Utilization of semi‐natural grassland through integrated generation of solid fuel and biogas from biomass. II. Effects of hydrothermal conditioning and mechanical dehydration on anaerobic digestion of press fluids

A procedure (Integrated Generation of Solid Fuel and Biogas from Biomass, IFBB) was developed which uses a screw press to separate the readily digestible constituents of mature grassland biomass into a press fluid for conversion into biogas and a fibrous press cake for processing into a solid fuel. Effects of mechanical dehydration and prior hydrothermal conditioning at different temperatures (5, 60 and 80°C) on concentrations of organic compounds in the press fluid and on methane production in batch experiments were evaluated for five semi‐natural grasslands typical of mountain areas of Germany. Results show that the crude protein concentration of the press fluids was higher and crude fibre concentration was lower than that of the parent material (herbage conserved as silage). Digestion tests in batch fermenters showed that the methane yield of the press fluids was double [397–426 normal litre (NL) kg^?1 volatile solids (VS) after 13 d] that of the whole‐crop grassland silage (218 NL kg^?1 VS after 27 d) but no consistent effect of higher temperature during conditioning was observed. Within 13 d of fermentation the decomposition of the organic matter (OM) that occurred in the press fluids was 0·90, whereas after 27 d of fermentation more than 0·40 of the OM remained undigested in the whole‐crop silage, pointing at a marked reduction in retention time for anaerobic digestion of press fluids in continuous systems. Press fluids produced 0·90 of the maximum methane yield after 4 to 7 d compared with 19 days for the whole‐crop silage.     

Effects of cutting frequency on plant production, N-uptake and N2 fixation in above- and below-ground plant biomass of perennial ryegrass–white clover swards

Nitrogen (N), accumulating in stubble, stolons and roots, is an important component in N balances in perennial ryegrass–white clover swards, and the effects of cutting frequency on the biomass of above‐ and below‐harvest height were studied during two consecutive years. Total dry matter (DM) and total N production, and N₂ fixation, were measured at two cutting frequencies imposed in the summers of two years either by cutting infrequently at monthly intervals to simulate mowing or by frequent cutting at weekly intervals to simulate grazing. Total DM production harvested was in the range of 3000–7000 kg DM ha^?1 with lower DM production associated with the frequent cutting treatment, and it was significantly affected by the different weather conditions in the two years. The higher cutting frequency also reduced the biomass below harvest height but the different weather conditions between years had less effect on stubble and, in particular, biomass of roots. The biomass of roots of white clover was significantly lower than that of roots of perennial ryegrass and remained at a relatively constant level (200–500 kg DM ha^?1) throughout the experiment, whereas the biomass of perennial ryegrass roots increased from 2400 kg DM ha^?1 in the year of establishment to 10 200 kg DM ha^?1 in the infrequent cutting treatment and 6650 kg DM ha^?1 in the frequent cutting treatment by the end of the experiment, giving shoot:root ratios of 4·7–16·6 and 0·5–1·6 for white clover and perennial ryegrass respectively. Annual N₂ fixation was in the range of 28–214 kg N ha^?1, and the proportion of N fixed in stolons and roots was on average 0·28. However, as weather conditions affect the harvested DM production and the shoot:root ratio, care must be taken when estimating total N₂ fixation based on an assumed or fixed shoot:root ratio.     

Performance and environmental effects of forage production on sandy soils. I. Impact of defoliation system and nitrogen input on performance and N balance of grassland

Grassland and its management is central to the productivity of and nitrogen (N) losses from dairy farms in north‐west Europe. Botanical composition, production and N surplus of grassland were assessed during five consecutive years. The experiment consisted of all combinations of five defoliation systems: cutting‐only (CO), rotational grazing (GO), grazing + one (MSI) or two silage cuts (MSII) and simulated grazing (SG). Four mineral N fertilization rates (0–300 kg N ha^?1 year^?1) and two slurry levels (0 and 20 m³ slurry ha^?1 year^?1) were applied. Fertilizer N was more efficient in producing net energy (NEL) in grazing‐dominated, low white clover systems (GO and MSI systems: 70 and 88 MJ NEL kg^?1 N) than in white clover‐rich systems (MSII, CO and SG systems: ≤60 MJ NEL kg^?1 N). While sward productivity in system MSI was similar to that in system GO, system MSII benefited from increased N₂ fixation at low N rates. There were small differences in NEL concentrations of the herbage between defoliation systems. Crude protein concentration of the herbage increased with increasing N supply from fertilizer, excreta and N₂ fixation. N surpluses (?63 to +369 kg N ha^?1 year^?1) increased with increasing grazing intensity and increasing N fertilization rate. The average response in N surplus applied was 0·81, 0·59, 0·40, 0·33 and 0·24 kg N ha^?1 in systems GO, MSI, MSII, CO and SG respectively.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 4. The effect of seasonal pattern of nitrogen fertilizer application and annual stocking rate

Greyface (Border Leicester × Scottish Blackface) ewes, mated in October, were housed in winter and turned out after lambing in late March to one of four treatments replicated three times on perennial ryegrass (Lolium perenne)-dominated pastures. On three of the treatments the stocking rate was 12·5 ewes plus lambs ha^?1 annum^?1 (SR_12·5), whereas on the fourth it was 15·0 ewes plus lambs ha^?1 annum^?1 (SR_15·0). There were two levels of applied fertilizer nitrogen (N), 152 kg N ha^?1 annum^?1 (N₁₅₂) and 205 kg N ha^?1 annum^?1 (N₂₀₅). Three patterns of nitrogen application were used: predominantly in spring (E), predominantly in autumn (L), and mainly in spring and autumn (E + L). Grazed sward surface height was controlled within the range 3·5–5·5 cm during spring and summer, and supplementary feed was offered when sward height was below 3·5 cm. The effects on animal performance, yield of silage and requirement for supplementary feed were measured over 3 years (1986–88). Management of the sward height within the specified limits resulted in similar levels of individual animal performance for all treatments, but treatment SR_15·0N₂₀₅E + L produced a significantly (P < 0·05) greater output of lamb per hectare. There was no evidence to suggest that, by increasing the amount of N fertilizer applied in the autumn, ewe reproductive performance was increased. Neither the treatment with the lower level of N applied in the spring (SR_12·5N₁₅₂L) nor the high stocking rate treatment (SR_15·0N₂₀₅E + L) was self-sufficient in winter feed (silage) production. SR_15·0N₂₀₅E + L also required more supplementary feed in both the lactation (38·1 kg ewe^?1) and the mating (9·1 kg ewe^?1) periods. SR_12·5N₁₅₂L required the second greatest amount of supplementary feed during lactation (36·1 kg ewe^?1), whereas SR_12·5N₂₀₅E + L required the least supplementary feed over both periods (27·8 kg and 4·8 kg ewe^?1). Taking all treatments together, there were significant (P < 0·05) differences between years in lamb weaning weight (kg), lamb output (kg ha^?1), yield of silage (kg ewe^?1) and supplementary feed required (kg ewe^?1), arising mainly from a lower level of herbage production in one year. Treatment SR_12·5N₁₅₂E generated the highest gross margin per hectare.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK: 7. Sustainability of white clover in grass/clover swards with reduced levels of fertilizer nitrogen

The sustainability of white clover in grass/clover swards of an upland sheep system, which included silage making, was studied over 5 years for four nitrogen fertilizer rates [0 (N₀), 50 (N₅₀), 100 (N₁₀₀) and 150 (N₁₅₀) kg N ha^?1]. A common stocking rate of 6 ewes ha^?1 was used at all rates of N fertilizer with additional stocking rates at the N₀ fertilizer rate of 4 ewes ha^?1 and at the N₁₅₀ fertilizer rate of 10 ewes ha^?1. Grazed sward height was controlled, for ewes with their lambs, from spring until weaning in late summer by adjusting the proportions of the total area to be grazed in response to changes in herbage growth; surplus pasture areas were harvested for silage. Thereafter sward height was controlled on separate areas for ewes and weaned lambs. Areas of pasture continuously grazed in one year were used to make silage in the next year. For treatments N₀ and N₁₅₀, white clover stolon densities (s.e.m.) were 7670 (205·4) and 2296 (99·8) cm m^?2, growing point densities were 4459 (148·9) and 1584 (76·0) m^?2 and growing point densities per unit length of stolon were 0·71 (0·015) and 0·67 (0·026) cm^?1 respectively, while grass tiller densities were 13 765 (209·1) and 18 825 (269·9) m^?2 for treatments N₀ and N₁₅₀ respectively. White clover stolon density increased over the first year from 780 (91·7) cm m^?2 and was maintained thereafter until year 5, reaching 8234 (814·3) and 2787 (570·8) cm m^?2 for treatments N₀ and N₁₅₀ respectively. Growing point density of white clover increased on treatment N₀ from 705 (123·1) m^?2 to 2734 (260·7) m^?2 in year 5 and it returned to the initial level on treatment N₁₅₀ having peaked in the intermediate years. Stolon density of white clover was maintained when the management involved the annual interchange of continuously grazed and ensiled areas. The non‐grazing period during ensiling reduced grass tiller density during the late spring and summer, when white clover has the most competitive advantage in relation to grass. The increase in stolon length of white clover in this period appears to compensate for the loss of stolon during periods when the sward is grazed and over winter when white clover is at a competitive disadvantage in relation to grass. The implications for the management of sheep systems and the sustainability of white clover are discussed.     

Effect of continuous stocking by sheep at four sward heights on herbage mass, herbage quality and tissue turnover on grass/clover and nitrogen-fertilized grass swards

The effects of continuous stocking by sheep at sward surface heights (SSH) of 3, 5, 7 and 9 cm in grass/clover (GC) and nitrogen-fertilized grass (GN) swards were examined in relation to herbage mass and quality, clover content, tiller density and rates of herbage production and senescence in two periods in each of three grazing seasons (1987-89). The GN swards received a total of 300 kg N ha^?1 each year in six equal dressings from March; GC swards received a single dressing of 50 kg N ha^?1 in March each year. Herbage mass measured from ground level increased linearly with SSH with overall mean herbage masses of 0·89, 1·38, 1·78 and 2·12 t OM ha^?1 (s.e.m.0·024, P < 0·001) at SSH of 3, 5, 7 and 9 cm respectively. GN and GC swards had mean herbage masses of 1·58 and 1·51 t OM ha^?1 (s.e.m. 0·051, NS) respectively. Mean N content of herbage on GN swards was greater than that on GC swards and declined with increasing SSH. Crude, fibre (CF) content of herbage was similar for both sward types and increased with increasing SSH. Clover content of GC swards remained low throughout the experiment, ranging from 0·002 to 0·074 of herbage mass. However, from tissue turnover rates it was estimated that its contribution to herbage production was in the range of 0·049–0·219 of net herbage growth. Total growth increased with increasing SSH in both sward types, with maximum growth rates in GN swards of 143 and 130 kg DM ha^?1 d^?1 and in GC swards of 88·2 and 85·4 kg DM ha^?1 d^?1 in Periods 1 (up to early July) and 2 (after July) respectively. Senescence rates ranged between 13·3 and 50·1 kg DM ha^?1 d^?1 and tended to be higher in Period 2 than in Period 1. Net production increased with increasing SSH in Period 1, while in Period 2 net production declined at SSH above 6·5 cm. The increased net herbage production in taller swards was not associated with greater utilized metabolizable energy production at sward heights above 5 cm.     

Effect of plant spacing and nitrogen fertilizer levels on the growth,dry‐matter yield and nutritive quality of Columbus grass (Sorghum almum stapf) in southwest Nigeria

A field experiment was conducted in 2006 and 2007 to determine the agronomic performance and nutritive value of Sorghum almum for introduction in the derived savannah area of Nigeria. The experiment was arranged in a 2 × 4 factorial design with 2 plant spacings (0·5 × 0·5 m and 1·0 × 1·0 m) and 4 nitrogen (N) fertilizer levels (0, 60, 120 and 180 kg N ha^?1). Plant height, tiller number, leaf proportion, biomass yield and nutritive value of the herbage were evaluated as part of the search for alternatives (especially drought tolerant) to local forages for dry season feeding of ruminants. Herbage yield data were tested for linear, quadratic and cubic trends to identify the optimal fertilizer levels for both spacings. Spacing × N interactions (P < 0·05) were observed for plant height and tiller number in both years. Agronomic performance was marginally better in 2007 compared with 2006. The maximum dry‐matter (DM) yield of 3500 and 3740 kg ha^?1 for the more dense row spacing (0·5 × 0·5 m) was achieved at N fertilizer levels of 144 and 149 kg N ha^?1 for 2006 and 2007 respectively. For the less dense (1·0 × 1·0 m) row spacing, the maximum DM yield of 3020 and 3240 kg ha^?1 was achieved at 51 and 97 kg N ha^?1 for 2006 and 2007 respectively. The crude protein content of the grass ranged from 61 to 89 g kg^?1 DM, while the neutral detergent fibre (NDF) content ranged from 700 to 734 g kg^?1 DM. The ability of S. almum to persist into the second year in this region is seen as a promising index as persistence is one of the characteristics of a good forage plant. Considering the exorbitant price of N fertilizer, less dense row spacing with N fertilizer rate in the range of 50–100 kg N ha^?1 is hereby recommended for this region.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 3. The effect of choice of genotype, level of nitrogen fertilizer and lamb:ewe ratio

Grazed sward surface height was controlled within the range 3·25–4·75 cm during spring and summer in two experiments. In Experiment 1, the effects of stocking two breeds of ewe of similar size but different potential levels of reproductive performance [Brecknock Cheviot (C) and Beulah Speckled Face (B)] at different annual stocking rates of twelve (SR₁₂) and twenty (SR₂₀) per hectare, rates of nitrogen fertilizer of 100 (N₁₀₀) and 200 (N₂₀₀) kg N ha^?1 annum^?1 and different lamb:ewe ratios (C_1·2, B_1·2 and B_1·5) were measured in four treatments (SR₂₀N₂₀₀C_1·2; SR₂₀N₂₀₀B_1·2; SR₂₀N₂₀₀B_1·5; SR₁₂N₁₀₀C_1·2) replicated three times. In each of three years animal performance and yield of silage from areas of pasture surplus to grazing requirements were measured. In Experiment 2, breed B was compared with the Welsh Mule (W) breed, a larger with a higher potential reproductive performance, at two stocking rates, two rates of nitrogen fertilizer and two lamb:ewe ratios set on the basis of results from Experiment 1 (SR₁₈N₂₀₀B_1·5; SR₁₂N₁₀₀B_1·5; SR₁₈N₂₀₀W_1·5; SR₁₈N₂₀₀W_1·7). The treatments were replicated three times. The same terminal sire (Suffolk) was used in both experiments. A primary aim of the experiments was to test the validity of the experimental procedures used for comparing breeds of sheep where nutrition is provided predominately from grazed pastures. In Experiment 1, there was no difference between breeds C and B in the live weights of individual lambs at weaning at the same SR (20), N rate (200) and lamb:ewe ratio (1·2). Breeds C and B produced similar total yields of lamb (633 kg lamb ha^?1± 10·5) and silage (193 kg DM ewe^?1± 37·7), but breed B had a higher level of potential reproductive performance (1·59 vs. 1·37 lambs ewe^?1: P < 0·001). The treatments SR₂₀N₂₀₀B_1·5 and SR₁₂N₁₀₀C_1·2 produced, respectively, greater and lesser yields of lamb (725 vs. 384 kg lamb ha^?1, P < 0·001) and lesser and greater yields of silage (123 vs. 327 kg DM ewe^?1, P < 0·001). In Experiment 2, the live weight of lambs at weaning from breed W were heavier than from breed B (29·1 vs. 26·2 kg lamb^?1, P < 0·01) but there was no significant difference in total yield of lamb weaned between breeds W and B at the same SR (18), N rate (200) and lamb:ewe ratio (1·5) (747 kg lamb ha^?1± 19·2), or in the yield of silage (66 kg DM ewe^?1± 16·4), but breed W had a higher potential reproductive performance (1·85 vs. 1·58 lambs ewe^?1, P < 0·05). The treatments SR₁₈N₂₀₀W_1·7 and SR₁₂N₁₀₀B_1·5 produced, respectively, greater and lesser yields of lamb (840 vs. 473 kg lamb ha^?1, P < 0·001) and similar and greater yields of silage (60 vs. 141 kg DM ewe^?1, P < 0·05). The experimental approach adopted and the management protocols used provided a basis for ranking the performance of the breeds of ewes examined at appropriate levels of annual stocking rate, N-fertilizer input and lamb:ewe ratio.     

Dry direct-seeding of rice for mitigating greenhouse gas emission: field experimentation and simulation

Conventional puddled transplanted rice (TPR) is a major source of greenhouse gas (GHG), particularly methane, causing global warming. Direct-seeded rice (DSR) is a feasible alternative to mitigate methane emission, besides saving water and labor. A 2-year field experiment was carried out to quantify GHG mitigation and water- and labor-saving potentials of the DSR crop compared to TPR in three villages in Jalandhar district of Punjab, India. The InfoRCT simulation model was used to calculate the emission of CO₂ besides CH₄ and N₂O in different districts of Punjab, India. Total global warming potential (GWP) in transplanted rice in various districts of Punjab ranged from 2.0 to 4.6 t CO₂ eq. ha^?1 and in the DSR it ranged from 1.3 to 2.9 t CO₂ eq. ha^?1. Extrapolation analysis showed that if the entire area under TPR in the state is converted to DSR, the GWP will be reduced by 33 %, and if 50 % area is converted to DSR the GWP will be reduced by 16.6 % of the current emission. The DSR crop saved 3–4 irrigations compared to the transplanted rice without any yield penalty. Human labor use also reduced to 45 % and tractor use to 58 % in the DSR compared to TPR.     

Nitrogen and winter cover crop effects on spring and summer nutrient uptake

Overseeded winter annuals in bermudagrass [Cynodon dactylon (L.) Pers.] improve annual dry‐matter (DM) yield and capture nutrients in fields receiving manure application. This study determined the DM and nutrient uptake responses of annual ryegrass (Lolium multiflorum L.), cereal rye (Secale cereale), berseem clover (Trifolium alexandrinum L.) and bermudagrass‐winter fallow to 0, 50, 100 and 150 kg N ha^?1 applied approximately 2 months before a single spring harvest, and in addition to swine‐effluent N (258 and 533 kg ha^?1 in summer 2000 and 2001, respectively). Under drought conditions in 2000, DM yield at the spring harvest was highest in ryegrass, and summer DM yield of bermudagrass was greater at 100 and 150 kg N ha^?1 than 50 kg N ha^?1(P < 0·05). The concentration and uptake of N at the spring harvest increased linearly across N rates in both years (P < 0.05). Cover crops differed in N uptake in 2000 (P < 0.01) and values ranged from approximately 141 kg N ha^?1 in berseem clover to 86 kg N ha^?1 in rye. Per unit of N applied, uptake of N increased by approximately 0·409 kg ha^?1 in 2000 and 0·267 kg ha^?1 in 2001; uptake of P increased by 0·029 and 0·014 kg ha^?1 respectively. In 2000, uptake of P was responsive to N rate and this relationship was significant (P < 0·01) in winter fallow (slope = 0·032) and ryegrass (slope = 0·057). Increased uptake of N and P at the single spring harvest was due mainly to higher concentrations in herbage and not higher DM yield.     

Effects of different levels of fertilizer application to veld on growth of steers and chemical composition of the herbage

The effects of different levels of N fertilization (no N, 40 kg N and 80 kg N ha^?1 year^?1), P fertilization (no P, 21 kg P ha^?1 year^?1 and 21 kg P plus 53 kg K ha^?1 year^?1) and stocking rates (0·52 large stock units (LSU) ha^?1, 0·78 LSU ha^?1 and 1·56 LSU ha^?1) on the chemical composition and in vitro dry matter digestibility of the herbage and the liveweight gains of steers were determined in the western variant of the Bankenveld in South Africa. The average daily liveweight gains (ADLGs) of the steers increased with increasing level of N fertilization. Fertilization with P had a positive effect on ADLG only when 53 kg of K was applied with 21 kg of P ha^?1. Higher stocking rates reduced ADLGs. The liveweight gains ha^?1 increased as the rates of N and P fertilization increased. The medium stocking rate (0·78 LSU ha^?1) gave a higher liveweight gain ha^?1 than the lowest stocking rate (0·52 LSU ha^?1), but the highest stocking rate (1·56 LSU ha^?1) reduced liveweight gain ha^?1. In general, in terms of chemical components, a higher nutritive value of the veld herbage resulted from N fertilization. The higher crude protein (CP) content of the herbage, resulting from higher stocking rates, should be seen against the background of lower liveweight gains ha^?1 at the highest stocking rate. On pasture with similar contents of CP and acid detergent fibre (ADF), higher ADLG of steers was found as a result of P and K fertilization, especially for herbage with a lower CP and a higher ADF content, implying better utilization of the nutrients in such herbage with P and K fertilization, although P was also supplemented through a lick.     

Radiation‐use efficiency for forage kale crops grown under different nitrogen application rates

Crop growth is related to radiation‐use efficiency (RUE), which is influenced by the nitrogen (N) status of the crop, expressed at canopy level as specific leaf N (SLN) or at plant level as N nutrition index (NNI). To determine the mechanisms through which N affects dry‐matter (DM) production of forage kale, results from two experiments (N treatment range 0–500 kg ha^?1) were analysed for fractional radiation interception (RI), accumulated radiation (R_acc), RUE, N uptake, critical N concentration (N_c), NNI and SLN. The measured variables (DM, RI and SLN) and the calculated variables (NNI, R_acc and RUE) increased with N supply. RUE increased from 0·74 and 0·89 g MJ^?1 IPAR for the control treatments to 1·50 and 1·95 g MJ^?1 IPAR under adequate N and water in both experiments. This represented an increase in RUE of 52–146% for the range of N treatments used in both experiments, whilst R_acc increased by 9–17%, compared with the control treatments. Subsequently, the total DM yield of kale increased from 6·7 and 8 t DM ha^?1 for the control treatments to ≥ 19 t DM ha^?1 when ≥150 kg N ha^?1 was applied. The DM yields for the 500 kg N ha^?1 treatments were 25·5 and 27·6 t DM ha^?1 for the two experiments. RUE increased linearly with SLN, at an average rate of 0·38 g DM MJ^?1 IPAR per each additional 1 g N m^?2 leaf until a maximum RUE of 1·90 g MJ^?1 IPAR was reached in both experiments. There were no changes in RUE with SLN of > 2·6 g m^?2 and NNI >1, implying luxury N uptake. RUE was the most dominant driver of forage kale DM yield increases in response to SLN and NNI.     

Sheep grazing and defoliation of contrasting varieties of organically grown winter wheat with and without undersowing

Field experiments in Gloucestershire, UK, in the 1990–91, 1991–92, 1993–94 and 1994–95 growing seasons explored the merits of grazing in spring a traditional tall wheat (Triticum aestivum) variety, Maris Widgeon, with more modern shorter varieties. In the first 2 years, defoliation was achieved by mowing at 7 cm in March and/or April. In the second 2 years, varieties sown at two sowing dates were grazed by sheep at a stocking rate of 42 × 50 kg sheep ha^?1 for 3 or 4 days in March. Defoliation reduced crop height and interception of photosynthetically active radiation (PAR). In 1991–92, mowing significantly reduced grain yield of some of the shorter varieties but not of Maris Widgeon. This interaction was related to the amount of PAR intercepted. In this year, mowing improved the establishment of undersown white clover (Trifolium repens) and perennial ryegrass (Lolium perenne), but in subsequent years the conditions were much drier and undersowing failed. In the last two experiments, grazing in March did not significantly reduce grain yield of any variety. The quality of the forage eaten by the sheep had a modified acid-detergent fibre (MADF) content of less than 300 g kg^?1 dry matter (DM) and a crude protein (CP) content of more than 200 g kg^?1 DM in both seasons. Yield of DM and calculated metabolizable energy (ME) of different varieties removed by the sheep interacted strongly with sowing date. September-sown Maris Widgeon provided ≈ 0·7 and 0·3 t DM ha^?1 (or 7·8 and 3·4 GJ ME ha^?1) in March 1994 and March 1995 respectively. However, the shorter wheat varieties, Hereward and Genesis, only provided 0·3 and 0·1 t DM ha^?1 when sown at the same time in the 2 years. At later sowing dates all of the varieties only provided about 0·1 t DM ha^?1 when sown in October 1993, or 0·01 t DM ha^?1 when sown in November 1994. Sheep grazing reduced total weed biomass in June, and reduced the emergence of weed seedlings from soil samples collected after the wheat harvest. Effects of defoliation on foliar infection by Septoria tritici were inconsistent.     

Cattle and sheep grazing effects on soil organisms, fertility and compaction in a smooth-stalked meadowgrass-dominant white clover sward

This experiment was carried out to improve understanding of sward and soil responses to cattle and/or sheep rotational grazing of low-input (no N fertilizer), natural swards dominated by smooth-stalked meadowgrass (Poa pratensis) syn. Kentucky bluegrass and based on white clover (Trifolium repens). Treatments during two grazing seasons (1989–90) were: cattle grazing alone (C); cattle grazing followed by topping (CT); cattle grazing followed by sheep grazing (CS); and sheep grazing alone (S), Mean target pre- and post-grazing herbage masses were 2200 and 1100 kg dry matter (DM) ha^?1. Plants in sheep-grazed swards regrew more quickly and accumulated more herbage (8·28 compared to 5·35 t DM ha^?1 for cattle-grazed swards, unadjusted for rejected area) than in other treatments. After 2 years, soil in sheep-grazed areas contained 0·25% N, 5·7 kg available P ha^?1, and 379 kg K ha^?1, compared to an average of 0·19, 3·9, and 179 respectively for the same soil nutrients in cattle-grazed treatments. Besides differences in manure distribution and sward rejection, differences in soil compaction among treatments also may have affected soil organisms and thus plant growth. After 2 years, soil bulk densities (g cc^?1) were 1·37, 1·37, 1·27, and 1·12; soil penetrometer measurements (kg cm sec^?1 sec^?1) to 20-cm soil depth were 9·8, 9·3, 9·5, and 6·7; soil nematodes per 100 g of soil were: 5333, 8705, 2810, and 15208; soil rotifers per 100 g soil were: 288, 242, 715, and 33; and earthworms m^?2 (and their biomass (g m^?2)) were 262 (205), 157 (162), 344 (409), and 294 (343) for C, CT, CS, and S treatments, respectively.     

Herbage intake and N excretion by sheep grazing monocultures or a mixture of grass and white clover

In 1988 and 1989, swards of grass (G0), while clover (C0) and grass/white clover (GC0) receiving no N fertilizer, and a grass sward supplied with 420 kg N ha^?1 (G420), were grazed by non-lactating sheep to maintain a sward surface height of 6 cm. Herbage organic matter (OM) intakes averaged between 1200 and 1700 g OM ewe^?1 d^?1. For treatments G0, C0, GC0 and G420 respectively, the ewes' live weight gain was 102, 112, 100 and 110 g d^?1 and changes in body condition scores were +0·28, +0·52, +0·36 and +0·44 units season^?1. However, the effect of treatment was not significant for either variable. There were similar levels of output of faecal N ewe^?1 but significantly more urinary N ewe^?1 was excreted on treatments C0 and G420, where the concentrations of N in herbage laminae were also higher. For example, in 1989, total daily N excreted was 39·7, 64·4, 44·0 and 63·3 g N ewe^?1 for G0, C0, GC0 and G420 respectively. Taking into account the mean daily stocking rates, which were 19·4, 26·6, 27·2 and 36·5 ewe ha^?1, the total faeces and urine returns over the season were 161, 358, 249 and 484 kg N ha^?1 for each treatment respectively. The herbage OM intakes ewes^?1 d^?1 measured in September and October were similar for C0 and G420, and so the intake of herbage OM ha^?1 d^?1 was related to stocking rate, i. e. the estimated herbage intake ha^?1 over the growing season for the white clover monoculture was 73% of that for N-fertilized grass. Excretal nitrogen returns to the pasture from grazed mono-cultures of clover were high, and similar to those from a grass sward receiving 420 kg fertilizer N ha^?1. Consequently potential losses of N to the environment are high under these management systems.     

Effects of date of autumn closing and timing of winter grazing on herbage production in winter and spring

Growth of grass herbage in Ireland is highly seasonal with little or no net growth from November to February. As a result, feed demand exceeds grass supply during late autumn, winter and early spring. At low stocking rates [≤2 livestock units (LU) ha^?1], there is potential to defer some of the herbage grown in autumn to support winter grazing. This study examined the effects of four autumn‐closing dates and four winter‐grazing dates in successive years on the accumulation of herbage mass and on tiller density in winter and subsequent herbage production at two sites in Ireland, one in the south and one in the north‐east. Closing swards from grazing in early and mid‐September (north‐east and south of Ireland respectively) provided swards with >2 t DM ha^?1 and a proportion of green leaf >0·65–0·70 of the herbage mass above 4 cm, with a crude protein (CP) concentration of >230 g kg^?1 DM and dry matter digestibility (DMD) of >0·700. The effects of autumn‐closing date and winter‐grazing date on herbage production in the subsequent year varied between the two sites. There was no significant effect of autumn‐closing date in the north‐eastern site whereas in the south earlier autumn closing reduced the herbage mass in late March by up to 0·34 t DM ha^?1 and delaying winter grazing reduced the herbage mass in late March by up to 0·85 t DM ha^?1. The effects of later grazing dates in winter on herbage mass continued into the summer at the southern site, reducing the herbage mass for the period from late March to July by up to 2 t DM ha^?1. The effects of imposing treatments in successive years did not follow a consistent pattern and year‐to‐year variation was most likely linked to meteorological conditions.     

Production and nutritional value of sorghum and black oat forages under nitrogen fertilization

The effect of nitrogen (N) fertilization on the dry‐matter (DM) yield and nutritional value of sorghum (Sorghum sp., cv. Jumbo) and black oat (Avena strigosa cv., IPR 61) was investigated in the context of forage and livestock production in southern Brazil. Sorghum was cultivated with 0, 37·5, 75, 150, 225, 300 and 375 kg N ha^?1 during the summer crop seasons of 2010/11 and 2011/12. Black oat received 0, 40, 80, 120, 160, 200 and 240 kg N ha^?1 in the winter of 2011. According to the adjusted polynomial regression, sorghum DM yield increased in response to N up to 288 (12·9 t ha^?1) and 264 kg ha^?1 (5·6 t ha^?1) in 2010/11 and 2011/12 respectively. Crude protein (CP) content of sorghum was highest at 349 and 328 kg N ha^?1, but in vitro dry‐matter digestibility (IVDMD) was highest at 212–207 kg N ha^?1 in 2010/11 and 2011/12 respectively. Sorghum neutral detergent fibre (NDF) and acid detergent fibre (ADF) were not affected by N fertilization. In black oat, the maximum DM yield (6·0 t ha^?1) was obtained with 187 kg N ha^?1; the IVDMD, NDF and ADF were not affected by N fertilization, but the CP content increased up to 220 kg N ha^?1. It is concluded that these forage species can improve the year‐to‐year amount and quality of forage produced but high rates of N fertilizer are required to achieve high yields. Fertilizer N rates of 210–280 kg N ha^?1 in sorghum and 180 kg N ha^?1 in black oat in the crop rotation provide the greatest responses in DM yield consistent with good nutritional quality for livestock production.     

Spring and autumn establishment of Caucasian and white clovers with different sowing rates of perennial ryegrass

The effect of sowing date (SD) and sowing rate of perennial ryegrass (PRG) on the establishment of Caucasian and white clovers in New Zealand was assessed. Clovers were sown in spring on 24 September (SD1) and 9 November (SD2) 1999, and in autumn on 4 February (SD3) and 31 March (SD4) 2000. On each date, clovers were sown with 0, 3, 6 or 12 kg ha^?1 of PRG. Total herbage dry matter (DM) production up to 6 November 2000 was 13–16 t DM ha^?1 for SD1 and SD2 when sown with 3–12 kg ha^?1 of PRG, and 7–10 t DM ha^?1 for sown clover monocultures. For SD3 and SD4, total herbage production was 6–9 t DM ha^?1 with PRG, while total herbage production of clover monocultures was 5·4 t DM ha^?1 for SD3 and 2·6 t DM ha^?1 for SD4. By 6 November 2000, white clover contributed proportionately more than 0·15 of herbage mass when sown with 3–12 kg ha^?1 of PRG on SD1, SD2 or SD3, but less than 0·09 when sown on SD4. The proportion of Caucasian clover never exceeded 0·09 of herbage mass in any of the swards. White clover was successfully established in spring and in autumn with 3–12 kg ha^?1 of PRG provided the 15‐mm soil temperature was above 14 °C. None of the combinations of Caucasian clover and PRG provided an adequate proportion of legumes during the establishment year. This unsuccessful establishment of Caucasian clover with PRG was attributed to its inability to compete for available light as a seedling due to slow leaf area expansion from secondary shoot development and a high root:shoot ratio. Alternative establishment strategies for Caucasian clover may include the use of slow establishing grasses, cover crops and temporal species separation.     

Biomass production and nutrient removal by tropical grasses subsurface drip‐irrigated with dairy effluent

Effluent lagoons on dairy farms can overflow and potentially pollute adjacent land and associated water bodies. An alternative solution to effluent disposal is needed by dairy operators in island environments. An attractive win‐win alternative is to recycle nutrients from this resource through effluent irrigation for forage grass production that minimizes environmental pollution. This study assessed biomass production and nutrient removal by, and high application rates to, tropical grasses that were subsurface drip‐irrigated with dairy effluent. Four grass species – Banagrass (Pennisetum purpureum K. Schumach.), California grass (Brachiaria mutica (Forssk.) Stapf.), Stargrass (Cynodon nlemfuensis Vanderyst) and Suerte grass (Paspalum atratum Swallen) – were subsurface (20–25 cm) drip‐irrigated with effluent at two rates based on potential evapotranspiration (ET_p) at the site (Waianae, Hawaii) ?2·0 ET_p (16 mm d^?1 in winter; 23 mm d^?1 in summer) and 0·5 ET_p (5 mm d^?1 in winter; 6 mm d^?1 in summer). Treatments were arranged in an augmented completely randomized design. Brachiaria mutica and P. purpureum had the highest dry‐matter yield (43–57 t ha^?1 year^?1) and nutrient uptake especially with the 2·0 ET_p irrigation rate (1083–1405 kg ha^?1 year^?1 N, 154–164 kg ha^?1 year^?1 P, 1992–2141 kg ha^?1 year^?1 K). Average removal of nutrients by the grasses was 25–94% of the applied nitrogen, 11–82% of phosphorus and 2–13% of the potassium. Average values of crude protein (90–160 g kg^?1), neutral detergent fibre (570–620 g kg^?1) and acid detergent fibre (320–360 g kg^?1) were at levels acceptable for feeding to lactating cattle. Results suggest that P. purpureum and B. mutica irrigated with effluent effectively recycled nutrients in the milk production system.     

Liveweight gains of lambs from Caucasian clover/ryegrass and white clover/ryegrass swards on soils of high and low fertility

The high nutritive value and persistence under a wide range of climatic and soil fertility conditions make Caucasian clover a potentially useful forage legume but there is little information about the performance of livestock grazing Caucasian clover/grass swards. This study compared liveweight gains of lambs grazing Caucasian clover/perennial ryegrass and white clover/perennial ryegrass swards on high fertility (Olsen P 20 mg L^?1, SO₄‐S 12 mg kg^?1) and low fertility (Olsen P 11 mg L^?1, SO₄‐S 7 mg kg^?1) soils from 1998 to 2001 in the South Island of New Zealand. Mean annual liveweight gains were 1178 kg ha^?1 for Caucasian clover/perennial ryegrass and 1069 kg ha^?1 for white clover/perennial ryegrass swards at high fertility compared with 1094 kg ha^?1 and 1015 kg ha^?1, respectively, at low fertility. There was a higher mean proportion of clover in Caucasian clover/perennial ryegrass (0·19) than white clover/perennial ryegrass (0·11) swards, but there were no differences in total herbage production between the two clover/perennial ryegrass swards. The mean concentration of crude protein in the herbage of Caucasian clover (302 g kg DM^?1) was higher than that in white clover (287 g kg DM^?1) and grass herbage (227 g kg DM^?1). Estimated mean metabolizable energy concentrations in the herbage were 12·5 MJ kg DM^?1 for the two clovers and 11·6 MJ kg DM^?1 for grass herbage. The difference in liveweight gain between swards on soils of high and low fertility was associated with an increase in total herbage production of similar composition and nutritive value, giving a greater number of grazing days for the swards on soils of high than low fertility.