The morphology and position of the shoot apex in field swards was studied in 12 grasses for 12 months, in eight related grasses in 2 years, and in seedlings, young tillers and older tillers of Lolium perenne.

Lolium multiflorum had relatively large numbers of primordia, long apices, which were above ground or near ground level, and a small length of apex per primordium. Festuca arundinacea had few primordia, a large length of apex per primordium, and apices which were well below ground or near ground level. Lolium perenne, Festuca pratensis and Lolium × Festuca hybrids were intermediate between Lolium multiflorum and Festuca arundinacea in numbers of primordia and length of apex per primordium. Festuca rubra and Dactylis glomerata had rather small numbers of primordia, whereas Phleum pratense had relatively large numbers of primordia and of unemerged and emerged leaves.

The numbers of leaf primordia in Lolium perenne increased as the seedling main shoots or the tillers grew older, while the numbers of unemerged leaves per shoot remained more constant.

The morphology, position and protection of shoot apices are discussed in relation to differences between species in rate of establishment and persistence.

The patterns of N uptake and dry matter synthesis by sugarcane (Saccharum hybrid spp.) were studied at four locations in Mauritius with 15N–labelled ammonium sulphate (100 kg N/ha) applied either in a single dressing in September or in two split applications in September and the following February. More than 80% of the total N recovered at harvest (100–120 kgN/ha) was absorbed by the sugarcane during an active uptake period from October to January. Split application prolonged this active N uptake until April only and had no effect on dry matter accumulation. While total Nabsorbed by above-ground sugarcane showed no decline over time, 10–20 kg N/ha of the 15N–labelled N was lost from the green tops even when the N was applied on two occasions. The fertilizer N losses from above-ground sugarcane were, however, not evident when fertilizer N recovery with time was studied by the difference method. In view of the observed losses of fertilizer N from the aerial parts of sugarcane, measurement of fertilizer N recovery at harvest by the N isotope dilution technique underestimates fertilizer N uptake by sugarcane and attributes too large a fraction of N loss to denitrification/volatilization of NH3.

Field experiments with the South American grain crop, quinoa, were carried out at two sites in Denmark in 1988–90 in order to study the effects of varying the nitrogen fertilization rate, seed rate, row spacing, harvesting method and harvest date. Although there was a significant yield increase when the amount of nitrogen fertilizer was increased from 40 to 160 kg N/ha, quinoa seems to be well adapted to poor soils. Yield decreased by 24–1% when the nitrogen supply was reduced from 160 to 40 kg N/ha, while the yield decrease was 120 and 2–7% when the nitrogen supply was reduced to 80 and 120 kg/ha, respectively.

A model expressing yield as a function of plant density, for three experiments analysed as one, showed an optimal plant density with respect to yield of 327 ± 220 plants/m2. This plant density was the top point of the curve relating yield to plant density. However, the large standard deviation indicates that apparently a rather wide range of plant densities would provide similar yields. When the row spacing was varied, it was shown that plots with a row spacing of 50 cm, which were hoed, gave a higher yield than plots with 25 or 12·5 cm row spacing, which were unhoed. There was an overall increase in yield when changing from combined harvesting to swathing; however, when comparing the yields from the optimal harvest dates for the two methods, no yield differences could be detected. The optimal harvest date for swathing was found to be the stage when the inflorescences start to turn brown, whereas for combining, the optimal harvest date was the stage when most of the inflorescences are already brown.

Progeny tests for resistance to potato leafroll virus using true seedlings in a glasshouse in Scotland ranked progenies by the percentages of seedlings showing primary symptoms, in accordance with the known phenotypes of their parents. Symptoms were more obvious in seedlings grown under sodium lamps than in those grown under fluorescent strip lights. These glasshouse seedling progeny tests were then evaluated by comparing them with field clonal trials. The progeny tests were found to identify effectively those progenies most resistant to potato leafroll virus but were not effective for identifying the most resistant clones within progenies.

In the first of two series of experiments the effects of barley straw disposal by burning, chopping and spreading or baling and removing on winter oilseed rape were tested after seedbed preparation either by ploughing in the residue or incorporation in the soil by tine cultivation. These treatments were compared in four field experiments on silty clay loam soils at Rothamsted, UK from 1986 to 1989. The winter rape was either sown in late August or mid-September in seedbeds where either none or 50 kg N/ha had been applied.

In the first season, August-sown rape was successfully established after tine cultivation but very dry conditions prevented seedbed preparation after ploughing, consequently all ploughed treatments were sown in September. Continuing dry conditions delayed emergence of the September-sown crop, the resultant small rape seedlings suffered substantial winter kill in some treatments during a period of abnormally low temperatures. Yield from the August-sown treatments was large (c. 40 t/ha) and showed no effect of straw disposal treatment or additional seedbed N. The yield of the September-sown crop was influenced by the amount of winter kill sustained; the smallest yields resulted from tine incorporation, and the largest after ploughing, where they approached those of the early sown crop.

In the following three seasons more plants emerged from September than from August sowings. The application of seedbed N increased the plant population of the August-sown crop where the straw had been burnt. Plant losses over winter ranged from 15 to 20% and were unaffected by straw disposal treatment. There were significant differences in yield resulting from season and sowing date. Incorporating chopped straw by tine cultivation significantly decreased yield which, coupled with a lower oil content in the September-sown crop, gave a significantly smaller oil yield.

In a second series of field experiments from 1987 to 1989, the effects of improving the timeliness of rape establishment after winter wheat by broadcasting rape seed into standing wheat was compared with conventional sowing after preparing a post-harvest seedbed. After cereal harvest, straw was disposed of either by baling and removing or chopping and spreading over the rape seed. The application of 50 kg N/ha to the stubble or seedbed was also tested, as was the effect of increasing the seed rate from 8 to 16 kg/ha in two seasons.

There were always fewer plants established from broadcasting than from drilling. Generally there were fewer winter losses from broadcast seed than from drilled. Applying N to seedbed or stubble had no effect on plant population or survival except where 16 kg/ha seed was sown in 1989 and increased yield in two of the three seasons.

In spite of a smaller plant population from broadcast seed, yields were often larger from broadcast than drilled treatments. On average broadcasting the seed and baling the straw gave the largest yield although this was significant only in 1989.

Inoculation of Brassica napus cv. ISN–129 with Azotobacter chroococcum following the application of different amounts of nitrogen produced the greatest increase in seed yield and total dry matter when no external nitrogen had been applied. The yield increase in response to inoculation could be attributed to a greater number of primary branches and pods, associated with a higher leaf area index, particularly at the pod-filling stage, and a faster crop growth rate.

Two commercial bacterial inoculants (Lacto-flora and Ecosyl) were added to kikuyu grass (Pennisetum clandestinum) at ensiling, in 1985 and 1988 respectively, at Cedara, South Africa, using laboratory silos. In 1985 (Expt 1), Lacto-flora was added on its own and in combination with the enzymes Celluclast or SP249. In 1988 (Expt 2), Ecosyl was added on its own and in combination with molasses, at two levels of addition.

The addition of Lacto-flora alone did not significantly increase the lactic acid bacteria or the lactic acid content of the treated silage. However, treated silage contained 53·6% less iso-butyric acid and 53·7% less ammonia than the control silage. Kikuyu silage supplemented with a combination of Lacto-flora and Celluclast or SP249 had higher numbers of lactic acid bacteria at ensiling (0·231 × 108/ml) than the control silage or silage receiving Lacto-flora alone. However, only silage supplemented with the combination of Lacto-flora and Celluclast had a significantly higher lactic acid content (2·23 compared with 0·04, 0·18 and 0·13% DM for the control silage, silages with Lactoflora and with a combination of Lacto-flora +SP249, respectively). Nevertheless, this silage contained 19·78% more acetic than lactic acid.

Silage supplemented with Ecosyl on its own did not differ significantly in digestibility, loss of dry matter, ammonia, total non-structural carbohydrates, lactic acid and crude protein, from the untreated silage. A significant decrease in silage pH (from 5·08 to 4·70) was observed when Ecosyl was added together with molasses at the higher level of addition only. However, no other benefit was obtained by the addition of Ecosyl in combination with molasses.

For the production of hybrid and synthetic varieties, high rates of cross-fertilization are needed. Two aspects of cross-fertilization in Vicia faba L. were studied at Wageningen in 1989 and 1990. The occurrence of cross-fertilization between pollen receptor lines in large-scale assays for crossfertilization was determined. Furthermore, the contribution of the genotype of the donor, of the receptor, and of their specific interactions in terms of cross-fertilization rate were studied.

Inter-receptor cross-fertilization may represent from 2 to 70% of the total cross-fertilization. Interreceptor cross-fertilization increases when donors and receptors do not match for flowering height.

The genotype of the receptor appeared to be of importance for the cross-fertilization rate. No differences in cross-fertilization rate due to genetic differences between pollen donors were noticed. Also no significant specific donor x receptor interaction effect on cross-fertilization rate could be observed.

The influence of weight of stakes planted on subsequent cassava yields and the stability of yields was investigated in a 4-year study (1986–90) in Nigeria using two cultivars (TMS30572 and TMS91934). Harvest yields were dependent on the weight of stakes planted and an optimum weight of 875 kg/ha for both cultivars was established; which corresponds to an average stake weight of 88 g. Cultivar TMS30572 consistently outyielded TMS91934 (P <0·05). Tissue analysis of 25 cm long stakes from the mainstem and from the primary and secondary branches of both cassava cultivars showed differences in the amounts of food reserves stored in the stakes. More carbohydrate was found in each of the three stakes of the mainstem than in the stakes from the primary and secondary branches of both cultivars. The yields of each cultivar for the three growing seasons did not vary significantly, which suggests that sustainable high root yield appears to be achievable and is greatly aided by the appropriate management of the stakes.

Effects of agronomic factors on yield of winter oilseed rape were examined in multifactorial experiments, with a single-low (low erucic acid, high glucosinolate) cultivar (Bienvenu) in 1984/85 to 1987/88 and a double-low (low erucic acid, low glucosinolate) cultivar (Ariana) in 1986/87 to 1988/89. Establishment of September-sown plots was better than that of August-sown plots in 1984, 1987 and 1988, but not in 1985 when September was very dry. The total dry matter (DM) (kg/ha) of August-sown plots was much greater than that of September-sown plots throughout autumn and winter but by harvest the plant DM of late-sown plots was slightly greater. Combine-harvested yields of late-sown plots were greater than those of early-sown plots in 1984/85 (cv. Bienvenu) but not in 1988/89 (cv. Ariana); effects of sowing date on yields were smaller in other seasons, although late-sown plots generally had larger yields. Insecticide treatments increased combine-harvested yields in 1987/88 (cv. Bienvenu) and 1988/89 (cv. Ariana) and increased hand-harvested yields in 1984/85, by increasing the number of plants/m2. Fungicide spray treatments increased yields in all years except 1989, by increasing 1000-seed weights. Application of growth regulator sprays increased yields in 1986/87 to 1988/89; effects on cv. Ariana were associated with increased numbers of pods/plant. There were no consistent effects of spring nitrogen rates or timing on yield or yield components.

Field experiments were conducted during the two monsoon seasons of 1985 and 1986 at Kharagpur, West Bengal, to investigate the effect of pigeonpea cultivars and their planting pattern on the performance of a groundnut–pigeonpea intercrop. In intercropping the crops were also sown at 100% population of their sole crops. Groundnut plant growth and development was affected by intercropping with pigeonpea and the decline in pod yield ranged from 7 to 50% of the sole crop yield. The compact, short-statured and short duration pigeonpea cultivar, ICPL87, intercepted only 50% of the incoming solar radiation as against the 70% intercepted by LRG30 at the peak vegetative stage. The significantly higher groundnut yield (48%) obtained from the intercrop with the former pigeonpea cultivar as compared to the latter justifies the belief that the performance of the groundnut was light-related. This was further confirmed when the light interception by pigeonpea was reduced by increasing the row spacing from 90 to 150 cm and there was a consequent increase in groundnut yield. The cultivar and row arrangement of pigeonpea that allowed equal utilization of light by both crops gave increased productivity.

The effects of periods of drought occurring during different phases of reproductive growth of faba bean (Vicia faba L.) cv. Xichang Dabai on dry matter production, seed yield, photosynthetic rate and stomatal size were investigated in pot experiments in 1987/88 and 1988/89 at Xichang Agricultural College, China. Six treatments were imposed: no drought (control), and drought from floral initiation to first flowering (D1), from first flowering to full bloom (D2), from full bloom to initiation of podset (D3), from initiation of pod-set to full pod-set (D4), and from full pod-set to maturity (D5).

Photosynthetic rate, chlorophyll content, leaf area, stomatal pore breadth, biomass and seed yield were decreased by all drought treatments, but stomatal frequency and respiratory rate were increased. The light saturation point for photosynthesis was decreased from 950 µmol/m2/s (PAR) to 570 µmol/m2/s (PAR) in leaves from drought-stressed plants, which also showed maximum stomatal opening between 08.00 and 11.00 h followed by progressive stomatal closure.

The response of faba bean to drought varied during the different reproductive growth stages. Plants subjected to drought at stage D1 were less affected than those at other stages, while plants at stage D4 were most sensitive to drought, which reduced seed yield by c. 45% in 1987/88 and by c. 43% in 1988/89 relative to the control plants, suggesting that stage D4 is the stage of reproductive development most sensitive to soil drought in the faba bean.

Field experiments were carried out in which three different sowing techniques: sowing by hand, with a conventional seed drill and with a precision drill, were used to plant an indeterminate and a determinate cultivar of Vicia faba at two sowing dates and at three population densities in 1989 and 1990 in Southern Germany.

Delayed sowing reduced field emergence rates in both years. Hand sowing produced the poorest stands in some instances due to an insufficient sowing depth being achieved. Only at late sowing dates did precision drilling give greater field emergence rates than conventional drilling. During the early stages of growth, hand and precision sowing resulted in crops with the greatest light interception and dry matter production. However, these differences between sowing techniques decreased later on. Lodging was most severe in conventionally drilled crops, particularly at high population density. Thus, when lodging occurred, dry matter and grain yields decreased with increasing plant density in conventional sowings, although they tended to increase in hand-sown and precision-drilled crops. Overall, apart from this interaction, there was no significant effect of sowing technique on grain yield. Grain yields and dry matter production were generally higher in the indeterminate cultivar Herz Freya than in the determinate cultivar Ticol, but there were no differential effects of sowing technique.

The largest yields of wheat and potatoes came from the combination of longer ley plus optimum fertilizer N but yields of winter beans were decreased where N had been given to the previous crops. Without fertilizer N, two year old leys significantly increased yields compared to one year leys and the effect of longer leys was small except for the first wheat, when grain yields were large and plateaued after the three year ley.

Exponential response curves were fitted to the wheat yields and an exponential plus linear trend to the potato yields after each of the leys. Maximum yields and maximum economic yields and their associated N dressings were then estimated. Maximum economic yields of wheat in 1987 ranged from 811 to 914 t/ha grain and the fertilizer N needed declined from 174 kg/ha after the one year ley to 48 kg/ha after the six year ley. For potatoes in 1988, yields ranged from 63 to 71 t/ha tubers but the N required (137–150 kg/ha) varied little with ley age. For winter wheat, in 1989 yields ranged from only 5·51 to 6·99 t/ha grain, because of drought but, as with the potatoes, the N required (203–218 kg/ha) varied little. For each crop the six individual N response curves could be shifted to bring them into coincidence, and the benefits of the ley estimated in terms of a quantity of fertilizer N applied in spring (horizontal shift) and effects other than spring N (vertical shift). The spring N effects relative to the one year ley varied with ley age; for the first wheat the range was from 6 to 126 kg N/ha for the two to six year leys respectively. Spring N effects were negligible, however, for potatoes (average 6 kg/ha) and also for wheat in the third year (6 kg/ha). Benefits other than those which could be ascribed to spring N increased yield of the first wheat, on average, by 0·94 t/ha grain for the two to five year leys; for potatoes they ranged from 3·5 to 8·1 t/ha tubers for the three to six year leys; for the third crop wheat they ranged from 0·86 to 1·49 t/ha grain for the three to six year leys.

On average, the first wheat recovered only 34% of the applied fertilizer N whilst potatoes and the following wheat recovered 55 and 56% respectively. There was a benefit from the longer leys which affected the efficiency with which fertilizer N was used.

Increasing ley age up to five years increased total soil carbon by a maximum of 0·17%C; 18% of the carbon content of the soil in the one year ley plots. This small increase in soil organic matter provided up to 230 kg/ha mineral N in the first autumn after ploughing. Between 17 October 1986 and 27 April 1987 the average loss of NO3-N from soils following three to six year leys was equivalent to 202 kg N/ha, whilst the average uptake of N by 11 May in the above-ground wheat was only 88 kg/ha; the net loss was 114 kg N/ha. A computer simulation, which included mineralization of organic N during this period together with N uptake and nitrate leaching losses, computed a loss of 250 kg N/ha following the six year ley, and this would have given 400 mg NO3/1 in the 275 mm through drainage that winter.

Studies were conducted to evaluate amounts of fatty acids in the oil as possible indicators of crop maturity in the groundnut, cultivar NC2, grown in St Vincent, Eastern Caribbean. Percentage fatty acids in oil of the composite samples of seeds collected between 99 and 141 days after planting for a period of 3 years (1985–87) was determined by gas-liquid chromatography. Results indicated variation in the amounts of individual fatty acids with crop maturity. There were definite trends, however, with respect to oleic and linoleic acids. As seeds matured, percentage oleic acid increased and percentage linoleic acid decreased, and consequently, the oleic:linoleic acid ratio in oil of the composite seeds increased significantly. The percentage oleic acid peaked significantly at a value of 55.8 ± 0.59 at optimum harvest dates. The results clearly suggested therefore that percentage oleic acid in oil could be used as a reliable reaping index for groundnut.

To develop an effective breeding programme for rainfed production of the common bean (Phaseolus vulgaris L.), the inheritance of seed yield under such conditions should be understood, preferably considering the effects of environment to account for site or season specificity. Thus, heritability, expected and realized gain from selection, and combining ability were evaluated for a nine-parent diallel of common bean without reciprocals but including parents, at two locations each in Mexico and Colombia, using the F2 and F3 population bulks. Heritability estimated from regressions of F3 on F2 ranged from 0·09 ± 0·18 (S.E.) to 0·75±0·25 for seed yield, from 0·26±009 to 0·34±009 for days to maturity and from0·57±004 to 0·80±004 for 100-seed weight. Expected gain from selection in the F2 was estimated as a percentage of the population mean, selecting the upper 20% of the populations. Expected gain in seed yield ranged from 1·8 to 8·4% in Mexico and from 6·5 to 28·1% in Colombia. Realized gains in seed yield in the F3 were 0·4–7·4% in Mexico and 2·9–15·7% in Colombia. Realized gain values for days to maturity were < 2·2%, and for 100-seed weight > 13·4%. General combining ability (GCA) mean squares (estimated using Griffing's Method 2, Model 1) were significant (P <0·01) and larger than those for specific combining ability (SCA) for all traits at all locations. The parents from the Mexican highlands tended to have a positive GCA effect for yield in Mexico but negative values in Colombia, whereas parents adapted to mid-elevation tropical environments showed the opposite tendency. However, all significant GCA values of breeding line V8025 were positive in both countries.

Water use efficiency (WUE) was measured on fourteen genotypes of groundnut (Arachis hypogaea L.) grown in containers under adequately irrigated and water-limited conditions. The genotypes used similar amounts of water but produced different quantities of dry matter. WUE accounted for > 92% of the variation in dry matter production under both irrigated and water-limited conditions. There was a significant increase in WUE under water-limited conditions. Four genotypes selected from the container experiment as having either a high or a low WUE under non-limited or limited water input conditions were further tested under prolonged water deficit conditions in a field experiment. WUE varied significantly between genotypes and there was a positive correlation between WUE and the quantity of dry matter produced by the genotypes. The results suggested that, in three out of four genotypes, the WUE measured in the container experiment was positively correlated with the WUE estimated under field conditions.

Although direct selection for seed yield under water deficit can result in genetic gains in the common bean (Phaseolus vulgaris L.), progress could be enhanced through selection for additional traits that are related to underlying mechanisms of adaptation to water deficit. Carbon isotope discrimination (Δ) has received considerable attention as an indicator of water use efficiency and adaptation to water deficit. To test the utility of Δ as a selection criterion, Δ and other traits were measured in F2 and F3 generations of a nine-parent diallel grown under rainfed conditions at two locations in Colombia with contrasting soil types. An irrigated trial was also conducted at one location. Significant (P 0·05) differences among parents, F2 and F3 were found for carbon isotope discrimination (Δ), leaf optical density (OD), leaf nitrogen (N) and potassium (K) concentrations, relative duration of pod-filling period (RDPF), shoot dry weight (SDW) and harvest index (HI). Effect of location and water regime and their interactions with genotype were also frequently significant. Heritability estimates, determined by regressing the F3 on the F2, ranged from 0·11±011 (S.E.) to 0·33 ±0·10 for OD, 0·22 ± 0·07 to 0·44±0·09 for N, 0·04±0·05 to 0·29±0·08 for K, 0·40 ± 0·08 to 0·43 ± 0·15 for RDPF and 0·30±0·22 to 1·00±0·24 for SDW. All values for Δ and HI did not differ significantly from zero. Correlations between seed yield and OD and RDPF were negative, whereas those with N, K, SDW, and HI were positive. For all traits, mean square values for general combining ability (GCA) were usuall significant and larger than those for specific combining ability (SCA). All significant GCA effects for Δ for ‘Rio Tibagi’, ‘San Cristobal 83’ and ‘Apetito’ were negative, while those for ‘Bayo Rio Grande’, ‘Bayo Criollo del Llano’, ‘Durango 222’ and BAT1224 were positive. Although Δappears unsuitable as an indirect criterion for selection for yield under water deficit, further study of genotypes exhibiting contrasting values of A might reveal differences in mechanisms of adaptation to water deficits, thus leading to other selection criteria or identification of valuable parental lines.

A field plot experiment of 271 days duration was conducted on New Zealand irrigated pastures, commencing in the summer (January) 1988, on a Templeton silt loam soil (Udic Ustochrept) by applying 35sulphur (35S)-labelled urine (250 μCi/g S with 1300 μg S/ml) to field plots (600 × 600 mm) at a rate equivalent to that normally occurring in sheep urine patches (150 ml/0·03 m2) to investigate the distribution, transformations and recovery of urinary S in pasture soil–plant systems and sources of plant-available soil S as influenced by the available soil moisture at the time of urine application and varying amounts of applied irrigation water. Results obtained showed that c. 55–90% of 35S-labelled urine was incorporated into soil sulphate (SO42−), ester SO42− and carbon (C)-bonded S fractions within the major plant rooting zone (0–300 mm), as early as 27 days after urine application. Hydriodic acid (Hl)-reducible and C-bonded soil S fractions showed no consistent trend of incorporation. On day 271, labelled-S was found in soil SO42−, Hl-reducible S and C-bonded S fractions to a soil depth of 500 mm, indicating that not only SO42− but also organic S fractions from soils and 35S-labelled urine were leached beyond the major rooting zone. A large proportion (c. 59–75%) of 35S-labelled urine was not recovered in pasture soil–plant systems over a 271-day period, presumably due to leaching losses beyond the 0–300 mm soil depth. This estimated leaching loss was comparable to that (75%) predicted using the S model developed by the New Zealand Ministry of Agriculture. The recovery of urinary S in soil–plant systems over a 271-day period was not affected by different amounts of irrigation water applied 7 days after urine application to soil at either 50 or 75% available water holding capacity (AWHC). However, significantly lower S recovery occurred when urinary S was applied to the soil at 25% AWHC than at field capacity, suggesting that urinary S applied at field capacity might not have sufficient time to be adsorbed by soil particles, enter soil micropores or be immobilized by soil micro-organisms. Both soil ester SO42− and calcium phosphate-extractable soil S in urine-treated soils were found to be major S sources for pasture S uptake. Labelled S from 35S-labelled urine accounted for c. 12–47% of total S in pasture herbage.

Titan broiler chickens kept in batteries at the Universidad Agraria, Lima, were fed diets containing duckweed (Lemna gibba) in proportions of 0, 10, 15 and 25%. The weight gain of broilers fed 15% duckweed was similar to that of the controls; 25% duckweed in the diet resulted in a significant decrease in feed consumption and weight gain.

To determine if Titan and Arbor Acres broiler chickens could be maintained on duckweed diets under commercial conditions, birds were fed diets containing 0 and 5% duckweed. Female birds (Titan and Arbor Acres) fed diets containing 5 % duckweed showed increased final weights. The pigmentation of all birds receiving the diet containing duckweed was significantly increased.

Duckweed used at levels of up to 15 % in the diets of broiler chickens could represent an important protein source for poultry feed in developing countries where soyabean meal or fish-meal are not available.