In this paper we present the analysis of yield data from a broad cross-section of crop variety evaluation programmes (CVEP) conducted in Australia. The main sources of variety by environment interaction are ‘non-static’ interactions, namely those linked to seasonal influences. These contributed an average of 41·3% of the total variance. In contrast the static component accounts for only 5·3% of the total.

We develop methods for determining the relative accuracy of CVEP based on selection of newly promoted entries. The accuracy of the current testing regimes for the Australian CVEP under study is determined. The accuracy of alternative schemes, with different numbers of years of testing, numbers of locations per year and numbers of replicates per trial is also examined. Cost effective methods for improving the accuracy of CVEP are discussed.

Trials, reflecting the feed needs in dry Mediterranean environments of small-ruminant production systems based on barley, were established at two sites in Syria in 1982. They compared various 2-course rotations of barley with feed legumes, fallow or more barley. This paper summarizes a 14-year sequence of results from an incomplete factorial combination of four rotations (B-V, B-L, B-F, B-B) of barley with vetch (Vicia sativa), lathyrus (Lathyrus sativus), fallow, and barley, with two fertilizer regimes, zero control and biennial NP applied to the barley phase, in terms of long-term mean yields, production stability and yield trends over time.

On a 2-year rotational basis, most barley was produced by barley-only rotations, and differences between B-F and B-B were small; but, in terms of total biomass production, feed legume rotations (B-V and B-L) outyielded barley-only rotations by 29% at one site and 19% at the other. Responses to biennial fertilization were large but did not interact significantly with rotation treatment. The crude protein status (%N) of barley grain and straw was strongly determined by seasonal rainfall, but that of the grain could be enhanced, irrespective of rainfall, by a preceding feed-legume crop; and, altogether, the total mean crop nitrogen output of legume-based rotations exceeded that of barley-only rotations by 80% and 64% at the two sites. The inclusion of legumes thus enhances both quantity and quality of feed production.

Annual yield fluctuations, attributable mainly to rainfall difference, were greater at the drier site. No consistent effect from fertilizer was observed, but at the wetter site rotation differences were appreciable, with B-F rotation giving the most stable yields. A number of time trends in yield values were tentatively identified. On a relative basis, some widening over time of the gap between fertilized and unfertilized treatments was observed in feed-legume yields at both sites and barley yields at the wetter site; over 14 years, yields in unfertilized plots had apparently declined relative to those receiving biennial NP. But, apart from a probable decline in lathyrus productivity compared to that of common vetch, changes in relative yield performance between rotations were difficult to detect. Regression models developed to describe absolute yield trends indicated a real decline over time in barley grain yields in continuous barley (B-B) at both sites and in unfertilized plots of all four rotations at the wetter site.

Rotations of barley with feed legumes produce more biomass and crude protein than barley-fallow and continuous barley sequences, but scope remains to improve the potential value to farmers of feed legume-based systems. This paper summarizes 6-year results from two sites from 2-year rotations of barley with: narbon vetch (Vicia narbonensis) and lathyrus (Lathyrus sativus), each harvested mature; and common vetch (Vicia sativa), harvested by simulated green-grazing and mature, all in factorial combination with four NP fertilizer regimes applied biennially to the barley.

Mean yield differences between rotations were quite small, but at the drier site the narbon vetch rotation was significantly superior in both total biomass and crop total nitrogen. Other results implied yield compensation between barley and legume phases: barley performance was relatively depressed at the wetter site after high-yielding narbon vetch but was relatively enhanced at both sites after green-grazed common vetch. Evidence from year-round soil-water monitoring suggests that the benefit following green grazing may have arisen, in part, from a small carry-over of profile moisture between crops not much inferior to that residual from a fallow year. Both crop phases responded strongly to biennial P fertilizer; and barley responded strongly to three rates of N-fertilizer, but a sometimes significant curvilinear component to this response reflected a tendency for grain yields to be depressed by added nitrogen in the driest years. But interactions between N-rates and rotations were not significant.

It was concluded that narbon vetch may have greater potential than common vetch and lathyrus for mature harvest in drier areas, but its unsuitability for grazing green is a limitation. Flexibility of utilization is important, to accommodate the needs of different farmers and the exigencies of different seasons. The green-graze option has major potential where there is a demand for high-quality spring grazing; and indications that barley may be as productive after green-grazed vetch as after a year of fallow suggest an alternative approach for farmers who have previously avoided legumes in order to maximize barley production.

Results from monocropped barley treatments in long-term rotation (RTN) and continuous barley (CB) trials at two sites were examined for fertilizer effects on yield means and long-term yield trends. In RTN trials, mean responses to fertilizer (N[ratio ]P2O5) applied annually at rates of 20[ratio ]60 at the drier and 40[ratio ]60 at the wetter site were almost double those from biennial application, confirming the need for annual fertilization in monocropped barley systems. In CB trials, with N and P applied annually in nine factorial combinations, at rates up to 120[ratio ]90, responses to each nutrient were curvilinear and dependent on the presence of the other nutrient. Trend analysis showed a decline in grain yields over time where NP fertilizer had not been applied or applied only at low annual rates (< 60[ratio ]45 or < 60[ratio ]90, according to site); but straw yields, at worst, remained approximately stable in the absence of fertilizer and generally increased strongly with higher NP rates. Uncertainties in the interpretation of trend-analysis results indicate the need for methodology improvements, to include (i) additional single-value parameters of the growth environment, to improve the model's ability to account for seasonal variability, and (ii) a more flexible, non-linear function for time.

It was concluded that barley monocropping is not necessarily non-sustainable in the medium term, provided adequate annual fertilization is maintained; but risks of pest or disease build-up, in addition to the superiority of legume-barley systems in biomass and crude protein output demonstrated in preceding papers, undoubtedly favour the introduction of some forage legumes into long-term barley sequences. The most practicable (and acceptable) systems may well be ones in which continuous barley is interrupted by a legume, or even a bare fallow, every third or fourth year. Above all, farmers should be helped to experiment with different forage legumes, barley–legume sequences, and modes of legume harvest, to optimize outputs in relation to their evolving and individual enterprise needs.

A field study was conducted on an experimental field of the Maize Research Institute Zemun Polje- Belgrade (latitude: 44° 49′ N), Yugoslavia over a 3 year period (1994–1996). The objective of this study was to find the optimal spatial arrangement of a maize–beans intercrop in irrigated and rainfed farming systems.

Plant arrangement patterns in an intercropping system did not significantly affect LAI values in maize compared with a sole crop, while irrigation had a greater positive influence on it. Leaf area values of beans were more sensitive to the same treatments. Microenvironmental conditions in maize–bean mixtures were more favourable for bean crop than for sole beans.

An intercropping system had a greater influence on yield components of maize. Component combination 1/2[ratio ]1/2 (maize[ratio ]bean) was most effective in all yield components of maize. Intraspecific competition appears to be more intense than interspecific competition in both crops. Yield component of bean was more sensitive to water regime of the site than to planting pattern in an intercrop. Irrigation increased all yield components of bean (especially pod number). The intercropping system decreased harvest index in both crops compared with monocrops. Maximum total grain yield was in 1994 in irrigated maize–bean intercrop 1/2[ratio ]1/2, with highest efficiency being in an intercrop in irrigation in 1995. The Land Equivalent Ratio (LER), based on grain yield, was consistently greater than 1·0 in an irrigation water regime in 1995. Proportion of maize[ratio ]bean = 1/2[ratio ]1/2 gave the highest increase of yield (LER = 1·54). Under conditions of chernozem soil type in Zemun Polje, with often-expressed dry periods, irrigation is a very important measure for increasing maize–beans intercrop productivity.

Two sets of experiments were conducted on sandy loam soils at Anand, India during the rabi (winter) seasons of three years (1993/94–1995/96) to study the effects of farmyard manure, nitrogen, phosphorus and potash as well as the method and time of sowing and irrigation on the growth and yield of chicory. Application of farmyard manure and phosphorus had no beneficial effect, whereas the application of nitrogen at 100 kg/ha and potassium at 50 kg/ha increased yield by 12·09 and 3·33%, respectively, on a pooled basis. Crops sown either in rows 30 cm apart or broadcast performed equally well with respect to dry root yield. Sowing of chicory on 5 November gave the highest dry root yield. Delayed sowing significantly reduced the dry root yield. Scheduling irrigation at an irrigation water: cumulative pan evaporation ratio of 0·7 produced maximum dry root yield.

A pot experiment was carried out at Nahshala Farm, about 50 km from Al-Ain, UAE, during the 1998/99 growing seasons, using six halophytes: Spartina sp., Distichlis palmeri, Paspalum vaginatum, Juncus roemerianus, Salicornia bigelovii and Batis maritima, under two levels of leaching fraction, 0·25 and 0·50 and three levels of irrigation salinity, 10, 20 and 40 g/l. The objectives of the experiment were twofold: (1) to find out the optimum and threshold of saline water irrigation to keep salinity level down as much as possible in the soil using the leaching fraction technique; and (2) to study the response (growth and biomass production) of some halophytes to different levels of salinity. The experiment was conducted in triplicate with a split-plot design arranged in a randomized complete block. Results indicate that these halophyte species can be grown productively at a leaching fraction between 0·25 and 0·50 when salinity of the irrigation water is less than 20 g/l. At higher salinities, Salicornia bigelovii can grow and yield satisfactorily under these conditions, while the other species may require more frequent irrigation at higher leaching fractions. Some of these tested halophytes may be able to revegetate the salt-affected lands and be a potential source of forage in these harsh habitats. This study supports the idea of seawater agriculture by demonstrating the possibility of using some high salt-tolerant halophytes at relatively higher leaching fraction in order to maintain satisfactory yield production of such halophytes.

For welfare reasons, fattening pigs on organic farms are raised on deep litter in the open with simple, flexible climate tents for shelter. Within this system, the nitrogen (N) flow both during fattening of the pigs from 17 to 100 kg liveweight in winter and during composting of the deep litter from the enclosures in summer was studied. During the fattening period, the pigs were provided with barley straw at four daily rates (0·67, 1·21, 1·32 and 1·87 kg) per kg increase in liveweight. During the summer period, N balances from four enclosures receiving straw at around the 1·32 kg rate were examined. Temperatures in the deep litter mat and in the compost heap were determined, as well as concentrations of ammonia (NH3) and nitrous oxide (N2O) in the compost heaps. The temperature increased after 4 weeks to between 40 and 70 °C in the deep litter mats receiving > 1·21 kg straw; the highest temperatures were observed in the mats with the highest straw rate. Temperatures exceeded 50 °C in all compost heaps. In the deep litter mats and compost heaps the highest temperatures were recorded for the longest periods in the material containing the most straw. The initial concentration of NH3 in the gas phase of the compost heaps was > 10 mg NH3-N/m3, which dropped to zero within 1 month. After the NH3 concentration had fallen, the amount of N2O increased significantly for a period in the two heaps with 1·21 and 1·32 kg straw. Over 120 days in summer, an average of 16·3±6% N was lost from the four enclosures strawed at a rate of 1·32 kg (±0·2 kg) straw per kg increase in liveweight. During the winter 12–24% of the N excreted was lost during a fattening period of 119–134 days, and 15–42% of the N stored was lost during the following composting period of 143 days. In total, 29–54% of the N added to the deep litter mat in excretion and straw was lost during the fattening period (119–134 days) and subsequent storage (143 days). The lowest loss was recorded from deep litter strawed daily with 1·32 kg straw per kg increase in pig liveweight.

The study examined the reliability of predicting faeces output of cattle from chromium oxide (Cr2O3) released from a device (CRD) inserted in the rumen. Sixteen steers were selected from four genotypes and were offered a diet of low quality pasture hay with a protein meal supplement. The steers were placed in metabolism crates which allowed for total collection of faeces over two 5-day periods, days 6–9 (period 1), and days 13–16 (period 2), of a 20-day extrusion cycle of the CRD. Three faeces samples were taken from each steer per rectum; grab samples in the a.m. and p.m. and a daily subsample, that is, a sample of each daily total collected output. Cr2O3 release rates were derived for each sampling regime (a.m., p.m. and daily from the Cr2O3 content of faeces). These derived rates were compared with the release rate specified by the supplier to determine differences and any bias associated with the sampling regimes. Release rates were also derived from the predicted expiry date calculated from plunger travel in the CRD. Organic matter digestibility of the diet was determined from measurements of feed intake and faeces output over the 4 days for each steer and from an in vitro technique on diet samples. Predicted forage intakes were estimated using the mean faeces output collected over 4 days in combination with either the in vivo or in vitro digestibility estimates. Correlations between actual forage intake and predicted forage intake for each method were calculated and the bias in predicted forage intake between methods was compared.

The daily data revealed significant effects of steer (and/or CRD) and sampling period on the estimated release rate of Cr2O3 from the CRD. However, whilst there was only a period effect on the release rate with p.m. sampling there was a linear decline in release rate with the a.m. sampling. The correlation between predicted and actual forage intake was greatly reduced when in vivo digestibility was replaced by in vitro digestibility.

The results of this study suggest that the CRD had release rates less than specified and therefore devices should be calibrated for both the animals and the pastures prior to use. Furthermore, faeces sampling should be restricted to <13 days post-dosing to minimize bias.

The current experiment was conducted to study the effect of different doses of tannic acid, a hydrolysable tannin, on ruminal degradation and post-ruminal digestion of treated soya bean meals (SBM) in sheep. Samples of SBM were prepared by spraying 100 g SBM with 100 ml distilled water containing 0, 1, 5, 10, 15 or 25 g of commercial tannic acid (S0, STA1, STA2, STA3, STA4 and STA5, respectively). Three ruminally cannulated ewes, that had never consumed tannic acid previously, were used to determine in situ degradability of tannic acid-treated SBM. Intestinal digestibility of protein remaining after 16 h rumen incubation was estimated in vitro. Extent of rumen degradation of SBMs was significantly (P < 0·05) affected by the tannic acid treatment. All doses of tannic acid used in this experiment, even the lowest one (STA1), significantly decreased the extent of N degradation but only doses higher than that used to treat STA3 reduced the extent of DM degradation. This reduction in the extent of DM and N degradation was mainly due to a marked decrease in the immediately degradable fraction (a), which was observed in all treated SBM, and to a lower rate of degradation (c), observed in meals STA3, STA4 and STA5. Intestinal digestion of the non-degraded protein was decreased (P < 0·05) by treatment with the two highest doses of tannic acid (those used to treat meals STA4 and STA5). It was therefore concluded that tannic acid can exert a negative effect both on rumen degradation and on intestinal digestion of SBM, this effect being clearly dependent on the dose used to treat the SBM.

The concentration of n-alkanes in the cuticular wax of plants can be used to estimate the composition of the diet selected by free-ranging animals. The aims of this study were to characterize the n-alkane profiles of developing leaves and evaluate the degree of chemical discrimination between six browsed broadleaf tree species: European ash (Fraxinus excelsior L.), flowering ash (Fraxinus ornus L.), hornbeam (Carpinus betulus L.), hazel (Corylus avellana L.), mountain ash (Sorbus aucuparia L.) and beech (Fagus sylvatica L). The effect of the stage of development was examined by considering five different vegetative stages: dormant bud (DB), late bud (LB), young leaf (YL), mature leaf (ML) and senescing leaf (SL). Five samples per each vegetative stage and species, gathered in a mixed woodland of the Italian Eastern Alps between February and October, were analysed for their n-alkane concentrations (C23–C36).

The residual coefficient of variation was 15·5% on average for the individual n-alkanes considered. There were noticeable differences in individual and total n-alkanes content between species. In particular, C27 was the predominant n-alkane in beech and C33 was found in high proportions in the two species of Fraxinus; hazel and flowering ash had a higher total n-alkanes content than the overall mean, while the lowest values were found in hornbeam and beech. The n-alkane profile also underwent important changes during the vegetative development, with different extent and direction according to the species. In the three successive leaf stages, a tendency for a progressive increase in the longest chain homologues was observed. In any case, the young leaf stage differed most from the contiguous stages.

Canonical discriminant analysis indicated that the n-alkane profile of buds and leaves were mathematically distinguishable and the chemical differences between species were persistent over the plant vegetative development.

This group, which is concerned with the applications of mathematics to agricultural science, was formed in 1970 and has since met at approximately yearly intervals in London for one-day meetings. The thirty-second meeting of the group, chaired by Professor D. Scholefield of the Institute of Grassland and Environmental Research, North Wyke, was held in the Kohn Centre at the Royal Society, 6 Carlton House Terrace, London on Friday, 14 April 2000 when the following papers were read.