg ha⁻¹. This will lead to an increase in soil organic carbon and soil structure in the long term and a reduction in soil erosion, thereby further improving soil productivity, while at the same time, protecting the environment from nitrate pollution and soil degradation. Our study demonstrates that cotton under conservation tillage system in combination with rye cover crop and rotational corn cropping could use large quantities of PL thereby avoiding serious potential environmental hazards.     

Organic matter and seed survival of Striga hermonthica – Mechanisms for seed depletion in the soil

Seed survival of Striga hermonthica is influenced by amendments of organic matter; however, the role of organic matter quality (C:N ratio) and mechanisms for enhanced seed decay are inadequately understood. In a field experiment, plots received a single dose of 6 t organic matter per hectare but with large differences in quality in terms of C:N ratio. Soil moisture, soil temperature and soil ethylene concentrations were measured, while buried nylon seed bags were periodically withdrawn from the soil and assayed for seed viability and germination. Organic matter amendments incorporated in the soil significantly depressed S. hermonthica seed survival. The effect was strongest with organic matter of high quality. Organic matter of low-quality enhanced soil water content during the first five days after a rainfall event and resulted in a 0.5 °C lower soil temperature. The highest observed ethylene concentrations in the soil were between 2 and 3 ppm, high enough to stimulate S. hermonthica seed germination. Maximal seed germination in vitro was obtained after 48 h of exposure to 1 ppm ethylene. However, observed changes in seed germination and viability of retrieved seed batches (seed survival) did not correlate with soil ethylene concentrations. The latter in turn did not differ between qualities of the applied organic matter. Seed survival decreased with increasing time of burial, especially after 4–8 weeks. As S. hermonthica attachment mainly occurs during the first four weeks of the cropping season the observed effect of seed decay may hardly be beneficial for the on-going cropping season. Nutrient release through decomposition of organic matter, enhancing decay of S. hermonthica seeds, is proposed as the probable cause of seed depletion in the soil.     

Forage quality of leaf fodder from the main woody species in Iceland and its potential use for livestock in the past and present

Woody species played, and in many Nordic regions still play, a very important role in livestock feeding. However, forage quality (contents of macroelements and fibre fractions) of the leaves of common woody species is often inadequate. The aim of our study was to determine forage quality of leaves of Betula nana, Betula pubescens, Salix lanata, Salix phylicifolia and Sorbus aucuparia from Iceland and to compare it with the forage quality of the common native grass Deschampsia cespitosa and the introduced grass Alopecurus pratensis used by contemporary Icelandic farmers for forage production. Samples were collected at four localities in Iceland in late June 2013 and analysed for nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), neutral and acid‐detergent fibre and lignin concentration. Analyses were compared with the optimum range for cattle and sheep nutrition. The nutritive value of leaves of the Icelandic woody species was relatively high, and analysis showed their nutritive content satisfied both cattle and sheep nutrient requirements for N, P, K, Ca and Mg, but the relatively high content of indigestible lignin in all woody species could cause problems for livestock metabolism. Grasses were characterized by lower P, Ca and Mg, but substantially higher K concentrations, and higher N:P and K:(Mg + Ca) ratios. The forage quality of leaves of woody species increased in the order B. nana < B. pubescens < S. phylicifolia < S. aucuparia < S. lanata. Results are discussed in relation to use of leaf fodder in the past, when woody species, particularly Salix spp., are likely to have played an important role in livestock feeding.     

Formulation of a biodegradable, odor-reducing cat litter from solvent-extracted corn dried distillers grains

Cats are among the most popular pets in the U.S., and the majority of these animals are kept indoors where litter boxes containing some type of absorbent litter material are needed. Dried distillers grains (DDGs) are a major co-product of the ethanol industry, and are primarily sold as animal feed. We have been studying value-added uses for DDGs by extracting valuable phytochemicals from them with a variety of organic solvents. The objective of this research was to determine if the extracted DDGs could be formulated as cat litter. Extracted DDGs absorbed significantly more water (termed hydration capacity) than unextracted DDGs, although sorting the extracted DDGs by particle size had no effect on hydration capacity. Through the addition of glycerol as a dust retardant and guar gum as a clumping agent, a formulation was obtained with desirable physical properties. The addition of copper sulfate to this formulation significantly reduced the release of a volatile odor compound that is chemically similar to the odor compound produced by the decomposition of cat urine. From these results it appears that extracted DDGs have potential as commercial cat litter.     

The invertebrate fauna of grassland and its influence on productivity. III. Effects on soil fertility and plant growth

The effects of grassland invertebrates on organic matter decomposition, soil fertility and plant growth are reviewed. Their role as primary decomposers is limited because of relatively low rates of metabolic and enzymatic activity compared with microorganisms. However, they greatly facilitate decomposition by fragmenting and incorporating litter into the soil and by stimulating microbial activity. Earthworms are the main litter consumers in productive temperate grasslands and termites in the tropics, while the activities of dung beetles, dipterous larvae and earthworms are essential for efficient dung decomposition. Earthworms and microbial-feeding invertebrates facilitate mineralization and release into the soil solution of plant nutrients. Earthworms have a major influence on soil structure through burrowing, soil ingestion and mixing and they significantly increase plant growth.
Herbivorous invertebrates at non-outbreak densities normally consume less than 10% of net primary production in grassland, but consumption bears little relationship to overall effects on productivity. These depend on factors such as the nature of the damage caused and regrowth potential, tolerance for damage and effects on animal production at the time of attack. Sap feeding insects may cause wilting and reduced growth and selective feeding on preferred species can alter botanical composition, while aphid-transmitted virus disease can depress yield. On the positive side, low levels of herbivory can stimulate growth, weed feeding insects may limit the distribution of pasture weeds, while the role of flower-visiting insects can be important in the pollination of legume seed crops. Pest management approaches incorporating biological control, alteration of botanical composition, adjustment of stocking densities and accurately timed insecticidal applications offer prospects for the control of recurring pests such as grass grub and porina in New Zealand.     

Soil chemical properties,plant species composition,herbage quality,production and nutrient uptake of an alluvial meadow after 45 years of N,P and K application

Little is known about the long-term effects of mineral N, P and K application on the nutritional status of mown alluvial grasslands. We asked how long-term fertilizer application affected soil chemical properties, plant species composition, herbage production, nutrient concentrations in soils and plants and balance of nutrients. Six treatments (control, PK, N50PK, N100PK, N150PK and N200PK) were investigated at the Černíkovice Experiment (Czech Republic) established in 1966 on an Alopecurus pratensis meadow, using annual application rates of 50, 100, 150 and 200 kg N, 40 kg P and 100 kg K ha⁻¹. Data were collected and analysed for 2007, 2008 and 2009. Although fertilizers had been applied over 45 years, differences in soil chemical properties between fertilization treatments were small. The legumes Lathyrus pratensis and Trifolium repens responded highly positively to PK application, and tall grasses, A. pratensis in particular, to NPK application. Herbage quality was high in terms of content of major nutrients, and its chemical properties varied considerably between treatments, cuts and years. Mean annual herbage yield ranged from 6·1 in the control to 9·7 t ha⁻¹ in the N200PK treatment. Herbage production was N-limited in 2007 and 2009, but not in 2008. Seasonal N agronomical efficiency ranged from 4·2 to 22·9 kg of DM herbage per kg of applied N. The herbage N:P and N:K ratios did not reflect the actual response of herbage production to N application. A negative balance between N applied and N removed in harvested herbage was recorded in all treatments. We concluded that in highly productive alluvial grasslands, mineral-rich soils can respond weakly to N, P and K application, fertilizer application modifies plant species composition and herbage production is not N-limited in all years. Nutrient ratios must be interpreted with caution for the estimation of nutrient limitation.     

Seasonal nitrogen effects on nutritive value in binary mixtures of tall fescue and bermudagrass

The addition of cool‐season, tall fescue [Lolium arundinaceum (Schreb.) Darbysh.], to warm‐season, bermudagrass [Cynodon dactylon (L.) Pers.], pastures can improve forage productivity and nutritive value. Effects of four binary mixtures consisting of cv. Flecha (incompletely summer dormant) and cv. Jesup (summer active) tall fescue overseeded into established stands of cv. Russell and cv. Tifton 44 bermudagrass and three seasonal N treatments were evaluated on dry‐matter (DM) yield, crude protein (CP), in vitro true digestible DM (IVTDDM), acid detergent fibre (ADF) and neutral detergent fibre (NDF). Nitrogen‐timing treatments were 168 kg N ha^?1 (as ammonium nitrate) split into three applications per season with an additional 8·6 t ha^?1 of broiler litter (as‐is moisture basis) split into two applications varied to favour either tall fescue (in October and January), bermudagrass (in March and May) or both grasses (in January and March). Treatment effects were determined in samples of mixed herbage harvested in April, May, July, August and September of 2009 and 2010. Regardless of bermudagrass cultivar, herbage DM yield was greater (P < 0·05) in Flecha–bermudagrass than Jesup–bermudagrass in July of both years and in August 2010. Nutritive value generally was greatest in Jesup–Tifton 44, based on high CP and IVTDDM, and low ADF and NDF. Averaged across mixtures, avoiding fertilizer N and litter applications beyond April increased (P < 0·01) DM yield in April and May and IVTDDM in July (603 vs. 629 g kg^?1; 2‐year average) and August (618 vs. 660 g kg^?1) compared with applications in January–July. The timing of N and broiler litter applications on tall fescue–bermudagrass to favour growth of tall fescue appeared to increase fescue cover during the cool season and nutritive value of the mixed herbage during the warm season.     

Calibration and validation of optical chlorophyll‐measuring devices for use in predicting crude protein concentration in tropical grass herbage

The objective of this experiment was to evaluate the Fieldscout CM 1000 NDVI and Yara N‐Tester as easy‐to‐use and cost‐effective tools for predicting foliar chlorophylls (a, b and total) and crude protein (CP) concentrations in herbage from three tropical grass species. Optical chlorophyll measurements were taken at three stages (4, 8 and 12 weeks) of regrowth maturity in Guinea grass (Panicum maximum) and Mulato II (Brachiaria hybrid) and at 6 and 12 weeks maturity in Paspalum spp (Paspalum atratum). Grass samples were harvested subsequent to optical measurements for laboratory analysis to determine CP and solvent‐extractable chlorophylls (a, b and total) concentrations. Optical chlorophyll measurements and CP concentrations were highly correlated (Yara N‐Tester: r² = 0·77–0·89; Fieldscout CM 1000 NDVI: r² = 0·52–0·84). Crude protein prediction models from the Yara N‐Tester and Fieldscout CM 1000 NDVI accounted for 70–89% and 44–73% CP variability, respectively, in Mulato II and Guinea grass. The Yara N‐tester produced more accurate and reliable CP estimates based on very high concordance correlation coefficient [CCC (0·73–0·91)] and low rMSPE, mean and regression bias. It is concluded that the Yara N‐Tester produces more accurate and reliable CP estimates of tropical pastures.     

Nitrogen recovery and loss in a fertilized elephant grass pasture

Limited information is available regarding the recovery and loss of fertilizer nitrogen (N) applied to intensively managed tropical grass pastures. An experiment was carried out in Brazil to determine the fertilizer‐N recovery and ammonia volatilization loss in an elephant grass (Pennisetum purpureum, Schum.) pasture fertilized with 100 kg N ha^?1 as urea or ammonium sulphate, labelled with ¹⁵N, in late summer (LS) or in mid‐autumn (MA). Herbage mass was highest and litter mass was lowest in LS (P < 0·05). The N concentration of herbage was highest in autumn (P < 0·05) and the total N content in soil was lower in LS than in MA (P < 0·05), reflecting the high N uptake capacity of the grass. Proportionately higher ¹⁵N recovery in litter mass (P < 0·05) was observed in autumn (0·094) than in LS (0·0397) and the ¹⁵N recovery in herbage was 0·046 higher for ammonium sulphate‐fertilized pastures (P < 0·05; proportionately 0·243 for ammonium sulphate and 0·197 for urea). Around 0·60 of the fertilizer‐¹⁵N recovered was retained in soil and in non‐harvestable fractions of the plant. The NH₃ volatilization loss was higher in LS and most of the N loss occurred soon after fertilizer application. Urea and ammonium sulphate fertilizers were equally effective in sustaining herbage dry matter yield in the short term. However, the use of ammonium sulphate, rather than urea, would be preferable for LS applications when the objective is to reduce NH₃ volatilization losses.     

Root growth response of serradella species to aluminium in solution culture and soil

Serradella (Ornithopus) species are high‐quality pasture legumes that originate from the Mediterranean basin and have been increasingly used in southern Australian temperate grazing systems. They are generally regarded as tolerant of soils with low pH and, by inference, elemental toxicities such as aluminium (Al). No studies have examined the effect of high Al concentrations on the growth of French serradella (Ornithopus sativus Brot.) or newly developed cultivars of yellow serradella (O. compressus L.). Several cultivars/accessions of each species were grown in low ionic‐strength nutrient solutions at pH_Ca 4.5 containing a range of Al concentrations. Their susceptibility to root growth inhibition by Al was benchmarked against reference species ranging from Al‐sensitive to Al‐tolerant. Most serradella cultivars had moderate‐to‐high Al tolerance in solution culture but one yellow and two French serradella cultivars ranked alongside the Al‐sensitive reference species. A subset of cultivars and reference species were then grown in an Al‐toxic soil to test the validity of the solution culture results; these cultivars spanned the apparent range in Al sensitivity/tolerance indicated by the solution culture experiment. Variation in the relative root length achieved in Al‐toxic solution culture explained ~59% of the variation in the relative root length achieved in the acidic Al‐toxic soil. This result supports the conclusion that Al tolerance varies among serradella and that some cultivars may not thrive in soils with pH_Ca < 4.5 and elevated extractable Al concentrations.