A dynamic model has been derived to predict the day-to-day changes in the growth and nutrient composition of crops grown in the field with different levels of nitrogen and potassium fertilizer. Equations are included in the model to represent processes such as re-distribution of nutrients down the soil profile after rain or evapotranspiration, transformations between the various forms of potassium, transport of potassium ions through the soil to the roots and the dependence of growth and nutrient uptake on incoming radiation, plant composition, and soil water stress.

The model was tested by using it to forecast the responses of a test crop, cabbage, to fertilizers in four separate field experiments at WeUesbourne. From data describing the initial soil conditions and weights of the plant, the soil and crop characteristics and the daily weather conditions, the model correctly predicted the pattern of responses in each experiment, although, in some instances the absolute values of the theoretical and experimental yields differed somewhat. Of special significance was the ability of the model to forecast the effects of different weather conditions on crop response and the interactions between the effects of N and K fertilizers on the growth and chemical composition of plants.

Fungicide applications in Malawi have shown improvements in groundnut kernel yield. Improved fertility of sulphur-deficient soils contributes to such gains when sulphur dust is used as the fungicidal agent. Application of sulphur alone to deficient soils lowered the oil/protein ratio of kernels, whereas a singular fungicidal effect raised the oil content, probably through delayed plant maturity.

Application of methyl decanoate to a potato crop about the time of tuber initiation reduced the total yield and the yield of tubers in the grade 2·5–5·5 cm though neither of these reductions were significant. However, application of 2,3,5-triiodobenzoic acid increased the yield of tubers 2·5–5·5 cm by up to 20% while having no significant effect on total tuber yield. This change in the tuber size distribution was due to a more even partition of photosynthate between tubers and not to an increase in the total number of tubers.

In two experiments three dates for time of last irrigation were combined factorially with four rates of application of nitrogen fertilizer and two varieties of cotton. Early termination of watering (when the crop had set 70 bolls/m2) combined with heavy application of nitrogen (168and225 kg/ha) decreased fibre strength, micronaire and yarn strength, particularly in 1973. In two other experiments three frequencies of watering were combined factorially with several rates of application of nitrogen. Frequent watering (weekly) combined with heavy application of nitrogen (168 kg/ha) decreased uniformity of fibre length, micronaire and yarn strength and appearance. In both experiments application of nitrogen increased fibre length. The responses of both varieties were similar except for effect of nitrogen on micronaire. Application of nitrogen decreased the micronaire of Deltapine 16 more than that of Acala 1517 BRI.

The response of the fibre properties to variation in crop nitrogen and water supplies are interpreted in terms of the effects of these factors on (i) the intrinsic fibre properties of bolls maturing at the same time, (ii) the change in the fibre properties of bolls maturing progressively later in the season, (iii) the proportion of total yield contributed by bolls maturing at different times and (iv) delay in harvest and consequent variation in exposure to weather prior to harvest. Yarn strength did not respond as much as fibre properties to the experimental treatments and in particular did not reflect the influence of weathering on fibre properties to the degree anticipated.

Midas, a barley variety very susceptible to brown rust (Puccinia hordei), and two less susceptible varieties (Julia and Mazurka) were given three amounts of nitrogen (50, 100 or 150 kgN/ha) either at sowing (in March), in May, or half at each time. Benodanil sprays were applied to one half of each plot in June and again in July to control brown rust. Brown rust became more severe in 1973 than in 1974 and was most severe on Midas with 150kgN/ha. In 1973, there was most brown rust where all or part of the nitrogen was applied in May, but in 1974 there was least brown rust where all the nitrogen was applied in May, probably because dry weather limited its uptake.

In 1973, when ample rain fell in spring and summer, grain yield was increased more by nitrogen given in May than in March, especially when benodanil was given. In 1974, little rain fell until July and then March nitrogen increased grain yield most whether or not benodanil was given. Top dressing of N (in May) produced a smaller straw yield than seed-bed dressing did in each year.

Benodanil spray much decreased brown rust and increased yield of grain, but not of straw; the increase was greater in 1973 than in 1974, when brown rust was less abundant. Benodanil increased yields of all varieties, but that of the rust susceptible variety, Midas, most. Benodanil increased grain yield more, as more N was given to the barley, and more with N given in May than in March. It increased the amount of N removed by the barley grain, but not by the straw.

The net assimilation rates (NAR) of three genotypes of cotton differing in their growth habit were studied under different spacings. The NARs of a very bushy type, G 67, and a comparatively less spreading type, IAN 560, were the same but that of a compact type, IAN 579, was twice as much when the leaf area index (LAI) was one. Though subsequently in G 67 and IAN 560 NAR under varying spacings either decreased less rapidly or remained steady, the decrease was nearly Hnear with increasing LAI. However, for IAN 579 dependence of NAR on LAI was generally positive indicating genotypic improvement. Under different spacings the leaf-density dependance of NAR appeared to have been decreased in IAN 560, but was nearly absent in IAN 579 with more efficiency towards increasing the yield of seed cotton.

Evidence is presented that, in Italian ryegrass, the ability to survive in the sward into a second year after sowing may be assessed on spaced plants or on closely planted rows. There is no indication that selection for the ability to survive into the second year need cause loss of yield in the first year after sowing. In an earlier paper based on the same experiment (England, 1975) incorrect formulae were used for calculating family heritabilities and genetic correlations. In an appendix the correct formulae are derived and the consequent changes in the conclusions of the previous paper are described.

A series of five metabolism trials was made to determine apparent nitrogen digestibility and metabolizable energy (ME) contents of protein rich feedingstuffs. The mean nitrogen digestibilities of fish meal, groundnut, mustard, sesame and cottonseed cakes were 66, 69, 68, 57 and 40%, respectively. Corresponding values for metabolizable energy values were 1820, 2460, 2330, 1870 and 1530 kcal/kg, respectively. The metabolizable energy contents of coconut cake, niger cake and blood meal were 1190, 2360 and 2190 kcal/kg, respectively. The quantity of protein, its digestibility and crude fibre content in the cakes are the prime factors for this trend in MB. Simple and multiple regression equations were derived from biologically assayed metabolizable energy and chemically analysed energy-yielding nutrient contents of the feedingstuffs. The simple regression equation is:

ME kcal/kg = 32·95 (% crude protein + % ether extract × 2·25

+ % available carbohydrate)–29·20.

The multiple regression equation is:

ME kcal/kg = 370·29 + (24·47 × % crude protein)

+ (65·77 × % ether extract)

+ (44·07 × % available carbohydrate)

- (8·15 × % crude fibre).

The correlation coefficients of simple and multiple regression equations were 0·72 and 0·73, respectively, indicating that there is very little advantage for prediction in using the multiple regression equation. The usefulness of the equation for routine checking of poultry feeds for ME is apparent since the nutrients required to predict metabolizable energy can be analysed within a short period of time.

Equations to predict the leaching of nitrate either uniformly incorporated to a known depth or uniformly distributed in field soils can be reduced to the approximate form:

where f is the fraction of nitrate leached below h cm in a soil of field capacity Vm (% by volume) after P cm of drainage has passed through the profile. If nitrate is initially incorporated uniformly to a depth of w cm, then x = h – ½w(where h ≥ w); if nitrate is distributed uniformly throughout the whole profile, then x = ½h. For surface-applied nitrate x = h (Burns, 1975).

Observed mean displacements in published experiments have been compared with predictions from the equations and from equations in which the mean movement of nitrate and water are assumed equal. The new equations give better agreement with the observed data.

In seven experiments involving a total of 300 Large White pigs, moist maize preserved with propionic acid was compared, at dietary inclusion levels of approximately 85%, in whole (W) or rolled (R) forms with maize taken from the same samples, dried and then ground (DrG). Propionic acid lost in drying was returned to give identical levels in all three forms. In the first two experiments the moist maize contained 37·4% moisture, was included in diets to which no synthetic tocopherol was added and had been in storage for approximately 1 year when drying was effected and experiments on acceptability (using 54 pigs offered diets based on the three forms simultaneously in Expt 1) and digestibility and nitrogen retention (using 12 pigs on two occasions in Expt 2) were started. The moist maize used in Expts 3, 4, 5, 6 and 7 contained 45·8% moisture and was dried 2 months after harvesting. Between this time and 12 months post-harvesting experiments were made, with all diets supplemented with 10 g/t δ-α-tocopherol, on digestibility and nitrogen retention (using 18 pigs on two occasions in Expt 3) and performance between approximately 20 and 72 kg live weight (using three sets of 48 ad libitum group-fed pigs per set in Expts 5, 6 and 7). A further performance study (Expt 4) of factorial design and conducted over a similar live-weight range, between 2 and 5 months post-harvesting, investigated, using 72 individually but restrictedly fed pigs, responses from R, W and DrG based diets with or without the addition of 10 g/t δ-α-toeopherol.

Four months post-harvesting the δ-α-tocopherol levels of the moist and dried maize used in Expts 3–7 were 0·5 and 7·2mg/kg D.M. respectively. Five-six months post-harvesting the peroxide values of the other extractable fat of the moist maize markedly increased. In Expt 1 the diet based on the DrG form was eaten to the virtual exclusion of the diets based on the other two forms but performance responses were poor and symptoms (partially confirmed) of a tocopherol deficiency apparent. However, in Expt 4 there were no significant differences in response to the zero and 10 g/t δ-α-tocopherol supplementation. Overall, the DrG and R forms of maize gave similar utilization and growth (up to 8 months post-harvesting) responses. Compared with these responses those from the W form were inferior (in most cases significantly). When the moist cereal in R and W forms was fed after 8 months of storage (Expts 1, 6 and 7) the daily intakes of D.M. and induced growth responses obtained were lower than those obtained from the DrG form.

For the purposes of compounded feed formulation an important assumption with regard to the digestible energy (DE) content of ingredients is made. It is assumed that the energy contents of individual ingredients in a feed are additive and therefore that, irrespective of the combinations in which the various ingredients occur, the energy contributed per unit of a particular ingredient remains constant. This implies that the DE content per unit of that ingredient is the same at all concentrations of the ingredient in the feed mixture. In other words, as one ingredient is substituted in increasing amounts for another in a dietary mixture, there is a linear change in the DE content of the whole feed. The purpose of this experiment was to determine whether this assumption is valid.

The inheritance of the units of the character complex which differentiates Avena nuda from Avena sativa was studied in F1 hybrids and in the F2 generation derived from inter-crossing five cultivars of A. saliva with four cultivars of A. nuda. The 14 derived F1 hybrids could be classified into four types depending on the level of dominance of the sativa or nuda character expression. Type-I hybrids involving the cultivar Milford as parent showed a high level of dominance of the sativa-type expression, whereas the F1 hybrid from the cross, Condor × China, type IV, had the character expression typical of the A. nuda parent. Segregation in the F2 generation indicated that the entire character complex was under the control of a major gene, and supported the suggestion from previous work that modifying genes interact with the major gene to alter the expression of the homozygous nuda genotype towards the heterozygous phenotype

Homozygous nuda and heterozygous genotypes were shown to exhibit a gradient in the expression of the nuda character complex from the apex to the base of the panicle, the nuda-type characters being most pronounced in the apical spikelets. It is suggested that the variation of character expression within single panicles of homozygous nuda and heterozygous genotypes indicates the operation of an inhibitor-type gene action rather than a mutation to loss of function.

The effect of season of harvest and previous seasonal applications of fertilizer N on the response of perennial ryegrass/white clover swards to pre-cut applications of fertilizer N was studied in three consecutive years on different sites. Herbage D.M. yield responded in a curvilinear manner to increased pre-cut N application rates. There was a tendency in all experiments for the marginal response of herbage D.M. to increased pre-cut N application rates to decrease as previous seasonal fertilizer N application rates increased. Although the effect of season of harvest on the response of herbage D.M. to pre-cut N application rates varied with site/years, it was concluded that the marginal response of herbage D.M. to pre-cut N application rate varies little throughout the greater part of the growing season. The exceptions to this are the very early and late harvests and swards that receive low supplies of N from the sward/soil complex. The results are discussed in relation to other published data and to their possible use in the control of the seasonal pattern and total seasonal supply of herbage D.M. for rotational grazing management systems.

The effects of maleic hydrazide (MH) and chlorocholine chloride (CCC) on S. 23 perennial ryegrass grown for seed were investigated in a series of field experiments from 1972 to 1974. MH significantly decreased straw length and lodging, but also decreased all yield components, seed yield and germination percentage. All growth stages and harvest date were delayed and the seed production mechanism impaired. CCC had little effect on length of fertile tillers or lodging but seed yield was increased in 1972 and 1973 when the chemical was applied at spikelet initiation. In 1972 an increase in 1000-grain weight and in 1973 small but insignificant increases in numbers of fertile tillers and seeds per spikelet were responsible. This chemical had no visible effects on the growth and development of the crop or on germination percentage of the seed.

The effect of daily herbage allowance on herbage intakes and growth rates lambs grazing perennial ryegrass and red clover was investigated in two experiments. Herbage allowances defined as g herbage D.M./kg live weight (LW)/day were controlled by varying the areas of plots grazed for 2 days by groups of six lambs.

In the first experiment five herbage allowances in the range 20–120 g D.M./kg LW/day were offered on two areas of a perennial ryegrass (cv. S. 23) sward that received nitrogen fertilizer applications of 39 or 78 kg N/ha/28 days. In the second experiment five herbage allowances in the range 30–160 g D.M./kg LW/day were offered on perennial ryegrass (cv. S. 23) and red clover (cv. Hungaropoly) swards.

Asymptotic curves were fitted to describe the relationship between herbage allowance and daily intake of herbage. In Expt 1 nitrogen fertilizer rates did not affect the yield of herbage or animal performance. In Expt 2 intakes were higher on the clover sward than on the ryegrass sward at the higher herbage allowances.

The asymptotic curves to describe the relationship between herbage allowance and growth rate of lambs differed widely between periods. Growth rate of the lambs increased linearly with increase in digestible organic matter intake. Live-weight gain per unit of digestible organic matter intake was higher on the red clover than on the ryegrass.

The conclusion is drawn that if the herbage present to ground level is not more than three times the daily intake of the animals, intake of herbage of the animals may bo restricted.

Total VFA concentrations, individual VFA proportions and ammonia concentrations in the rumen of cattle grazing tropical pastures for 7 months during the dry season were compared with concentrations of these metabolites in cattle grazing in the wet season and in cattle given two pasture hays in pens.

Neither total VFA nor ammonia concentrations were altered by periods of new pasture growth within the dry season although responses in live weight occurred. Further evidence that concentrations of total VFA were insensitive to differences in feed quality was shown in the pen experiment.

VFA concentrations were 53% higher in the rainy season than in the dry season and ammonia concentrations doubled from 62 mg/1 in the dry to 128 mg/1 in the wet season. Ruminal ammonia was related to ingested bolus N concentration (r = 0·58, P < 0.001) during the dry season.

Individual VFA proportions did not vary greatly. The highest acetic (79·1%) and lowest butyric acid (5.10%) proportions occurred in the same sample. Iso-valeric and valeric acid proportions were related positively to ruminal ammonia (P < 0·001).

In grazing cattle, concentrations of VFA and ammonia in their rumen taken at hourly intervals between 07.00 and 18.00 h did not vary greatly with time. Samples taken before 10.00 h had higher VFA and ammonia levels.

Seven field experiments were made on the effect of two harvesting dates on the nitrogen requirements of sugar beet. All were on Rauceby series soils overlying oolitic limestone in Lincolnshire.

Nitrogen fertilizer increased sugar yield in all experiments, and yield was considerably higher at the mid-December harvest than in early October. On average, the sugar-yield response to nitrogen was greater at the late harvest, and the requirement for nitrogen was about 45 kg/ha higher then than at the early harvest. Sugar content was depressed less at the late harvest than at the early by increasing nitrogen rate.

These results suggest that farmers should apply more nitrogen to fields that they plan to harvest late than to early-harvested fields; they also have implications for the conduct and interpretation of nitrogen response experiments on sugar beet.

In three separate experiments, lucerne hay was sprayed with solutions of formaldehyde as it was being baled. Moisture content at baling was respectively 20, 28 and 34% in Expts 1, 2 and 3, the latter being considered higher than normal. Dry matter lost during 4 months of storage averaged 6·7% and was unaffected by formaldehyde treatment.

Increasing rates of formaldehyde application decreased the amount of plant nitrogen digested in the microbial stage of an in vitro system and increased the amount of nitrogen digested in the subsequent acid-pepsin stage (Expt 1 only). When the hays were fed at constant intake to sheep in metabolism cages, formaldehyde treatment depressed the concentration of ammonia and volatile fatty acids (VFA's) in rumen fluid and lowered the molar proportions of iso- and n-valeric acids, but caused either very little or no depression in apparent energy digestibility. It was concluded that formaldehyde treatment of the hays reduced protein degradation by rumen microorganisms and probably increased the amount of protein digested in the post-ruminal region of the digestive system, and that this was achieved without any serious effect on energy digestion.

The hays were also fed for 50 days at restricted and ad libitum intakes to young Komney sheep kept in outdoor pens, followed by a 55-day post-treatment period on spring pasture. Voluntary intake was high in both experiments and was unaffected by formaldehyde treatment in hay baled at normal moisture content. There was a tendency for formaldehyde treatment to cause a small increase in voluntary intake in hay baled at the highest moisture content, but this was counteracted by its effect in depressing digestibility, giving no increase in digestible dry-matter intake. Live-weight gains were low in relation to intake, giving a weight loss in most treatment groups. Formaldehyde treatment significantly reduced weight loss and the effect was still present at the end of the post-treatment period. From regressions of weight change on digestible energy intake, it was considered that formaldehyde treatment had brought about a small improvement in the efficiency with which energy was used below maintenance.

Wool growth rates appeared normal for the levels of intake achieved and were increased 14·5% by formaldehyde treatment at ad libitumintake and 5·5% at restricted intake. Residual responses to formaldehyde treatment in the post-treatment period averaged 8%. The total amount of extra clean wool produced from formaldehyde treatment over both periods was 46and94g respectively at the restricted and ad libitum intakes, representing only 1·5 and 3·0% of the annual fleece production. Wool growth on diets treated with formaldehyde in sheep feed at the maintenance level of energy intake is discussed in relation to the concentration of protein-bound sulphur-containing amino acids (SAA's) in the diet dry matter. It was concluded that large responses in wool growth from protein protection of forage diets are unlikely unless the concentration of SAA's in the dry matter can be considerably increased from their present low levels. It is suggested that the possibility of achieving this through plant breeding techniques be investigated.

The effect of six intervals between harvests and three levels of N application on digestibility, digestible yield and nitrogen content and yield was studied in four ryegrass(Lolium) varieties during a 30-week period in the first harvest year in a field experiment.

Digestibility was higher with a 3-week than with a longer interval between harvests. Yield of digestible organic matter was increased by extending the interval from 3 to 6 weeks, but was slightly reduced by extending from 6 to 10 weeks.

Increase in the level of applied N increased the degree of curvature downwards in the response to extending the interval in both yield of digestible organic matter and yield of N, supporting the view that N use should be accompanied by shortened intervals between harvests.

Digestibility varied by up to 15 units D-value from one time of the year to another with a constant interval between harvests. The highest values were in the spring. Autumn values were low in spite of a relatively high proportion of green leaf.

During the period immediately following the main period of stem development, doubling the interval from 4 to 8 or from 5 to 10 weeks reduced digestibility by 10 units and reduced digestible yield by 22%.

In the absence of applied N, the N yield of S. 321 was 31% greater than the average of S. 22, S. 23 and S. 24. However, the apparent recovery of applied N in S. 321 was much lower than in the other varieties.

The results of field experiments on the influence of nitrogen fertilization on the yield components, starch and prussic acid content of two of the cassava cultivars recommended for cultivation in Nigeria are presented. The two cultivars 53101 (local) and 60506 (improved) were harvested at 9, 12 and 15 months. In general, the improved cultivars appeared to respond better to N fertilization, but high rates of N (150 kg N/ha) tended to reduce the yield performance of the two cultivars. The local cultivar produced maximum yields of 31·5, 37·5 and 55·7 fresh tuber t/ha with 60 kg N/ha at 9, 12 and 15 months, respectively, while the improved cultivar gave maximum yields of 31·5 and 48·4 t/ha with 120 kg N/ha at 9 and 12 months, respectively, and 64·1 t/ha with 90 kg N/ha at 15 months. By allowing the crop to grow up to 15 months, the starch yield was more than doubled and about three times the yield obtained at 9 months. The 53101 strain seemed to produce maximum starch yields with 60 kg N/ha while the 60506 type tended to give maximum starch yields with 90 kg N/ha. Influence of N treatments was significant up to 12 months of age but not at 15 months.

The HCN content of both cultivars diminished considerably with the age of the plant, dropping at 15 months to about half the level at 9 months. While the HCN concentration of the local cultivar tended to increase with higher N-fertilization, that of the improved cultivar diminished, particularly at 12 months after planting. At 15 months however, the HCN content of both cultivars rose with increasing N. fertilization.