In order to make informed decisions about the timing of harvests of grass crops, it is helpful to be aware of the changes that are taking place in the crops as they grow. Most people growing grass commercially or experimentally have a general awareness of the more obvious changes. However, greater awareness and understanding should lead to greater precision and greater success in the relevant enterprises. The present review considers some of the more important changes that are of interest from an agricultural point of view and for which sufficient information is available in the scientific literature. It is intended for relevant students, lecturers, research workers, advisers and producers.

Grass-legume associations may offer a way of improving the N efficiency of dairy farming, but may also have an adverse impact on the environment by increasing leaching losses. Nitrate leaching from four cropping sequences with different grassland frequency and management (long-term grazed, long-term cut, cereals followed by 1 and 2-year grazed leys) were investigated on a loamy sand in central Jutland for both unfertilized grass-clover (perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.)) and fertilized perennial ryegrass (300 kg N/ha) swards during 1997–2002. Furthermore, 1 year (2001) of N2 fixation in 1-, 2- and 8-year-old grass-clover pastures was determined. Nitrate leaching from grazed unfertilized grass-clover was always considerably lower than from grazed fertilized ryegrass. The effect of grassland age on nitrate leaching was insignificant in grass-clover but clear in grazed ryegrass, where levels increased dramatically with sward age. In production years 6–8, leaching from grass-clover was only 9–13% of the comparable losses from ryegrass. Under the cutting regime grass-clover showed a significant reduction in both yield and N-removal with increasing sward age, whereas for ryegrass these figures did not show any decreasing trend. N2 fixation was lower in 8-year-old swards compared with fully established 2-year-old swards as a consequence of lower dry matter production, lower clover content and a lower proportion of clover-N derived from the atmosphere. The results from the present study indicate that the higher leaching losses observed in fertilized grass compared with unfertilized grass-clover systems were caused by (1) a reduction in N2-fixation in grass-clover over time and (2) a reduction in dry matter production in grass-clover over time, lowering the grazing intensity and the recycling of grassland N via animal excreta.

Two field experiments examined the nutritional responses of the white lupin (Lupinus albus L.) agronomic cultivar Lucyanne to lime-amended soil. In the first, plots and boundaries of a pre-existing lime-rate experiment were sampled in 1993. The maximum shoot dry matter production occurred between soil pH 4·9 and 7·2. Whole-shoot Al concentrations increased below soil pH 4·9, and plants died at pH 4·4. Although dry matter production declined in soil above pH 7·2, no chlorosis or plant death was seen. Only the whole-shoot soluble Ca concentration changed from neutral to alkaline pH soil: it was greatest when grown in the alkaline-pH soil. In the second experiment, plants were grown in neutral pH or limed soil in 2000. Shoots were divided into specific tissue types and analysed for Fe III and Fe II, as well as soluble and insoluble Ca fractions. When sampled in April after over-wintering, the higher Ca concentration in the limed compared with neutral-pH soil-grown plants was due mainly to insoluble Ca. No plants were chlorotic and no differences between the treatments in the concentrations of either form of Fe were found. In June no plants were chlorotic, however the concentrations of both total and soluble Ca fractions were greater in the limed than the neutral-pH soil-grown plants, and there was more stem Fe III and less leaf Fe II in these plants. The present study shows that the cultivar Lucyanne is not a reliable crop plant above pH 7·2, and the loss of shoot dry matter can be attributed to nutritional responses at a sub-chlorotic level of stress.

Field work on rainfed cowpea (Vigna unguiculata (L.) Walp. cvs TC-9-6 and M-28-6-6) was conducted in the Orinoco lowlands to explain the changes in dry-mass partitioning and radiation-use efficiency (RUE) as compared with other cultivars over four consecutive seasons. Growth features were assessed in early-maturing, prostrate-canopy (TC-9-6), and medium-maturing, erect-canopy (M-28-6-6) cowpeas. These cultivars were sown in consecutive middle-wet and late-wet seasons in double peak rainfall conditions. Dry mass accumulation by cultivars was assessed as a function of leaf-area duration and the efficiency with which radiation was converted into dry mass throughout the season (i.e. radiation-use efficiency). Cultivar differences in canopy architecture and duration of leaf area had a minor effect on the total dry mass production. In the early-maturing TC-9-6, RUE for a middle-wet and a late-wet season was 0·90±0·04 and 0·65±0·05 g/MJ, respectively. In the medium-maturing M-28-6-6, the values were 0·97±0·05 and 0·72±0·03 g/MJ, respectively. A season with rainfall below 100 mm had a negative effect on phenology and RUE. When average rainfall was above 100 mm, the total dry mass accumulation was not affected by differences in cultivars and seasons. The rate of harvest index (HI) changes was negatively related to pod-filling duration. The changes in assimilation distribution depended on the process of partitioning as modulated by the limited pod-sink and the photosynthate supply. However, the photosynthate source was not depressed by the sink activity of the pod-filling. Partitioning to non-reproductive sinks was maintained. M-28-6-6 with high dry-mass production and delayed senescence did not effectively divert a large amount of assimilate to pod-filling. Pod sink activity in cowpea was limited by genotype. Harvest index in M-28-6-6 decreased with the increasing dry mass. The final HI and rate of linear increase in HI differed between cultivars and were lower in M-28-6-6. The results of the present work in the Orinoco lowlands are relevant for a wide range of savannahs with a late wet season.

The Japanese rice cultivar, Akenohoshi, has numerous spikelets in a panicle (extra-heavy panicle type) and achieves a large yield sink capacity. However, this cultivar, as well as other extra-heavy panicle types, does not always produce higher yields because of poor grain filling of the spikelets on the secondary branches in a panicle. To determine whether the poor grain filling found in Akenohoshi was due to source-limited or sink-limited conditions, the present study examined the responses of grain-filling characteristics to several spikelet-removal treatments immediately after heading. Only when the spikelets on secondary branches remained was a significant increase in filled grain percentage in this spikelet position observed. This increase seemed to be associated with the increases in rate and duration of the grain-filling process and in single grain weight in this spikelet position. These results clearly indicate that the poor grain filling in the spikelet on secondary branches of Akenohoshi could mainly be attributed not to sink-limited conditions, but to source-limited conditions probably at specific stages of grain filling.

Growth environment and plant nutrition are two important factors influencing growth, yield and quality of aromatic rice (Oryza sativa L.). The present study was conducted at Kalyani, India to determine the effect of two planting dates and four fertilizer levels on different aromatic rice cultivars during the dry seasons of 1995/96 and 1996/97, while nine cultivars were evaluated during the wet seasons of 1996 and 1997. Thermal and photoperiodic conditions significantly influenced the vegetative (leaf area index and light extinction co-efficient) and reproductive (filled spikelets/panicle) growth of the crop. Delayed planting (23 February) significantly reduced the grain yield by 0·88 t/ha, amylose content by 0·5% and duration by 10 days; but increased the summed heliothermal units (17806 v. 18505). Thus, the cultivars became less efficient (27%) in heat use with delay in planting from 2 to 23 February. Relative availability of NH4+-N from urea and Azolla influenced the crop growth (leaf area index [LAI], tiller production and leaf chlorophyll content) and nutrient uptake. Supply of inorganic N either alone or in conjunction with Azolla significantly increased grain yield (18–41%) and protein content (0·1–0·7%) over 15 t/ha of Azolla alone. However, combined application of Azolla and urea lowered the amylose content below that achieved by application of either substance alone. Correlation studies among quality attributes indicated that long-grained varieties had lower head rice recovery (r=−0·69) due to more breakage during milling and greater test weight (r=0·93).

Crop rotation serves as a mechanism for developing sustainable crop production systems. Crop-rotation trials are used to identify agronomic input factors suitable for use in a cropping system. In crop-rotation trials, experimental errors within the same plot over time are correlated. The form of the covariance structure of the plot errors may be specific to the data from a rotation trial, but is unknown and is generally assumed. Statistical analyses are usually based on the assumption that plot errors are independent, or have constant covariance. An experiment was conducted using wheat-based, three-course rotations containing tillage treatment subplots over 12 years at ICARDA's experimental station at Tel Hadya, a moderately dry area in northern Syria. This study examined several covariance structures for temporal errors arising over the rotation plots and tillage subplots, in order to model wheat yield data. Eighteen covariance structures were examined, and the best pair was selected using the Akaike Information Criterion. The best pair comprised first-order autocorrelation and homogeneous variance for temporal errors in rotation plots, and uniform correlation with heterogeneous variances for temporal errors in tillage subplots. Using the 12 years of data obtained for wheat yield and the best pair of covariance structures, the tillage and rotation effects were found to be statistically significant and to have significant interactions with the cycle of rotation. The precision of the means calculated differed from those calculated using a control structure based on homogeneous error variances and constant correlation. The cumulative yield build-up over time differed significantly over the rotations and the tillage methods. An increasing yield trend was observed for the bread wheat rotation, while a yield decline was observed in durum wheat when the rotation was repeated. When evaluating the effects of input factors in crop rotations, we therefore recommend that the covariance structures be examined and that a suitably chosen structure be used.

By a variety of exposure routes it is possible that the toxic heavy metals cadmium, arsenic and mercury could enter the diet of farm animals and hence contaminate food products derived from those animals. Therefore, there is a need to be able to assess the likely levels of contamination in animal tissues if exposed to contaminated feed and also to estimate how rapidly an animal will decontaminate once the source of contamination is removed from the feed. The development of dynamic models to predict changes in the degree of heavy metal contamination in tissues of ruminants have been hindered by the lack of data on the transfer and excretion rates of these metals from tissues. A study is described during which dairy cows were given a single intraruminal administration of 109Cd, 73As and 203Hg and measurements made of the subsequent concentrations of the radioisotopes in body tissues and milk. The resultant data were used to adapt previously developed compartment models describing the behaviour of the metals in sheep for use with dairy cows. Two changes were made to the sheep models: (i) a new excretion route was included to describe transfer to milk; (ii) the rate coefficients (with the exception of those involving gut absorption and transfer) were adjusted according to the ratio of the metabolic live-weights (live-weight (kg)0·75) of the sheep to that of the cattle. The models predicted levels of the metals in the cattle tissues and milk reasonably well.

The alkane technique allows estimates of intake and diet composition. For the latter a correction for incomplete recovery of faecal alkane concentrations has to be made. Feeding level and diet proportions have been discussed as factors possibly influencing recovery. A balance trial was conducted to study these effects on faecal alkane recovery rates and their consequences on estimates of roughage intake in sheep. The diets consisted of force-dried pelleted alfalfa meal (A) and wheat whole meal (W) in three levels each (360, 480, 600 and 270, 360, 450 g/day, respectively); the wheat was partly labelled with beeswax to provide a distinctive alkane pattern. Each diet was fed to four wethers. Despite significant effects (P<0·05) of A and W on organic matter digestibility, no such effects were observed for alkane recovery rates. Estimates of alfalfa intake were better if alkanes with a higher coefficient of variation of recovery were not included in diet composition estimates. Furthermore, in spite of the lack of significance of the dietary factors A, W and A×W, faecal alkane concentration correction based upon diet-specific faecal recoveries gave better estimates of alfalfa intake than based on overall recoveries. The estimate of alfalfa intake differed from known intake by −1·7 to −2·6%, depending on the method of estimation. The relative mean discrepancy was regarded as a tool to assess estimated intakes of individual animals. It ranged from 4·4 to 14·2% for dietary treatments and was 7·6% for all animals. The poor quality of estimates for individual animals may result from the variation of faecal recovery rates and needs further investigation.

An experiment was carried out to evaluate the utilization of the n-alkane technique and the chromium sesquioxide (Cr2O3)/acid insoluble ash (AIA) procedure to estimate feed intake of meadow hay by two breeds of cattle. The animals were housed in individual pens, and offered known amounts of meadow hay as the sole diet component. One group of 4 Barrosã cows (average weight, 457±24 kg) and another group of 4 Holstein–Friesian cows (average weight, 635±148 kg) were dosed with intra-ruminal controlled-release capsules (CRC) that contained alkane markers or Cr2O3 in separate capsules. During intake estimation, meadow hay and faeces were sampled twice daily. There was no significant effect of grab sampling time on the meadow hay intake estimation, due to the fact that no differences were observed in the faecal marker concentrations.

The mean real intakes, measured as the difference between the dry weight of feed offered each day and the dry weight of daily feed refusal, were 5·64 and 7·76 kg DM/day for Barrosã and Holstein–Friesian cows, respectively. For Barrosã cows the mean estimated intakes when using the CRC release rates documented by the manufacturer (MRR) were 5·66, 6·59 and 6·90 kg DM/day, using the Cr2O3/AIA procedure, C31[ratio ]C32 and C33[ratio ]C32 n-alkane pairs, respectively. For Holstein–Friesian cows the same markers gave values of 7·72, 8·51 and 8·95 kg DM/day, respectively. Mean daily intake estimation was improved when the release rate calculated as the reduction rate in CRCs payload performed in a additional experiment (CRR), was used. The differences from the real intake values, obtained using C31[ratio ]C32 and C33[ratio ]C32 alkane pairs, decreased from 950 and 1260 g/day to 140 and 420 g/day, respectively, for Barrosã cows and from 750 and 1190 g/day to 290 and 90 g/day for Holstein–Friesian cows. The intake estimation using the Cr2O3/AIA procedure was not affected by correcting the CRC release rate, because the release rates of both MRR and the CRR were similar.

The results indicate that controlled-release capsules provide a uniform marker release in cattle, but also suggest that to obtain accurate estimates of intake, it is better to measure release rates within the context of particular experiments.

This experiment examined the effects of immunizing against ACTH (adrenocorticotrophic hormone) and GnRH (hypothalamic peptide gonadotrophic releasing hormone) on growth and carcase composition of entire ram lambs from 6 to 35 weeks of age. There were four experimental groups (each of 17 animals) in a 2×2 factorial design: (1) a non-immunized control group, (2) immunized against ACTH, (3) immunized against GnRH and (4) immunized against both antigens. After booster injections, experimental lambs exhibited antibody titres to the two antigens presented, resulting in significantly lower cortisol and testosterone levels (P<0·001) in peripheral blood. The fall in blood cortisol levels in response to ACTH immunization was later matched by a similar decline in control animals to a point where they were not different.

In GnRH-immunized animals, antibodies disrupted the pituitary-gonadal axis, thereby impacting severely on testes development in growing lambs to the degree that by day 119 their testes were smaller than at the commencement of the experiment. Towards the end of the growth phase of the animals, GnRH-immunized lambs had significantly lower body weights at day 189 (P<0·05) and day 204 (P<0·01) while ACTH-immune lambs were not different in weight from control animals. Also, GnRH-immunized lambs were found to have greater GR measurement (P<0·05). Although ACTH immunization was capable of lowering cortisol for a brief period during the current experiment, the results were variable and detrimental to the efficacy of the immuno-castration vaccine (GnRH).

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-sixth meeting of the group, chaired by Dr T. R. Wheeler of The University of Reading, was held in the Kohn Centre at the Royal Society, 6 Carlton House Terrace, London on Friday, 26 March 2004 when the following papers were read.

A somewhat unpredicted effect of the 2001 Foot and Mouth crisis, has been to ‘derail the TB control programme both as regards cattle measures and the badger culling trial’ (EFRA 2003). Sadly, cattle TB is now out of control, rising by c. 20% a year, and back to 1960s levels. Unfortunately attention has focused to such an extent on badgers that many now seemingly do not understand how TB works in cattle and why annual testing and movement bans are the answer: they brought cattle TB down to tiny southwest hot-spots by the mid-1970s without any badger culling (Hancox 2000, 2002, 2003).