The possibilities for increasing total grain yield in organic cereal production through manipulation of crop rotation design were investigated in a field experiment on different soil types in Denmark from 1997 to 2000. Three experimental factors were included in the experiment in a factorial design: (1) proportion of grass-clover and pulses in the rotation, (2) catch crop (with and without) and (3) manure (with and without). Three four-course rotations were compared. Two of the rotations had 1 year of grass-clover as a green manure crop, either followed by spring wheat or by winter wheat. The grass-clover was replaced by winter cereals in the third rotation. Animal manure was applied as slurry in rates corresponding to 40% of the nitrogen (N) demand of the cereal crops.

Rotational grain yields of the cereal and pulse crops were calculated by summing yields for each plot over the 4 years in the rotation. The rotational yields were affected by all experimental factors (rotation, manure and catch crop). However, the largest effects on both dry matter and N yields were caused by differences between sites caused by differences in soils, climate and cropping history. The rotation without a green manure crop produced the greatest total yield. Dry matter and N yields in this rotation were about 10% higher than in the rotation with a grass-clover ley in 1 year in 4. Therefore, the yield benefits from the grass-clover ley could not adequately compensate for the yield reduction as a result of leaving 25% of the rotation out of production. There were no differences in dry matter and N yields in grains between the rotations, where either spring or winter cereals followed the grass-clover ley. The N use efficiency for ammonium-N in the applied manure corresponded to that obtained from N in commercial fertilizer. There were only very small yield benefits from the use of catch crops. However, this may change over time as fertility builds up in the system with catch crops.

Small-scale silos (60-litre polyethylene barrels) were used to examine the chemical composition of grass silage after the application of slurry, at 40 m3/ha, at a range of timings, at two sites with contrasting rainfall; North Wyke, in Devon (high rainfall) and Reaseheath College, Cheshire (low rainfall). Grass plots (60 m2) received cattle slurry via surface broadcast (S), shallow injection (I) or surface placement by trailing shoe (T) techniques at 10, 6 or 2 weeks before an early silage (first) cut in May/June, and 6 or 2 weeks before a second cut in June/July. Control plots (C) received no slurry treatment. The harvested grass was compressed and sealed in the experimental silos and samples of the herbage at ensiling and of ensilage (after >100-day fermentation) were analysed for various chemical components. Herbage yield was measured when the harvests were taken. Wetter than average weather conditions in both years resulted in silages with variable DM content (range 140–277 g/kg) being made at both sites. Generally, silages were poorly preserved with high pH and NH4+-N and low lactic acid contents. In particular, the silages from treatment S where slurry was applied 2 weeks prior to harvest exhibited characteristics indicative of clostridial growth, with high pH (range 4·0–5·2) and NH4+-N (106–213 g/kg total N) and low lactic acid (16–86 g/kg DM) contents. Damage to herbage caused by the injection tines on taller swards (treatments I at 6 and 2 weeks before cutting) was evident and the injection process was impeded by tall grass. This contributed to herbage contamination with soil and slurry on these treatments and, consequently, to poor silage fermentation. Silages made with slurry application method T at all timings showed improved fermentation characteristics compared with the other treatments, particularly at North Wyke. The results indicate that silage quality is unlikely to be compromised by slurry applications made in early spring, during February, March or even in April, where these are at agronomically sensible rates. Such practice will enable better utilization of slurry nitrogen (N), reducing risks of nutrient losses via leaching or surface runoff. Furthermore, shallow injection and, particularly, trailing shoe slurry application techniques may be used to increase flexibility of slurry management by allowing more immediate spreading before cutting than with conventional surface broadcasting, without detriment to silage quality.

Two systems for integrated weed control in winter wheat based around the combination of herbicides with cultural control have been investigated and compared with conventional practice in experiments between 1993 and 2001. These systems were (a) an overall spray of a reduced herbicide dose followed by spring tine harrow weeding and (b) the combination of herbicide applied over the crop row with a novel vision guided inter-row hoe. The latter required wheat to be established with a wider (22 cm) inter-row spacing than standard (12·5 cm). Experiments over 10 sites/seasons indicated that this increased spacing could be achieved without yield loss. Trials to measure the accuracy of hoe blade lateral positioning using the vision guidance system indicated that error was normally distributed with standard deviation of 12 mm and a bias that could be set to within 1 cm. This performance could be maintained through the normal hoeing period and the crop row location and tracking techniques were robust to moderate weed infestation. In the absence of weeds neither overall harrowing nor inter-row hoeing affected winter wheat yield, 1000-seed weight or specific weight in 12·5 or 22 cm rows. When combined with inter-row hoeing, manually targeted banded applications of fluazolate, pendimethalin or isoproturon reduced grass weed levels and increased yields over untreated controls, though better results were obtained using overall herbicides. However, improvements would be possible with more accurately targeted herbicide applications and more effective inter-row grass weed control. The implications and costs of using such an integrated system are discussed and requirements for future developments identified.

Each crop variety has a genotype-specific ability to maintain performance over a wide range of environmental conditions. This ability is usually referred to as the sensitivity or adaptability of a variety. Such an ability is an important property, because farmers naturally want to use varieties which perform well in their own fields. Assessing sensitivity has, however, proved difficult, because of problems involved in defining and measuring the wide diversity of natural environments. These problems often lead to split statistical analyses of trial data or statistical models including explanatory variables with no biological interpretation. That causes ambiguity in statistical inference and prediction. The present study shows how the latest advances in statistical research can be applied to overcome some of these difficulties. A key point is to use the conditional expectation of the yield given the environment as a latent explanatory variable. In this way the predicted yields of different varieties can be estimated at any expected environmental yield level. Discussion is restricted to yield data but similar methods can be applied to other performance characters. The Finnish statutory variety trial data are used to illustrate the methods and the results.

Field experiments were conducted at the Crop Research Centre of Govind Ballabh Pant University of Agriculture and Technology, Pantnagar during 1996/97 and 1997/98. Each experiment comprised 10 crop sequences: (a) wheat–rice, (b) chickpea–rice, (c) lentil–rice, (d) pea–rice, (e) wheat–mungbean green manure–rice, (f) wheat–Sesbania green manure–rice, (g) wheat–fodder–rice, (h) chickpea–fodder–rice, (i) lentil–fodder–rice and (j) pea–fodder–rice, in a randomized block design with four replications. The crop sequences were compared in terms of economic rice equivalent yield (REY), protein production, apparent nutrient balances and effect on soil fertility status. Amongst crop sequences involving two crops each year (200% cropping intensity), chickpea–rice gave highest REY and protein production. Of the sequences involving three crops each year (300% cropping intensity), chickpea–fodder–rice and wheat–fodder–rice were superior to others. The P balances were positive for all sequences, whereas K balances were generally negative except for sequences involving green manure legumes. Green manuring with Sesbania or mungbean helped restore soil fertility, indicating the advantage of green manure for higher productivity and sustainability of rice–wheat system. Chickpea–rice and chickpea–fodder–rice appeared promising alternatives to rice–wheat crop sequence.

Near-infrared reflectance spectroscopy was used to assess the mineral composition of both alfalfa (Medicago sativa L.) and white clover (Trifolium repens L.). Alfalfa (n=230) and white clover (n=97) plant samples from different locations in Uruguay representing a wide range of soil types were analysed. The samples were scanned for reflectance in a NIRSystems 6500 monochromator (NIRSystems, Silver Spring, MD, USA). Predictive equations were developed using modified partial least squares (MPLS) with cross validation to avoid overfitting. The coefficients of determination in calibration (R_{\rm cal}^{2}) and the standard errors in cross validation (SECV) were 0·93 (SECV: 1·6), 0·95 (SECV: 1·3), 0·93 (SECV: 1·9), 0·88 (SECV: 2·7), 0·82 (SECV: 0·3) and 0·75 (SECV: 4·7) for alfalfa and 0·98 (SECV: 0·8), 0·52 (SECV: 0·8), 0·97 (SECV: 2·7), 0·83 (SECV: 3·1), 0·82 (SECV: 1·9) and 0·45 (SECV: 2·6) for white clover, for N, Ca, K, P, Mg and S in g/kg on a dry weight respectively. Calcium, nitrogen and potassium were well predicted by NIRS in both alfalfa and white clover samples.

Tocopherols are the most important compounds having antioxidant activity in sunflower seeds. The objective of the present research was to study the genetic and environmental variation for tocopherol content and composition in sunflower. Thirty-six sunflower hybrids were grown at 13 locations across all major areas of sunflower cultivation in southern Spain. Seed yield, 100 seed weight, oil content and tocopherol content and composition were determined. Tocopherol content ranged from 314·5 to 1024·5 mg/kg seed and from 562·8 to 1872·8 mg/kg oil. The tocopherol fraction was largely composed of alpha-tocopherol, which accounted for 88·4% to 96·3% of the total tocopherols. Both genotypic and environmental effects were significant for tocopherol content and composition. For alpha-, beta- and total tocopherol content, the effect of the genotype was larger than that of the environment, whereas the latter had a greater effect on gamma-tocopherol content. Genotype×location interaction was significant for alpha-, gamma- and total tocopherol content. Tocopherol content was not correlated with seed oil or seed yield, indicating the possibility of selecting for this trait without affecting the performance of the genotypes.

In order to quantify the radiation hazard to humans through food, both migration and distribution of 95Zr in Chinese cabbage/soil system were examined by using the radioisotope tracer technique. When 95Zr was administered with simulated irrigation or simulated rainfall, 95Zr was detected in every part of Chinese cabbage, which indicated that 95Zr could be translocated to above-ground parts. Although concentrations of 95Zr in different parts of Chinese cabbage were different in the two treatments used in the present study, the patterns of 95Zr distribution in different parts of the plant were similar. Concentration of 95Zr in each part of Chinese cabbage followed the order of root>leaf>lower part of petiole>upper part of petiole>bud in the case of simulated irrigation. Moreover, the 95Zr could be accumulated in leaves after being taken up by roots. In the simulated irrigation treatment, 95Zr concentrations were 1·7 and 2·9 times higher in the leaf than in the petiole and bud, respectively. In the case of simulated rainfall, a portion of applied 95Zr precipitated on the above-ground parts of Chinese cabbage, which led to a higher concentration here than in the case of simulated irrigation. The results of the present study clearly indicate that there is a distinct possibility that foodstuffs produced in the 95Zr-contaminated area are radioactively contaminated. More than 90% of total 95Zr in soil was retained in the upper layer (0–8 cm), which indicated 95Zr could not easily move downwards because of strong adsorption to soil.

Nutrient intake, digestibility and live-weight changes were compared for groups of grazing cattle on two Swiss Alpine pastures in different regions (R1 and R2; both >1500 m above sea level) during 2 years (1997 and 1998). The R1 site was an improved pasture, while R2 was an unimproved pasture of poor nutritional quality. Replicated over 2 years, R1 groups comprised four Scottish Highland suckler cows together with their calves and four Brown Swiss dairy cows (17·8 kg/day milk) kept at high stocking rates (approx. 7 cows/ha) in short rotations (intensive management system). R2 groups comprised four Highland cows with calves managed at low density (approx. 0·4 cows/ha) and set-stocked (extensive management system). Grazing seasons lasted 77 days at R1 and 127 days at R2. Intake, digestibility and faecal excretion were estimated by the slow-release alkane indicator method. Average dry matter intakes in kg/day and g/kg W0·75/day (in parentheses) were 17·4 (151) for dairy cows at R1 and, significantly lower, 12·7 (133) and 11·1 (111) for beef cows at R1 and R2, respectively. Herbage dry-matter intake of calves was 1·2 kg/day at both locations. Calf weight gains measured over 77 days (0·69 kg/day) were similar at the two sites and thereafter declined only slightly at R2. The N content of the herbage selected was similar in the two regions, but in other respects the herbage at R2 was of significantly poorer nutritive quality as indicated by the lower digestibility of organic matter and neutral detergent fibre at R2 compared with R1. Through feed selection, nutrient intake by beef cows was sufficient to gain weight. In contrast, dairy cows at R1 lost on average more than 50 kg of weight. Calculations were made and discussed regarding N utilization and urinary N loss, and measured faecal N and mineral excretion to allow a quantitative assessment of nutrient returns to the sward. We conclude that Highland beef cattle make poorer use of improved Alpine pasture than dairy cows though they utilize pastures of poor nutritive quality under extensive management without loss of productivity.

In Volume 136, 407–426, you published a paper entitled ‘Responses of potato (Solanum tuberosum) to potassium fertilizers’ by M. F. Allison, J. H. Fowler and E. J. Allen. We consider that the authors' conclusions were not justified and they have mis-interpreted and criticized earlier published work. One of their criticisms is levelled at the use of exchangeable potassium (Kex – rapidly plant-available K) to categorize soils on the basis of the likely response of crops to an application of potassium (K) fertilizer. While Kex is not perfect, it is the best rapid method currently available (Johnston & Goulding 1990). To support their contention about Kex, the authors quote in Table 15 data from Rothamsted experiments done in the late 1950s and early 1960s. They state that despite the large amounts of K applied in fertilizers and manures the effect on Kex was relatively small. This comment fails to recognize that it is the K balance (K applied minus K removed) that must be related to Kex, not the K applied, and the inevitable transfer of part of the K balance from Kex to fixed K (less readily available K). Warren & Johnston (1962) showed that on these soil types as much as 60% of the K balance is rapidly transferred to fixed K.