The relevance of N fertilization for the amount of total greenhouse gas emissions in sugar beet cultivation

The agricultural sector is highly affected by climate change and it is a source of greenhouse gases. Therefore it is in charge to reduce emissions. For a development of reduction strategies, origins of emissions have to be known. On the example of sugar beet, this study identifies the main sources and gives an overview of the variety of production systems. With data from farm surveys, calculations of greenhouse gas (GHG) emissions in sugar beet cultivation in Germany are presented. Emissions due to the production and use of fertilizers and pesticides, emissions due to tillage as well as field emissions were taken into account. All emissions related to the growing of catch crops during fall before the cultivation of sugar beet were also included. The emissions are related to the yield to express intensity.The median of total GHG emissions of sugar beet cultivation in Germany for the years 2010–2012 amounted to 2626 equivalents of CO₂ (CO₂eq) kg ha⁻¹ year⁻¹ when applying mineral plus organic fertilizer and to 1782 kg ha⁻¹ when only organic fertilizer was applied. The CO₂eq emissions resulting from N fertilization exclusively were 2.5 times higher than those caused by diesel and further production factors. The absence of emissions for the production of organic fertilizers led to 12% less total CO₂eq emissions compared to the use of mineral fertilizer only. But by applying organic fertilizer only, there were more emissions via the use of diesel due to larger volumes transported (126 l diesel ha⁻¹ vs. 116 l ha⁻¹ by applying mineral fertilizer exclusively).As there exists no official agreement about calculating CO₂eq emissions in crop production yet, the authors conclude that there is still need for further research and development with the aim to improve crop cultivation and crop rotations concerning GHG emissions and the therewith related intensity.     

Effects of ozone on sugar beet grown in open-top chambers

Sugar beet (Beta vulgaris cv. Patriot) plants were grown on field plots and in open-top chambers (OTCs) in two successive years. In the OTC treatments, plants were exposed to charcoal filtered air, unfiltered air or unfiltered air enriched with additional ozone (O₃). Ozone exposure continued for almost 5 months and the 8-h average concentration was raised from 34 to 39 nL L⁻¹ in the ambient air chambers to 62 nL L⁻¹ in the ozone enriched chambers. In both years, the AOT40 exposure index in the ozone enriched chambers exceeded 30 μL L⁻¹ h during the 5-month exposure period compared to 6.5 and 2.9 μL L⁻¹ h in ambient air in 2003 and 2004, respectively. Visible symptoms in the form of small white necrotic flecks appeared in both seasons in the ozone enriched chambers. When the data for both years were analysed statistically, a significant reduction of root yield of 6% and a slight reduction of sugar content were detected. These changes resulted in an overall reduced sugar yield ha⁻¹ of about 9%. Although the sensitivity of sugar beet to ozone is highly variety-dependent, in general this biennial crop appears less sensitive than annual crops such as wheat and potato. Ozone has limited effects on quality parameters in sugar beet, although an increase in α-amino-N content was observed, in agreement with the increased nitrogen content resulting from ozone exposure of wheat and potato.Enclosure within the OTCs increased aboveground biomass but decreased root yield (fresh biomass) and sugar content. These effects were most likely caused by a reduction of radiation by the chamber walls and annulus. The increased temperature in the chambers reduced yield quality by increasing mineral content.     

Effect of plant density and nitrogen rates upon the leaf area of seed sugar beet on seed yield and quality

Three-year field trials were set up on eutric brown soil in northwestern Croatia (Zagreb) with the objective to determine the effect of plant density and nitrogen rates on the formation and size of leaf area of seed sugar beet, and on the yield and seed quality in seed production without transplanting. Investigations should also reveal how much the yield and quality of sugar beet seed depend on the leaf area index (LAI). Four plant densities of seed sugar beet were investigated after crop wintering (40 000, 80 000, 120 000, and 160 000 plants/ha) as well as three nitrogen rates (60, 120, and 180 kg/ha) applied in two identical topdressings: at the beginning of the spring growing period and immediately before shooting of inflorescence stalks. Leaf area formation was strongly influenced by weather conditions. An increase of plant density from 40 000 to 160 000 plants/ha led to a decrease of leaf area per plant. Raised nitrogen rates in topdressing caused an increase of leaf area, depending on the precipitation and soil fertility. Maximum LAI, achieved in the flowering stage, grew almost linearly with increasing plant density (LAI: 1.77–4.85 m²/m²), but was statistically significant only up to 120 000 plants/ha. Raised nitrogen rates in topdressing led to a significant increase of the LAI in the stage of inflorescence stalk shooting, though not in full flowering. On the basis of this research, seed yield and germination of seed sugar beet could not be predicted regarding LAI in the flowering stage.     

Yield,growth and grain nitrogen response to elevated CO2 in six lentil (Lens culinaris) cultivars grown under Free Air CO2 Enrichment (FACE) in a semi-arid environment

Atmospheric CO₂ concentrations ([CO₂]) are predicted to increase from current levels of about 400 ppm to reach 550 ppm by 2050. The direct benefits of elevated [CO₂] (e[CO₂]) to plant growth appear to be greater under low rainfall conditions, but there are few field (Free Air CO₂ Enrichment or FACE) experimental set-ups that directly address semi-arid conditions. The objectives of this study were to investigate the following research questions: 1) What are the effects of e[CO₂] on the growth and grain yield of lentil (Lens culinaris) grown under semi-arid conditions under FACE? 2) Does e[CO₂] decrease grain nitrogen in lentil? and 3) Is there genotypic variability in the response to e[CO₂] in lentil cultivars? Elevated [CO₂] increased yields by approximately 0.5 t ha⁻¹ (relative increase ranging from 18 to 138%) by increasing both biomass accumulation (by 32%) and the harvest index (by up to 60%). However, the relative response of grain yield to e[CO₂] was not consistently greater under dry conditions and might depend on water availability post-flowering. Grain nitrogen concentration was significantly reduced by e[CO₂] under the conditions of this experiment. No differences were found between the cultivars selected in the response to elevated [CO₂] for grain yield or any other parameters observed despite well expressed genotypic variability in many traits of interest. Biomass accumulation from flowering to maturity was considerably increased by elevated [CO₂] (a 50% increase) which suggests that the indeterminate growth habit of lentils provides vegetative sinks in addition to reproductive sinks during the grain-filling period.     

Trade-offs between water-use related traits,yield components and mineral nutrition of wheat under Free-Air CO2 Enrichment (FACE)

This study investigated trade-offs between parameters determining water use efficiency of wheat under elevated CO₂ in contrasting growing seasons and a semi-arid environment. We also evaluated whether previously reported negative relationships between nutrient content and transpiration efficiency among wheat genotypes will be maintained under elevated CO₂ conditions. Two cultivars of wheat (Triticum aestivum L.), Scout and Yitpi, purportedly differing in water use efficiency related traits (e.g. transpiration efficiency) but with common genetic backgrounds were studied in a high yielding, high rainfall (2013), and in a low yielding, very dry growing season (2014) under Free-Air CO₂ Enrichment (FACE, CO₂ concentration of approximately 550 μmol mol⁻¹) and ambient (approximately 390 μmol mol⁻¹) CO₂. Gas exchange measurements were collected diurnally between stem elongation and anthesis. Aboveground biomass and nutrient content (sum of Ca, K, S, P, Cu, Fe, Zn, Mn and Mg) were determined at anthesis. Yield, yield components and harvest index were measured at physiological maturity. Cultivar Scout showed transiently greater transpiration efficiency (measured by gas exchange) over cultivar Yitpi under both ambient and elevated CO₂ conditions, mainly expressed in the high yielding but not in the low yielding season. Nutrient content was on average 13% greater for the lower transpiration efficiency cultivar Yitpi than the cultivar with higher transpiration efficiency (Scout) in the high yielding season across both CO₂ concentrations. Elevated CO₂ stimulated grain yield to a greater extent in the high yielding season than in the low yielding season where increased aboveground biomass earlier in the season did not translate into fertile tillers in cultivar Yitpi. Yield increased 27 and 33% in the high yielding and 0 and 19% in the low yielding season for cultivars Yitpi and Scout, respectively. Intraspecific variation in CO₂ responsiveness related mechanisms of grain yield were observed. These results suggest CO₂-driven trade-offs between traits governing water use efficiency are related to both growing season and intraspecific variations, and under very dry finishes, the trade-offs may even reverse. The negative relationship between nutrient content and transpiration efficiency among wheat genotypes will be maintained under elevated CO₂ conditions.     

Effects of weather variables on sugar beet yield development (Beta vulgaris L.)

There is much data on the impact of weather variables on the growth of sugar beet from studies conducted under controlled conditions or single field experiments, but these data are of only limited validity for other sites or larger areas. The aim of the present study was to quantify the influence of weather conditions on the growth of sugar beet for the further development of simulation models, based on data representative of sugar beet cultivation in Germany. For this purpose, 27 field trials were conducted in 2000–2001 in commercial fields with variable climatic and soil conditions. From the end of May until the end of the season, beets were harvested manually every 4 weeks, the dry matter yield of leaves and taproot was determined and their growth rates were calculated. Temperature, solar radiation, rainfall and humidity were recorded daily for each site and the potential evapotranspiration and climatic water balance were estimated. The soil water content to a depth of 0.9 m was determined at every harvest date.Several functions were developed to describe the growth of sugar beet as affected by the given meteorological variables. From sowing to the end of June, the dry matter accumulation of both leaves and taproot was strongly enhanced by increasing temperature and during this period leaf dry matter increased linearly with thermal time. After reaching 700 °C d, the taproot dry matter accumulated exponentially with thermal time. The optimum mean daily air temperature for taproot growth was approximately 18 °C. Higher temperature occurring in July and August decreased final taproot yield, but by the end of the season, growth was independent of temperature. High solar radiation advanced growth during the first 65 days after sowing and again in October.Neither the water input by rainfall and irrigation nor the climatic water balance adequately described the growth of the leaves or taproot, but it was shown that the increase in taproot dry matter during July and August depended on the amount of available water in the soil. The maximum sugar yield that can theoretically be achieved in Germany and comparable agroclimatic regions was calculated as 24 t ha⁻¹. The present data reliable for a large agroclimatic region in Europe are of significant value as input for simulation models.     

Atmospheric CO2 enrichment affects potatoes: 1. Aboveground biomass production and tuber yield

Despite its economic and environmental importance, information about effects of future atmospheric carbon dioxide (CO₂) enrichment on aboveground biomass production and tuber yield of potato is still rare. Responses of potato (Solanum tuberosum L. cv. Bintje) were thus investigated in two full growing seasons under 380, 550 or 680 μmol mol^?1 CO₂ in open-top chambers (OTCs). When averaged over both years, aboveground stem biomass at canopy maturity was negatively related to CO₂ enrichment. Aboveground-to-belowground biomass ratio was negatively related to CO₂ enrichment as there was a positive relationship between CO₂ and total dry yield of potato tubers. The stimulation was mainly related to an increase in the tuber size fraction for commercial yield (tubers > 35 mm). For the largest size class (tubers > 50 mm), which is important for industrial processing, large CO₂-induced impacts were observed too, although these effects were not significant. Elevated CO₂ concentrations will thus affect biomass allocation of potato plants and result in improvements concerning the market value of the commercial tuber yield.     

Soybean (Glycine max (L.) Merr.) growth and development response to CO2 enrichment under different temperature regimes

The carbon dioxide (CO₂) concentration of the global atmosphere has increased during the last decades. This increase is expected to impact the diurnal variation in temperature as well as the occurrence of extreme temperatures. This potentially could affect crop production through changes in growth and development that will ultimately impact yield. The objective of this study was to evaluate the effect of CO₂ and its interaction with temperature on growth and development of soybean (Glycine max (L.) Merr., cv. Stonewall). The experiment was conducted in controlled environment chambers at the Georgia Envirotron under three different temperatures and two CO₂ regimes. The day/night air temperatures were maintained at 20/15, 25/20 and 30/25 °C, while the CO₂ levels were maintained at 400 and 700 ppm, resulting in six different treatments. Plants were grown under a constant irradiance of 850 μmoles m⁻² s⁻¹ and a day length of 12 h; a non-limiting supply of water and mineral nutrients were provided. Five growth analyses were conducted at the critical development stages V4, R3, R5, R6 and R8. No differences in start of flowering were observed as a function of the CO₂ level, except for the temperature regime 25/20 °C, where flowering for the elevated CO₂ level occurred 2 days earlier than for the ambient CO₂ level. For aboveground biomass, an increase in the CO₂ level caused a more vigorous growth at lower temperatures. An increase in temperature also decreased seed weight, mainly due to a reduction in seed size. For all temperature combinations, final seed weight was higher for the elevated CO₂ level. This study showed that controlled environment chambers can be excellent facilities for conducting a detailed growth analysis to study the impact on the interactive effect of changes in temperature and CO₂ on soybean growth and final yield.     

Organic fertilizer effects on growth,crop yield,and soil microbial biomass indices in sole and intercropped peas and oats under organic farming conditions

In a field experiment, peas (Pisum sativum L.) and oats (Avena sativa L.) were grown as sole crops and intercrops, fertilized with horse manure and yard-waste compost derived from shrub and garden cuttings at 10 t C ha⁻¹ each. The objectives were to compare the effects of these organic fertilizer and cropping system in organic farming on (a) yield of peas and oats, grown as the sole crop or intercropped, as well as N₂ fixation and photosynthetic rates, (b) the yield of wheat as a succeeding crop, (c) microbial biomass indices in soil and roots, and (d) microbial activity estimated by the CO₂ evolution rate in the field and the amount of organic fertilizers, recovered as particulate organic matter (POM). In general, organic fertilizer application improved nodule dry weight (DW), photosynthetic rates, N₂ fixation, and N accumulation of peas as well as N concentration in oat grain. Averaged across fertilizer treatments, pea/oat intercropping significantly decreased nodule DW, N₂ fixation and photosynthetic rate of peas by 14, 17, and 12%, respectively, and significantly increased the photosynthetic rate of oats by 20%. However, the land equivalent ratio (LER) of intercropped peas and oats exceeded 1.0, indicating a yield advantage over sole cropping. Soil microbial biomass was positively correlated with pea dry matter yields both in sole and intercropped systems. Organic fertilizers increased the contents of microbial biomass C, N, P, and fungal ergosterol in soil and CO₂ production, whereas the cropping system had no effects on these microbial indices. According to the organic fertilizer recovered as POM, 70% (manure) and 64% (compost) of added C were decomposed, but only 39% (manure) and 13% (compost) could be attributed to CO₂–C during a 101-day period. This indicated that horse manure was more readily available to soil microorganisms than compost, leading to increased grain yields of the succeeding winter wheat.     

Vulnerability of lodging risk to elevated CO2 and increased soil temperature differs between rice cultivars

Anthropogenic increases in atmospheric carbon dioxide concentration [CO₂], and subsequent increases in surface temperatures, are likely to impact the growth and yield of cereal crops. One potential means for yield reduction is for climate parameters to increase the occurrence of lodging. Using an in situ free-air CO₂ enrichment (FACE) system, two morphologically distinct rice cultivars, KH (Koshihikari) and SY (Shan you 63), were grown at two [CO₂]s (ambient and ambient + 200 μmol mol⁻¹) and two soil temperatures (ambient and ambient ± 1.8 °C) over a two year period to assess and quantify lodging risk. Elevated [CO₂] per se had no effect on lodging resistance for either cultivar. However, elevated [CO₂] and higher soil temperature increased the lodging risk for SY, due to a relatively higher increase in plant biomass and height at the elevated, relative to the ambient [CO₂] condition. Elevated soil temperature per se also increased lodging risk for both cultivars and was associated with longer internodes in the lower portion of the tillers. These findings illustrate that lodging susceptibility in rice, an important cereal crop, can be increased by rising [CO₂] and soil temperature; however, variation observed here between rice cultivars suggests there may be sufficient intraspecific variability to begin choosing rice lines that minimize the potential risk of lodging.     

Beet vinasse applied to wheat under dryland conditions affects soil properties and yield

The effect of six doses of beet vinasse (0, 3, 6, 10, 20 and 40 t ha⁻¹, respectively) on wheat (Triticum aestivum cv. Cajeme) yield in dryland conditions (Guadalquivir Valley, Andalusia, Spain) for 3 years on a Typic Xerofluvent was studied. The results showed that at low doses, beet vinasse is of agricultural interest due mainly to its organic matter concentration. The application of this byproduct to the soil increased soil microbial biomass and mineralization of its organic matter increased NO₃⁻–N concentrations in soil. This caused an increase in grain yield in the three seasons. When the vinasse was applied with high doses, NO₃⁻–N concentrations in soil, soil microbial biomass, soil structure, bulk density, electric conductivity, nutrient uptake, crop yield and grain quality were negatively affected. We assume that the high amounts of monovalent cations, particularly Na⁺, and of fulvic acids, which had been transported into the soil by the vinasse, destabilized the soil structure. This may have led to anaerobic soil conditions being presumably responsible for restricted N mineralization or even for denitrification. This explains the lower N supply to the crops reflected by the low N concentrations in the leaves of treatments A4 and A5.     

Sugar beet rotation effects on soil organic matter and calculated humus balance in Central Germany

In order to quantify the influence of land use systems on the level of soil organic matter (SOM) to develop recommendations, long-term field studies are essential. Based on a crop rotation experiment which commenced in 1970, this paper investigated the impact of crop rotations involving increased proportions of sugar beet on SOM content. To this end, soil samples were taken in 2010 and 2012 from the following crop rotation sequences: sugar beet–sugar beet–winter wheat–winter wheat (SB–SB–WW–WW = 50%), sugar beet–sugar beet–sugar beet–winter wheat (SB–SB–SB–WW = 75%), sugar beet–grain maize (SB–GM = 50%) and sugar beet-monoculture (SB = 100%); these were analysed in terms of total organic carbon (TOC) and microbial biomass carbon (MBC) content, MBC/TOC ratio and the TOC stocks per hectare. In addition, humus balances were created (using the software REPRO, reference period 12 years) in order to calculate how well the soil was supplied with organic matter. In the field experiment, harvest by-products (WW and GM straw as well as SB leaves) were removed. After 41 years, no statistically significant differences were measured between the crop rotations for the parameters TOC, MBC, MBC/TOC ratio and the TOC stock per hectare. However, the calculated humus balance was significantly affected by the crop rotation. The calculated humus balance became increasingly negative in the order SB–SB–WW–WW, SB–SB–SB–WW, SB monoculture and SB–GM, and correlated with the soil parameters. The calculated humus balances for the reference period did not reflect the actual demand for organic matter by the crop rotations, but instead overestimated it.     

Ultraviolet-B radiation and nitrogen effects on growth and yield of maize under Mediterranean field conditions

The effects of an increase in UV-B radiation on growth and yield of maize (Zea mays L.) were investigated at four levels of applied nitrogen (0, 100, 200 and 300 kg ha⁻¹ of N) under Mediterranean field conditions. The experiment simulated a 20% stratospheric ozone depletion over Portugal. Enhanced UV-B and N deficiency decreased yield and total biomass production by 22–49%. High UV-B dose reduced yield, total biomass and growth of N-fertilized maize plants but did not affect N-stressed plants to the same extent. The response of grain yield to N was smaller with enhanced UV-B radiation. The underlying mechanisms for these results are discussed.     

Can additional N fertiliser ameliorate the elevated CO2‐induced depression in grain and tissue N concentrations of wheat on a high soil N background?

Elevated CO₂ stimulates crop yields but leads to lower tissue and grain nitrogen concentrations [N], raising concerns about grain quality in cereals. To test whether N fertiliser application above optimum growth requirements can alleviate the decline in tissue [N], wheat was grown in a Free Air CO₂ Enrichment facility in a low‐rainfall cropping system on high soil N. Crops were grown with and without addition of 50–60 kg N/ha in 12 growing environments created by supplemental irrigation and two sowing dates over 3 years. Elevated CO₂ increased yield and biomass (on average by 25%) and decreased biomass [N] (3%–9%) and grain [N] (5%). Nitrogen uptake was greater (20%) in crops grown under elevated CO₂. Additional N supply had no effect on yield and biomass, confirming high soil N. Small increases in [N] with N addition were insufficient to offset declines in grain [N] under elevated CO₂. Instead, N application increased the [N] in straw and decreased N harvest index. The results suggest that conventional addition of N does not mitigate grain [N] depression under elevated CO₂, and lend support to hypotheses that link decreases in crop [N] with biochemical limitations rather than N supply.     

Yield decrease in sugar beet caused by reduced tillage and direct drilling

In a long-term series of on-farm tillage trials (10 loessial sites in southern and eastern Germany; annual mouldboard ploughing 0.25–0.3 m deep, mulching with a rigid-tine cultivator 0.1–0.15 m deep, direct drilling with no tillage except seedbed preparation for sugar beet solely) sugar beet yield was significantly decreased by direct drilling compared to ploughing. This study was conducted to (i) show that the lower plant density caused by mulching and direct drilling contributes to yield decrease but explains effects just partially, and (ii) determine the relation between soil structural properties and sugar beet yield. In 2003–2005 plant density experiments (53,000, 65,000 and 82,000 plants ha^?1) were introduced to tillage plots on five selected environments. Yield and soil structural properties of four layers representing 0–0.43 m soil depth were determined.White sugar yield (WSY) significantly declined with direct drilling compared to ploughing treatment, whereas mulching treatment diminished WSY less pronounced. Moreover, decreasing plant density significantly lowered WSY. No interactions between tillage and plant density occurred, revealing that both factors additively affected WSY.Decreasing tillage depth increased penetration resistance (PR) and dry bulk density (DBD), and diminished air filled pore volume (AFPV) in the topsoil down to 0.27 m depth. Several soil structural parameters were closely correlated with each other as well as WSY. Variation of single parameters explained up to 60% of WSY variance attributed to tillage. Combining DBD from 0.03 to 0.07 m depth, average PR from 0.03 to 0.27 m and AFPV from 0.03 to 0.18 m soil depth explained 77% of the tillage effect. Nevertheless, multi-collinearity of soil physical parameters allowed no clear conclusions on the cause-and-effect mechanisms.Conclusively, lowered plant density and soil structure degradation due to reduced tillage may independently decrease sugar beet yield. When grown on loessial soils this crop requires mechanical loosening down to 0.15–0.20 m depth to produce high yields.     

Yield of bolting winter beet (Beta vulgaris L.) as affected by plant density,genotype and environment

Winter beet roots and shoots might be a favorable substrate for biogas production in Central Europe. However, detailed information about the attainable yield of this crop is lacking. Thus, the impact of plant density, genotype and environmental conditions on total dry matter yield of winter beet crops that bolt after winter was investigated. A significant increase of the dry matter yield (esp. shoot) was expected by harvesting the 1st shoot after flowering in June followed by a final harvest of the whole plant in July. In 2009/10, 2010/11 and 2011/12, three series of field trials with (i) 3 target plant densities (148, 246, 370 thousand plants ha⁻¹) and (ii) 3 different sugar beet genotypes were conducted at Göttingen (Lower Saxony, GER) and Kiel (Schleswig-Holstein, GER); (iii), additional field trials with 5 different sugar beet genotypes cultivated at 2 target plant densities (148, 246 thousand plants ha⁻¹) were conducted in 2011/12, to investigate the relation between maximum taproot diameter and the shoot and taproot yield of bolting winter beet. The total dry matter yield considerably varied between 4 and 23 t ha⁻¹. It was predominantly affected by the environment and to a substantially lower extent by plant density. Increasing plant densities increased the total dry matter yield, resulting in a significantly higher total dry matter yield at plant densities ≥300,000 plants ha⁻¹ compared with lower plant densities. Genotypic differences in total dry matter yield were negligibly small. Pruning in June substantially increased the total dry matter yield in July by ca. 8 t ha⁻¹ only in one out of three environments.Final yield in June (without pruning) and July (pruning in June) was positively related with cumulated temperature and global radiation, but also with taproot dry matter yield before winter. The taproot, shoot (1st, 2nd) and total plant yield were positively correlated with maximum taproot diameter.In conclusion, high dry matter yields close to yields of established energy crops grown over winter were obtained with winter beet roots and shoots only under very favorable conditions (climate, single plant size). High yields can be achieved after good pre-winter development. However, for sufficient frost tolerance the taproot size of plants must be rather small. Hence, the cultivation of bolting winter beet under Central European climate conditions has to face a severe conflict of goals concerning winter survival and yield formation.     

Analysing the energy balances of sugar beet cultivation in commercial farms in Germany

Energy balances are increasingly used to assess the energy efficiency and productivity of agricultural production. In this study, energy balances for sugar beet cultivation in commercial farms in Germany were calculated. 109 farmers with 285 fields were interviewed about the sugar beet cultivation 2004. The energy input and the energy output were calculated with standardised balance-sheet approaches and energy equivalents. Calculated energy balance parameters were the energy gain (energy output less input), the output–input ratio (energy output versus input) and the energy intensity (energy input versus natural yield measured in Grain Equivalents). A factor analysis was performed to explain the variation of the energy balance parameters between the fields by crucial factors for energetic efficiency and productivity. Fields with similarly valued factors were grouped into common clusters by a cluster analysis and a discriminant analysis. The influence of specific growing conditions and cultivation methods on the energy balances were examined for the clusters.Total energy input (median: 17.3 GJ ha⁻¹), energy output (261.7 GJ ha⁻¹), energy gain (244.6 GJ ha⁻¹), output–input ratio (15.4) and energy intensity (87.4 MJ GE⁻¹) revealed a significant variation. The total energy input was significantly lower and the energy yield was significantly higher than in previous studies. Thus, the energy gain and the output–input ratio have clearly risen compared to earlier studies. Today, sugar beet cultivation is energetically more productive and efficient than the cultivation of many other arable crops in Middle Europe.The intensity of the cultivation measures irrigation, catch crop cultivation, tillage and N fertilisation as well as the management of all cultivation measures and the site were determined as crucial factors for energy efficiency and productivity. The intensity of the different cultivation measures influenced the total energy input significantly, but no influence on the energy output was determined. In contrast, the cultivation management (quality and adaptation of cultivation measures) was mainly responsible for the energy output. Whereas the cultivation management mostly explained the energy gain, the factor cultivation management and the factors representing cultivation intensity together were responsible for the output–input ratio.Cluster and discriminant analysis resulted in the formation of 13 clusters. For clusters with an above-average energy gain and output–input ratio, the intensity and in particular the management of cultivation measures were essential for optimising the energy balance.     

Efficiency in sugar beet cultivation related to field history

The concept of sustainable intensification in crop production has become more and more important over the last years. Calls for an efficient production demand an increase in yield without extending the agricultural area or increasing the amount of agricultural inputs. Thus, our study aimed to identify which variables influence the efficiency in crop cultivation in Central Europe and how we can explain the variances between fields. The data base for the present study was a survey among sugar beet farmers in all parts of Germany in the years 2010–2014. In order to structure the fields, variables representing environment, management and farm characteristics were extracted. The performed analysis according to components (principal component analysis) did not result in a nationwide structure of the data. Thus, fields were grouped according to similar preconditions such as regions and crop rotations. Sugar yield ranged from 12.5 t ha⁻¹ in 2010 to 15.4 t ha⁻¹ in 2014 on nationwide average. The median value for N fertilization over all fields and years was 137.4 kg ha⁻¹, the median treatment index (TI) reached 3.7, the median field evaluation index (Ackerzahl) was 70 and the median field size 8 ha. We found that over 50% of the variance among the data was explained by environment, management and farm characteristics. The comparison of fields on a regional basis was more sensible than on a nationwide basis as the variance of farms and fields was too broad for a useful clustering. It was concluded that the adaption of the farmer’s management to regional specific conditions is an opportunity to reduce yield gaps and to increase efficiency in terms of a sustainable intensification in sugar beet production.     

Effect of elevated carbon dioxide and temperature on phosphorus uptake in tropical flooded rice (Oryza sativa L.)

A field experiment was carried out to assess the impact of elevated carbon dioxide (CO₂) and temperature on phosphorous (P) nutrition in relation to organic acids exudation, soil microbial biomass P (MBP) and phosphatase activities in tropical flooded rice. Rice (cv. Naveen) was grown under chambered control (CC), elevated CO₂ (EC, 550 μmol mol⁻¹) and elevated CO₂ + elevated temperature (ECT, 550 μmol mol⁻¹ and 2 °C more than CC) in a tropical flooded soil under open top chambers (OTCs) along with unchambered control (UC) for three years. Root exudates were analyzed at different growth stages of rice followed by organic acids determination. Rhizospheric soil was used for analysis of soil phosphatase, MBP and available P. The total organic carbon (TOC) in root exudates was increased by 27.5% and 30.2% under EC and ECT, respectively over CC. Four different types of organic acids viz. acetic acid (AA), tartaric acid (TA), malic acid (MA) and citric acid (CA) were identified and quantified as dominant in root exudates, concentration of these was in the order of TA > MA > AA > CA. The TA, MA, AA and CA content were increased by 34.4, 31.1, 38.7 and 58.3% under ECT compared to that of UC over the period of 3 years. The P uptake in shoot, root and grain under elevated CO₂ increased significantly by 29, 28 and 22%, respectively than CC. Soil MBP, acid and alkaline phosphatase activity was significantly higher under elevated CO₂ by 35.1%, 27 and 36%, respectively, compared to the CC. Significant positive relationship exists among the organic acid exudation, MBP, phosphatase activities and P uptake by rice. The enhanced organic acid in root exudates coupled with higher soil phosphatase activities under elevated CO₂ resulted in increased rate of soil P solubilization leading to higher plant P uptake.