Interactions between N supply and N uptake by perennial ryegrass, 15N recovery and soil pH for four acid Scottish soils

The effects of NH₄⁺−N, NO₃⁻-N or urea-N addition on N uptake by perennial ryegrass ( Lolium perenne ), ¹⁵N recovery and pH of four limed and unlimed soils were determined in a pot experiment over 10 weeks. The best form of N in terms of herbage N uptake and fertilizer recovery differed between the soils. Recovery of applied ¹⁵N in herbage was greatest for the soil with the lowest pH and highest organic matter content, and overall recovery in the soil–plant system was influenced more by soil type than by N form. There was always an apparent mineralization of soil N when perennial ryegrass was present. Soil pH changes ranged from +0·11 to −0·58 units for the unlimed soils and from +0·03 to −1·06 units for the limed soils. The use of NO₃⁻-N rather than NH₄⁺-N or urea-N avoided further acidification. Lime increased herbage N only from the soils with the lowest pH values. Although the acidifying effect of NH₄⁺-fertilizer was alleviated, liming may increase nitrification and possibly N loss via denitrification and/or leaching in the field.
The major influence of soil type on herbage N uptake, pH response to the treatments and fertilizer recoveries implies that liming and fertilizer N management decisions should consider soil characteristics, such as organic matter, clay contents and pH.     

The influence of surface and sub-surface application methods for pig slurry on herbage yields and nitrogen recovery

Experiments were conducted on a grassland site at Wrest Park, Silsoe, Bedfordshire between 1987 and 1989, to compare herbage yields from slurry applied by deep and shallow injection, low trajectory and conventional vacuum tanker methods. Slurry application rates for all spreaders were calibrated at 86 ± 5 t ha^-1, an equivalent of c. 200 kg NH₄⁺-N ha^-1 applied in autumn or in spring.
As expected, herbage yields following spring applications were higher than from autumn applications, with average mineral fertilizer equivalents of 122 and 89 kg N ha^-1 respectively. Yields from the conventional and low trajectory spreaders showed no consistent differences. However, in both years, first cut yields from plots were significantly lower ( P < 0·05) where slurry had been injected than where surface applications had been used by an average of 0·7 t DM ha^-1. Subsequent cuts in 1988 demonstrated higher residual effects from injection so that annual total yields were similar from all slurry applications irrespective of spreader type.
Analysis of N content revealed high N levels in herbage from deep injection plots. Mean concentrations of N in the herbage, expressed as a percentage of the dry matter, were 1·43 for surface treatments and 1·79 for deep injection in 1988, and 1·84 for surface treatments, 2·13 for shallow injection and 2·68 for deep injection in 1989.     

The response of Whitegrass [Cortaderia pilosa (D'Urv.) Hack.] to nitrogen nutrition

To investigate the potential for increasing Falkland Island Whitegrass [ Cortaderia pilosa (D'Urv.) Hack.] pasture production through application of nitrogen (N) fertilizer, two hydroponic experiments were conducted. First, 5 mg l^–1 N was supplied to plants as nitrate (NO₃^–), urea [CO (NH₂)₂], ammonium (NH₄⁺), or a nine parts NH₄⁺: one part NO₃^– mixture. At harvest, plants grown in a NO₃^– medium had about half the biomass of plants grown in a NH₄⁺ medium. In the second experiment plants were supplied with 1, 3, 10, 30 or 100 mg l^–1 NH₄⁺-N. Plants at 1 and 3 mg l^–1 N had the largest biomass of young root and the lowest shoot–root ratios. Leaf extension rate was low in the 1 mg l^–1 N treatment. Plants given 10 mg l^–1 N had the greatest proportion of green shoot material but little root growth; while those at 100 mg l^–1 N produced very little shoot and root biomass. Preferential assimilation of NH₄⁺-N and a low N requirement make Whitegrass well adapted to dominating vegetation on much of the Falkland Islands.     

Herbage production and nitrogen recovery from slurry injection and fertilizer nitrogen application

An experiment was carried out during 1986 and 1987 to examine the effects of mid-season slurry injection and fertilizer-nitrogen (N) application on herbage dry matter (DM) yield and N recovery. Cattle and pig slurry were injected at 56 and 112 m³ ha⁻¹ into an established sward. Five rates of fertilizer-N, as calcium ammonium nitrate, ranging from 0 to 120 kg ha⁻¹ in 30-kg increments, were superimposed on these treatments, and in both years DM yield was measured in one cut after 70 d regrowth. Slurry treatments increased herbage DM yields significantly ( P < 0-001). The efficiency of slurry total N compared with calcium ammonium nitrate-N averaged 53% in 1986 and 86% in 1987. The mean apparent recovery of slurry total N in herbage was 55% in 1986 and 40% in 1987. Fertilizer-N application increased ( P < 0.001) the mean yields of herbage in both years but when combined with some of the slurry treatments, DM yields over the five N-levels did not differ significantly, giving rise to interactions in 1986 ( P < 0-001) and 1987 ( P < 001). It is concluded that mid-season injection of slurry can be an effective means of utilizing slurry-N in terms of herbage DM production and consequent N use.     

The effect of rate and timing of phosphate fertilizer on the yield and phosphate off take of grass grown for silage at moderate to high levels of soil phosphorus

A series of twenty-one trials was undertaken during 1985–1988 to investigate the effect on lowland silage crops of 0, 40 or 80 kg ha⁻¹ phosphate (P₂O₅) fertilizer applied as triple superphosphate (46% P₂O₅) in the autumn, spring or as a split application (spring and after first cut). All sites had moderate to high sodium bicarbonate-extractable soil phosphorus contents (18–34 mg P 1⁻¹ in air-dried soil).
Significant yield responses were obtained at eight of the forty-two individual cuts (two cuts per site). When meaned over all sites, spring or autumn applied phosphate increased dry matter yield at both first and second cut (mean total increase 0·32 t ha⁻¹), though the effect was significant only at the highest phosphate rate. The time of phosphate application had no overall effect on yield. Herbage P concentration and phosphate off take were significantly increased at both cuts by both rates of phosphate. Generally, the most recent application had a significantly greater effect than other timings. These findings indicate that DM yield responses to freshly available phosphate can occur on soils of moderate P status.     

生物炭与硝化抑制剂联合施用对热带菜地土壤硝化过程及N2O排放的影响

本研究以热带菜地土壤为对象,通过室内培养试验探讨生物炭与硝化抑制剂联合施用下土壤无机氮含量和强度及N₂O排放的变化规律,旨在明确施用生物炭和硝化抑制剂对热区土壤硝化过程的调控作用及对N₂O的减排效应。本试验设置4个处理：单施氮肥（N）,氮肥配施生物炭（N+Bc）,氮肥配施硝化抑制剂（N+Ni）以及氮肥同时配施生物炭和硝化抑制剂（N+Bc+Ni）。结果表明：培养期间,生物炭施用下土壤NO₃^--N强度显著提高15.8%,表明添加生物炭能够显著促进土壤硝化过程;硝化抑制剂添加下土壤NH₄⁺-N强度显著提高33.4%,表明硝化抑制剂的施用显著减缓硝化过程;此外,硝化抑制剂能够削弱由生物炭添加引起的激发硝化过程的效应,表明生物炭和硝化抑制剂对硝化过程影响存在交互效应。施用生物炭或硝化抑制剂都能降低NO₂^--N强度,其中硝化抑制剂作用更加显著;此外,生物炭或硝化抑制剂单独施用能够降低菜地土壤15.1%~68.3%的N₂O排放量,二者联合施用在一定程度上能够发挥更强的减排作用。综合来看,生物炭与硝化抑制剂联合施用有望在热带菜地土壤中发挥固碳和减排的双重功效。     

Organic and inorganic fertilization compared in a natural Mediterranean grassland

The effect of goat slurry on species composition and herbage production as compared to inorganic fertilizer was studied in a natural grassland dominated by warm and cool season perennial grasses in Macedonia, Greece. Goat slurry was applied in early spring every 1 or 2 years at a rate of 40 t ha^-1 being equivalent to about 160 kg N ha^-1 and 100 kg, P₂O₅ ha^-1. Inorganic fertilizer was also broadcast in early spring at a rate of 80 kg N ha^-1 and 100 kg P₂O₅ ha^-1 every 2 years. Measurements of the basal cover of the dominant species or groups of species and herbage yields were taken for 6 years at the end of the growing period in June, while in the seventh year the experiment was grazed with goats. It was found that goat slurry improved species composition more than the inorganic fertilizer by depressing the less palatable warm season grasses and favouring the subdominant cool season grasses and legumes. Goat slurry significantly increased herbage yields in most of the years. It is suggested that the optimum rate of goat slurry is 40 t ha^-1 every 2 years as this encourages plants most preferred by goats.     

Intake, rumen fermentation, degradability and digestion kinetics in beef cattle offered autumn grass herbage differing in regrowth interval

The effects of a 10-d increase in regrowth interval (35 and 45 d) of a predominantly perennial ryegrass sward harvested in two periods in the autumn in Ireland on feed intake, rumen fermentation, in situ degradability and rumen digesta kinetics was examined using six ruminally cannulated Holstein–Friesian steers in three replicates of a 2 × 2 crossover design. The longer regrowth interval had a higher grass dry-matter (DM) yield of herbage by 615 kg DM ha⁻¹ and a lower crude protein (CP) concentration of herbage by 27 g kg⁻¹ DM. There was no effect of regrowth interval on DM intake, rumen pH, total volatile fatty acid concentration or the molar proportions of acetate, propionate or butyrate in the rumen but the concentration of rumen ammonia (NH₃-N) was lower on the longer regrowth interval. The longer regrowth interval had a lower apparent total tract digestibility of DM, organic matter (OM), N and neutral-detergent fibre (NDF). There was no effect of regrowth interval on the in situ degradability of DM, OM, N or NDF. The passage rates ( k _p) of DM and OM were higher while the rate of digestion ( k _d) of DM and NDF was lower with the longer regrowth interval. The results indicated that, although increasing the regrowth interval by 10 d in autumn reduced the apparent digestibility of the grass herbage, there was no adverse effect on DM intake, rumen fermentation pattern or in situ rumen degradability. The reduction in rumen NH₃-N concentrations, reflecting the lower herbage CP concentration in herbage for the longer regrowth interval, may potentially reduce nitrogen excretion to the environment.     

Effects of different rates and timing of application of nitrogen as slurry and mineral fertilizer on yield of herbage and nitrate-leaching potential of a maize/Italian ryegrass cropping system in north-west Portugal

Efficient use of cattle-slurry to avoid nitrogen (N) leaching and other losses is important in designing intensive dairy systems to minimize pollution of air and water. The response in dry-matter (DM) yield of herbage and nitrate-leaching potential to different rates and timing of application of N as cattle slurry and/or mineral fertilizer in a double-cropping system producing maize ( Zea mays L.) silage and Italian ryegrass ( Lolium multiflorum Lam.) was investigated in north-west Portugal. Nine treatments with different rates and combinations of cattle slurry, and with or without mineral-N fertilizer, applied at sowing and as a top-dressing to both crops, were tested and measurements were made of DM yield of herbage, N concentration of herbage, uptake of N by herbage and amounts of residual soil nitrate-N to a depth of 1 m, in a 3-year experiment. Regression analysis showed that the application of 150 and 100 kg of available N ha⁻¹ to maize and Italian ryegrass, respectively, resulted in 0·95 of maximum DM yields of herbage and 0·90 of maximum N uptake by herbage. Residual amounts of nitrate-N in soil after maize ranged from 48 to 278 kg N ha⁻¹ with an exponential increase in response to the amount of N applied; there were higher values of nitrate-leaching potential when mineral-N fertilizer was applied. The results suggest that it is possible in highly productive maize/Italian ryegrass systems to obtain high DM yields of herbage for maize silage and Italian ryegrass herbage with minimal leaching losses by using slurry exclusively at annual rates of up to 250 kg available N ha⁻¹ (equivalent to 480 kg total N ha⁻¹) in three applications.     

Effectiveness of cattle slurry as a sulphur source for grass cut for silage

Three trials were carried out in separate years during 1987–89 to investigate the effectiveness of cattle slurry as a source of sulphur (S) for grass cut four times per year for silage. They were located on different areas of the same field in Dorset, UK, in an area known to be sulphur deficient for intensive grass production. Yields of dry matter and S off takes in response to sulphur in slurry were investigated and compared with those from gypsum treatments supplying 0–100 or 0–75kg S ha⁻¹. Slurry was applied at two times of year, November or February, and at two rates, either alone or in combination with the two lowest rates of gypsum.
Annual increases in yield from the slurry applied in February compared with the yield when no slurry was applied were significantly related ( r ²= 0·96) to the rate of slurry sulphur applied. For applications in November, the relationship was not significant. Sulphur in slurry increased annual dry-matter yield with an average efficiency of 55% when compared with the sulphur in gypsum. The annual apparent recovery in the herbage of S from slurry was 21·8%, compared with 44·7% from the two lowest rates of gypsum.
Cattle slurry, in these and other trials in southwest England, contained on average 0·35 kg S m⁻³ and, at rates currently applied in farming practice or likely to be applied in the future, would be insufficient to satisfy annual requirements for silage in sulphur-deficient areas.     

Surface application and shallow injection of cattle slurry on grassland: nitrogen losses, herbage yields and nitrogen recoveries

An experiment was carried out over 2 years on grass and grass/clover swards in SW England lo compare herbage yields and N recovery following surface application or shallow injection of cattle slurry at three different times of application. In the second year, losses of N via ammonia volatilization, denitrification and nitrate leaching were measured from applications to the grass sward. On the grass sward, there was no significant effect of time or method of application on dry-matter (DM) yield in the first year, although shallow injection reduced apparent N recovery (ANR) in the herbage by 45% when compared with surface application. In the second year, shallow injection reduced DM yields by 26% and ANR by 48%. On the grass/clover sward, there were no significant effects of time or method of application on DM yields or ANR in either year Inclusion of dicyandiamide (DCD) in the October slurry applications had no significant effect in the first year, but in the second year on the grass sward increased DM yield by 31% and 14% and ANR by 156% and 42% for shallow injection and surface applications respectively. Measurements in the second year on the grass sward showed a reduction in N loss by ammonia volatilization using shallow injection of 40% and 79% for March and June applications respectively. Losses due to denitrification were greatest following October application. Shallow injection increased denitrification losses following March application, but there were no significant differences following October or June applications. N losses due to leaching were small, with no significant difference between treatments. Reasons for the reductions in DM yield and ANR following shallow injection, despite the large reduction in N loss by ammonia volatilization, are discussed.     

Influence of growth stage and season on the energy value of fresh herbage. 2. Relationships between digestibility and metabolizable energy content and various laboratory measurements

This paper gives details of a study which has examined the effect of herbage growth type and season on the relationships of digestible organic matter in the dry matter (DOMD) and metabolizable energy (ME) contents measured in vivo to various laboratory measurements including three in vitro estimates of DOMD based on rumen fluid pepsin (RFP), pepsin cellulase (PC) or neutral detergent cellulase (NCD). Seventy herbages harvested over two years and comprising 32 spring primary growths, 14 summer regrowths and 24 autumn growths were used.
For DOMD in vivo , significantly different regression relationships were required for spring and autumn-harvested herbage. Equations based on PC were:
Spring herbage: DOMD (g kg^-1 DM) = 436 + 0·501 PC (g kg^-1 DM) ²= 76·7%; r.s.d. = 25·4
Autumn herbage: DOMD (g kg^-1 DM) = 594 + 0·195 PC (g kg^-1 DM) ²= 15·5%; r.s.d. = 23·1
For autumn herbages there were no significant relationships with ME. As with DOMD in vivo the PC method was shown to provide the most accurate relationship with ME concentration of spring herbage. The relationship was:
ME (MJ kg^-1 DM) = 6·16 + 0·0094 PC (g kg^-1 DM) ²= 69·8%; r.s.d. = 0·57
For both DOMD and ME the relationships for spring herbage based on PC were the only ones which did not differ significantly from those of an earlier study.
It is concluded that even where significant relationships for summer and autumn herbages were developed, the predictors accounted for substantially less of the variability than in spring herbages. This appeared to be largely due to reduced range in the DOMD and ME content in summer and autumn herbages.     

Reseeding in the Falkland Islands. Herbage production of a range of grass species and cultivars

The productivity of 20 cultivars from a range of 13 grass species was compared by harvesting four times during each of three successive growing seasons. In the experiment, 120 kg N ha⁻¹, 42 kg P₂O₅ ha⁻¹ and 42 kg K₂O ha⁻¹ were applied annually.
Mean annual yield was 3229 kg DM ha⁻¹ and 2147 kg DOM ha⁻¹. Cultivars were arranged in seven groups for comparison. Three of the groups, Lolium, Phleum and 'others' (the latter consisted of Festuca arundinacea cv. Dovey and Poa pratensis cv. Bensun A.34) appeared significantly lower yielding than the Dactylis, Festuca (fine-leaved), Agrostis and Holcus groups.
In the Lolium group, cv. Gremie outyielded cv. Melle every year. No cultivar of Dactylis was significantly better than any other in its group. Phleum CVS Motim and Eskimo were similar and superior to cv. S.50. Festuca ovina cv. Novina and Agrostis canina cv. Kingstown were marginally the best in their respective groups. The two cultivars of Holcus performed virtually identically. Festuca arundinacea cv. Dovey was a good producer of early spring grass. Poa pratensis cv. Bensun A.34 was generally low yielding and subject to fungal rust attack in autumn. The pattern of seasonal DM production was 16% in early spring (cut in October/November), 39% in mid-season (cut in December), 40% in late summer (cut in February/March) and 5% in autumn (cut in April/May). Quality of the herbage was superior to the main indigenous grass Cortaderia pilosa.
It was concluded that although the experiment was conducted under a cutting regime it provided useful guidance for seeds mixture formulation and stock carrying capacity calculations.     

Mineral concentrations in herbage and soil in a Pinus radiata silvopastoral system in north-west Spain after sewage sludge and lime application

Silvopastoral systems in north-west Spain can reduce the risk of fires and promote multi-purpose forest land use. Fertilizer application is important for optimal pasture and tree production. The application rate of sewage sludge as a fertilizer is regulated and is based on its nutrient concentration, especially nitrogen. The aim of this study was to assess the effect of three consecutive years of application of different application rates of sewage sludge and inorganic fertilizer, with or without lime (2·5 t CaCO₃ ha⁻¹) on the ammonium, nitrate and exchangeable K, Ca and Mg contents in soil, and on the crude protein (CP), K, Ca and Mg concentrations in herbage in a silvopastoral system established under a 5-year-old Pinus radiata D. Don plantation with a density of 1667 trees ha⁻¹. The experiment was started in autumn 1997, when a pasture mixture was sown (25 kg ha⁻¹ Lolium perenne , 10 kg ha⁻¹ Dactylis glomerata and 4 kg ha⁻¹ Trifolium repens ). Changes in ammonium and nitrate content in the soil in response to liming and sewage sludge application reflected the initial pH of the soil. In general, liming increased the available Ca and Mg content in soil, and CP and Ca concentrations in herbage, but reduced exchangeable K content in the soil in the first year. Application of sewage sludge increased all of the measured nutrients in both soil and herbage.     

Negative effects of winter- and spring-applied cattle slurry on the yield of herbage at simulated early grazing and first-cut silage

Experiments were earned out on seven UK sites during 1985–1988 to evaluate the importance of negative effects (smoethering and scorch) of winter and spring-applied cattle slurry on grass yield, assessed at the time of early grazing or first-cut silage. Slurry application has both positive and negative effects on herbage growth. Positive effects, usually associated with herbage yield increases, derive from the nutrient value of the slurry. Negative effects, often resulting in herbage yield decreases, are caused by smothering and/or scorch. The net effect on herbage depends on the balance between these positive and negative effects. These experiments were designed to isolate the negative effects of slurry whilst attempting to minimize the positive effects. Yield reductions of up to 20% for early grazing and 5% for first-cut silage were recorded, following applications of cattle slurry in February and March. Earlier applications smaller yield reductions. The threshold for the occurrence of yield reduction was estimated at 3–4 t ha^?1 of slurry solids applied, at 6% solids content. In practice this would mean an application of 50–65 m³ ha^?1 at 6% dry matter, which would supply 150–200 kg ha^?1 total nitrogen, based on typical slurry analyses. Within the limits of application rates tested in these experiments, yield depression tended to increase with increasing rate of slurry applied above this threshold. Although the results suggest that the effects are more likely to occur following spring applications of slurry, earlier (autumn or winter) applications would increase the risk of losses of slurry nitrogen by leaching and denitrification. These results, therefore, confirm current advice in the UK that, where possible, cattle slurry is best applied to grassland in early spring according to the fertilizer needs of the crop. High rates of application should be avoided after early March for cutting areas and, more especially, for early grazing.     

Effect of fertilizer nitrogen rate and timing on herbage production and nitrogen use efficiency for first-cut silage

Eight field-plot experiments were carried out on established grassland swards between 1984 and 1988 to examine the effects of date and rate of application of calcium ammonium nitrate (CAN) on herbage dry matter (DM) yield and apparent efficiency of nitrogen (N) use at first-cut silage.
CAN application significantly increased ( P <0 ·001) the mean yields of herbage and N uptakes by herbage in all experiments. Herbage yields were similar ( P > 0·05) with N rates of 100 kg ha⁻¹, 125 kg ha⁻¹ or 150 kg ha⁻¹ in five experiments but in the other three there were increases above 100 kg ha⁻¹. Date of N application had a significant effect on DM yield in three experiments; this effect was inconsistent for both single and split dressings. Lower production was associated with reduced uptake of N, a trend that primarily reflected lower DM yields and not wide herbage N content variation.
It is concluded that selection of the date on which to apply fertilizer N in early spring to obtain optimum herbage yields at first-cut silage often required little precision. The use of fertilizer N rates >100 kg ha⁻¹ should be questioned where there are likely to be appreciable quantities of available N derived from non-fertilizer sources.     

Nitrate leaching from cut grassland as affected by the substitution of slurry with nitrogen mineral fertilizer on two soil types

A field experiment was conducted to find out whether there is any difference in risk of N leaching to groundwater when cattle slurry and/or mineral fertilizer-N was applied to cut grassland. The experiment was carried out over two consecutive years on two sites (one with a relatively wet sandy soil and one with a relatively dry sandy soil). Treatments were mineral fertilizer-N at annual rates of 0–510 kg N ha⁻¹ year⁻¹ and combinations of sod-injected cattle slurry (85, 170, 250 and 335 kg N ha⁻¹ year⁻¹) and mineral fertilizer-N (289, 238, 190 and 139 kg N ha⁻¹ year⁻¹). Yield responses indicated that in the short run, 0·44–0·88 (average 0·60) of the slurry-N was as available as mineral fertilizer-N. The total N input from mineral fertilizer and slurry was a worse predictor of nitrate leaching (     0·11) than the N surplus (i.e. the difference between total N input and harvested N) (     0·60). The effective N surplus, based on the difference between the summed inputs of the plant-available N and harvested N, proved to be the best indicator of leaching (     0·86). Annual N application rates of up to 340 kg plant-available N ha⁻¹ complied with the target nitrate concentration in groundwater of 11·3 mg N L⁻¹ set by the European Union in both years on the wet sandy soil, whereas on the dry sandy soil none of the treatments did.     

茶园土壤NO3——N含量与净硝化速率的研究

调查采集了我国130个茶园的土壤,用0.5mol/L的K₂SO₄提取法和实验室恒温培养法分别测定了土壤NO₃^--N含量和净硝化速率。结果表明,茶园土壤NO₃^--N含量在0~286.8mg/kg之间,平均为41.7mg/kg,40.8%的土样低于20mg/kg;土壤NO₃^--N浓度的高低主要取决于施氮量,与土壤净硝化速率相关性不显著,与pH呈二次方程关系：Y=738.0-289.9X+28.8X²（r²=0.2033,P<0.001）。土壤净硝化速率在-6.08~6.54mg/kg·d之间,平均为1.62mg/kg·d,变异系数高达119%;其中,10%的土壤净硝化速率低于零,表明这些土壤处于氮固定化状态中;土壤净硝化速率与施氮量呈显著正相关,与pH呈反函数方程关系：Y=10.14-33.96/X（r²=0.253,P<0.001）。文章对茶园土壤中NO₃^-积累、硝化作用与pH的关系等进行了讨论。     

Effect of spreading method, application rate and dilution on ammonia volatilization from cattle slurry

Results from a series of five small-scale plot experiments which simulated different strategies for lowering ammonia volatilization following slurry application to grassland are reported. Strategies studied were band spreading, shallow-channel application, spike injection, rate of surface application and dilution. Volatilization was measured over the first 4 h following application with ventilated enclosures. Band spread slurry resulted in 0·4 of the volatilization that occurred from surface application of the same rate of slurry. The benefit of band spreading was shown to arise from higher application rates in the bands when compared with the same quantity of slurry spread over the surface. When surface-spread slurry was applied to the same depth of slurry as in bands, the volatilization per unit volume of slurry was the same. Shallow-channel application was more effective than band spreading and lowered volatilization per unit volume of slurry to <0·1 of that from surface-spread slurry. Spike injection was equally effective as shallow-channel application but, owing to perceived difficulties in machine design, construction and operation, was deemed impractical. Shallow-channel application has potential, though further work is required to optimize centre-to-centre spacing of the channels. As the application rate of surface-applied raw slurry increased, ammonia volatilization per unit volume of slurry applied decreased. Application at 50 m³ ha⁻¹ resulted in 0·4 of the specific volatilization per unit volume of slurry that occurred at 6·3 m³ ha⁻¹. Within the dilution treatments, the amount of water added to the slurry was linearly and inversely related to volatilization. At a dilution of 0·9-1·2:1 water: slurry the specific volatilization per unit volume of slurry was 0·5 of that from undiluted slurry.     

Implications of grazing by sows for nitrate leaching from grassland and the succeeding cereal crop

Outdoor pig production may have benefits in terms of animal welfare but could be undesirable in terms of nutrient losses. In paddocks on sandy soil grazed by lactating sows, nitrate leaching was determined using the suction cup technique from the start of grazing in October to after the following barley/pea wholecrop with perennial ryegrass. The inorganic N concentration in soil was uneven after sow grazing, with the highest values found near the feeding area. In contrast to low nitrate leaching in the year of grazing (25–30 kg of N ha^–1), losses were considerable in the following autumn and winter. Throughout the measuring period of 18 months, nitrate leaching inside paddocks was on average 320 kg of N ha^–1 with the major part near the feeding area. Ten metres from the feeding area, leaching losses were 500 kg of N ha^–1 and, at 16 m distance, losses were 330 kg of N ha^–1. At 22 and 28 m distance from the feeding area, about 200 kg of N ha^–1 was leached and outside paddocks about 100 kg of N ha^–1. The combination of a sandy soil with high winter rainfall leads to a large proportion of the N surplus being lost by nitrate leaching near the feeding area. To reduce nitrate leaching, stocking density and the level of dietary nutrient input must be adjusted, and more uniform distribution might be achieved by manipulating the excretory behaviour of the sows.