Farmers commonly apply slurry when soil conditions are suitable for spreading. In order to improve slurry nitrogen (N) use efficiency, effects of split application of pig slurry according to the crop N demand on yield were tested in 1994/95–2001/02. The crop rotation was winter oilseed rape (OSR) – winter wheat – winter barley. N was applied as pig slurry or as mineral N fertilizer (each of 0, 40 or 80 kg N/ha, total N amount: 0–240 kg N/ha) at three dates. Each year, the treatments occurred in all three crops of the rotation and were located on the same plots. On average, mineral N fertilizer led to higher grain yields in all crops (+0·33 t/ha in OSR, +0·57 t/ha in wheat, and +0·20 t/ha in barley) compared with slurry application, presumably due to a slower N mineralization of the organic fraction. However, the large year to year variation resulted in high error estimates, leading to no significant differences in yield. Taking only the ammonium amount of the slurry into account, there was no significant difference in yield between the two N sources. Yield potential was similar in both slurry and mineral N treatments, but higher N amounts were necessary on the slurry plots. Therefore, slurry N-use efficiency (NUE) remained lower than that of mineral N. However, compared with a single dose, growth-specific slurry application according to the crop demand, as made with mineral N fertilizers, increased NUE.

High spatial and temporal variability of nitrogen application via livestock urine on grazed pasture make meaningful measurement of leaching of nitrate very difficult. The present study was aimed at estimating the mean annual nitrogen loadings and concentrations leached to an underlying aquifer beneath unfertilized irrigated and non-irrigated paddocks of a dairy farm at OB Flat 10 km south of the city of Mount Gambier (37°50′S, 140°40′E), South Australia. Urine was collected in the milking shed and applied to 1 m deep monolith lysimeters in three separate seasons in 1992. Some lysimeters received two applications. Drainage and N fluxes and concentrations were recorded 1 year before urine application and for 3 years following urine applications. A negative binomial function was used to specify the appropriate proportions of pasture subject to 0, 1 or 2 loadings in a year, and the lysimeter drainage measurements were then scaled across seasons and paddock area to estimate mean annual leaching under the whole of each paddock. It was found that the timing of urine application had a profound effect on the leaching of nitrogen. Results indicated that the nitrate flux leaching from the root zone in the irrigated paddock was 26–33 kg N/ha/year at 13–17 mg N/litre and in the non-irrigated paddock, 10–13 kg N/ha/year at 9–11 mg N/litre. These estimates are not inconsistent with nitrate concentrations measured in groundwater but cannot be independently verified. The current transition from non-irrigated to irrigated pastures is likely to double nitrogen loads to the aquifer and cause nitrate concentrations in groundwater to exceed drinking water guidelines, unless alternative pasture management strategies are developed.

Near-infrared spectroscopy (NIRS) was used to analyse the crude protein content of dried and milled samples of wheat and to discriminate samples according to their stage of growth. A calibration set of 72 samples from three growth stages of wheat (tillering, heading and harvest) and a validation set of 28 samples was collected for this purpose. Principal components analysis (PCA) of the calibration set discriminated groups of samples according to the growth stage of the wheat. Based on these differences, a classification procedure (SIMCA) showed a very accurate classification of the validation set samples: all of them were successfully classified in each group using this procedure when both the residual and the leverage were used in the classification criteria. Looking only at the residuals all the samples were also correctly classified except one of tillering stage that was assigned to both tillering and heading stages. Finally, the determination of the crude protein content of these samples was considered in two ways: building up a global model for all the growth stages, and building up local models for each stage, separately. The best prediction results for crude protein were obtained using a global model for samples in the two first growth stages (tillering and heading), and using a local model for the harvest stage samples.

Knowledge of nitrogen accumulation to the grains is of great importance for identifying breeding and growing strategies to improve cereal yield and quality. The aim of this study was to investigate post-anthesis N translocation in the spike and into different spikelets of two cultivars of spring wheat (Triticum aestivum L.) grown to maturity in solution culture. Sport (short grain filling time, low yield and high grain protein concentration) and WL (normal grain filling time, high yield and low protein concentration) were the cultivars used. Plants received stepwise declining rates of N on a daily basis, until 109 days after planting (DAP). Anthesis for cv. Sport was 92 DAP and for cv. WL 78 DAP. On seven occasions (from anthesis in cv. WL until maturity), 15N was given to selected groups of plants for 4 days. Then these plants were sampled and separated into plant parts. Spikelets and grains were separated according to spikelet position. Plant parts were weighed and analysed for N and 15N.

The N concentration in the grains was uniform for the spikelets in cv. WL but differed in cv. Sport. Final N concentration in a spikelet position was obtained at 126 DAP in cv. Sport and 112 DAP in cv. WL and was constant to the end of experiment at 154 DAP in cv. Sport and 147 DAP in cv. WL. A positive correlation between % atom excess 15N to spikelet position numbered from the base of the spike was exhibited in the lowermost part of the spike just after anthesis. Later, during grain filling, a negative correlation between % atom excess 15N to spikelet position was exhibited (−0·991 P=0·000). A positive correlation between % atom excess 15N to grain weight in the top of the spike was exhibited. Accumulation of 15N proceeded 14 days longer in the lowermost fertile spikelets than in the uppermost spikelets. It was concluded that the duration of N accumulation in the spikelets was dependent on spikelet position and uppermost spikelets had a shorter N accumulation period and contained lighter grains than lowermost spikelets.

Six S5 lines of maize, previously identified as having contrasting responses to nitrogen (N) supply, were used to carry out a complete series of diallel crosses. The resulting 15 hybrids were grown in a field at two N levels. The general combining ability (GCA) and specific combining ability (SCA) were estimated using the method 4, model I analysis of Griffing for grain yield kernel weight, grain number, harvest index, green leaf number, ear leaf area, N utilization efficiency, total plant N, grain N content, anthesis-silking interval, chlorophyll content and prolificacy. For the majority of the traits, GCA was more important than SCA and there was an increase of non-additive effects under low N. Significant interactions were observed between GCA and N levels for grain yield, grain number and chlorophyll content, indicating the selection of different lines for each N level. The lines with the largest effects of N supply per se on grain yield, were those with the largest effects of GCA for this trait. This association indicates that the response of the lines to N supply, should be considered in breeding programmes in order to achieve acceptable hybrids for environments with both high and low N.

Assessment of the stability of micronutrients is important in breeding for the enhanced nutritional quality of staple food crops as a means to alleviate malnutrition. Twenty early-maturing elite tropical maize (Zea mays L.) genotypes were evaluated over 2 years at three locations representing three distinct agroecologies in West and Central Africa (WCA). The objectives were to analyse the pattern of genotype×environment interactions (GEI) and environmental stability of iron and zinc concentrations in grain using the Additive Main Effects and Multiplicative Interaction (AMMI) statistical model. Results indicated that the effects of genotypes, environments and GEI were significant (P<0·05) for both micronutrients. The effect of GEI was about double the contribution of the genotypes for grain iron and more than double the effect of genotypes for grain zinc. Partitioning of GEI indicated that variety×location was the dominant source of a significant amount of GEI for both micronutrients. Scores of the first two interaction principal component axes (IPCA1 and IPCA2) from the AMMI were significant and accounted for 0·68–0·75 of the pattern of GEI for both micronutrients. About half of the genotypes evaluated were stable for grain iron and zinc concentration over the set of environments. The AMMI model identified ACR98TZEMSR-W as the most stable genotype for grain iron and MAKA-SRBC5 was the most stable for grain zinc. However, the yellow genotype, AK94-DMR-ESR-Y was the most promising, with high and moderately stable concentrations of iron and zinc in the grain. Because it is yellow, with beta-carotene content and high concentrations of iron and zinc in the grain, it might significantly contribute to an improved intake of these micronutrients in populations who rely on maize for a major portion of their daily diet.

An algorithm to fit boundary lines, using cubic smoothing splines, was written and used to identify yield responses to changes in soil properties. This method involves fitting a curve that represents the maximum yield response to each predictor value, which represents the yield potential at each soil property value. Boundary-line yield responses to individual soil properties were found to differ from responses found by fitting curves through the data scatter. The effects of correlated variables appeared to be lessened using the boundary line approach. Multivariate boundary-line models, based on the Law of the Minimum, were found to be useful for the identification of site-specific causes of yield variation and yield potentials. The boundary line was found to be a useful complement to more traditional data analysis techniques.

Damping-off and stem rot of cowpea is an important soil-borne disease worldwide. Cowpea fields were randomly chosen in each agro-ecological zone in Benin and surveyed in 2001 and 2002 to determine the occurrence of the diseases throughout the country. Diseased plants, prevailing environmental conditions and cowpea grower cultural practices were recorded and causal agents associated with the disease identified. Results indicated that damping-off and stem rot were distributed throughout Benin. The disease incidence was higher in the South (0·074) and Centre zones (0·063) than in the other zones (<0·02) in the country. Among factors influencing the disease incidence, cultural practices such as sole crop and no-till systems appeared to be most important. Isolated fungi included Sclerotium rolfsii, Fusarium spp., Pythium ultimum, Rhizoctonia solani, Phoma sp., Rhizopus sp. and Trichoderma harzianum. None of the Fusarium, T. harzianum or Rhizopus sp. isolates were pathogenic in the greenhouse. Pythium ultimum, R. solani and Phoma sp. were infrequently isolated and few isolates caused the disease symptoms in the greenhouse. However, this is the first report of Phoma sp. causing damping-off and stem rot of cowpea in Benin. Sclerotium rolfsii was by far the most common species isolated from all the agro-ecological zones and all isolates were pathogenic on cowpea in the greenhouse. Sclerotium rolfsii was considered to be the main causal agent of cowpea damping-off and stem rot in the Republic of Benin due to its wide distribution, high incidence and predominance on plants with damping-off and stem rot symptoms.

Maize improvement at the International Institute of Tropical Agriculture (IITA), which began in the 1970s, built on the germplasm and experience of earlier years. The main breeding emphasis was to develop maize cultivars and hybrids with high yield potential and durable resistance to diseases and pests with specific adaptation to the different agro-ecological zones of West and Central Africa. Over the years, open-pollinated cultivars have been developed with different levels of resistance to biotic and abiotic stresses. Identification of the factors that contributed to improvements in the maize cultivars developed during the past decades may be useful to sustain the genetic gain from selection in the future. A study was conducted to quantify genetic gains in yield and associated traits of open pollinated maize cultivars released from 1970 to 1999 in the West African savannas. The genetic gain in grain yield was 0·41% per year and seems to be associated with increases in total biomass and kernel weight, and reductions in plant height and days to flowering (anthesis and silking). There was no significant change in harvest index of the cultivars.

Mathematical models have been developed that describe possible sources of the free amino acids (AA) present in the red blood cells (RBC). These models reflect three hypotheses, namely (i) direct transport between plasma and RBC, (ii) enhanced direct transport by deformation of the RBC during passage through capillaries and (iii) direct exchange between tissues and RBC. The latter implies that RBC samples from appropriate blood vessels might offer an alternative to tissue biopsies in protein turnover studies.

These compartmental models were tested against data from ovine studies. For hypothesis (i), a single dose of [U-13C] AA was added to blood in vitro. The rate of disappearance of label from plasma was low (kP=0·0009–0·004 per min), indicative of slow direct transport between plasma and RBC. For hypotheses (ii) and (iii), a single dose of [1-13C] AA was administered intravenously to sheep. Label disappeared from plasma quicker (kP=0·33–0·53 per min) than in vitro, with the appearance of labelled AA in the RBC higher than could be explained from direct transport alone. The model reflecting enhanced exchange of free AA between plasma and RBC due to capillary action over-predicted RBC enrichments and pool sizes by up to five-fold. The third hypothesis, namely that AA in the RBC are predominantly derived from exchange with tissues, gave better agreement. This model suggested that at least 0·63 of the AA in the RBC might come from exchange with tissue.

To investigate whether peripheral tissues (skin and muscle) might be involved in such exchange, an additional experiment was conducted in five sheep prepared with arterio-venous catheters across the hindquarters. [1-13C,15N] leucine was continuously infused, with both blood samples and tissue biopsies taken. The ratio of [1-13C] leucine to [1-13C,15N] leucine was 1·8–2·9 fold greater in muscle and skin compared with arterial plasma, indicative of intracellular transamination. If free leucine exchanged directly between tissues and RBC then the ratio should be higher in RBC isolated from venal caval compared with arterial blood. In practice, the ratios from the RBC in aorta and vena cava were similar (P=0·30). These findings suggest that, for leucine, RBC enrichments do not form an alternative to tissue biopsies to estimate the enrichment of the precursor pool in protein turnover studies of the hindquarter. Instead, other tissues must play a more important role in the exchange of AA with the RBC.

Forage degradability data from pooled forage samples were compared to those obtained from field samples using an in situ technique. Four fistulated sheep were employed as part of a Split Plot design within a 4×2 factorial (four times of incubation as plots and two forages as subplots) over a 4×4 Latin Square. The field site sample technique led to more realistic confidence limits for all parameters when modelling forage degradation and suggested the possibility of working with a single fistulated ruminant. Such a technique meets animal welfare requirements, saves experimental work and may stimulate the use of the in situ technique with simpler designs.

Over the last two decades, dairy cattle management in Malawi has been oriented towards increasing milk yield per animal. One consequence of this process has been reliance on Holstein Friesian bull semen from temperate regions. The aim of the current study was to evaluate the performance of Holstein Friesian cows on large-scale farms in Malawi. A data set of 60640 test-day records from Holstein Friesian cows in first, second and third lactation from three large-scale dairies in Malawi were utilized. Fixed effects of herd, year and season of calving were tested. (Co)variance components were estimated through the restricted maximum likelihood (REML) procedure. Heritability, genetic and phenotypic correlations for milk yield, lactation length, age at first calving, and calving interval were determined. In general, milk yield decreased over the years and there was significant (P<0·001) variation in milk yield between herds. The genetic base, as indicated by the genetic trend, remained almost constant in the studied period. This entails genotype by environment interaction, culminating in the additive genetic effect not expressing itself fully in the phenotype. It is therefore apparent that considerable improvement could be achieved by improving the production environment.

The composition of yeast communities in the rumen of cattle was investigated using comparative DNA sequence analysis of yeast 26S rDNA genes. 26S rDNA libraries were constructed from rumen fluid (FF), rumen solid (FS) and rumen epithelium (FE). A total of 97 clones, containing a partial 26S rDNA sequence of 0·6 kb length, were sequenced and subjected to an on-line similarity search.

The 41 FF clones could be divided into five classes. The largest class was affiliated with Pezizomycotina class (85·4% of clones), and the remaining classes were related with the Urediniomycotina (2·4%), Hymenomycetes (4·9%), Ustilaginomycetes (4·9%) and Saccharomycotina (2·4%) classes. The 26 FE clones could be divided into three classes and the Saccharomycetes class (92·4% of clones) was the largest group. The remaining classes were related with either Pezizomycotina (3·8%) or Ustilaginomycetes (3·8%). The 30 FS clones were all affiliated with Saccharomycotina. Saccharomycotina were predominant in rumen epithelium and rumen solid while Pezizomycotina were predominant in rumen fluid. Yeast belonging to the Saccharomycotina class was predominant in the rumen as a whole (57%). One clone (FF34) had less than 90% similarity to any sequence in the database and was thus apparently unrelated to any previously described yeast.

A model was published by Lewis et al. (2002) to predict the mean age at first egg (AFE) for pullets of laying strains reared under non-limiting environmental conditions and exposed to a single change in photoperiod during the rearing stage. Subsequently, Lewis et al. (2003) reported the effects of two opposing changes in photoperiod, which showed that the first change appears to alter the pullet's physiological age so that it responds to the second change as though it had been given at an earlier age (if photoperiod was decreased), or later age (if photoperiod was increased) than the true chronological age. During the construction of a computer model based on these two publications, it became apparent that some of the components of the models needed adjustment. The amendments relate to (1) the standard deviation (S.D.) used for calculating the proportion of a young flock that has attained photosensitivity, (2) the equation for calculating the slope of the line relating AFE to age at transfer from one photoperiod to another, (3) the equation used for estimating the distribution of AFE as a function of the mean value, (4) the point of no return when pullets which have started spontaneous maturation in response to the current photoperiod can no longer respond to a late change in photoperiod and (5) the equations used for calculating the distribution of AFE when the trait is bimodal.