A method for quantifying treatment comparisons for a situation in which there are too many zeros in the dataset for a conventional analysis of variance to be valid is presented. The method assumes the existence of a latent variable such that zero observations correspond to values below a threshold, and non-zero observations are transformed to fit the part of the distribution above the threshold. The method is known as Tobit analysis in econometrics. Parameters are estimated by maximum likelihood and standard errors obtained, all using standard numerical routines. Use of the method is demonstrated by analysis of a dataset of crop lodging, and it is anticipated to be widely applicable to other types of data for which high numbers of zeros prevent conventional analysis.

Greater white clover (Trifolium repens L.) competitive ability can increase the forage quantity and quality of clover-grass mixed stand (MS) cropping. The present work assessed the relationship of clover competitive ability with morphophysiological traits, and the efficiency of direct and indirect selection procedures for increasing clover dry matter (DM) yield in MS. Some 165 large-leaved clover genotypes representative of Italian Ladino germplasm and 13 clover genotypes from an elite small-leaved population were clonally evaluated for one year in pure stand (PS) and in MS environment with Italian ryegrass (Lolium multiflorum Lam.) and tall fescue (Festuca arundinacea Schreb.) that reproduced the level of interspecific interference met by the clover over a multi-year crop cycle. Results for all genotypes and their subsets indicated that the level of leaf size variation among tested genotypes can affect the results. Wider variation decreased the relative importance of clover genotype×evaluation environment interaction, because competitive ability was mainly correlated with traits (longer petiole; larger leaflet) contributing to scale foraging in MS and yielding ability in PS. Competitive ability tended to be more closely associated with other traits (high stolon density; plasticity of petiole elongation) contributing to foraging ability, i.e. the ability to make fine-scale exploitation of light and nutrients in MS, within germplasm of similar leaf size. Leaf size variation also affected the relative efficiency of selection procedures estimated from expected responses to clonal selection. Results for all entries indicated direct selection in MS as 23% more efficient than selection in PS based on a selection index including three traits associated with competitive ability (petiole length; stolon density; leaflet size) which, in turn, was predicted to be 16% more effective than selection in PS based on DM yield. The advantage in relative efficiency of direct selection was almost doubled when considering only large-leaved germplasm. In a second experiment, evaluating 16 clover half-sib progenies of elite large-leaved parents for 2 years in PS and in MS with Italian ryegrass, tall fescue and cocksfoot (Dactylis glomerata L.), direct selection was estimated to be over three-fold and 68% more effective than indirect selection in PS based on DM yield and the selection index, respectively, based on expected responses to genotypic selection. The selection index may improve the efficiency of preliminary, PS-based clonal selection. Further evaluation of elite genotypes and/or their polycross progenies in MS is recommended for final selection.

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.

Breeding of temperate forage grasses is aimed at improving the economic and environmental sustainability of production from cattle and sheep. The primary objective is to ensure that forage can be the main source of feed for ruminants. This requires consistent production of herbage with a high feeding value, usually under nitrogen-limiting conditions. The most important traits affecting the feeding value of herbage are in vitro dry matter digestibility (DMD), the ratios of crude protein, water-soluble carbohydrate and fibre, and the concentration of alkaloid toxins. Improvements in these primary quality traits must be combined with good plant persistency, adequate tolerance to a range of environmental stresses, adequate resistance to a large number of different pathogens and invertebrate pests, and adequate seed yield. Forage grasses also have considerable potential to produce material for refining, to provide protein extracts for feeding to monogastric animals and carbohydrate for fermentation into fuel or into feedstocks for other industries.

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.

The water-insoluble phosphorus (P) component (‘residue source’) was separated from four commercial triple superphosphate (TSP) products and its agronomic effectiveness evaluated. Two of the TSP products were sourced from the USA and two from the UK. Effectiveness was measured using a pot trial technique with ryegrass as the test crop. The residue sources were evaluated on 13 soils varying in key properties: readily plant-available P, texture, pH and organic matter content. Four of the soils were from Germany, one from Spain, five from the UK and three from France. Grass dry-matter yield and P offtake were measured at every cut on every soil. For both of these variables, significant responses to applied P were obtained on all soils. Mono-calcium phosphate (MCP) was used as the comparative P source and effectiveness of the residue sources was estimated relative to that of MCP. Using dry-matter data, the residue sources were 44–87% as effective as MCP; P offtake data provided corresponding estimates of 35–79%. Both methods of estimation indicated the same ranking of residue sources in terms of relative effectiveness, those derived from USA products being more effective than those derived from UK products. The ranking was the same for all soils. The effectiveness of the residue sources relative to that of MCP appeared little affected by measured soil properties: texture, pH, available P or organic carbon content. The results indicate there is little difference in agronomic effectiveness of TSP products with water solubility greater than 85%.

Field experiments were conducted over 3 years to assess the effect of a triazole fungicide programme, and additions of strobilurin fungicides to it, on nitrogen uptake, accumulation and partitioning in a range of winter wheat cultivars. Commensurate with delayed senescence, fungicide programmes, particularly when including strobilurins, improved grain yield through improvements in both crop biomass and harvest index, although the relationship with green area duration of the flag leaf (GFLAD) depended on year and in some cases, cultivar. In all years fungicide treatments significantly increased the amount of nitrogen in the above-ground biomass, the amount of nitrogen in the grain and the nitrogen harvest index. All these effects could be linearly related to the fungicide effect on GFLAD. These relationships occasionally interacted with cultivar but there was no evidence that fungicide mode of action affected the relationship between GFLAD and yield of nitrogen in the grain. Fungicide treatments significantly reduced the amount of soil mineral N at harvest and when severe disease had been controlled, the net remobilization of N from the vegetation to the grain after anthesis. Fungicide maintained the filling of grain with both dry matter and nitrogen. The proportionate accumulation of nitrogen in the grain was later than that of dry matter and this difference was greater when fungicide had been applied. Effects of fungicide on grain protein concentration and its relationship with GFLAD were inconsistent over year and cultivar. There were several instances where grain protein concentration was unaffected despite large (1·5 t/ha) increases in grain yield following fungicide use. Dilution of grain protein concentration following fungicide use, when it did occur, was small compared with what would be predicted by adoption of other yield increasing techniques such as the selection of high yielding cultivars (based on currently available cultivars) or by growing wheat in favourable climates.

Three experiments were carried out to investigate the dry matter production of nine white clover (Trifolium repens L.) varieties grown with the same variety of perennial ryegrass (Lolium perenne L.) and subjected to rotational grazing by sheep over a period of 10 years. The experiments differed only in the nitrogen fertilizer added: no nitrogen, 100 kg/ha per year and 200 kg/ha per year. Dry matter (DM) yields of white clover and perennial ryegrass components of the sward were recorded at approximately 6-week intervals during the growing season.

Without applied nitrogen, 10-year mean white clover annual DM yields ranged from 2·89–4·54 t/ha. Mean clover content for all varieties ranged from 31–50% for the first 9 years, declining to 20% in the 10th year. The most consistently high yielding variety, AberVantage, gave yields greater than 3·5 t/ha in every year. Similar results were observed for the variety Aran. The 10-year mean annual DM yield of the perennial ryegrass companion (variety Talbot) ranged from 4·41–5·57 t/ha depending on the white clover variety in the mixture. Variation in perennial ryegrass DM yield was of a similar range and pattern as for white clover.

In the experiment in which 100 kg N/ha per year was added, 10-year mean white clover annual DM yields ranged from 2·27–3·87 t/ha. The varieties AberVantage and Aran showed yields that fell below 3 t/ha per year in only 1 or 2 years, respectively. Mean clover content for all varieties ranged from 26–38% for the first 9 years, declining to 17·5% in the 10th year. There was no consecutive annual decline in white clover DM yields. The 10-year mean annual DM yields of the perennial ryegrass companion ranged from 6·03–7·57 t/ha.

With applied nitrogen fertilizer of 200 kg N/ha per year (Experiment 3), 10-year mean white clover annual DM yields ranged from 1·21–2·67 t/ha. Mean clover content ranged from 12–27% for the 10 years. AberVantage and Aran showed yields consistently above 2 t/ha. No general decline in white clover DM yields was observed although some varieties showed consecutive annual reductions in years 8, 9 and 10. The 10-year mean annual DM perennial ryegrass yields ranged from 7·27–8·68 t/ha.

The results show that, under rotational grazing by sheep, white clover can give reliably high yields over a 10-year period. With moderate to high applications of nitrogen fertilizer white clover yields were lower than without nitrogen but they were consistent and sufficient to make a considerable impact on forage quality. There was no evidence for a general decline in clover content until the 10th year of the experiment and no cyclical pattern of annual variation in white clover yield was observed. The implications of these results for the role of white clover in UK agriculture are discussed.

Influences of cultivar and environment, i.e. cultivation year and fertilizer rate, on amount of protein groups and amount and size distribution of mono- and polymeric proteins, were investigated in four sets of wheat (Triticum aestivum L.). The cultivars were chosen in order to obtain a high range of variation in protein concentration and gluten strength. Environmental influences on protein concentration and gluten strength were investigated, as well as relations between variation in protein concentration and gluten strength and variation in protein groups and amount and size distribution of mono- and polymeric proteins.

The results showed that cultivar and environmental influences giving rise to variation in protein concentration also gave rise to variation in most of the investigated protein components. Protein concentration was significantly positively correlated to the total amounts of glutenins and gliadins and amounts of most mono- and polymeric proteins. However, the correlation with the amount of gliadins and sodium dodecyl sulphate (SDS)-soluble mono- and polymeric proteins were often higher than the correlation to the glutenins and the SDS-insoluble mono- and polymeric proteins. Cultivar influences giving rise to variation in gluten strength were found to influence the relation between SDS-soluble and -insoluble polymeric proteins, leading to a significant positive correlation between the gluten strength and the percentage of total unextractable polymeric protein (TUPP) in the total polymeric protein and large unextractable polymeric protein (LUPP) in the total large polymeric protein. Environmental variation in gluten strength was found to be significantly positively correlated to SDS-insoluble proteins and negatively correlated to SDS-soluble proteins. This also led to a significant positive correlation with the percentage of LUPP and/or TUPP.

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.

A field experiment was initiated at the Central Soil Salinity Research Institute, Karnal, India between 1994 and 1998 involving use of NPK fertilizers alone and in combination with green manure (Sesbania bispinosa) or farmyard manure (FYM) in a rice–wheat cropping sequence. An attempt was made to evaluate the effect of the substitution of inorganic fertilizers with organic manures on yields of grain and nutrients, economy and soil fertility during 1997–98 and 1998–99. Application of NPK and its combination with green manuring and FYM increased the rice yield significantly. Applying inorganic fertilizers resulted in similar nitrogen use efficiency (NUE) in rice as compared with organic manures along with inorganic fertilizers, but NUE was increased in wheat by the residual effect of organic manures along with inorganic fertilizers. The responses of rice to the application of the full recommended amount of inorganic fertilizers (120 kg N, 26 kg P and 42 kg K/ha) and its combined use with green manure or 10 t/ha FYM and 150% recommended amount (180 kg N, 39 kg P and 63 kg K/ha) were 2·98, 4·27, 4·10 and 3·54 t/ha, respectively. Further, with green manure or 10 t FYM/ha in combination with 50% recommended amount, the mean rice yield (5·8 t/ha) was similar to the yield (5·5 t/ha) obtained from the 100% NPK recommended treatment. Application of green manure or 10 t FYM/ha thus saved 60 kg N and 13 kg P/ha inorganic fertilizer in rice. The residual effect of green manure or FYM plus the full recommended fertilizer amount (120 kg N, 26 kg P and 42 kg K/ha) was significantly greater than that of the full recommended amount of fertilizer. Addition of green manure or FYM resulted in higher removal in crops, increase of soil N, P, K and organic C, and reduced soil pH. Application of the full recommended amount of fertilizer only maintained the N, P and K status in soil. Higher profit was obtained when inorganic fertilizer was combined with organic manures.

The effects of additions of four organic amendments to an Oxisol on soil pH, exchangeable and soil solution Al, extractable P and maize growth were compared with those of lime and P in a glasshouse experiment. The organic amendments were: grass residues, household compost, filter cake (a waste product of sugar mills) and layer poultry manure and they were added at a rate equivalent to 20 t/ha with or without the addition of either lime (equivalent to 0, 5 or 10 t/ha) or P (equivalent to 0, 10 or 50 kg/ha). Lime applications to the control (unamended) treatment resulted in a marked reduction in exchangeable Al, and concentrations of total (AlT) and monomeric (Almono) Al in soil solution and the proportion of AlT present as Almono. In unlimed soils, amendment additions increased pH and decreased exchangeable Al in the order: poultry manure>filter cake>household compost>grass residues>control. The addition of all the organic amendments increased soil pH and reduced AlT and Almono to low concentrations regardless of whether lime was applied or not. As a result, there was no yield response to applied lime in any of the amended treatments. Olsen-extractable P concentrations in soils followed the order: poultry manure>filter cake>household compost>grass residues>control and there was no yield response to applied P for the poultry manure and filter cake treatments. The decrease in adsorption of subsequently added P induced by additions of organic amendments followed the order: poultry manure>household compost>filter cake>grass residues. It was concluded that the addition of organic amendments to acid soils is a practicable way of liming them and reducing the potential for Al toxicity and it can also reduce fertilizer P requirements.

A field experiment lasting 9 years was initiated in 1987 to study the effect of integrated nutrient management involving incorporation of wheat straw (WS) or farmyard manure (FYM) alone or in combination with inorganic fertilizer on a fine loamy mixed hyperthermic udic Ustochrept. Soil physical properties and the productivity of a rice–lentil cropping sequence were examined in a dry land farming system.

At the end of the ninth cropping season, addition of organic materials had increased organic carbon, aggregate stability, moisture retention capacity and infiltration rate of the surface soil while reducing the bulk density. Application of inorganic fertilizer alone decreased the stability of macro aggregates and moisture retention capacity but increased the bulk density values. Treatment effects on moisture retentivity were more pronounced in the higher (0·3–1·5 MPa) suction range. During the first six experimental years, sole application of inorganic fertilizers produced 10–17% higher grain yield of rice, compared to sole application of organic sources or combined organic and inorganic sources. Annual applications of wheat straw and farmyard manure gave higher grain yields of rice from the seventh year onwards. Grain yields of lentil were higher with organic sources either alone or combined with inorganic nutrients.

Associations of characters were studied in linseed using data of 60 accessions evaluated in a randomized complete block design with three replications under glasshouse and field conditions during 2000 and 2001. The main objectives were to determine the magnitude of correlations between yield and its components under variable environments, and identify stable and major yield attributes that could support further improvements of linseed productivity. The degree of character association varied considerably across years and locations, due mainly to climatic factors (e.g. temperature, moisture levels, etc.) and disease incidences. However, seed yield per plot was significantly (P<0·01) and positively associated with seed yield per plant, 1000 seed weight and bolls per plant across environments. These three yield attributes were also strongly and positively correlated with plant height, branches per plant, days to flowering and maturity. Oil yield was significantly and positively associated with polyunsaturated (linoleic and linolenic) fatty acids, whereas it was negatively correlated with saturated (palmitic and stearic) fatty acids. Oil yield also had a weak positive relation with monounsaturated oleic acid. The quality of linseed oil, which is dependent on the levels of these fatty acids, can be influenced by the correlated responses of these variables in reaction to different environmental factors. Thus, knowledge on the causes and effects of these correlated responses are necessary to undertake sound and effective selection programmes.

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.

Field experiments were undertaken during 1998–2000 at Askov Experimental Station and Lundgård Experimental Site, Denmark, to investigate the fertilizer value of anaerobic and aerobic sewage sludges (SS1 and SS2), composted household waste (Compost) and farmyard manure (FYM). The organic residues were applied at two rates with or without supplementary mineral nitrogen (N). The effects of residue application on spring cereal dry matter (DM) yield and N-offtake were related to reference treatments with increasing rates of calcium ammonium nitrate (CAN). DM yields at the high application rates of aerobic sewage sludge (198 kg N/ha/year) and farmyard manure (300 kg N/ha/year) were comparable to the reference treatments receiving 90 kg mineral-N/ha/year. The comparable high application rate of anaerobic sewage sludge was 138 kg N/ha/year only and the DM yield was less. In contrast, the yield effect of Compost was very poor; even the high application rate of 321 kg N/ha/year yielded less than the low application rates of aerobic sewage sludge and farmyard manure, 66 and 100 kg N/ha/year, respectively.

The nitrogen fertilizer replacement value (NFRV) of the organic residues was estimated for all four combinations of the response variables DM-yield and N-offtake and the independent variables of total-N and ammonium-N applied. NFRV was in the range 49–68% for the sewage sludges and FYM based on the DM-yield[ratio ]total-N relation, and slightly smaller for the N-offtake[ratio ]total-N relation, 29–53%. The highest values were obtained for the aerobic sewage sludge, having a potential manurial value comparable to FYM. In contrast, the NFRV of Compost was low, about 10%.

The concentration of ammonium-N in organic residues and manures is often used for predicting the fertilizer value. Ammonium-N based NFRV of 160–210% for the sewage sludges indicate that water extractable ammonium-N underestimates the NFRV, probably due to the content of easily degradable organic matter in digested sewage sludge. The estimated NFRV for Compost was above 100% but connected with high uncertainty. In contrast, the ammonium-N based NFRV for FYM was only 70–87%, probably due to ammonia volatilization caused by incomplete incorporation of large quantities and the high ammonium-N[ratio ]total-N ratio in this residue.

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.

The present study investigated how increasing silica content modifies the chemical and morphological characteristics and microbial degradation of rice straw. Two rice straws grown on culture media with different silica contents were collected and analysed for chemical and morphological composition and ultrastructure. Silica content (g/kg DM) of the two straws was high (98·0, straw H) and low (0·0, not detected, straw L). The ground (2 mm) straws were incubated in the rumen of three ruminally cannulated cows for 4, 8, 16, 24, 48 and 96 h for in sacco degradability measurements. The main fractions (stem, leaf sheath and blade) of each straw were incubated for 24 h. Kinetics were fitted to an exponential model with lag time. Scanning electron microscopy was used to examine intact fragments of stems and fragments incubated for 6, 24, 72 and 96 h in cow rumen. X-ray analysis was carried out on non-incubated fragments for silica mapping. A reduction of stem content from 320 to 270 g/kg straw, and an increase in leaf sheath content from 360 to 400 g/kg straw, were found for an increase in silica content from 0 to 100 g/kg DM. Chemical composition differed little between straws H and L, except for ash and silica contents. The ash originated mainly from the leaves and increased with silica content from 70 to 140 g/kg DM. The DM degradability was lower in the H than in the L straw. This reduction came mainly from a lower non-NDF component degradation in straw H. Stems were more degraded than leaf fractions for DM, NDF and non-NDF components; their degradation was depressed in the H straw. X-ray analysis showed that the deposition of silica on the stem epidermis was different, with a thick layer on H stems and no deposition on L stem surfaces. As a consequence, microbial colonization and degradation were faster on the epidermis of straw L. Epidermal silica did not hinder degradation from the internal cavity.

A significant genotype–environment interaction can limit gains in selecting superior genotypes since the best genotype in one locality may not be the best one in another locality. The efficiency of indirect selection is related to the heritability of the trait and to the genetic correlation between localities. Since a major objective of Eragrostis curvula (lovegrass) breeding programmes in Argentina is to select superior genotypes from new cultivar introductions, research on the relative effectiveness of direct and indirect selection is necessary in order to identify localities under which the efficiency of indirect selection could be maximized. To do this, experiments using a set of 18 hybrids were carried out in three localities from the semi-arid region of Argentina. Aerial biomass yield, leaf length, crown diameter, panicle number and panicle length were measured and an analysis of variance and covariance were performed. The high genetic correlation obtained suggests that the genetic mechanisms involved in the expression of these traits would be the same, or at least very similar, in Río Cuarto, Villa Mercedes and Bahía Blanca environments where the hybrids showed a stable performance. In general, the heritability obtained was higher in Villa Mercedes and Bahía Blanca than in Río Cuarto. For a given selection intensity the expected correlated response in Villa Mercedes and Bahía Blanca to indirect selection was compared with the expected gain with direct response to selection in Río Cuarto. For dry matter yield, indirect selection in Bahía Blanca did not differ from selection done in Río Cuarto (−3%). However, for performance in Villa Mercedes indirect selection was shown to be less efficient (−29%). For the other traits considered, indirect selection was variable and less efficient, ranging from −18 to −34%. The estimated decrease in efficiency of selection for all the traits considered in the locality of Río Cuarto was higher than in the other localities, suggesting that this place was not a good choice for carrying out indirect selection. Conversely, genetic progress would be faster if selection was carried out in Villa Mercedes, because the evaluations provide higher and more accurate estimates of the heritabilities than in the other localities.

Multivariate cluster and canonical variate analyses were undertaken for 10 genotypes of linseed (Linum usitatissimum L.) that were tested in a four-times replicated randomized block design across 18 environments (six localities by 3 years) of Ethiopia. The main aims of this study were to determine the similarities and differences of the genotypes and their testing environments, and to compare applicability of the two statistical methods. Cluster analysis grouped the genotypes into five classes in accordance with their original sources. The six locations and 18 environments were stratified into four and seven clusters, respectively. Three sites (Bekoji, Kulumsa and Sinana) were separately stratified, while three other ones (Holetta, Asasa and Adet) showed closer similarity. Canonical variate analysis indicated that ‘D33C’ and ‘D24C’ were distinguished from the other genotypes by their high oil contents. ‘N10D’ and ‘Norlin’ had closer values and were thus preferred for their good seed yield and earliness. Days to flowering and maturity, oil contents and lodging per cent played major roles in discriminating the genotypes. Comparison of the two methods showed clearer differentiation by cluster analysis than canonical variate analysis. Canonical variate analysis also contributed information on how each variable discriminated the genotypes and their test environments. Thus, both methods complement each other in providing useful information for more efficient variety development programmes.