1. Biological trials have been carried out to determine the efficacy of petroleum ether as solvent for the extraction of pyrethrum flowers for analysis. 95% of the toxic material was extracted from flowers one year old after only 3 hr. percolation. An extraction period of 8 hr. with petroleum ether is suggested.

2. A method of preparing colourless extracts of pyrethrum and analytical data for such extracts are given. They are shown to be of value for the preparation of concentrates of the pyrethrins. The preparation of a colourless concentrate containing 93% of total pyrethrins, as determined by a modified Seil method, is described.

The fatty acid composition of the plasma free fatty acid and adipose tissue triacylglycerol fractions was determined in lean and fat selection lines of Texel-Oxford and Scottish Blackface sheep at the 6th year of divergent selection. The mean proportion of 18[ratio ]2n-6 in the triacylglycerol of subcutaneous backfat was 1·3-fold higher in the phenotypically fatter sheep in the fat lines than in the phenotypically leaner sheep in the lean lines. Regression analysis indicated a positive relationship between this fatty acid and backfat depth whereas the proportion of 18[ratio ]1n-9 in the tissue triacylglycerol was negatively related to fatness. The proportions of 18[ratio ]2n-6 and of other polyunsaturated fatty acids in the plasma free fatty acid fraction were much higher than in adipose triacylglycerol. For the Scottish Blackface sheep in the fed state, the mean proportion of 18[ratio ]2n-6 in plasma free fatty acid (measured on all sheep) was 1·4-fold greater in the fat line than in the lean line. Regression analysis indicated a positive relationship between the plasma content of this fatty acid and backfat thickness whereas the proportion of 18[ratio ]1n-9 in plasma free fatty acid showed a negative relationship with fatness. The relationship between the plasma proportion of 18[ratio ]2n-6 and fatness was not observed after 48 h of fasting; instead, the plasma proportion of 18[ratio ]0 was found to be positively related to fatness in the fasted state. In summary, this paper shows how plasma and adipose tissue fatty acid profiles differ, and it quantifies the effects of selection on the plasma profiles. Possible reasons for the difference in fatty acid profiles between adipose tissue and plasma are discussed in the paper. It is suggested that plasma 18[ratio ]2n-6 levels during the early post-weaning growth period should be investigated as indicators of future fatness.

A missing value technique for the analysis of data where repeated measurements are taken on each experimental unit is proposed. The method suggested, which is a natural multivariate analogue of the well-known technique for univariate analyses, fits those missing values which minimize the determinant of the sums of squares and products matrix and provides the necessary downward adjustment to the residual degrees of freedom. A simulation exercise provides evidence that the method is fairly reliable.

A study designed to investigate the effect of K nutrition on the yield, components of yield and on macro- and micronutrient concentration of maize showed no significant effect of K on yield in forest alfisols derived from basement complex rocks and in savannah alfisols derived from sandstones in the tropics. Potassium addition significantly decreased lodging, but had little influence on cob length, ear weight, shelling percentage or moisture content.

Ear-leaf N and K were significantly increased, while Ca and Mg were decreased by K application. All the micronutrient concentrations (Zn, Fe, Mn, Cu) were significantly increased by K application in the forest and savannah zones. Yield was positively correlated with ear-leaf N on both soils.

The objective of this research was to assess the adoption of circular agricultural practices as a tool to improve the recovery use efficiency of phosphorus (P) applied to tropical soils. Two Brazilian farms (1 and 2) that are under long-term no-till and cropped year-round with cover and/or cash crops were used in this study. Soybean, maize and common bean were grown during the summer season (October–February), followed by wheat, common bean and maize during the winter season (February–August). Brachiaria ruziziensis was intercropped with off-season maize. Farm 1 also grew sweet potatoes in rotation with grains. In the integrated crop–livestock system, the leftovers from the silos and crop residues were used to feed beef cattle, while the residues not used in the confinement were turned into compost and applied in the production fields. During the last 3 years, 80 (farm 1) and 71 (farm 2) kg/ha/year of P-fertilizer was applied to meet the demand of the different crops and 56% (farm 1) and 58% (farm 2) of P-fertilizer was exported through the crops and livestock. P-recovery represented more than 50% on both farms. Around 60% of the P consumed by animals was excreted in the form of faeces and urine and the animal manure was used to produce organic compost. Therefore, most of the P consumed by the livestock was returned back to the field to serve as organic fertilizer. This study showed that circular agricultural practices can enhance P-recovery.

Transfer was made of 2958 sheep ovarian oocytes, cultured in growth medium for 24–30 h, to the oviducts of 142 oestrous sheep; 132 were bred and ten remained unbred. Forty-two per cent of oocytes were recovered, mainly 4–24 h after transfer; tubal flushings were examined for sperm. Evidence of a sperm within the vitellus of follicular oocytes was found in nine recipients, the earliest at 6 h 50 min after transfer. Pronucleate eggs were most frequent 9–14 h after transfer; a limited number of eggs showing normal cleavage wasrecovered.

The United Kingdom produces enough barley grain to meet its needs for animal feed and brewing. The Scottish grain whisky trade, however, imports large quantities of high-diastase barley from Canada (Hayter & Allison, 1975). The breeding of highdiastase cultivars which could be grown in Scotland and so replace these imports has been pursued at the Scottish Crop Research Institute (SCRI).

Near-isogenic lines of mungbean (Vigna radiata) were produced from backcrossing two Thai recommended cultivars, KPS 1 and CN 36, with the multiple leaflet line, V 5926, until BC9. The isogenic lines were evaluated against the two recipients at Kasetsart University, Thailand, in the rainy season of 1996 and the dry season of 1997. The effect of the gene controlling the multiple leaflet on physiological and agronomical characters was investigated. Seed yield, plant height, and number of pods per plant were greater in the trifoliate leaflet cultivars than in the multiple leaflet near-isogenic lines, whereas the numbers of seeds per pod and 1000-seed weights were not significantly different. Light saturation and photosynthetic rate did not differ, while light interception and dry matter accumulation were greater in the trifoliate leaflet cultivars than in the multifoliate lines. The leaf area index (LAI) of the trifoliate parents was greater at the vegetative stage but lower at the flowering and young pod stages, due to the greater number of leaflets per plant of the multifoliate lines. After the beginning of the podding stage, the LAI of the multifoliate lines was less than that of the parents, as the number of leaflets per plant of these lines hardly changed while that of the trifoliate parents increased.

The management of non-leguminous annual forage crops can affect dry matter (D.M.) yields, chemical composition, and nutritive (feeding) values largely because of the stage of maturity at which the crop is harvested. After studies for selecting high-yield forage oat varieties for a highaltitude tropical climate (Haile, 1976), it was considered necessary to look into the management of forage oats so that the time of harvesting for maximum forage and crude protein yield could be established.

Quantifying reasonable crop yield gaps and determining potential regions for yield improvement can facilitate regional plant structure adjustment and promote crop production. The current study attempted to evaluate the yield gap in a region at multi-scales through model simulation and farmer investigation. Taking the winter wheat yield gap in the Huang-Huai-Hai farming region (HFR) for the case study, 241 farmers’ fields in four typical high-yield demonstration areas were surveyed to determine the yield limitation index and attainable yield. In addition, the theoretical and realizable yield gap of winter wheat in 386 counties of the HFR was assessed. Results showed that the average field yield of the demonstration plots was 8282 kg/ha, accounting for 0.72 of the potential yield, which represented the highest production in the region. The HFR consists of seven sub-regions designated 2.1–2.7: the largest attainable yield gap existed in the 2.6 sub-region, in the southwest of the HFR, while the smallest was in the 2.2 sub-region, in the northwest of the HFR. With a high irrigated area rate, the yield gap in the 2.2 sub-region could hardly be reduced by increasing irrigation, while a lack of irrigation remained an important limiting factor for narrowing the yield gap in 2.3 sub-region, in the middle of the HFR. Therefore, a multi-scale yield gap evaluation framework integrated with typical field survey and crop model analysis could provide valuable information for narrowing the yield gap.

1. Soil samples were incubated at 60% W.h.c. at 20° C. and leached after 8 and 20 weeks. On subsequent incubation, the rate of nitrate production in the leached samples was greater than that in unleached control soils. The increase in nitrate production seems to be due to an increased rate of ammonification.

2. Adding 100 p.p.m. of nitrate nitrogen to the soil before incubating had no effect on mineralization.

3. Adding a leachate of incubated soil to new soil samples reduced the rate of mineralization on incubation. This reduction is not due to nitrate or any other anion, since deionized leachate was equally effective.

Many biological experiments and almost all quantitative genetic studies draw conclusions from differences between families. Such differences are caused as much by heritable as by non-heritable sources. This paper investigates the impact of seed quality on the expression of quantitative variability among 20 highly inbred lines of Nicotiana rustica using ten seed categories representing different pollination times, seed sizes, seed positions in the capsule and seed maturity. Analysis of variance revealed that while the mean performance of the inbred lines remained more or less the same across all the seed categories, their individual performances differed widely, showing a highly significant interaction between lines and seed categories. This interaction accounted for up to 12% of the total variation and was largely attributable to late pollinations and immature seed. Seed categories were also the main source of heterogeneity among the within-line variances, but only immature seed lowered the correlation between the inbred means. In general, seed quality affected the developmental characters much less than the traits measured at or after flowering, and the expression of genetic variation was not critically affected by seed size or position. Immature seed, on the other hand, generated the highest level of unreliability in the comparative performance of lines and such seeds should therefore not be used in quantitative genetic experiments under any circumstances. Further implications of seed quality effects on the interpretation of genetic components are discussed in detail.

The objective was to evaluate energy partitioning and predict the relationship between metabolizable energy (ME) and digestible energy (DE) in hair sheep fed tropical diets at three feeding levels (maintenance, intermediate and high). To evaluate the energy partition, a database with 114 records (54 non-castrated males and 60 females) from comparative slaughter studies was used. To estimate the ratio ME:DE, 207 observations (74 non-castrated males and 133 females) were used from six studies in a multi-study approach, two indirect calorimetry studies (n = 93) and four comparative slaughter (n = 114), using a mixed model and study as random effect. A simple linear regression equation of the ME against DE was fitted to predict the efficiency of DE to ME conversion. Gas losses were greatest (P < 0.05) for animals fed at maintenance level (7.92% of gross energy intake). The variations of energy losses in the urine were 2.64, 2.06 and 2.08%; faecal losses were 34.37, 37.80 and 36.91% for maintenance, intermediary and high level of feeding, respectively. The regression analysis suggested a strong linear relationship between ME and DE, generating the model ME (MJ/day) = −0.1559 (±0.07525) + 0.8503 (±0.005864) × DE (MJ/day). This study highlights the importance of the relationship ME:DE. Equation/factor 0.85 presented herein is alternative that could be used for the calculation of ME from DE in feedlot diets tropical. In conclusion, we suggest that for hair sheep fed tropical diets the conversion factor 0.85 is more adequate to predict ME from DE.

Available pasture, liveweight gain, milk yield and supplementary feeding of Awassi sheep were monitored for four seasons (1991/92 to 1994/95) on pasture fertilized with superphosphate between 1984 and 1990. The experimental plots received three rates of phosphate (0, 25 and 60 kg P2O5/ha) annually, but no application after September 1990. The experiment was grazed at low (1·1 sheep/ha per year) and high (2·3 sheep/ha per year) stocking rates. The experimental site was typical of communally owned grasslands within the cereal zone of west Asia, where cropping is not possible because of shallow, stony soil and steep slopes. Plots with residual phosphate contained significantly more herbage and supported heavier animal liveweights, especially in the first two seasons. Milk yield and lamb production were greater and the need for supplementary feeding was reduced due to increased herbage. The results suggest that benefits of residual phosphate on pasture and livestock production can be considerable and should be included when assessing the value of applying fertilizer to degraded marginal lands in west Asia. Provided that the stocking rates remain within the range tested in the study, the pasture would suffer no harm. However, the higher stocking rates now practiced in the spring under communal grazing might severely limit flowering and seed-set. The property right to own or use the grazing land is seen as a key factor, deserving attention from governments in west Asia in order to apply new technologies to improve degraded marginal lands.

The experiments described in the following pages were made with a view to discover how far purely physical and chemical processes, known to take place in the soil, may be expected to give rise to nitrites and nitrates. Scattered throughout the extensive literature on nitrification are occasional papers tending to show, what might also be expected on theoretical grounds, that non-bacterial processes may be important sources of nitrates. Formerly these processes were considered to be the only sources, then came the brilliant researches of Schloesing and Muntz, Warington, Winogradsky, and others on nitrifying organisms, and non-bacterial processes were forced into the background. Now that a full knowledge of the various sources of nitrogen compounds in the soil has become so indispensable to the agriculturist, it seemed desirable to make a careful examination of the various chemical and physical processes known to take place in the soil, and to ascertain whether they make any direct or indirect contribution to its stores of nitrates. To this end we have repeated and extended such of the recorded observations bearing on the subject as seemed to merit repetition; we have also devised other experiments to make the examination as complete as possible.

Estimates of inbreeding effects in a landrace are necessary in order to acquire information on the presence of different types of gene action for important traits. Twelve lines with different levels of inbreeding coefficients (F=0, 0·25, 0·50 or 0·75) were developed from three phenotypically selected families of a winter squash landrace (Cucurbita moschata Duchesne) between 2000 and 2002 in the area of Thermi-Thessaloniki, Greece. During 2003, a field experiment was established at this location to evaluate the lines. The agronomical characters measured were: the number and weight of total commercial fruits, days to first female blossom, seed weight, size of pollen grains and water-stress tolerance. Comparisons were also made of morphological characters, the dry matter, the total soluble solids and the pH of fruits. Lines with inbreeding coefficient F=0·50 were found to have the highest values for most of the measured characteristics. Significant family×inbreeding interactions were found, revealing different trends for the linear, quadratic and cubic components of each family with inbreeding coefficients. Three F=0·50 lines selected from within each representative family were evaluated along with four winter squash landraces from the C. moschata collection of the Greek Gene Bank, during 2004 in the area of Thermi. These F=0·50 lines showed a superior performance of three components contributing to yield, indicating that one generation of selfing improved the agronomic performance maintaining concurrently the substantial characteristics of the landrace.