At Shika in a subhumid environment of Nigeria, a 3-year study was carried out to select newly developed groundnut varieties fur use in crop livestock production systems. The study examined 11 groundnut varieties. Emergence time, plant stands at full emergence, forage and seed yields and yield components were examined. Whole plant samples were analysed for crude protein (CP) content. Varieties ICGV 87123 gave the lowest forage yield and cultivar M517-80I, the highest, with seven varieties recording forage yields above 5 t/ha. The CF content of forage was lowest (14.8%) for variety M576-80I and highest (21.6%) For variety M554-76. Mean seed yield (over 3 years) varied significantly from 0.73 to 1.68 t/ha. Only two varieties had mean seed yield > 1 t/ha. The relationship between seed and forage yields was positive and significant (r = 0.529. P < 0.006). Varieties RMP 12, 88-80I acid M517-80 were most promising for both forage and seed production.
Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) has caused significant losses to wheat and barley in many parts of the world. Two RWA resistant lines with flat leaves were crossed with each other and with two RWA susceptible lines producing rolled leaves when infested with RWA. F-1, F-2 and BC1F1 seedling leaves were classified according to their leaf shape as flat, longitudinally folded, or rolled after artificial infestation. Leaf chlorosis in the phenotypes of F-2 plants was also recorded. The F-2 populations of flat x rolled crosses segregated in 9:3:4 (flat: folded: rolled) ratios, suggesting a two dominant gene model for control of leaf shape. Folded leaves appeared only in F-2 seedlings. The F-1 seedlings of flat x flat cross showed only flat leaves, while the F-2 population segregated in a 13: 3 (flat: rolled) ratio. Chlorosis ratings and leaf shape scores of F-2 seedlings were not independent. F-2 seedlings with lower chlorosis scores were more likely to have flat leaves; however, some susceptible F-2 seedlings also had flat leaves. Resistant F-2 seedlings may have rolled leaves. It was concluded that recording leaf shape is not a reliable visual rating method to evaluate host plant response to RWA, because the inheritance of resistance and leaf shape in wheat are under two different gene systems.
There is the potential for arsenic to enter the human food chain via ingestion by grazing animals. Data on the transfer of arsenic to ruminants have been too sparse to allow the development of dynamic models to predict changes in the arsenic contents of different tissues following ingestion. A study is described during which a group of 6-month-old lambs were given a single oral administration of (AsCl3)-As-73. Subsequently, concentrations of As-73 in the tissues of groups of lambs slaughtered at intervals over a period of 181 days were determined. A true absorption coefficient of 0.46 +/- 0.055 (mean +/- S.E.) was determined which is considerably lower than expected from previous studies of non-ruminant animals which demonstrate complete absorption for inorganic arsenic. The resultant data were used to develop a compartment model to describe arsenic behaviour in sheep tissues. The derived model accounted for 80 % (n = 100) of the observed variation in the data. The model predicts that arsenic concentrations in tissues rapidly (< 40 days) reach equilibrium with the dietary intake level. Equilibrium transfer coefficient values (the ratio of the arsenic concentration in a tissue to the daily dietary intake of arsenic) for the important food-chain tissues were calculated as: (2.5 +/- 0.67) x 10(-3) days/kg calculated as: (2.5 +/-0.67) x 10(-3) days/kg for muscle, (9.1 +/- 1.96) x 10(-3) days/kg for liver and calculated as: (2.5 +/- 0.7) x 10(-3) days/kg (1.1 +/- 0.14) x 10(-2) days/kg for kidney.
Dried lucerne (Medicago sativa), dried Italian ryegrass (Lolium multiflorum,) and wheat (Triticum aestivum) straw, in the latter case supplemented with soyabean meal, were each fed to cattle, sheep and rabbits in each of 2 years. In both years. plant parts of the three diets were tested for in vitro digestibility, in both milled and chopped (1 cm lengths) form, and for cell wall content (as NDF). In the first year. the plant parts were analysed for lignin and both the plant parts and the faeces were examined microscopically for the proportions of thick-walled, thin-walled and epidermal cells in cross-sectional area and for the thickness of the cell walls. The plant parts with the lowest proportion of thick-walled cells in cross-sectional area (0.05) were the lucerne leaflets and those with the highest proportion of thick-walled cells (0.68) were the stems of wheat straw. The cell walls of the thick-walled tissues were thinnest (0.7-0.8 mum) in Italian ryegrass leaf blades and sheaths. Within each cell type for the whole crop, the order of cell wall thickness was wheat straw > lucerne > Italian ryegrass. In vitro digestibility of DM was lower (by 0.031-0.085 g digestible DM/g total DM) in chopped than in milled stems of lucerne, ryegrass and wheat and in leaf sheaths of wheat. This suggests incomplete and/or delayed access of rumen microorganisms to some of the cell wall in chopped material in vitro and probably, therefore, also in chewed material in vivo. The concentrations of NDF and lignin in both ryegrass and wheat were in the order leaf blades < leaf sheaths < stems. The lucerne crops were more mature than the ryegrass crops and there was no consistent difference between lucerne and ryegrass in intake of DM or intake of NDF. The intake of wheat straw DM was 0.52 that of lucerne and ryegrass, whereas the intake of straw NDF was 0.89 that of lucerne or ryegrass NDF. Intake of both DM and NDF in relation to metabolic body weight was highest (87-93 g DM and 45-48 g NDF/kg W-0.75) with cattle on lucerne and ryegrass and rabbits on ryegrass and lowest (33-34 g DM and 29-30 g NDF/kg W-0.75) with sheep and rabbits on straw. The output of faeces/kg W-0.75 was particularly high (38-41 g DM and 30-32 g NDF) from rabbits fed lucerne or ryegrass. Digestibility of DM was highest (0.726-0.732 g/g) with cattle and sheep fed ryegrass, followed by cattle and sheep fed lucerne and sheep fed straw. Digestibility of NDF was highest (0.708-0.752 g digestible NDF/g total NDF) with cattle and sheep fed ryegrass and sheep fed straw. Digestibility of NDF with rabbits was lower than with cattle or sheep, but was higher than might have been expected, in a small. hind-gut fermenter, with ryegrass (0.339 g/g) and straw (0.492 g/g). The proportion of thin-walled cells was much lower in the faeces than in the diets, but there was an appreciable proportion (0.10-0.27) of these cells in the cross-sectional area of faecal particles. The cell walls of all cell types were thinner in the faeces than in the diets, e.g. those of the thick-walled cells were thinner by 0.35 mum in lucerne, by 0.11 mum in Italian ryegrass and by 0.41 mum in wheat straw. The faeces from rabbits had higher proportions of thick-walled and epidermal plant cells in cross-sectional area, and a lower proportion of thin-walled cells, than the faeces from cattle and sheep.
Seed crops of the variety Estima were grown in each of 2 years using two planting dates. two harvest dates. two plant densities and two irrigation regimes to product seed tubers which had experienced different cultural and environmental conditions. The effects of these treatments on tuber characteristics, sprout production and stem development in the ware crop were then determined in subsequent experiments using storage regimes of 3 and 10 degreesC. Time of planting the seed crop affected numbers of eyes, sprouts acid above ground stems in the subsequent ware crop because environmental conditions around the time of tuber initiation appeared to alter tuber shape. Cooler. wetter conditions in the 7 days after tuber initiation were associated with tubers which were longer, heavier and had more eyes, sprouts and above ground stems. In contrast, the time of harvesting the seed crop did not affect tuber shape or numbers of above ground stems acid there was no interaction with tuber size. The density of the seed crop had no effect on any character measured and irrigation well after tuber initiation did not affect tuber shape, numbers of sprouts or numbers of stems. Seed production treatments, which resulted in earlier dormancy break. were associated with tubers that produced more sprouts and above ground stems. in contrast to the conventional understanding of apical dominance. Storage at 3 degreesC gave fewer sprouts, a lower proportion of eyes with sprouts and fewer stems than storage at 10 degreesC. The major effects on stem production appear to result from environmental conditions at the time of tuber initiation of the seed crop and sprouting temperature.
The research was carried out at the animal experimental station of the National Agricultural Research Institute of the French West Indies (Guadeloupe) in 1999. Effects on intake and digestion by sheep of addition of Gliricidia leaves to a diet of 35-day-old Digitaria decumbens (pangola) hay, have been studied. In a first trial (a 4 x 4 Latin Square design), four rams were fed four diets: hay (GO); hay plus 1300 g of Gliricidia (G0.25), hay plus 2600 g of Gliricidia (G0.50), hay plus 3900 g of Gliricidia (G0.75). Total dry matter intake (DM), hay and Gliricidia intake, total tract and rumen digestibility of DM and its components, microbial and total nitrogen flows were estimated. In a second trial (a 2 x 2 Latin Square design), the same animals received hay (GO) or Gliricidia (G 1.00) ad libitum to estimate the rumen turnover of pangola and Gliricidia fibrous particle. Neutral detergent fibre and crude protein content of the Digitaria decumbens hay and Gliricidia were 746 and 51, 458 and 198 g/kg dry matter respectively. Total dry matter intake (DM) varied from 42.7 to 76 g DM/kg LW0.75 from G0 to G0.75. The rate of substitution of pangola by Gliricidia (decrease of pangola intake for one unit Gliricidia consumed) was 233 g/kg. The digestibility of cell-wall linearly decreased with increasing level of Gliricidia in the diet. No digestive interaction was registered in the mixed diets. The total nitrogen and microbial nitrogen duodenal flows increased with the level of Gliricidia in the diet. The rumen turnover of fibrous particles of Gliricidia was double that of pangola. The incorporation of Gliricidia in diets increases their nutritive value by higher intake and intestinal nitrogen duodenal flows, but no positive digestive interaction was observed between pangola hay and Gliricidia leaves.
Genetic parameters were estimated for purebred and crossbred lambs of a local breed using a single trait animal model. The traits recorded were: birth weight (BWT), weight at 30 days (WT30), weaning weight (NWT), average daily gain from 1 to 30 days (ADG1) and average daily gain from 30 to 90 days (ADG2). Five different animal models were fitted for each trait; all including additive direct genetic variance and various combinations of additive maternal and environmental maternal effects. The most appropriate model was chosen based on likelihood ratio tests. Additive maternal and permanent environmental effects were important (P < 0.05) for birth weight in purebred and crossbred lambs, when compared with a model containing only additive direct effects. Inclusion of maternal permanent environmental effects provided a better fit (P < 0.05) for weaning weight in purebred lambs than a model containing only additive direct effects. Estimates of heritability from the model containing additive direct, maternal effects and maternal permanent environmental effects, but not additive direct-maternal correlation, for combined purebred and crossbred lambs were 0.32 for BWT, 0.19 for WT30, 0.24 for WWT, 0.26 for ADG1 and 0.12 for ADG2. Estimates of additive maternal and maternal permanent environmental variances, respectively, as a proportion of phenotypic variance were 0.06 and 0.07 for BWT, 0.05 and 0.02 for WT30, 0.02 and 0.03 for WWT, 0.03 and 0.05 for ADG1 and 0.00 and 0.03 for ADG2. Estimates of direct-maternal correlation in subsequent analyses were significant and ranged from -0.16 to -0.95 for live weights and from -0.73 to -1.0 for daily gains. However, the very large negative correlations probably resulted from undefined non-genetic covariances as well as possible antagonistic genetic effects. These results indicate that it would be possible to improve growth traits in a local sheep breed through genetic selection.
Experiments were conducted in Bangkok clay soil to investigate the influence of planting date, tiller separation and plant density on the yield and yield attributes of parent and clone plants of two transplanted rice varieties. The 15 July transplanting of mother crop and collected vegetative tillers and retransplanting on 15 August showed significantly high grain yield (3.8 t/ha). The photoperiod-insensitive variety RD23 gave higher yield (3.8 t/ha) than the photoperiod-sensitive variety KDML105 (3.0 t/ha). Tiller separation up to 4 tillers/hill did not adversely affect the mother crop. Vegetative tillers transplanted with 2-4 tillers/hill gave a similar yield as the mother crop in both the seasons. Vegetative tillers gave a higher yield than nursery seedlings transplanted on the same date. The yield components, i.e. weight of 1000 grains, grains/panicle and per cent filled grains, showed better responses with early transplanting of KDML105 in the mother crop and vegetative tillers except for particle number and particle length of vegetative tillers with RD23. The results suggest that in some flood-prone lowlands, where the transplanted crop is damaged by natural hazards, vegetative propagation using tillers separated (maximum 4/hill) from the previously established transplanted crop is beneficial for higher productivity.
This study was established to quantify the uptake of N-15-labelled nitrogen (urea) applied in the first and second years of perennial ryegrass (Lolium perenne L.), tall fescue (Festuca arundinacea Schreb.) and browntop (Agrostis capillaris L.) seed crops, and the availability of the residual fertilizer N to a subsequent wheat (Triticum aestivum L.) crop under field conditions in Canterbury, New Zealand. Total recovery of N-15-labelled nitrogen fertilizer was approximately 100% when fertilizer was applied to the grass seed crops in spring, At harvest in year 1, grass straw and seed contained 34-47% and 6-15% of the applied N respectively; 27-35% remained in the soil (0 150 mm depth). Recovery of N-15 in straw and soil was higher in fescue and ryegrass than in browntop, but recovery in roots was lower. At harvest in year 2, most of the N-15 was present in the soil (30-37%) with only small amounts in the seed (0.7-1.0%), straw (3.6-4.9%) and roots (5.2-12.7%). In year 3, 2.5-3.5% of the residual N-15 was recovered in the wheat and 18-26% in soil. Losses of N-15 were minimal until ploughing after the second harvest, when there was an apparent loss of 11-35% of the fertilizer N applied. Losses were not directly associated with the fertilizer but indirectly following release of fertilizer N previously immobilized in plant roots and soil microorganisms. Small losses also occurred directly from autumn-applied N, probably through leaching. Despite these losses, overall there was an accumulation of fertilizer N in the soil organic pool, suggesting that ryegrass fescue and browntop seed crops have a role in contributing to the N fertility of the soil.
The objective of this study was to assess the efficiency of a pedigree intra-cultivar selection: based on widely spaced individual plant performance, in a traditional snap bean (Phaseolus vulgaris L.) cultivar, aiming to restore or even improve the cultivar. The programme started with the target of earliness and yield stability, and was progressively advanced with the target of seed shape uniformity. Two parallel pathways were followed: under greenhouse conditions (four generations of selection) and under field conditions (two generations of selection). The average response to selection was 2.43-3.15 and 0.13-0.42 pods/plant per generation for earliness and yield, respectively. The coefficient of variability (CV) of earliness decreased from 81.33 to 39.43% and from 61.31 to 42.51% for greenhouse and field grown progenies, respectively. For yield, the CV showed a low decreasing rate, and was stabilized at the end-value of almost 28 %. The results were confirmed during two direct evaluation tests. Firstly, the evaluation of 21 families, as individual spaced plants, showed mean values for earliness of 18.99-22.94 pods/plant and for yield of 32.89-33.09 pods/plant. Secondly, the evaluation of improved selections from the greenhouse and the field and of the source cultivar, in a dense stand, showed that all the selections produced high and stable early fresh pod harvest even 53 days after planting, while the control was still at the vegetative phase. The yield of selected progenies was 219-242 % superior compared with source material. Also, seed stocks of all selections were of the normal long shape. Short-seed progenies were excluded from the breeding programme, since they lacked earliness and stability of performance. The results demonstrate conclusively that it is possible to simultaneously improve earliness and pod yield through diminishing plant-to-plant variability.
Morphophysiological characters, designated as descriptors by the International Union for the Protection of New Varieties of Plants (UPOV) and the International Plant Genetic Resources Institute (IPGRI), and allozyme variation were used to study genetic diversity among four cabbage (Brassica oleracea L. var. capitata L.) open pollinated (OP) populations. The morphological and physiological characters, and gene frequencies among OP populations were analysed by using cluster (CPI) and principal component analysis (PCA). Both methods gave the same clustering of OP populations. The relationships found among OP populations by analysing UPOV descriptors (30 characters) and IPGRI descriptors (30 + 14 characters) were similar. The relationships among OP populations obtained from gene frequencies were not similar to those obtained from morphophysiological characters, but two of the four OP populations were clustered together by both categories of data. The biggest correlation between the relationships among OP populations obtained from morphophysiological characters and those obtained from gene frequencies was r = -0.44 and r = -0.38 given by PCA and CA respectively. The importance of each character or allele with respect to the relationships among OP populations were also detected by PCA.
Two studies were undertaken to evaluate the effects of cellulase and endoxylanase enzymes on the chemical composition and the fermentation characteristics of grass silage, using the gas production technique. Perennial ryegrass was ensiled in 1 litre glass containers for 90 days with cellulase (0.2 g/kg grass on fresh weight basis) and endoxylanase in the concentrations of 0.05 g/kg grass (Endox 0.05) and 0.2 g/kg grass (Endox 0.2). Subsequently, dried samples, ground through a 1 mm screen, were used in chemical analysis and gas production measurements. In Expt 1, the enzyme treatment significantly decreased silage NDF (P < 0.001), ADF (P < 0.001) and acetic acid (P < 0.01) concentrations and increased lactic acid (P < 0.001) production. In Expt 2, lower concentrations of NDF (P < 0.001) and ADF (P < 0.001) in treated silages resulted in increased sugar concentration (P < 0.001). In this experiment, butyric acid was detected. Addition of cellulase and Ender 0.05 enzymes did not alter silage digestibility. In both studies, cellulase and Ender 0.2 treatments tended to increase the rate of gas production within 10 hours of inoculation with rumen fluid whereas Endox 0.05 had no effect. The volume of gas produced was however greater for the untreated silage than for the enzyme-treated silage samples after 48 h of incubation. The strategy of applying cellulase and endoxylanase to the herbage in the ensiling process proved to be effective in modifying the chemical composition and increasing sugar concentration and the rate of gas production of the silages. Further research on the factors determining enzyme effectiveness is therefore suggested to elucidate the mechanisms leading to higher utilization of the released sugars.
A field experiment was conducted for 2 years (1993-95) at Central Institute of Medicinal and Aromatic Plants, Field Station, Bangalore, India to evaluate the nitrification inhibitors, benzotriazole, o-nitrophenol, m-nitroaniline and dicyandiamide in a perennial aromatic grass, Java citronella. Citronella responded to applications of high doses of nitrogen (300 kg N/ha/year). The interaction between N doses and nitrification inhibitors was significant. Nitrification inhibitors performed better at the highest N dose (450 kg N/ha/year) and the increase in the essential oil yields was to an extent of 27.3 to 34.6 % when compared with 'N alone' treatment. The nitrification inhibitors also increased the apparent N recoveries by citronella considerably. The oil content in the herb and its quality were not affected by the treatments. The nitrification inhibitors increased citronella yields and improved N economy.
Eighteen experiments were carried out over a B-year period (1989-94) on three different soil types to compare the effects of a broad-spectrum fungicide, applied as 1-, 2- or 3-spray programmes at different growth stages, to control foliar diseases on early and later-sown Blenheim malting barley. Powdery mildew, caused by Erysiphe graminis (Blumeria graminis) f. sp. hordei, was the dominant disease in all 6 years. Sowing date had a major effect on grain yield and ex-farm quality of the malting barley. The earlier-sown treatments gave significantly greater yield than the later-sown in 13 of the experiments, and significantly lower grain N concentrations and screenings (small grains < 2.2 mm) in 14 and 16 of them, respectively. Early and more frequent fungicide applications improved grain yield and reduced grain screenings but had no significant effect on grain N. Early-applied fungicide (i.e. before GS 33) was generally the most effective in controlling disease, increasing yield and reducing screenings. The magnitude of the response depended on disease severity. In those years when disease was low on the early-sown crops (1989, 1991 and 1994), the early-applied 1-spray programme and 2-spray programmes increased grain yields by relatively small amounts in both early and late-sown crops. In the other 3 years (1990, 1992 and 1993), when disease severity was greater, the early-applied 1-spray programme and 2-spray programmes gave much greater grain yield increments on both early and late sowings. The 3-spray fungicide programme gave the greatest yields in most of the experiments but they were not significantly greater than the best of all the: other treatments. Grain screenings were reduced by fungicide applications in both early and late-sown crops, but the early-applied 1-spray programme and 2-spray programmes were generally the most effective in reducing screenings.
An experiment was carried out from August to early November 1994 to examine differences in diet selection, herbage intake, grazing behaviour and animal performance between weaned lambs rotationally grazing swards of annual ryegrass (Lolium multiflorum)/white clover (Trifolium repens) and Yorkshire fog (Holcus lanatus)/T. repens with or without Lotus corniculatus. There were four replicate groups of six lambs per treatment. The effects of condensed tannins (CT) on lamb production were assessed by twice-daily oral administration of 10g polyethylene glycol (PEG; molecular weight 4000) to half the lambs on each sward. The Lotus content of all swards was very low, and results are presented here for main sward comparisons meaned over lotus treatments. Overall mean estimates of pre-grazing herbage mass and sward surface height for the annual ryegrass and Yorkshire fog swards respectively, were 5820 v. 4360 +/- 190 kg DM/ha (P < 0.001) and 29 v. 21 +/- 0.6 cm (P < 0.001). The coefficient of organic matter digestibility (OMD) of the diet selected and herbage intake were higher on Yorkshire fog than on annual ryegrass (0.78 v. 0.74 +/- 0.080 g/kg; P < 0 05, and 1070 v. 860 +/- 57 g OM per lamb per day, P < 0 05 respectively), reflecting the higher content in the diet of grass green leaf (980 v. 930 g/kg +/- 14 g/kg, Pt 0 05) and the lower content of dead material (80 v. 110 +/- 15 g/kg, P < 0.08). Lambs grazing on Yorkshire fog swards had higher clean wool growth rate (1470 v. 1280 +/- 30 mg/cm per day, P < 0.01) and greater fibre diameter (31 v. 29 +/- 0.2 mu, P < 0.001), greater liveweight gain (152 v. 108 +/- 5.5 g/day, P < 0.001), final weight (42 v. 38 +/- 0.5 kg, P < 0.001), carcass weight gain (89 v. 69 +/- 2.5 g/day, P < 0.001), carcass weight (19 v. 17 +/- 0.3 kg, P < 0.001) and soft tissue thickness (GR value 11 v. 8 +/- 0.5 mm, P < 0.01), and lower faecal egg counts (FEC; square root transferred values 9.2 v. 11.0 +/- 0.4 eggs/g fresh faeces, P < 0.01) than lambs grazing annual ryegrass swards. Similar dietary concentrations of condensed tannins (CT) between Yorkshire fog and annual ryegrass swards (4.2 v. 3.7 DM +/- 0.2 g/kg, P < 0.08) increased clean wool growth (1440 v. 1310 +/- 32 mg/cm(2) per day, P < 0 05), fibre diameter (30.7 v. 29.5 +/- 0.21 , P < 0.01) and liveweight gain (141 v. 120 +/- 4.3 g per lamb per day, P < 0.01), although differences in carcass weight (17.9 v. 18.2 +/- 0.3 kg) and FEC transformed values (9.6 v. 11.0 +/- 06 eggs/g fresh faeces) were not significant. The effects of CT on animal performance were greater in Yorkshire fog swards. CT had no significant effects on diet selection, herbage intake and grazing behaviour patterns.
Cotton (Gossyphium hirsutum L.) yield and quality is affected by altered fruiting patterns with progress in season. The present study was conducted to analyse normal and altered (abnormal) boll (fruit) development at maturation phase, Both normal and abnormal bolls of the same age groups were analysed for growth in terms of dry weight, water content and endogenous abscisic acid (ABA) content of fibre and seed. Endogenous level of ABA was estimated by using antibodies raised against ABA-protein conjugate. To amplify the reaction, indirect ELISA (Enzyme Linked Immuno Sorbent Assay) was performed. A marked decrease in dry matter accumulation (DMA) of seed and fibre was observed in abnormal bolls as the season progressed. Fibre from the abnormal bolls showed marked variation in endogenous ABA content, however, in abnormal seeds water content and endogenous abscisic acid content showed significant variation compared to that of normal bolls. From the results, it is concluded that a marked decrease in seed dry weight may be because of a decrease in water content and accumulation of higher endogenous abscisic acid content, whereas, the major reason for reduced fibre weight may be due to accumulation of endogenous abscisic acid.
Labelling using the stable 15 isotope of nitrogen allows a close monitoring of the fate of the fertilizer applied to arable crops. Because N-15 data give direct estimates of nitrogen transformation rates, they also provide more stringent tests for N models than those based on bulk inorganic N dynamics. They may therefore point at flaws in models that had previously gone unnoticed, especially if N-15 was monitored on short time steps which capture even rapid processes like nitrification. Here we tested the simple, process-based model SUNDIAL on two such data sets obtained in Northern France under winter wheat and winter rape crops receiving various doses and forms of fertilizer N. In both experiments, microplots (approximate to 1 ml in size) within larger blocks were dressed with 2.0 atom-% enriched labelled N-15, as urea, or ammonium-nitrate as NH4+-(NO3-)-N-15 or (NH4+)-N-15-NO3-. Replicate micro-plots were subsequently sampled on four occasions after fertilizer application, and N-15 enrichment was monitored in plant roots and tops, and at several depths in the soil in inorganic and organic forms. Comparison between observed and simulated data showed that, shortly after application, SUNDIAL either underestimated (rapeseed) or overestimated (wheat) the rates of crop uptake, Also, the gradual incorporation of N-15 into soil organic matter was too quick in autumn and too slow in spring under the rapeseed crop. The simulation of the rapid depletion of the labelled soil inorganic N pool was correct under wheat, whereas under rape, SUNDIAL predicted an accumulation of nitrate which was not observed. After a longer time interval (1-2 months), the simulated and observed amounts of fertilizer-derived N in the crop and in the soil became more comparable. However, SUNDIAL only accounted for part of the unrecovered labelled N. Additional measurements indicated that denitrification and ammonia volatilization were responsible for most of the losses, with discrepancies occurring because SUNDIAL failed to volatilize ammonia after fertilizer spreading. The other major source of error lay in the simulation of crop demand for nitrogen, which may be improved based on sounder ecophysiological concepts, such as that of a regulation of plant uptake by shoot biomass.