The effects of nitrogen (N) rate and timing on need for fungicide application in winter wheat (Triticum aestivum) were investigated in 3 years of field experiments on loamy sand soils in Denmark. A two-factor completely randomized experimental design was used, comprising seven combinations of different N fertilizer rates and application times, and five doses of fungicide (co-formulation propiconazole and fenpropimorph). Two different varieties of winter wheat with high susceptibility to powdery mildew (Blumeria graminis) were used, Florida in the first season and Pepital in the last two seasons. The severity of powdery mildew and septoria leaf spot (mainly Septoria tritici) varied between seasons from slight to moderate with powdery mildew dominating in the first season and septoria leaf spot in the last season. The severity of both powdery mildew and septoria leaf spot assessed as the Area Under the Disease Progress Curve (AUDPC) was increased by application of N in all years, and more so by early applied N. Grain yields increased with increasing N rate and fungicide dose. However, the observed grain yields did not reveal any N×fungicide interactions. Regression models were therefore fitted, relating grain yield to rate and timing of N fertilizer and to AUDPC of powdery mildew and septoria leaf spot, and relating AUDPC to rate and timing of N fertilizer and to fungicide dose. They demonstrated that septoria leaf spot had a considerably higher impact on grain yield than mildew. The optimal fungicide dose and N rate were defined as those giving the highest economic return. The regression models were used to estimate the effect of N rate and timing on optimal fungicide dose, and the effect of fungicide application on optimal N rate. The optimal fungicide dose increased almost linearly with N rate above a minimum N rate, but with a large dependency on price relations. Early applied N caused a higher demand for disease control. The fungicide applications in the model were mainly driven by the need to control septoria leaf spot, whereas powdery mildew gave a poor net return for control. The estimated optimal N fertilizer rate for untreated diseased crops was 60 kg N/ha lower than for crops without disease. The use of fungicides with an efficacy twice that of the EBI-fungicides used in this experiment would increase the optimal N rate by c. 20 kg N/ha.

Data from a two-factorial experiment carried out during 3 years were used to analyse the effects of crop nitrogen (N) status on disease development, and the effects of N supply and disease on light interception (IPAR) and radiation use efficiency (RUE) in winter wheat (Triticum aestivum). The factors in the experiment comprised seven strategies of N fertilizer application including different N rates and timing of application, and five doses of fungicide application for control of the leaf diseases powdery mildew (Blumeria graminis) and septoria leaf spot (Septoria tritici). Light interception was estimated from weekly measurements of crop spectral reflectance. The increase of crop dry matter was mainly affected by N fertilizer and disease through effects on IPAR. Early N application increased IPAR and thus dry matter growth more than later N application. A split N strategy may ensure both high N uptake and high growth rates of the crop. Only septoria leaf spot significantly reduced RUE. Septoria leaf spot was found to be up to nine times more detrimental to grain yield than powdery mildew for similar severity levels. Fungicide applications may therefore be reduced in cases of low powdery mildew severity combined with low crop susceptibility to this disease. This low susceptibility was found to be obtainable with split N application strategies, as the severity of both powdery mildew and septoria leaf spot increased with increasing leaf N concentration. A similar but smaller correlation was obtained between disease severity and canopy size. Measurements of canopy size using spectral reflectance may be used as a simple indicator of general crop susceptibility to disease, whereas measurements of leaf N concentration may be used as input into decision support systems for fungicide application.

Yield, straw length, ripening, damage, grain composition and quality were determined on seven winter oat varieties included in trials grown in Northern Ireland between 1990 and 2000. Three management regimes were applied to the varieties in each year: (1) with fungicide but without plant growth regulator applications (+F−PGR); (2) with plant growth regulator and fungicide applications (+F+PGR); and (3) with neither fungicide nor plant growth regulator applications (−F−PGR). Disease control significantly improved yield, kernel content and the proportions of groats above 2·0- and 2·2-mm sieves but delayed ripening and increased the content of free kernels. Application of chlormequat significantly reduced straw length and the content of empty husks and increased the content of good oats but reduced kernel content. Specific weight, grain weight and the proportions of grain above 2·0- and 2·2-mm sieves were not significantly affected by either control of disease or application of chlormequat.

The combined effects of disease control and chlormequat significantly reduced leaning and brackling while lodging was reduced but not significantly. Rather than an increased incidence following disease control which was reduced by application of chlormequat, the two management strategies resulted in similar small incremental reductions in straw damage. In years with severe straw damage lower specific weight, grain weight and kernel content may have been attributable to the damage but quality was also poor in some years when there was little damage. Grain and groat size were only poor in those years when severe lodging or brackling occurred.

Year had the greatest influence on most characteristics and variety to a lesser extent. Disease control and to a lesser extent chlormequat application had smaller effects on fewer characteristics. While the effect of disease control on yield is of economic significance, the effect of chlormequat appears to be mainly of psychological significance.

Resistance to pod shatter was studied within and between populations of the resynthesized Brassica napus line DK142, grown under glass or in the field, at sites in the UK and Belgium. All populations showed similar ranges of resistance that were greater than that of a commercial cultivar (Apex). The increase in range was at least three-fold greater than the range found in Apex. Only sowing time affected the descriptive statistics of shatter resistance of each line, with spring-sown populations more shatter susceptible than winter-sown populations. The partitioning of dry matter to individual tissues of the pod was different for the two lines, with dry matter biased to the seed in Apex and to the receptacle in the more resistant DK142. In DK142 and Apex, as well as F1 and F2 populations derived from crosses between DK142×Apex, correlations for pod shatter resistance and mature pod characters were high, particularly the weight and length of the valves and septum. Shatter resistance increased in plants when pod numbers were reduced by the removal of whole racemes.

The efficiency of poultry litter nitrogen (N) utilization was studied in seven field experiments in eastern England during harvest years 1991 to 1994. Poultry litter was applied at different application rates in winter or spring, prior to sugar beet or potatoes. The mean manure N efficiency based on crop yields was 33% (range 25–43%) for sugar beet and 36% (range 13–66%) for potatoes. For potatoes, the manure N efficiency was greater from spring (mean 43%) than from winter application timings (mean 30%). The manure readily available N applied (i.e. ammonium-N+uric acid-N) and fertilizer N replacement values were well related (P<0·05) for both sugar beet and potatoes. Similarly, there was a good relationship (P<0·001) between the amounts of readily available N applied in the poultry litter dressings and measured elevations in spring soil mineral N supply. Where the poultry litter dressings supplied >600 kg/ha total N to sugar beet, root sugar concentrations were depressed (P<0·05) and amino-N concentrations increased (P<0·01). The soil mineral N supply following harvest of the sugar beet and potato crops was also increased where application rates supplied >600 kg/ha total N. Yield increases were also recorded in cereal crops grown the following season, but only where high rates of manure N (>600 kg/ha) had been applied. The current work has shown that the fertilizer N replacement value of poultry litter can be predicted based on the amounts of total and readily available N applied, providing guidance to farmers on appropriate reductions in inorganic fertilizer N applications to make allowance for poultry litter N supply.

Near-infrared reflectance spectroscopy (NIRS) was used for the analysis of soil samples for silt, sand, clay, calcium (Ca), potassium (K), sodium (Na), magnesium (Mg), copper (Cu) and iron (Fe). A total of 332 samples of different soils from Uruguay (South America) were used. The samples were scanned in a NIRS 6500 (NIRSystems, Silver Spring, MD, USA) in reflectance. Cross validation was applied to avoid overfitting of the models. The coefficient of determination in calibration (R^2_{\rm cal}) and the standard errors in cross validation (SECV) were 0·80 (SECV: 6·8), 0·84 (SECV: 6·0), 0·90 (SECV: 3·6) in per cent for sand, silt and clay respectively. For both macro and microelements the R^2_{\rm cal} and SECV were 0·80 (SECV: 0·1), 0·95 (SECV: 2·9), 0·90 (SECV 0·8), for K, Ca, Mg in g/kg respectively, and 0·86 (SECV: 0·82) and 0·92 (SECV: 25·5) for Cu and Fe in mg/kg. It was concluded that NIRS has a great potential as an analytical method for soil routine analysis due to the speed and low cost of analysis.

The yield stability of intercropping systems is important in developing cropping systems that produce economic yields over a wide range of environments. Field studies were conducted during the 1997/98 and 1998/99 growing seasons at three locations in the forest and forest–savannah transition zones of Ghana to determine yield, land use efficiency and yield stability of cassava (Manihot esculenta), maize (Zea mays), soya bean (Glycine max) and cowpea (Vigna unguiculata) intercrop systems. The cropping systems consisted of a factorial combination of two cassava varieties: ‘Gblemoduade’ (an improved, highly branched variety) and ‘Ankra’ (a local variety with fewer branches) and three spatial arrangements. Cowpea rows were planted in the minor season into cassava as a successive crop to maize and soya bean after their harvest in the major season. Intercropping significantly reduced grain or tuber yield of maize, cassava ‘Gblemoduade’ and cassava ‘Ankra’ by 23–70%, 16–49% and 24–64%, respectively. Maize yield decreased with increased number of soya bean rows. ‘Gblemoduade’ outyielded ‘Ankra’ by more than 100% under both intercrop and sole crop. The yield of soya bean increased with increased number of soya bean rows, but did not differ in response to the cassava variety. However, cowpea yield was higher when intercropped with ‘Ankra’ than with ‘Gblemoduade’. The intercrops had higher land use ratios (LER=1·27–2·83) and were more stable than the sole crops. Intercrops involving ‘Ankra’ had higher LER (2·14–2·18) than systems with ‘Gblemoduade’ (LER=1·83–1·99), but their yield stabilities were similar.

Lentil (Lens culinaris Medik.) cultivars (Jordan 1 and Jordan 2) were sensitized to chlorsulfuron herbicide. Both cultivars were subjected to three doses of gamma-irradiation (90, 100 and 110 Gray) to develop plants tolerant/resistant to this herbicide. The herbicide-tolerant plants as well as the sensitized plants were subjected to acetolactate synthase (ALS) enzyme assay to reveal the biochemical basis of plant tolerance. The results indicated that as the radiation dose increased, the tolerance to the herbicide application decreased in both lentil cultivars. Cultivar Jordan 1 showed sensitivity to chlorsulfuron herbicide at all treatments compared with that of Jordan 2. ALS enzyme activity in the two lentil cultivars was inhibited by chlorsulfuron. The irradiated plants (90 Gray) in both treated seeds plants (M1) and seeds of tolerant plants (M2) showed a lower level of inhibition to high concentration (250 μg/l) of chlorsulfuron herbicide. The results suggested an alteration of the expression system of ALS gene(s) leading to overproduction of altered ALS enzyme at the herbicide binding site of the enzyme in lentil plant.

The outer surfaces of plant leaves and stems are covered with a waxy layer, a considerable fraction of which comprises n-alkanes which are not digested and, therefore, can be used as markers in animal nutrition studies. Most plant species have a characteristic pattern of n-alkane concentrations in their cuticular wax and this enables the diet composition to be estimated by comparison with the pattern of the n-alkanes in faeces. N-alkane recovery in faeces was determined in a digestibility trial involving three different diets given to four goats, six cows and five calves. The validity of using n-alkane markers to determine diet composition was examined in in vivo feeding trials with goats and cows. The recovery of the odd chain length n-alkanes increased linearly with n-alkane chain length, with no significant differences between treatments. Estimates of diet composition were affected by the faecal n-alkane recovery rate. N-alkanes in plant cuticular wax can be used as natural markers for estimating diet composition, but a recovery factor should be used to correct for incomplete recovery in faeces. More research is needed to extend the findings to wider ranges of diets, animals, environmental conditions and physiological and reproductive states.

Urinary purine derivative (PD) excretion was estimated to examine the effect of rumen protozoa on total PD excretion in goats fed hay and a concentrate diet. The effect of increasing protozoa number in the rumen on nitrogen (N) balance and urinary PD excretion was determined after inoculation. Protozoa increased slowly until 4 days after inoculation, and on the 5th day after inoculation rapidly, finally (10 days) reaching 4·1×105/ml of rumen contents similar to that before defaunation. Urinary N excretion showed a small (non-significant) decrease. Urinary PD excretion did not change until the 7th day, and then the level decreased on the 8th day after faunation presumably due to the effect of increased protozoa in the rumen. The mean urinary total PD excretion significantly (P<0·05) decreased in the defaunated group compared with that in the faunated group. Comparable changes were not seen in plasma PD level of faunated and defaunated groups.

An experiment was carried out to determine endogenous excretion of allantoin (AN) in lambs and kids fasted and fed on a purine-free diet (milk replacer: MR). After weaning (40–50 days after birth), the animals were reared by feeding on MR until they were 120 days old. At 8 months of age, they were fasted for 8 days, and then re-fed on MR for 13 days. After weaning, AN excretion gradually decreased almost to a constant level at 80–120 days after birth (mean 0·14 mmol/kgW0·75/day). In goat kids, there was variation but no definite trend in urinary AN excretion in the period 40–120 days (mean 0·35 mmol/kgW0·75/day). Urinary AN excretion was very low after fasting for 8 days, mean values (per kgW0·75/day) being 0·13 mmoles for lambs and 0·17 mmoles for goat kids. In lambs, urinary AN excretion did not increase following subsequent re-feeding of MR, and for goat kids the increase was small. Changes in plasma AN concentration after fasting and re-feeding showed a similar response to that of urinary AN excretion for both sheep and goats so that there was a high positive correlation between the plasma AN and urinary AN excretion (r=0·881 for lambs and r=0·853 for kids). It is concluded that, in these young animals, urinary AN excretion rapidly responds to changes in plasma AN and is therefore likely to be a useful practical indication of endogenous PD excretion.

The degree to which grazers maintain the amount (organic matter intake) or the quality (organic matter digestibility) of their diet without adversely affecting the other component was addressed by investigating how sheep managed trade-offs between quantity and quality throughout the grazing season in an upland area of central France. Two groups of five dry ewes, grazing two plots of contrasting areas from April to the end of September 2000, were studied. On the smaller plot (1500 m2), the application of a high stocking rate (HSR) produced a resource of good quality but in low quantity; and on the larger plot (3000 m2), a low stocking rate (LSR) created a sward of low quality but in good quantity. In spring, in both conditions, the sheep maintained their intake of digestible organic matter (OM) at between 1000 and 1250 g/day. Both organic matter intake and digestibility remained high at both stocking rates. In summer, the intake of digestible OM decreased to between 750 and 1000 g/day. On HSR, this was mainly due to a decline of intake in relation to the decrease of intake rate and bite weight. On LSR a decrease in digestibility and to a lesser extent in intake was involved. At both stocking rates, the sheep maximized the digestibility of their diet by selecting the green laminae throughout the grazing season. In spring, the sheep modulated their daily grazing time to compensate the decrease in intake rate and maintained a high daily intake. In summer and autumn, the sheep failed to maintain their daily intake at the same level as previously observed. On both plots they modulated their daily grazing time to cover their needs (730 g/day), but they did not increase it further to maximize daily intake. This may be attributable to the costs involved in selecting (LSR) or taking (HSR) the best components from the sward.