As a prerequisite for developing crop-yield/water-use functions for potatoes using the results of historical irrigation experiments, it was necessary to develop a water-use model which could operate with a limited data set. The general form of this model has been reported by Wright et al. (1994), and its application to the sugarbeet crop by Hamer et al. (1994). In this paper the development and validation of the model for potatoes is described.

The canopy was modelled in terms of intercepted incoming solar radiation using functions based on thermal time and time. Four phases of growth were identified: emergence, expansion, plateau and senescence. An empirical drought factor was included to allow for the effects of water stress on canopy development during the expansion phase. Root development was described using a two-phase model: linear and maximum depth (both time dependent).

Independent data from various sources were then used to validate the model in terms of its capacity to predict crop canopy development, with and without drought stress, soil water extraction at different depths and soil water deficits during the season. The study confirmed the validity of the model for predicting the water-use of potatoes.

Deer farming commenced in New Zealand (NZ) in 1969, and since then the number of farmed deer has progressively increased, to reach 1·3 million in 1993 (Game Industry Board (GIB), personal communication). These comprise 85% European red deer (Cervus elaphus), with the remainder being composed of elk (Cervus elaphus canadensis), elk/red deer crossbreds, fallow deer (Dama dama) and small numbers of other species. Initially, deer were obtained from the capture of feral animals, introduced to NZ over 100 years ago, but in the last 10 years the increase has come from breeding on deer farms. The industry has a strategic marketing plan to coordinate all sectors in order to maintain profitability. This plan has been implemented and financed by the GIB, through the collection of compulsory levies on venison and velvet sales. With the formation of the GIB in 1984, the NZ Deer industry has been strongly export market-led, and thus differs from the NZ sheep and cattle industries, which developed with a production driven philosophy. Key aspects of the market-led approach have been to produce and market venison which is consistently tender and of low fat content, and at the carcass weight range and times required by the markets.

The progenies of six crosses, made in 1987, between the best available hooded barley line and six selected awned barley lines were used to study the effect of the hooded gene on the performance of barley under rainfed conditions in Cyprus. A single dominant gene was found to control the hooded character. Awned genotypes on average outyielded hooded genotypes by 17%, but the difference between the two genotypes was smaller in the central plain than in the coastal area. The effect of the hooded gene on yield varied also with the combination of parents, as the superiority of the awned genotypes varied with cross from 13 to 30%. Hooded lines giving a higher grain yield than their hooded parent were identified. On average the awned genotypes had higher 1000-grain weight (5·0 g), were slightly later in heading date (1·1 days), had slightly higher volume weight (1·3 kg/hl) than hooded genotypes, but had similar plant height. The 1000-grain weight of most hooded lines was significantly higher than that of their hooded parent.

In spite of the negative effects of the hooded gene on grain yield, it was concluded that it is possible to increase the yield of hooded barley for hay production by continued crossing and selection (with special emphasis on 1000-grain weight), by selecting special combinations of parents through the Bulk-Pedigree method and by growing hooded barley in suitable areas, making use of the locationdependent performance of the hooded gene.

The effects of root and shoot characteristics on the lodging resistance of four cultivars of winter wheat were investigated by combining results from a field trial (set up at Manchester University's Experimental Grounds, Jodrell Bank, in mid-September 1991) with morphological and mechanical measurements on their stems and anchorage systems. Cultivars showed contrasting lodging resistance: Widgeon was most susceptible, followed by Galahad, Riband and Hereward which, alone, did not lodge. Lodging resistance was not related to the strength and stiffness of the stems, which were usually adequate to withstand the forces to which they were subjected. Most plants instead failed in their root system which rotated through the soil. Resistance was associated with short and light stems (and hence on the force applied to the plants by wind and gravity) and with high values of the anchorage strength of the root system (and hence on the force resisting lodging). Lodging occurred during grain filling when the ears were heaviest and when the soil was wet. The anchorage strength of a plant depended on two characteristics of the root system: the bending strength and the angle of spread of the basal coronal roots. Plants with stronger, more widely spread coronal roots produced larger soil cones during anchorage failure and resisted larger forces. Future breeding for lodging resistance, therefore, should continue to select for plants with shorter stems and with stiffer, more widely spread, coronal roots.

An attempt was made to re-assess the results of irrigation experiments carried out in the UK during the last 30–40 years in order to develop functional relationships between crop yield and actual wateruse. It was first necessary to develop a model, based on relatively simple functions, which could be used to predict actual water-use (evaporation and transpiration). The derivation of this model, known as WATYIELD, is reported here, whilst its application and validation for sugarbeet and for potatoes are described in subsequent papers. Simple functions relate components of evaporation to the proportion of the incoming solar radiation intercepted by the crop canopy, reference crop evapotranspiration, the precipitation and irrigation amounts and the soil water deficit. Transpiration is also related to soil hydraulic characteristics, rooting density and potential evaporation rate.

As a prerequisite for developing crop-yield/water-use functions for sugarbeet using the results of historical irrigation experiments, it was necessary to develop a water-use model which could operate with a limited data set. The general form of this model has been reported by Wright et al. (1994). In this paper the development and validation of the model for the sugarbeet crop is described.

The canopy was modelled in terms of the leaf area index and the relative interception of incoming solar radiation using functions based on thermal time and time. Four phases of growth were identified: emergence, slow-growth, fast-growth and full-canopy. An empirical drought factor was included to allow for the effects of water stress on canopy development during the slow- and fastgrowth expansion phases. Root development was described using a three phase model: initial (temperature dependent), linear and maximum depth (both time dependent).

Independent data previously reported from Broom's Barn Experimental Station were then used to validate the model in terms of its capacity to predict crop canopy development, with and without drought stress, soil water extraction at different depths and soil water deficits during the season. The study confirmed the validity of the model for predicting the water-use of sugarbeet.

Three rates of phosphate (0, 25 and 60 kg/ha P2O5) were applied for 7 years to phosphate-deficient grassland at Tel Hadya, north Syria. Liveweight, milk yield, wool production and supplementary feeding of Awassi sheep were monitored for six seasons (1985/86 to 1990/91). The experiment was grazed at low (0·8 sheep/ha per year) and high (1·7 sheep/ha per year) stocking rates from the second to the fourth season, while in the fifth to seventh seasons stocking rates were increased to 1·1 and 2·3 sheep/ha per year, respectively. The experimental site was typical of communally owned, degraded grasslands within the cereal zone of west Asia, where cropping is not possible because of shallow, stony soils and steep slopes.

The results showed that annual applications of phosphate, even at 25 kg/ha, improved pasture and sheep productivity. Liveweights were higher on fertilized plots in five out of six years, significantly so in the last three. Milk production was also higher on phosphate-treated plots, and the need for supplementary feeding was reduced, especially in the last three years, when rainfall was below average. The results suggest that stocking rates can be significantly increased by annual applications of small amounts of superphospate, and that doing so is profitable.

Use of the results depends on the presence of native legumes, the level of soil phosphate, and the ability of farmers to control grazing of these communally owned grasslands. A strategy to fulfil these criteria is suggested.

Two cereal cropping systems are described which, through the introduction of a leguminous intercrop, increased productivity, nitrogen output and ground cover of the systems in the absence of added nitrogen fertilizer. Nitrogen-fixing legumes were cultivated between rows of wheat or barley grown at low levels of soil nitrogen, and mostly under rainfed conditions, in Mexico between 1989 and 1992. None of the legumes tested reduced yields of the cereal crop in comparison to controls where cereal yields were in the range of 1–4 t/ha, while the extra total biomass from legumes in some cases more than doubled productivity. Different legume crops were tested to demonstrate the adaptability of the system to the varying needs of farmers. The intercropped legumes achieved dry biomass yields as high as 6·5 t/ha in the case of a sequentially cropped forage crop of hairy vetch, or 1·4 t/ha of dry beans plus 3·5 t/ha of green residue in the case of Vicia faba. Total biomass in the intercropped situation gave land equivalent ratios as high as 1·54. Light measurements inside the crop canopies indicated that the intercropped systems intercepted a higher proportion of the incident solar radiation than the cereal monocrop, presumably accounting for the large differences in total biomass produced. In addition, with leaf nitrogen levels of 3·8%, it is assumed that the intercropped legumes fixed considerably more nitrogen than was removed by the wheat crop. The potential of the system to stabilize erodible soils by increasing ground cover as well as by raising inputs of soil organic matteris discussed.

Sixteen common bean (Phaseolus vulgaris L.) cultivars with different life cycles and growth habits were intercropped with four maize cultivars, to evaluate the competitive ability of each yield component, following a methodology similar to that used for diallel crosses. The experiments were done in 1991 at two sites in Brazil. The intercropping combinations were evaluated using an 8 × 8 quadratic lattice design with three replications. Two other experiments were done on monocultures, using a randomized complete block design with three replications. The variable considered was ‘maize equivalent yield’, obtained by adjusting for the price difference between the species. The method used showed that the differences in performance of the many intercropped combinations can be explained by ‘general complementing ability’ (gĉa) of each cultivar, since there was no significant effect of ‘specific complementing ability’ (sĉa). The best maize cultivars to be intercropped with common bean (indicated by high gĉa values) were BR–201 and C–525, which produced high grain yields when intercropped without detrimental effects on legume yields. FT–84–292, Carioca 300V and ESAL506 were the common bean cultivars with the highest yields when intercropped, which was also reflected in their good performance in monoculture. Significant cultivar × location interactions occurred only in monocultures, supporting the belief that intercropping is a more stable cropping system.

The growth of kernels at selected positions along the spike of barley was studied using three models: segmented, logistic and Gompertz. The segmented model divides the growth period into three segments: an initial constant stage, a middle period of ‘linear growth’, and a final constant stage. The identification of a period during which growth is approximately linear - the ‘linear phase’ - was estimated from the curvilinear functions by imposing some criterion to determine the period of ‘linear growth’ in order that the results were similar to those from the segmented model. From this a model of final growth, growth rate and duration of growth as a function of kernel position was developed and fitted to data from four different thinning treatments at five sowing dates. The model of final growth and growth rate was shown to have a family of gamma functions. The analysis of these models showed that there were marked interactions between sowing and thinning treatments for growth rate, less so for grain yield, but there was no substantial interaction for duration.

At the research farm of the Swedish University of Agricultural Sciences, Uppsala, above- and belowground production and changes with time in root length, mean root radius and root surface area of spring oilseed rape were studied during the growing seasons 1987 and 1990. In both years, the highest root growth rate was recorded during the stem elongation phase, and the highest shoot growth rate during flowering. The root: shoot ratio decreased throughout the whole period of root sampling, from 0·64 to 0·16, during the cool and wet first year. In the warmer and drier second year, the ratio increased to a maximum of 0·72 when flowering started, and thereafter decreased. More than 80% of the root dry matter was found in the topsoil. Roots were longer and thinner in the dry and warm 1990 than in the wet and cool 1987. Maximum root length was c. 4·9 km/m2 in 1990, and mean root radius varied between 01 and 0·7 mm. Increases in root surface area during periods of root growth were due to increased root length rather than to increased mean root radius.

Experiments were conducted in glasshouses at IRRI, Philippines, during 1987 and 1988 to identify varietal differences in apical development using six rice cultivars having extreme characters; Jirasar 280 (early senescence), Neo-Dunghan 1 (late senescence), Macunting (small seeds), ABB (large seeds), C12474–1 (long culm), and B581–A6–458 (short culm); and five cultivars, IR20, IR22, IR34, IR54, IR64, of the same growth duration.

The length of time from physiological panicle initiation (PI) to flowering varied from 25 to 50 days. The onset of physiological PI occurred when the fourth penultimate leaf was fully exserted. The visual panicle initiation stage (VPI) coincided with spikelet differentiation in all cultivars. Nitrogen top-dressing at 55–57 days before the anticipated maturity date (the present N management recommendation) did not coincide with the actual panicle initiation stage in any of the cultivars and the major yield determinants (i.e. the primary and secondary branches) therefore differentiated in conditions of internal nitrogen shortage. Spikelet abortion took place both before and after flowering. Reduction of pre-flowering abortion is important in increasing rice grain yields and could be achieved by improved N management. It is important to recognise cultivar differences and periods of loss of potential yield in developing efficient N management protocols.

The developmental phase in which photoperiod sensitivity for podding occurs was determined for two bambara groundnut genotypes grown in 1987 and 1990 in glasshouse experiments in the Netherlands, namely genotypes ‘Tiga Nicuru’ from Mali (day-neutral for flowering and photoperiod-sensitive for podding) and ‘Ankpa 4’ from Nigeria (photoperiod-sensitive for both flowering and podding). Eighteen photoperiod treatments were given to each genotype. Two treatments consisted of a constant 12 or 14 h photoperiod and started 21 days after sowing for ‘Tiga Nicuru’ and 18 days after sowing for ‘Ankpa 4’. Eight treatments were introduced by transferring plants with at least 20 flower buds (33-day-old plants of ‘Tiga Nicuru’ and 35-day-old plants of ‘Ankpa 4’) from a 12 to a 14 h photoperiod or vice versa. In ‘Tiga Nicuru’ transference was for 4, 8, 12 days or until harvest, and in ‘Ankpa 4’ it was for 8, 12, 16 days or until harvest. Another eight similar treatments were given to plants transferred after having had at least 20 open flowers (48-day-old plants of ‘Tiga Nicuru’ and 62-day-old plants of ‘Ankpa 4’). Transferring plants of ‘Tiga Nicuru’ to the 12 h photoperiod for at least 8 days induced podding. Plants were susceptible to podding induction for nearly 4 weeks: podding was induced in plants which had been in the natural photoperiod (≥ 15·5 h) for 21 days, followed by 12 days in the 12 h photoperiod and subsequently in the 14 h photoperiod until harvest, and it could still be induced in 48-day-old plants that had had > 20 open flowers. However, transference to the 12 h photoperiod for 16 days did not induce podding in ‘Ankpa 4’. Transferring plants from the 12 to the 14 h photoperiod or vice versa caused differences in the number of flowers and pods/plant, petiole length and leaf area. The influence of photoperiod was most obvious on the number of pods/plant. Leaf area and number of pods/plant seem suitable parameters for modelling crop growth under different photoperiods. Leaf area development correlated with the number of developing pods/plant, but was also more directly influenced by the prevailing photoperiod.

Maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) were each sown at four plant densities, including zero, in a bivariate factorial design at Kiboko Rangeland Research Station, Kenya during the long and short rains of 1990. The design gave nine intercrops with different proportions of maize and beans, and six sole crops, three of maize and three of beans. Seed yields in both the sole crops were not significantly affected by plant density, so the mean yield was used to calculate the Land Equivalent Ratio (LER), which averaged 1·09 in the long rains but only 0·87 in the short rains. These low values were apparently due to the fact that beans failed to nodulate and fix nitrogen in the study area. The difference in LER between seasons was probably caused by differences in the amount and distribution of rain in relation to crop growth. Maize was more competitive than bean, each maize plant being equivalent to between 0·7 and 3·4 bean plants depending upon the treatment and the season.

A model was developed to assess the suitability of land in England and Wales for growing newly developed genotypes of autumn-sown determinate white lupins. The model used soil pH, the number of degree-days accumulated for mainstem leaf production before the apical meristem of the mainstem became floral, and the number of machinery work days in autumn. Interactions between these three components were used to set thresholds to determine land suitability within 5 × 5 km grid squares of the National Soil Map.

Of the potential 13·75 Mha of arable land in England and Wales, a total of 7·54 Mha are well or moderately suited to growing these lupin genotypes. This is equivalent to c. 2 Mha of land within the arable rotation each year. It was estimated that, because of low soil pH, lupins would be the preferred legume on 0·3 Mha out of this 2 Mha. The model was also used to assess the risk of soil acidification and nitrate leaching following mineralization of lupin residues. This exercise indicated that there was little risk of either on much of the land suited to lupins.

Early reports on new, nutritionally superior, white-flowered (zero-tannin) faba bean cultivars indicated that they may show poor emergence under field conditions. The field emergence of 23 winter and spring type white and coloured-flowered lines and cultivars was investigated in relation to fungicidal seed dressing in 1989/1990 and 1990/1991 in the UK. These trials showed no definite emergence problems in white-flowered faba beans, probably because of favourable soil and weather conditions. Further experiments were therefore conducted in relation to emergence under controlled environmental conditions. The emergence of lines near-isogenic except for flower colour (the coloured line SCI v. the white line SWI) was investigated in relation to a range of soil moisture levels (soil water potential (SWP) ranging from −1·02 to 0·0 MPa (waterlogged)) and to three temperatures (22, 12 and 5°C) in a clay loam soil. Emergence was rapid and high at the SWP range from −0·52 to −0·24 MPa in both lines, depending on temperature. Any decrease or increase in SWP beyond this range resulted in a substantial reduction and delay in emergence in both lines. Emergence of SWI was more adversely affected than SCI when the temperature decreased from 22 to 5 °C. The emergence of six winter and six spring lines/cultivars was tested in relation to fungicidal seed dressing using wet soil (-0·06 MPa) at 5 °C under controlled environmental conditions. White-flowered winter lines (WWI, Polar and WD) and the spring line, SWI, had poor emergence (56–85%) compared to coloured types (86–98%). In some lines there was a slight improvement when using a fungicidal seed dressing.

Leaf development was studied in eight related grasses, grown in field swards cut at 5-week intervals, during the year of sowing and the subsequent year (1989 and 1990). The rate of leaf expansion was in the order Westerwolds ryegrass > Italian ryegrass (Lolium multiflorum), Italian ryegrass × meadow fescue > hybrid ryegrass > perennial ryegrass × meadow fescue, meadow fescue (Festuca pratensis), tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne). The order of grasses was similar, but not identical, for rate of leaf appearance, rate of leaf extension, weight of leaf blade emerging per shoot per week and rate of increase in length of exposed leaf sheath, and the order was approximately the reverse for weight per unit area of emerging leaf blade. The area per leaf blade increased greatly between May and October of the year of sowing, particularly in Westerwolds, Italian and hybrid ryegrasses and Italian ryegrass × meadow fescue. Area per leaf blade in tall fescue increased greatly between May and July of the year of sowing and May–July of the subsequent year. Rate of leaf expansion in meadow fescue was much higher in May of the year after sowing than in the previous May.

The effects of particle size on the nitrogen degradability of four tropical forages were studied in 1991 in Guadeloupe. Samples of pangola grass (Digitaria decumbens) 22 and 47 days old, Gliricidia sepium and Leucaena leucocephala were prepared as follows: grasses were (1) freshly cut with scissors to 0·5–1·0 cm in length and frozen at – 18 °C; or for later study were dried at 80 °C and ground to pass a (2) 0·5 mm, (3) 10 mm or (4) 20 mm screen. Nitrogen degradability (ND) was determined by placing samples in nylon bags with two different pore sizes (25 and 46 μm) which were then put into the rumen of cows for 2, 4, 8, 16, 24 and 48 h. The kinetics of nitrogen degradation were examined using Ørskov's model. Particle losses through the nylon bags, dry matter (DM) and nitrogen solubility of the samples were also measured in vitro. The sample preparation and the type of forage were the main sources of variation in the rapidly degradable nitrogen fraction, the slowly degradable nitrogen fraction, the degradation rate, the potentially degradable nitrogen fraction and ND. Nitrogen degradability was 55·8,46·7, 640 and 46·5% for pangola grass (at 22 and 47 days regrowth), Gliricidia and Leucaena samples, respectively. Mean ND was 47·9, 59·4, 56·1 and 49·6% for freshly cut and 0·5, 1·0 and 2·0 mm dried ground samples, respectively. Sample preparation had little effect on nitrogen solubility. For samples dried and ground at 0·5 and 1·0 mm, particle losses were 18·8 and 15·0% of DM, respectively. The insoluble but degradable fraction was 60·8, 51·9, 42·5 and 42·7% for freshly cut and 0·5, 1·0 and 2·0 mm dried ground samples, respectively. The freshly cut material appeared to be suitable for the estimation of ND in tropical forages.

In 12 field experiments in England (1985, 1991 and 1992), on soils infested with potato pale cystnematode (Globodera pallida), oxamyl increased yields of susceptible and partially-resistant potatoes and lessened nematode multiplication at some sites but not others. Attempts to explain these site differences were unsuccessful. In a heavily infested peaty loam, large amounts of aldicarb or oxamyl, smaller amounts of both conjointly or 6·8 kg oxamyl/ha incorporated in the top 10 cm of the soil were needed to prevent G. pallida multiplication on susceptible Wilja potatoes. In three experiments, 1,3-dichloropropene at 250 or 225 1/ha increased tuber yields more than oxamyl did but had little or no effect on G. pallida multiplication. Ethoprophos at 11 kg/ha or fosthiezate at 4 kg/ha lessened G. pallida multiplication on Désirée potatoes in a silt loam soil but not in a peaty loam soil.

The multiplication of G. pallida was reliably controlled in ten experiments by partially-resistant Morag or Santé potatoes. Soil population densities of G. pallida were greatly decreased by one or two crops of Cara potatoes uprooted when the first female nematodes were visible on the roots.

It is concluded that granular nematicides and 1,3-dichloropropene are best employed to lessen injury to susceptible and partially-resistant potatoes and that G. pallida increase is best controlled by partially-resistant potatoes protected by a nematicide. Soil infestation levels can be decreased rapidly by soil fumigation or trap cropping with Cara potatoes.