Supplying a proportion of the N requirement of a wheat crop via the foliage would potentially reduce immobilization of fertilizer N in the soil organic matter and N losses by leaching or denitrification. A field experiment was carried out at Harper Adams in Shropshire to investigate the effect on crop yield of supplying the spring N application to winter wheat as different proportions of urea as a solution rather than as conventional soil-applied urea, and to determine the physiological basis of any yield differences. A solid ammonium nitrate treatment was included to represent alternative commercial practice to solid urea. Treatments were repeated on the same plots over the 3 years 1992, 1993 and 1994. Solid fertilizer was applied as a single dressing, whereas urea sprays were split over a number of days to reduce scorch. Nitrogen as urea sprays produced similar grain yields to N applied conventionally to the soil as solid ammonium nitrate or urea, but effects on above-ground dry matter production and harvest index depended on the time of application. Application of a large proportion of N as urea sprays, such that some of the N as urea solution was applied later in relation to crop development, produced less above-ground dry matter, but compensated by increasing harvest index. It is concluded that application of N as urea sprays could be successfully used to substitute for soil-applied N fertilizer at stem extension in winter wheat without loss of yield. Extra application costs, however, are likely to outweigh any efficiency or environmental benefits, except where applications of solid N are made to dry soils.

A field experiment was carried out at Harper Adams in Shropshire to investigate the effect of supplying the spring N application to winter wheat as different proportions of urea as a solution, rather than as conventional soil-applied solid urea, on N recovery in the above-ground crop, autumn soil mineral N and nitrate leaching over the subsequent winter. A solid ammonium nitrate treatment was also included to represent alternative commercial practice to solid urea. Treatments were repeated on the same plots over the 3 years 1992, 1993 and 1994. N recovery was measured in all 3 years by difference in N uptake between fertilized and unfertilized plots, and in 1993 for selected treatments, N was applied as 15N-labelled fertilizer to determine direct uptake of fertilizer N in the crop and soil. Both urea sprays and solid soil N applications were labelled with 15N. Urea sprays were split over several days to reduce scorch, whereas solid fertilizer was applied as a single dressing. For some urea spray treatments, apparent N recovery in the above-ground crop in 1992 and 1994 was less compared with soil-applied N treatments. These urea spray treatments were applied in the morning rather than the evening, and gaseous losses, most likely by volatilization, are suggested. In 1992 application of a large proportion of N as urea sprays, such that application of some N as urea solution was delayed to around GS 37, was associated with an increase in physiological N use efficiency. In 1993, there was no difference in direct or apparent recovery of fertilizer N in the crop or soil for N applied as ammonium nitrate, solid urea or as urea sprays. Mean nitrate concentration in the drainage water at 1 m was elevated for all N treatments in all years, but only in 1992 did nitrate concentration and leaching loss decrease with increasing proportion of N applied as urea sprays. It may therefore be possible to reduce gaseous losses by application of urea sprays under cool conditions in the evening and exploit the increased physiological N use efficiency for urea sprays applied later, such that total fertilizer N applied and N losses are reduced.

This study compared phosphorus (P) speciation and the relationship between bicarbonate extractable (Olsen) P and 0.01 M CaCl2 extractable P (a measure of potentially mobile P) in soils from plots of the Park Grass experiment started in 1856 at IACR-Rothamsted, UK and with and without nitrogen as (NH4)2SO4 and with and without calcium carbonate (CaCO3, lime). A point, termed the change point, was noted in Olsen P, above which 0.01 M CaCl2-P increased at a greater rate per unit increase in Olsen P than below this point. Previous findings have shown a change point for soils with a pH>5.8 at 56 mg Olsen P/kg and at 120 mg Olsen P/kg for soils below this pH. Soils given (NH4)2SO4 annually since 1856 and with lime periodically since 1903 mostly had a pH between 3.7 to 5.7, some of these (NH4)2SO4 treated soils were limed to pH 6.5 and above from 1965. Irrespective of their pH in 1991/92 all the soils had a similar change point (120 mg Olsen P/kg) to that found for other soils with pH<5.8 (112 mg Olsen P/kg). In a laboratory study lasting 30 days, the addition of CaCO3 to acid soils from the field experiment that had received (NH4)2SO4 had a similar change point to soils with pH<5.8 irrespective of pH, suggesting soil P chemistry was controlled by the long period of soil acidity and this was not reversed by a short period at a higher pH. The effect of pH was attributed to the creation of P sorptive surfaces on aluminium precipitates compared with less acidic soils (pH>5.8) where there was less exchangeable Al to be precipitated. This was confirmed with solid-state 31P nuclear magnetic resonance, which indicated that for soils of similar total P concentration and pH, there was twice as much amorphous Al-P in soils given (NH4)2SO4 compared with those without. Changes in pH as a result of applications of (NH4)2SO4 or lime can greatly change the concentration of potentially mobile P due to the effects on Al solubility. Although there was less potentially mobile P in soils with pH<5.8 than in soils above this pH, it is usually advised in temperate regions to maintain soils about pH 6.5 for arable crops.

Relationships between leaf expansion and MeOH-soluble (cytosol) and cell-wall fractions, and their sugar composition prior to silking in flint corn lines were studied. A greater husk leaf area of one genotype, X-15 is mainly due to prolonged and higher rate of expansion. Prior to rapid expansion of husk leaf area, neutral sugars in the cytosol fraction accounted for most of the non-starch carbohydrates (56–62%), while hemicellulose and cellulose fractions accounted for less than 20%. In mature leaf parts, however, sugars in the cytosol fraction decreased but those in hemicellulose and cellulose fractions increased by 30% and 42%, respectively. The predominant sugar in the cytosol fraction was glucose (Glc), while in the hemicellulose fraction xylose (Xyl) and arabinose (Ara) dominated. During rapid expansion of husk leaves, 13C was incorporated at a higher rate into hemicellulose than cellulose, and this process was more active in X-15 than in other genotypes. During an identical period, 13C atom % excess in Xyl increased markedly in the hemicellulose fraction, however it remained low in the cytosol one. The current results suggest that synthesis of Xyl and xylan plays an important role in renewal of hemicellulose, which may be required for expansion.

No genetic estimates for resistance to Mal de Río Cuarto (MRC) disease in Zea mays (L.) are currently available in the literature. Therefore, the objectives of this investigation were (i) to estimate the variance and heritability of partial resistance to MRC disease and of other agronomic traits from maize families and (ii) to examine associations among MRC disease severity values across different environments and between MRC and other agronomic traits. These estimations, obtained in an endemic area, could contribute to the design of efficient enhancement programmes and evaluation activity for the improvement of MRC resistance. The research was conducted by testing 227 F3 derived-lines from a cross between a susceptible dent line, Mo17, and a partially resistant flint line, BLS14, for MRC disease at two Río Cuarto locations in each of 2 years. The resistance of the lines, measured with a disease severity index (DSI), was normally distributed across environments. Genotypic variances were highly significant on all scoring environments. Estimates of genotype–environment interaction were also significant, suggesting that certain genotypes have little stability over different environments. For disease severity index all estimates demonstrated moderate heritabilities ranging from 0.44 to 0.56 and were similar when based on individual environments or across environment. Confidence interval widths ranged from 34.88 to 50.30% as large as the heritability point estimate. The correlations between environments were small enough to indicate that families did not rank similarly in individual environments for MRC resistance. Disease severity index correlated significantly (P<0.01) with plant height, leaf surface, leaf border, leaf length and tassel type. Heritability estimates for plant height and tassel type were 0.48 and 0.38 respectively and for the various leaf traits heritability values were very low. On the basis of the substantial genotype–environment interaction and the little association between DSI values in the different environments, selection for an increased resistance to MRC disease would require evaluation of germplasm across multiple years and locations. Tassel type would be a useful predictor of DSI and can be used effectively to improve screening procedures.

Continuous honeycomb selection and testing in the absence of competition in a single environment, resulted in the isolation of recombinant inbreds in tomato that outperformed the hybrid only in that particular environment. Alternating selection and testing in two environments (open field v. glasshouse) reduced selection efficiency, by preventing exploitation of the whole constellation of genes contributing to heterosis. Selection in the F2 generation was most critical, as evidenced by the appearance of recombinant lines outperforming the hybrid as early as in the F3 generation. Exploitable genetic variation existed in advanced generations and even after the point of achieving theoretical homozygosity (F7 generation). In the future, and in order to fully exploit the unique possibilities offered by the honeycomb methodology (control of soil heterogeneity, high selection pressures, crop yield components), selection for reduced GE interaction should be practiced simultaneously over the target environments of adaptation.

The efficiency of the triple test cross (TTC) and the six-population biometrical analyses was compared in terms of assessing and quantifying the components of genetic variance for two faba bean crosses: Triple White×Giza 843 and NA112×Giza 429. Several traits were studied including days to first flower, plant height, branches/plant, pods/plant, seeds/pod, 100-seed weight and seed yield/plant. The results supported the triple test cross biometrical approach as it uses first degree statistics and can be applied to any population irrespective of its genetic architecture. Absence of a scalar relationship between triple test cross families (orthogonality) ensures independence between means and variance with no restrictive assumptions. Both methods provided evidence for epistasis, and both additive and dominance genetic components in the genetic control of the studied traits.

Cluster analysis has been commonly used in genotype-by-environment (G×E) analyses, but current methods are inadequate when the data matrix is incomplete. This paper proposes a new method, referred to as two-stage clustering, which relies on a partitioning of squared Euclidean distance into two independent components, the G×E interaction and the genotype main effect. These components are used in the first and second stages of clustering respectively. Two-stage clustering forms the basis for imputing missing values in the G×E matrix, so that a more complete data array is available for other G×E analyses. Imputation for a given genotype uses information from genotypes with similar interaction profiles. This imputation method is shown to improve on an existing nearest cluster method that confounds the G×E interaction and the genotype main effect.

Conception and lambing rate, and litter size were studied on data from a flock of Horro sheep. The CATMOD and GLM procedures of SAS were used for the analysis of these traits. A sire, direct additive genetic and a repeatability animal model were employed to obtain estimates of heritability and repeatability for litter size. The results obtained showed that year of mating, age and weight of ewes at mating and number of previous parities had significantly (P<0.01) affected the rate of conception and lambing while weight of rams at mating has shown no significant effect (P>0.05). An increase in both conception and lambing rates was observed with the increase in weight of ewes up to about 36 kg and declined thereafter. Ewes which previously had no or one parity had lower conception and lambing rates compared with ewes in later parities. However, a decline in both conception and lambing rates was also observed in old ewes. Year of lambing, parity and weight of ewes at mating had a highly significant (P<0.01) effect on litter size. The overall mean litter size in the flock was 1.34 with annual means ranging from 1.18 to 1.55. Litter size increased with parity from 1.26 in primiparous ewes to 1.44 for ewes of parities five and above. With respect to weight of ewes at mating, litter size increased by 2.5% for each kg increase in weight at mating. The estimates of direct heritability (h2) for litter size were 0.17, 0.11 and 0.06 under the sire, direct animal and repeatability models. Repeatability was estimated to be 0.12. Since heritability and repeatability estimates of litter size are low, genetic improvement by selection may not bring sizeable impact in increasing litter size. Therefore flock management for optimal age structure and optimal weight of ewes at mating should receive due consideration to improve rates of conception, lambing and litter size in Horro sheep.

A study of the physiological responses and energy expenditure of goats was carried out from June 1999 to May 2000 by conducting two experiments: one on bucks maintained on stall feeding in autumn 1999 (Expt 1) followed by year-round grazing on native ranges over three seasons: monsoon, winter and summer (Expt 2). Physiological responses and energy expenditure (EE) measurements of housed and grazing goats were recorded at 06.00 h and 14.00 h for 5 consecutive days in each season. Goats were fixed with a face mask and meteorological balloon for collection of expired air and measurement of EE. Respiration rate (RR) at 06.00 h was similar in all seasons (14 respiration/min) except in the monsoon, where a significantly (P<0.05) higher value (26 respiration/min) was recorded. At 14.00 h, RR was higher in monsoon and summer (81 and 91 respiration/min) than in winter (52 respiration/min). Irrespective of the season, heart rate (HR) was higher at 14.00 h (86 beat/min) than at 06.00 h (64 beat/min). The rise of rectal temperature (RT) from morning (06.00 h) to peak daily temperature (14.00 h) was 0.9 °C in housed goats in autumn and 1.0, 2.1 and 2.0 °C in grazing goats during monsoon, winter and summer, respectively. The mean value was 1.7 °C. Skin temperature (ST) was lowest in winter (30.1 °C) and highest at 14.00 h in summer (40.3 °C). Energy expenditure of goats at 06.00 h was 32.7 W in winter and significantly (P<0.05) increased to 52.0 W in summer and 107.8 W in monsoon. At 14.00 h, EE was 140.2 W in winter and increased to 389.0 W and 391.3 W respectively in monsoon and summer. It is concluded that monsoon and summer are both stressful seasons in semi-arid regions. Animals should be protected from direct solar radiation during the hottest hours of the day to ameliorate the effect of heat stress.

The influence of weather conditions on the average yield of honey in one apiary over a period of 30 years in the UK has been studied. In highly significant multiple regression equations weather variables accounted for over 80% of the variation in annual average honey yield. Weather in March, May and June had the major effects. Implications and applications of the equations are considered.