K. W. Jaggard

Future Climate Impact on the Productivity of Sugar Beet (Beta vulgaris L.) in Europe

The impact of future climate change on sugar beet yields is assessed over western Europe using future (2021–2050) climate scenario data from a General Circulation Model (GCM) and the Brooms Barn simulation model of rain-fed crop growth and yield. GCM output for the 1961–1990 period is first compared with observed climate data and shown to be reliable for regions west of 24° E. Comparisons east of this meridian were less reliable with this GCM (HadCM2) and so were omitted from simulations of crop yield. Climate change is expected to bring yield increases of around 1 t/ha of sugar in northern Europe with decreases of a similar magnitude in northern France, Belgium and west/central Poland, for the period 2021–2050. Averaged for the study area (weighted by current regional production), yields show no overall change due to changed climate. However, this figure masks significant increases in yield potential (due to accelerated growth in warmer springs) and in losses due to drought stress. Drought losses are predicted to approximately double in areas with an existing problem and to become a serious new problem in NE France and Belgium. Overall west and central Europe simulated average drought losses rise from 7% (1961–1990) to 18% (2021–2050). The annual variability of yield (as measured by the coefficient of variation) will increase by half, from 10% to 15% compared to 1961–1990, again with potentially serious consequences for the sugar industry. The importance of crop breeding for drought tolerance is further emphasised. These changes are independent of the 9% yield increase which we estimate, on the basis of work by Demmers-Derks et al. (1998), is the likely direct effect of the increase in atmospheric CO2 concentration by 2021–2050.

Climatic impact on the productivity of sugar beet in Europe, 1961–1995

A recent study showed that drought stress was the major factor causing yield loss of the sugar beet crop in the UK. That study has been extended here by modelling potential and rain-fed yields (1961–1995) for European areas where irrigation of sugar beet is uncommon. The inputs to this study are an improved crop growth model, the European monthly half-degree gridded meteorological data time series, and a map of soil texture and available water capacity in sugar beet growing regions. Model outputs were scaled using a ratio of national mean to experimental plot yields to reflect commercial performance of a hypothetical 1998 variety for all years. The model was run on daily weather data reconstructed from monthly values. Potential yields increased from north to south and from west to east due to increased radiation receipts. Drought losses were greatest in east Ukraine and southern Russia, at over 40% of potential yield (5 t ha−1). Losses were intermediate (15–30% or about 2 t ha−1) in central Ukraine, west Poland, east Germany and England (sandy soils) and lowest in NW Europe and west Ukraine. Increasing continentality decreases the number of rainy days per month during summer and the fraction of diffuse radiation; this reduces the radiation use efficiency by as much as 11%. Model output was also used to examine the efficiency of sugar beet production across Europe; at the extremes, NW European farmers deliver about 80% of the potential rain-fed yield while Polish farmers are only able to deliver 40%. This study demonstrates the importance of breeding for drought stress tolerance in Europe.

The relative effects of drought stress and virus yellows on the yield of sugarbeet in the UK, 1980–95

Drought stress and virus yellows disease are two of the major problemsn of sugarbeet crop production in the UK. We have calculated the annual national drought losses from 1980n to 1995 by using long term data sets for two sites (IACR-Brooms Barn, Suffolk and ADASn Gleadthorpe, Nottinghamshire) to relate yield loss to cumulative potential summer moisture deficit, andn combining these relationships with regional meteorological records, soil type and crop distribution data. Experimentally measured relationships between yield losses and the timingn of virus yellows infection were combined with annual survey data of the extent of the problem,n and calculated infection dates from the UK aphid suction trap network, to calculate actual national annual losses to the disease. Potential losses in the absence of control measures weren then calculated by use of data from trials and surveys of pesticide use. The results showed a mean annual loss of production to drought stressn of 141000 t/year of sugar, 10·5% of production, with a loss to the industry of £27·9 million. Losses in individual years varied from zero to 2·5 times the mean figure. Actual losses to virus yellows were much smaller, due to the efficacy of treatments, averaging 24700 t/year of sugar (1·8%n of national yield, financial loss £5·5 million). Average potential virus yellows losses in the absence of controln measures were approximately double this. Control of virus yellows is a major, cost-effective contributor to rising and consistent sugarbeet production. Nationally, irrigation has made little impact on drought lossesn and, due to constraints in surface water supply, this situation appears likely to continue. Improvedn drought stress tolerance represents the largest single opportunity for yield and profitability improvement of the sugarbeet crop in the UK at present. Predicted climate change appears likely to increasen the severity of both drought and disease stresses. Drought stress appears relatively less importantn in other NW European sugarbeet-growing areas.

The impact of climate change on sugarbeet yield in the UK: 1976-2004

Since the 1970s, the delivered sugar yield per hectare has risen at an average annual rate of 0·111 t/ha, while the sugar yield in the official variety trials has increased at an average annual rate of 0·204 t/ha. These increases are usually considered to be the result of improvements in varieties and in beet agronomy. The present paper considers the possible impact of recent changes in climate on UK sugar yields by using the Brooms Barn Crop Growth Model and daily weather data collected over the last 30 years. Simulations of sugar yield using weather in eastern England since 1976 increased by an average annual rate of 0·139 t/ha, which accounted for about two thirds of the rate in the official variety trials. This increase was not an artefact of the accuracy of weather recording but it was, in part, accounted for by the trend to earlier sowing. Although it was not statistically significant, the earlier sowing trend was associated with an increase of 0·025 t/ha per year and was an indirect effect of the climate change. The annual deviations from these trends have not tended to become significantly bigger or smaller over the three decades. The model is not variety-specific, so it makes no allowance for variety improvements during the last 30 years. Clearly, varieties have improved so the implication must be that some of the changes in agronomy have tended to decrease the yields significantly. The changes in agronomic practice most likely to be responsible are the extension of the crop processing campaign, leading to greater post-harvest storage losses, and a decrease in the irrigated area.

Dependence of sugar beet yield on light interception and evapotranspiration

Abstract This paper presents an analysis of the growth of sugar beet crops in the UK between 1980 and 1991. The objective was to account for considerable variation in yield, in response to the weather and to irrigation, using simple relationships between yield and foliage cover, irradiance, vapour pressure deficit ( D ) and evapotranspiration ( E T ). The analysis considers an adaptation of the model of Doorenbos and Kassan [Doorenbos, J., Kassan, A.H., 1979. Yield response to water. FAO Irrigation and Drainage Paper 33, FAO/UN, Rome.] in which yield could be expressed in terms of both intercepted radiation ( I ) and E T . The relative importance of either depends on the parameter k y . Average growth rates of rain-fed and irrigated crops were 1.44 and 1.52 g MJ −1 ( ϵ ), with respect to I alone, and 6.49 and 5.87 g kg −1 ( q ) with respect to E T alone, but there was significant year to year variation. In rain-fed crops, ϵ was inversely correlated with average solar radiation and in irrigated crops, q was inversely correlated with D , but the expected constancy of qD was not found. Instead, variation in yields could be better accounted for by relating yield to both I and E T . Further improvements were possible by allowing crop growth rates to decay during the season, particularly with respect to I , when a common initial ϵ (1.76 g MJ −1 ) could be fitted that declined faster in rain-fed crops. The balancing parameter, k y , was estimated at 0.62, the amount of yield loss per unit of E T loss. These analyses provide a basis for simple yield forecasting models which rely on few meteorological variables and have only few easily estimated parameters.

The effects of drought on sugar beet growth in isolation and in combination with beet yellows virus infection

The effect of drought stress in isolation, or in combination with beet yellows virus infection, on sugar beet growth was studied in the field and glasshouse. Drought reduced total plant weight by 26%, due to 20 and 29% reductions in foliage and storage root yields respectively. Sugar extraction efficiency was depressed by an increase in amino-nitrogen impurities. Drought did not limit water extraction depth, despite decreasing lateral root growth in proportion to total weight. During the field experiments, total crop cover was decreased in all the droughted treatments (halved in some cases) for at least part of the season. Consequently, these treatments intercepted 12% less light, which in combination with a 16% decrease in the dry matter/light conversion coefficient, led to the decrease in growth. The decrease in conversion coefficient was due to temporary closure of the stomata rather than a function of drought-induced damage to the photosynthetic mechanism. The absolute effect of drought remained the same irrespective of whether the plants were infected with beet yellows virus, i.e. there was no interaction between the two stresses. The reasons for this lack of interaction are discussed but it is likely that the stress effects were mediated at different times of the day and season.

Integration of nitrate cover crops into sugarbeet ( Beta vulgaris ) rotations. I. Management and effectiveness of nitrate cover crops

Between 1989 and 1993, 17 experiments tested the effect of cover crop species, sowing date and destruction date on cover crop dry matter (DM) yield, N uptake and on soil mineral nitrogen (SMN) content. All the experiments were carried out in Suffolk, Norfolk, Lincolnshire and Yorkshire on sandy-loam textured soils after crops of cereals or oilseed rape had been harvested. The largest DM yields were obtained with early sowings and averaged 1.6t/ha. Cover crop N uptake was less dependent upon sowing date and averaged 35 kg N/ha. The average reduction in SMN was from 46 to 32 kg N/ha. Differences between cover crop species were small when compared with season/site variations. Cereal cover crop DM yields were closely related to the thermal time accumulated from the first significant rainfall after sowing, whilst the yields of non-cereal cover crops were more affected by the moisture content of the soil at sowing. The amount of SMN in the soil at sowing had little or no effect on cover crop yield. The yields of cereal cover crops were much more predictable than those of non-cereal cover crops. Water usage by cover crops was estimated to be 20 mm/t DM and large cover crops delayed the onset of leaching and reduced the amount of water leached. However, even in dry autumns and winters, soils are likely to reach field capacity before the following beet crop is sown. Due to their large C :N ratio (20:1) little N would be mineralized after cover crop destruction. Cover crops comprising volunteer cereals and weeds often performed as well as the other cover crops and in most cases will be the most cost-effective cover crops.

Effects of sowing date on plant establishment and bolting and the influence of these factors on yields of sugar beet

This study examined the effect of early sowing of sugar beet on plant establishment, bolting and yield and whether or not the standard of establishment and degree of bolting determined the most appropriate harvesting sequence. At Arthur Rickwood Experimental Husbandry Farm four experiments were made between 1974 and 1978 testing four sowing dates of four varieties each harvested on three occasions during the autumn. At Brooms Barn three dates of sowing of two varieties were tested in three experiments between 1976 and 1978. Sowing dates throughout the experiments covered a range from late February to late April. Also, at Brooms Barn in 1977 there were many bolters (plants which have a tall, flower-bearing stem) where the crop was sown on 4 March. The effects of bolter-control treatments, either cutting down the inflorescence or removing the plant, on sugar yield were compared. Sowing before mid-March often resulted in very gappy crops and many bolters; in consequence yields were seriously reduced. Late-March sowings were almost free from plant establishment problems and, where the bolting-resistant variety ‘Nomo’ was used, bolters were few; yields of Nomo were greater than where sown in early April. Progressively more yield was lost by delaying sowing throughout April. Variation in the extent of bolting between sites, seasons and sowing-date treatments was accounted for by variation in the number of cool days (with a maximum temperature of less than 12 °C) after sowing. Yield was lost at a rate of 0·7% for every 1% of bolters over the range 5–40% bolting. During the autumn, crops at Arthur Rickwood which had more than 5% bolters and/or less than 60000 plants/ha gained 0·45 t/ha less sugar than did those with full, bolterfree plant stands. In 1977 many of the early-sown plants bolted; pulling the bolters or cutting the inflorescences improved yield, but not sufficiently to raise yields to the level produced by later-sown, bolter-free crops.

Modelling radiation interception and radiation use efficiency for sugar beet under variable climatic stress

European sugar beet crops suffer drought stress, and climate change is likely to increase the frequency and severity of drought. Changes in rainfall pattern may also affect the radiation environment. Modelling is an appropriate tool to assess the scale of these problems. In a sugar beet model we included the effects of water stress on foliage dynamics (radiation interception) and of variable radiation use efficiency (RUE). Foliage expansion and senescence were related to the relative water content in the root zone and drought response factors were calibrated from rain-shelter experiments for early and late drought in England. Simulating variable drought response in different growth phases explained 70–96% of the foliage variation for rain-fed growth. The dependence of RUE on the fraction of radiation that is diffuse was described theoretically; measured variation of RUE (0.9 g DM MJ−1) matched well the empirical representation of this theoretical relationship. We evaluated these modifications using experimental total dry matter and sugar yields in the UK and in Germany (1965–1995). Including foliage dynamics and variable RUE improved the simulation of observed yields in the UK in some years. For continental sites mean sugar yields were well described when differences in the antecedent soil water balance were accounted for. The agreement between estimated and observed yields was close to 1:1, explaining between 30 and 45% of observed variation, though not appreciably different from when the original model was used. This was because the test data included only a few seasons with either severe water stress or abnormal fractions of diffuse sunlight. Ideally the model should be tested against crop growth data from more extreme environments. Nevertheless, we conclude that the expanded model is now more suitable for use across much of Europe and future climatic change.

An analysis of the agronomic, economic and environmental effects of applying N fertilizer to sugarbeet ( Beta vulgaris )

The effects of different rates of N fertilizer (0-180 kg N/ha) were tested on the growth, yield and processing quality of sugarbeet in 34 field experiments in England between 1986 and 1988. The experiments were performed using soil types, locations and management systems that were representative of the commercial beet crop in the UK. The responses obtained showed that current recommendations for N fertilizer use are broadly correct, but large differences occurred on some soil types, in some years, between the recommended amounts and the experimentally determined optima for yield. The divergence was largest when organic manures had been applied in the autumn before the beet crop. Calculations using a simple nitrate-leaching model showed that much of the N in the manures was likely to be leached, the extent of leaching being much less if the manure application was delayed until spring. In these circumstances, spring measurement of inorganic mineral N in the soil could improve fertilizer recommendations. In situations where higher than optimum rates of fertilizer N were used, the extra N had little effect on yield. Increasing the rate from 0 to 180 kg N/ha increased the amount of nitrate left in the soil at harvest by only 8 kg N/ha. The amount of inorganic N released into the soil from crop residues at harvest increased by 50 kg N/ha with N application rate, and the fate of this N has not been established.