15N-labelled fertilizer was applied in spring to winter wheat, winter oilseed rape, potatoes, sugarbeet and spring beans in field experiments done in 1987 and 1988 in SE England on four contrasting soil types – a silty clay loam, a chalky loam, a sandy loam and a heavy clay. The 15N-labelled fertilizers were applied at recommended rates; for oilseed rape, a two-thirds rate was also tested. Whole-crop recoveries of labelled nitrogen averaged 52% for winter wheat, 45% for oilseed rape, 61% for potatoes and 61% for sugarbeet. Spring beans, which received only 2·5 kg ha−1 of labelled N, recovered 26%. Removals of 15N-labelled fertilizer N in the harvested products were rather less, averaging 32, 25, 49, 27 and 13% in wheat grain, rape seed, potato tubers, beet root and bean grain, respectively.

Crop residues were either baled and removed, as with wheat and rape straw, or were flailed or ‘topped’ and left on the soil surface, as was the case with potato tops and sugarbeet tops. Wheat stubble and rape stubble, together with leaf litter and weeds, were incorporated after harvest. The ploughing in of crop residues returned 4–35% of the original nitrogen fertilizer application to the soil, in addition to that which already remained at harvest, which averaged 24, 29 and 25% of that applied to winter wheat, oilseed rape and sugarbeet respectively. Less remained at harvest after potatoes (c. 21%) and more after spring beans (c. 49%). Most of the labelled residue remained in the top-soil (0–23cm) layer.

15N-labelled fertilizer unaccounted for in crop and soil (0–100 cm) at harvest of winter wheat, oilseed rape, potatoes, sugarbeet and spring beans averaged 23, 25, 19, 14 and 26% of that applied, respectively. Gaseous losses of fertilizer N by denitrification were probably greater following applications to winter wheat and oilseed rape, where the N was applied earlier (and the soils were wetter) than with potatoes and sugarbeet. Consequently, it may well be advantageous to delay the application of fertilizer N to winter wheat and oilseed rape if the soil is wet.

Total inorganic N (labelled and unlabelled) in soils (0–100 cm) following harvest of potatoes given 15N-labelled fertilizer in spring averaged 70 kg N ha−1 and was often greater than after the corresponding crops of winter wheat and oilseed rape, which averaged 53 kg N ha−1 and 49 kg N ha−1, respectively. On average, 91 kg ha−1 of inorganic N was found in soil (0–100 cm) following spring beans. Least inorganic N remained in the soil following sugarbeet, averaging only 19 kg N ha−1. The risk of nitrate leaching in the following winter, based on that which remained in the soil at harvest, ranked in decreasing order, was: spring beans=potatoes>oilseed rape=winter wheat>sugarbeet. On average, only 2·9% of the labelled fertilizer applied to winter wheat and oilseed rape remained in the soil (0–100 cm) as inorganic N (NO−3+NH+4) at harvest; with sugarbeet only 1·1% remained. In most cases c. 10% of the mineral N present in the soil at this time was derived from the nitrogen fertilizer applied to arable crops in spring. However, substantially more (c. 21%) was derived from fertilizer following harvest of winter wheat infected with take-all (Gaeumannomyces graminis var. tritici) and after potatoes. With winter wheat and sugarbeet, withholding fertilizer N had little effect on the total quantity of inorganic N present in the soil profile at harvest, but with oilseed rape and potatoes there was a decrease of, on average, 38 and 50%, respectively. A decrease in the amount of nitrogen applied to winter wheat and sugarbeet in spring would therefore not significantly decrease the quantity of nitrate at risk to leaching during the following autumn and winter, but may be more effective with rape and potatoes. However, if wheat growth is severely impaired by take-all, significant amounts of fertilizer-derived nitrate will remain in the soil at harvest, at risk to leaching.

Detailed information on the timing of terminal spikelet formation, anthesis, maturity and the rate of leaf appearance is crucial to the predictive accuracy of the AFRCWHEAT2 growth simulation model for wheat. To obtain appropriate data under different growing conditions for two spring wheat (Triticum aestivum L.) cultivars (cvs Minaret and Canon), a main field experiment was conducted comprising eight sowing dates between mid-March and late June 1994; data from single sowings of Minaret in 1992 and 1995 were also included in the analysis. Minaret is the focus of a major European study of the impact of climate change factors on the growth and development of wheat, and data of the type reported here were essential to support the modelling aspects of the project involving AFRCWHEAT2.

The accumulated thermal time from emergence to critical developmental stages was similar for all sowings of both cultivars, even though biomass was greatly reduced in the later sowings. Although final leaf numbers were comparable for all sowing dates, the rate of leaf appearance was correlated with the rate of change of day length at crop emergence in Minaret. The unmodified AFRCWHEAT2 model did not predict the timing of critical growth stages and leaf numbers well, but removal of the vernalization and photoperiod factors from the developmental sub-model greatly improved the accuracy of such predictions. These results strongly suggest that fixed quantities of thermal time may be employed successfully to predict the timing of critical developmental stages of these spring wheat cultivars over a range of sowing dates, geographic locations and climatic conditions, since development appeared to be a linear function of temperature.

Despite removing the photoperiod and vernalization functions, the model consistently over-predicted final leaf number because leaf production by the model continued until 1·8 phyllochrons before anthesis, as compared to the three phyllochrons actually recorded for Minaret. AFRCWHEAT2 could therefore be further modified to reproduce more accurately the smaller number of leaves typical of these spring cultivars.

Simulation of phasic development in wheat is necessary in constructing wheat growth and yield models. It is also useful for evaluating cultivar adaptation and scheduling cultural practices. This paper describes a conceptual model of wheat development based on phenological principles, as affected by vernalization, photoperiod, thermal response and intrinsic earliness, and also reports the results of sensitivity analysis and validation of the model.

The model predicts when the plant will reach double ridge, terminal spikelet and heading. In the model, the daily thermal sensitivity of development following emergence is determined by an interaction of ‘relative vernalization completion’ and ‘relative photoperiod effectiveness’ for that day. After complete vernalization is reached, the daily thermal sensitivity is determined only by relative photoperiod effectiveness, which gradually increases from terminal spikelet to heading. A multiplication between the daily thermal sensitivity and thermal effectiveness generated daily flowering time, which was accumulated to trigger a particular developmental stage. Genotypic differences were characterized as vernalization requirement, photoperiod sensitivity and intrinsic earliness.

The model showed a sensitive response to environmental variables of temperature and daylength, and to genetic parameters of vernalization requirement and photoperiod sensitivity. Evaluation of the model using multiple experimental data involving various cultivars and planting dates exhibited a marked goodness of fit between simulation and observation with a root mean square error <5 days. The results indicate that the model can be used as a predictor for the major flowering stages, as well as functioning as a knowledge base for understanding the characteristics of different development components in wheat.

Fifty-six half-sib families of perennial ryegrass (Lolium perenne), derived from wild populations in Galicia, were examined for the presence of perennial ryegrass endophytes; 28 were endophyte-infected (E+) and 28 were endophyte-free (E−). All families were established in spaced-plant nurseries and trial plots at two locations in Galicia, in 1992. E+ families had a significantly (P<0·05) higher first cut, spring and total yield than E− families at one location in the third year after planting. At this location, water deficit was about 75% higher than at the other location in all three years of study. Endophyte did not affect crown rust susceptibility or forage quality (crude protein, water-soluble carbohydrate and in vitro digestibility). Ergovaline alkaloid concentration in the 28 E+ families varied from 0 to 0·55 μg/g dry matter (DM) (mean 0·15), with 14 families containing levels of ergovaline >0·1 μg/g DM. Thus endophyte infection may benefit the host in drought-prone areas of Galicia, with an increased chance of E+ plants being favoured by either natural or artificial selection.

New uses of natural fibres in industrial processes have increased the demand for linseed fibre which is normally discarded. In this investigation, 18 linseed and 10 flax varieties are evaluated for 13 developmental, seed yield and fibre yield traits with a view to identifying suitable genotypes which may have high yields of both seed and fibre, and therefore can be used as dual-purpose varieties and/or are likely to provide a suitable foundation for breeding new cultivars with an ability to produce high yields for seed as well as fibre.

Comparison of linseed and flax varieties has revealed that the two plant types have diversified to a great extent, particularly for those traits which have been subjected to direct or indirect selection during the past decades. However, considerable variation still exists among the linseed and flax varieties, and linseed shows more heritable variation than flax, for both seed and fibre traits. On the other hand, persistent selection of linseed and flax for commercially desirable phenotypes has not modified the genetic correlations to any appreciable level and both crops display almost identical correlations which do not differ significantly for any pair of traits. None of the flax or linseed varieties has shown such outstanding performance for seed yield as well as fibre weight which would have allowed them to be considered suitable for cultivation as a dual-purpose variety. In general, linseed × linseed and linseed × flax crosses would constitute better source materials for breeding high yielding dual-purpose cultivars compared to flax × flax crosses, particularly when seed will be the primary commercial product and fibre/straw a secondary commodity of such varieties.

Excessive applications of liquid pig manure (LPM) could result in nutrient accumulation in the soil, thereby increasing the potential for plant nutrient losses through movement in groundwater. The objective of this work was to measure the concentrations of total carbon (Ct), total nitrogen (Nt), total phosphorus (Pt) and Mehlich-3 extractable-P (PM3) with depth in a Le Bras silty loam soil growing maize (Zea maize L.) under reduced tillage conditions. The soil was fertilized annually with various rates of LPM (0, 30, 60, 90 and 120 m3/ha) in four completely randomized blocks since 1979. In autumn 1992, twenty soil plots were sampled in increments of 20 cm to a depth of 1·0 m and analysed for total C, total N, total P and Mehlich-3 extractable-P. LPM application rate (R), soil depth (D) and the interaction R × D had highly significant (P<0·001) linear effects on Ct, Nt, Pt and PM3 concentrations throughout the 100-cm depth profiles. At all depths, Ct, Nt, Pt and PM3 contents increased with increasing rates of LPM application. The zone of maximum accumulation of Ct, Nt, Pt and PM3 concentrations occurred at the first 0–40 cm depth. A significant relationship was found between soil organic matter and Nt, Pt and PM3. Differences in N and P concentrations between manure rates are due to manure and maize. The increase in PM3 was generally greater for soil samples with high Pt content. Results from this study indicate that long-term application of a high rate of LPM leads to greater total C, N and P concentrations in the soil profile.

The fatty acid composition of the plasma free fatty acid and adipose tissue triacylglycerol fractions was determined in lean and fat selection lines of Texel-Oxford and Scottish Blackface sheep at the 6th year of divergent selection. The mean proportion of 18[ratio ]2n-6 in the triacylglycerol of subcutaneous backfat was 1·3-fold higher in the phenotypically fatter sheep in the fat lines than in the phenotypically leaner sheep in the lean lines. Regression analysis indicated a positive relationship between this fatty acid and backfat depth whereas the proportion of 18[ratio ]1n-9 in the tissue triacylglycerol was negatively related to fatness. The proportions of 18[ratio ]2n-6 and of other polyunsaturated fatty acids in the plasma free fatty acid fraction were much higher than in adipose triacylglycerol. For the Scottish Blackface sheep in the fed state, the mean proportion of 18[ratio ]2n-6 in plasma free fatty acid (measured on all sheep) was 1·4-fold greater in the fat line than in the lean line. Regression analysis indicated a positive relationship between the plasma content of this fatty acid and backfat thickness whereas the proportion of 18[ratio ]1n-9 in plasma free fatty acid showed a negative relationship with fatness. The relationship between the plasma proportion of 18[ratio ]2n-6 and fatness was not observed after 48 h of fasting; instead, the plasma proportion of 18[ratio ]0 was found to be positively related to fatness in the fasted state. In summary, this paper shows how plasma and adipose tissue fatty acid profiles differ, and it quantifies the effects of selection on the plasma profiles. Possible reasons for the difference in fatty acid profiles between adipose tissue and plasma are discussed in the paper. It is suggested that plasma 18[ratio ]2n-6 levels during the early post-weaning growth period should be investigated as indicators of future fatness.

In order to assess relative thermal sensitivity between the day and the night, vaginal temperature (Tv), heat production (HP), heart rate (HR), respiration rate (RR), skin surface temperatures (from which mean skin temperature (Ts) was calculated) and standing time were measured at environmental temperatures (Te) of 23, 28, 33 and 38°C during the day (11.00–15.00 h) and during the night (23.00–03.00 h) using four Holstein heifers. Both Tv and mean body temperature (Tb) were greater during the night than during the day, increased with increased Te, and the rate of increase of both Tv and Tb with increased Te was greater during the night (P<0·05). Estimated mean HP was similar during the night and during the day, and HP did not increase with increased Te. Respiration rate was greater but not significantly different at night compared to during the day, and increased with increased Te. Mean skin temperature was similar between day and night, and increased with increased Te. The amount of time engaged in standing activity was greater but not significantly different during the night than during the day and standing activity increased with increased Te. The results suggest that thermal sensitivity is lower during the night than during the day, and consequently the greater night responses of Tv and Tb, over day responses, are a requirement for the maintenance of heat balance.

The phosphorus fertilizer requirements and long term productivity of nitrogen-fertilized Gatton panic (Panicum maximum cv. Gatton) pastures, grazed by lactating dairy cows, were evaluated over 7 years. Cows grazed at 2·6 cows/ha on pastures that received annually 100 or 300 kg N/ha at each of 0, 22·5 or 45 kg P/ha. Phosphorus treatments were applied as single superphosphate, balanced for calcium by applications of gypsum.

The soil had an initial available soil phosphorus content of 40 mg/kg (bicarbonate extraction). At zero P fertilizer (0P), extractable soil P declined at the rate of 1·9 mg/kg each year; at 22·5P it was maintained close to the original level while at 45P it increased at 6·6 mg/kg each year. Increased P fertilizer caused significant (P<0·01) increases in plant P concentration from year 2 onwards. In years 6 and 7 there was significantly less green pasture and leaf on offer in 300N pastures at 0P than with 22·5P and 45P. There was no influence of rate of P fertilizer at 100N on pasture quantity on offer in any year. There were clear trends at 100N of decreasing total pasture and green dry matter (DM) on offer over the 7 years, but not at 300N.

Cows at 300N consumed more leaf in the diet in autumn and winter than at 100N. Leaf was 55–60% of the diet in summer and autumn, but decreased to 21% (100N) and 37% (300N) in winter. Dead material in the diet was always higher at 100N. Pasture leaf percentage and leaf yield were the best individual predictors of leaf percentage in the diet. Diet P selected from pasture was reduced by the higher rate of N fertilizer in each season. Estimated P concentrations of the diet selected from pasture for summer, autumn and winter averaged 0·30, 0·38 and 0·28% DM for 100N and 0·19, 0·24 and 0·18% DM for 300N treatments, respectively.

The response to P fertilizer was dependent on the rate of N fertilizer applied. The critical bicarbonate extractable soil P level for this soil type, below which pasture responses occurred, was 30 mg/kg at 300N. The critical level at 100N was not reached, but was <23 mg/kg P.

The phosphorus fertilizer requirements and long term productivity of nitrogen-fertilized Gatton panic (Panicum maximum cv. Gatton) pastures, grazed by lactating dairy cows, were evaluated in a 7-year experiment. Cows grazed at 2·6 cows/ha on pastures that received annually 100 or 300 kg N/ha and each of 0, 22·5 or 45 kg P/ha. Cows received no energy supplements in years 1–3 and were offered molasses at 3·5 kg/day from year 4 to year 7. Cows grazed their experimental paddocks from the start of the wet season until they started to lose weight in the dry season.

In years 6 and 7 there was significantly less green pasture and leaf on offer in 300N pastures at 0P than with 22·5P and 45P. This was reflected in a reduced milk yield by cows at 300N/0P in these two years. There was no influence of rate of P fertilizer at 100N on milk yield in any year. Lactation milk yields at 300N in years 6 and 7 averaged 3930, 4310 and 4610 kg/cow (P<0·05) for 0P, 22·5P and 45P, respectively. Nitrogen fertilizer increased milk yield in each year (P<0·01) except the first. Milk yields at 100N and 300N averaged 2860 and 3320 kg/cow respectively in years 1–3 and 3720 and 4290 kg/cow in years 4–7.

The milk yield responses to P fertilizer were related to the greater amounts of pasture and green leaf on offer, which led to a higher proportion of leaf in the diet, and the response to P fertilizer was dependent on the rate of N fertilizer applied. Phosphorus intakes were estimated to be below that of published requirements for cows producing this quantity of milk. An annual model of P flow between plant, animal and soil pools demonstrated that at 100N/22·5P more P was returned to the soil as excreta (15·7 kg P/ha) than with 300N/22·5P (7·1 kg P/ha). The major pathway of return of P to the soil at 300N was through plant litter. Soil organic P was the largest, but least exploited, pool of phosphorus.

This study has illustrated how the demand for phosphorus by the plant in grazed pastures is modified by the input of N fertilizer, is poorly predicted from plant analysis and published standards for animal requirements, and indicates that a response in milk production may be mediated through the effects of P on leaf growth and not on dietary P content.

Dairy cows grazing a tropical grass pasture fertilized with 300 kg N/ha and with a 7-year history of phosphorus fertilizer at either 0 or 45 kg P/ha were given a P supplement in a 2 × 2 factorial experiment at Kairi Research Station, Queensland, Australia. Milk yield, fat-corrected milk yield, yields of milk fat, protein and lactose, and protein content of milk were increased (P<0·05) with P fertilizer. There was no response in milk yield or any component of milk to the provision of a P supplement. It is concluded that the milk response recorded in this experiment was due to P fertilizer leading to additional pasture on offer and increased pasture intake. The lack of response to additional P in the form of a supplement indicates that these pastures can supply adequate P for cows producing 20 kg/day even after 8 years without P fertilizer.

Groups of nine or ten cows were assigned, after calving, to treatments in which they were (i) machine milked three times daily (M3), (ii) machine milked six times daily (M6) or (iii) suckled three times daily in addition to being machine milked three times daily (S). Treatments were administered during the first 6 weeks postpartum. On one day, at weeks 1 and 6 postpartum, blood samples were collected from all cows at 30-min intervals between 06.00 and 13.00 h and these were analysed for plasma osmolality and plasma concentrations of Na+, K+ and Cl−. Milk yield was significantly higher in suckled cows than in cows milked six times daily, but significantly lower in cows milked three times daily. In cows milked six times daily, and to a greater extent in suckled cows, there was a reduction in plasma osmolality and monovalent ion concentrations (Na+, K+ and Cl−), which could increase the susceptibility of the cows to water intoxication. Moreover, suckling or milking the cows six times daily was associated with increased fluctuations in plasma osmolality and plasma Cl− concentrations. The decrease in plasma osmolality and ion concentration and the increased variation in plasma osmolality and Cl− were probably related to increased water intake and may be indicative of a severe challenge to homoeostasis regulation.