A methodology for multi-objective cropping system design based on simulations. Application to weed management

Weeds are harmful for crop production but important for biodiversity. In order to design cropping systems that reconcile crop production and biodiversity, we need tools and methods to help farmers to deal with this issue. Here, we developed a novel method for multi-objective cropping system design aimed at scientists and technical institutes, combining a cropping system database, decision trees, the “virtual field” model FlorSys and indicators translating simulated weed floras into scores in terms of weed harmfulness (e.g. crop yield loss, weed-borne parasite risk, field infestation), weed-mediated biodiversity (e.g. food offer for bees) and herbicide use intensity. 255 existing cropping systems were simulated with FlorSys, individual indicator values were aggregated into a multi-performance score, and decision trees were built to identify combinations of management practices and probabilities for reaching performance goals. These trees are used to identify the characteristics of existing cropping systems that must be changed to achieve the chosen performance goals, depending on the user's risk strategy. Alternative systems are built and simulated with FlorSys to evaluate their multi-criteria performance. The method was applied to an existing oilseed rape/wheat/barley rotation with yearly mouldboard ploughing from Burgundy which was improved to reconcile weed harmfulness control, reduced herbicide use and biodiversity promotion, based on a risk-minimizing strategy. The best alternative replaced a herbicide entering plants via shoot tips (during emergence) and roots after barley sowing by a spring herbicide entering via leaves, introduced crop residue shredding before cereals and rolled the soil at sowing, which reduced the risk of unacceptable performance from 90% to 40%. When attempting to reconcile harmfulness control and reduced herbicide use, the best alternative changed the rotation to oilseed rape/wheat/spring pea/wheat, replaced one herbicide in oilseed rape by mechanical weeding, delayed tillage before rape and applied the PRE herbicide before oilseed rape closer to sowing. This option reduced the risk of unacceptable performance to 30%. None of the initial or alternative cropping systems succeeded in optimal performance, indicating that more diverse cropping systems with innovative management techniques and innovative combinations of techniques are needed to build the decision trees. This approach can be used in workshops with extension services and farmers in order to design cropping systems. Compared to expert-based design, it has the advantage to go beyond well-known options (e.g. plough before risky crops) to identify unconventional options, with a particular focus on interactions between cultural techniques.     

Ertragsbildung von getreidereichen Fruchtfolgen und Getreide-monokulturen in einem extensiven und intensiven Anbausystem

Yield formation in cereal-rich crop rotations and monocultures in an extensive and intensive crop-management system
In a long duration trial, conducted from 1979/80 to 1992 at TU-Munich's research station in Roggenstein, the performance of monocultures of winter wheat, winter barley and winter rye, as well as numerous cereal-crop rotations were compared in an extensive and intensive crop-management system. The results obtained can be summarized as follows.
Over the course of 13 years, the influence of the immediately preceding crop on the yield of the main crops was of much greater significance than the rotation as a whole. With winter wheat, no yield differences could be observed between monoculture and cereal crop rotation (if the rotation did not include oats). Oats, rape, field bean, pea, potato and maize as preceding crops, however, in crop management systems, led to, on average, an increase in yield of 13 dt/ha from the following wheat. Winter barley yields were not significantly different in monoculture, cereal crop rotations and crop rotations containing 66% cereals. Furthermore, winter rye yields were the same in monocultures and cereal crop rotations. With all cereals, intensification of fertilizing and chemical plant protection led to a considerable increase in yield, but did not diminish the effects of the preceding crop. Hence, even with the use of modern agronomical techniques it is impossible to compensate for yield losses due to crop rotation.     

Interactive Effect of Sulphur and Nitrogen on the Oil and Protein Contents and on the Fatty Acid Profiles of Oil in the Seeds of Rapeseed (Brassica campestris L.) and Mustard (Brassica juncea L. Czern. and Coss.)

In long-term field experiments on loamy sand and sandy loam, legumes (pea and lupine) stimulated microbial activity in the rhizosphere more than cereals (winter rye, winter wheat and spring barley), maize and oil flax. In the rhizosphere of winter wheat and maize, microbial activity and the bacteria species Pseudomonas , Agrobacterium and Xanthomonas were more stimulated by organic manuring than by mineral fertilization. A positive correlation between the stimulated bacteria species and the growth of young plants was found. Various mineral nitrogen applications had no influence on the rhizosphere microflora. The leghemoglobin content of pea nodules – an indicator of nitrogen fixation activity – was reduced by high nitrogen application in crop rotation.     

The effect of lupins as compared with peas and oats on the yield of the subsequent winter barley crop

New high yielding early maturing cultivars of lupins have been introduced in north-west Europe as grain protein crops in crop rotations. This paper reports on a comparative study of lupins with peas and oats, and of their effect on yield of subsequent winter barley crops. These crops were given five levels of N under irrigated and non-irrigated conditions on sand and loam. Under rain fed conditions the grain yield of pea, oat and lupin varied between 24–36, 34–53 and 18–37 hkg DM ha⁻¹, respectively. Supplemental irrigation raised grain yield of oat to 50–60 hkg DM ha⁻¹, while grain yield in pea was not affected and grain yield in lupin in most cases decreased due to gray mould attack and excessive vegetative growth in the indeterminate lupin variety. Under rain fed conditions, the grain nitrogen content of pea, oat and lupin varied between 137–172, 61–80 and 189–226 kg N ha⁻¹, respectively, and was significantly higher in lupin as compared with pea. On sandy soil, similar low-root densities were found for pea, oat and lupin below 30 cm depth. On sand, at final harvest the residual soil-N of lupin and pea, as measured in a subsequent winter barley crop not supplied with N fertilizer, was 15 and 8–10 kg N ha⁻¹ higher than in winter barley following oat, respectively. The nature of the probably more N-root residues of lupin is discussed. On loam, the residual N of lupin and pea was similar, 18–27 kg N ha⁻¹. On sand, under rain fed conditions preceding lupin and pea as compared with oat, increased the barley grain yield at zero N-application 77 and 49%, respectively; the effect of lupin was significantly higher than that of pea until the highest N-level 120 kg N-application ha⁻¹. On loam under rain fed conditions preceding lupin and pea increased the barley grain yield at zero N-application by 36 and 62%, respectively, as compared with oat; at N-application>60 kg N ha⁻¹ the grain yield was similar after all three crops. For both soil types the same level of effect was found under irrigated conditions. Conclusions: Supplemental irrigation might result in lower grain yield in lupin due to gray mould attack and excessive growth if indeterminate lupin varieties are used. Grain nitrogen yield of lupin is significantly higher than that of pea. On sand, the effect of lupin on the subsequent winter barley grain yield is significantly higher than that of pea, probably due to greater N-root nitrogen residues. On loam, lupin and pea have similar effects on the subsequent winter barley crop.     

Mechanical wounding under field conditions: A potential tool to increase the allelopathic inhibitory effect of cover crops on weeds?

To increase the inhibitory effect of soil-incorporated cover crop residues on germination and early growth of weeds, the allelochemical content of the cover crop at the time of soil incorporation should be maximal. We investigated whether mechanical damaging in spring induced the production of allelochemicals in late-summer sown lucerne, winter rye and winter oilseed rape. Allelopathic activity and biomass of intact cover crop plants were determined throughout spring, and mechanically damaged plants were monitored till 14 days after wounding. Allelopathic activity was determined directly by lettuce seedling bioassays (lucerne and winter rye) or indirectly by glucosinolate quantification (winter oilseed rape). During spring, the allelopathic activity per unit biomass of intact plants showed a gradual decline for winter rye and lucerne, and a steep decline at the onset of flowering for winter oilseed rape. All cover crop species attained the highest allelopathic activity per unit area at the end of the sampling period as the increase in biomass surpassed the decline in allelopathic activity per unit biomass. Although mechanical wounding enhanced the allelopathic activity per unit biomass of all three species, the effect was only minor and often just sufficient to compensate for the loss in biomass resulting from wounding. This study therefore indicates that the best option for maximizing the inhibitory effect is to incorporate residues of intact cover crops as late as possible.     

Effects of 15N Split-application on Soil and Fertiliser N Uptake of Barley, Oilseed Rape and Wheat in Different Cropping Systems

In intensive farming systems, farmers split up and apply the N fertilization to winter cereals and oilseed rape (OSR) at several dates to meet the need of the crop more precisely. Our objective was to determine how prior fertilizer N application as slurry and/or mineral N affects contributions of fertilizer‐ and soil‐derived N to N uptake of barley (1997), oilseed rape (OSR; 1998) and wheat (1999). In addition, residual fertilizer N effects were observed in the subsequent crop. Since autumn 1991, slurry (none, slurry in autumn, in spring, in autumn plus in spring) and mineral N fertilizer (0, 12 and 24 g N m⁻²) were applied annually. Each year, the treatments were located on the same plots. In 1997–1999, the splitting rates of the mineral N fertilization were labelled with ¹⁵N. Non‐fertilizer N uptake was estimated from the total N uptake and the fertilizer ¹⁵N uptake. All three crops utilized the splitting rates differently depending on the time of application. Uptake of N derived from the first N rate applied at the beginning of spring growth was poorer than that from the second splitting rate applied at stem elongation (cereals) or third splitting rate applied at ear emergence or bud formation (all three crops). In contrast, N applied later in the growing season was taken up more quickly, resulting in higher fertilizer N‐use efficiency. Mineral N fertilization of 24 g N m⁻² increased significantly non‐fertilizer N uptake of barley and OSR at most of the sampling dates during the growing season. In cereals, slurry changed the contribution of non‐fertilizer N to the grain N content only if applied in spring, while OSR utilized more autumn slurry N. In OSR and wheat, only small residual effects occurred. The results indicate that 7 years of varying N fertilization did not change the contribution of soil N to crop N uptake.     

Energy balance of winter oilseed rape (Brassica napus L.) cropping as related to nitrogen supply and preceding crop

Data from a field experiment (1995–2000) conducted on a fertile sandy loess in the Hercynian dry region of central Germany were used to determine the energy efficiency of winter oilseed rape (Brassica napus L.) as affected by previous crop and nitrogen (N) fertilization. Depending on the previous crop, winter oilseed rate was cultivated in two different crop rotations: (1) winter barley (Hordeum vulgare L.)–winter oilseed rape–winter wheat (Triticum aestivum L.), and (2) pea (Pisum sativum L.)–winter oilseed rape–winter wheat. Fertilizer was applied to winter oilseed rape as either calcium ammonium nitrate (CAN) or cattle manure slurry. The N rates applied to winter oilseed rape corresponded to 0, 80, 160 and 240 kg N ha⁻¹ a⁻¹.Results revealed that different N management strategies influenced the energy balance of winter oilseed rape. Averaged across years, the input of energy to winter oilseed rape was highly variable ranging from 7.42 to 16.1 GJ ha⁻¹. Lowest energy input occurred when unfertilized winter oilseed rape followed winter barley, while the highest value was obtained when winter oilseed rape received 240 kg N ha⁻¹ organic fertilization and followed winter barley. The lowest energy output (174 GJ ha⁻¹), energy from seed and straw of winter oilseed rape, was observed when winter oilseed rape receiving 80 kg N ha⁻¹ as organic fertilizer followed winter barley. The energy output increased to 262 GJ ha⁻¹ for winter oilseed rape receiving 240 kg N ha⁻¹ as mineral fertilizer followed pea. The energy efficiency was determined using the parameters energy gain (net energy output), energy intensity (energy input per unit grain equivalent GE; term GE is used to express the contribution that crops make to the nutrition of monogastric beings), and output/input ratio. The most favourable N rate for maximizing energy gain (250 GJ ha⁻¹) was 240 kg N ha⁻¹, while that needed for minimum energy intensity (91.3 MJ GE⁻¹) was 80 kg N ha⁻¹ and for maximum output/input ratio (29.8) was 0 kg N ha⁻¹.     

Einfluß von Monoethanolamin auf den Ertrag von Kulturpflanzen

Effect of monoethanolamine on yield of crops
I. Studies on the effect of monoethanolamine on the grain yield and the nitrogen household in cereal plants (pot experiments)
The effect of monoethanolamine (EA, applied as foliar spray, 10 mg per pot) on grain yield and yield components was investigated in pot experiments with spring barley, winter wheat, and winter rye. Under conditions of a moderate drought stress the applied EA increased the grain yield of spring barley from 5 % to 7 % (significance only at α= 0.05). A stimulating effect of EA on the grain yield of winter wheat and winter rye was also obtained.
The positive influence of EA on the grain yield of spring barley was reproducible under the conditions of a limited water supply in small-scale plot experiments (increase of yield about 9 %).
In case of spring barley and winter rye the increase of the grain yield by EA, applied at growth stage 31 (= DC 31) was connected with a greater number of ear-bearing tillers. The increase of the winter wheat yield resulted from more grains per ear of the tillers.
The enhanced formation of tiller grain mass and total tiller biomass by EA was in correlation with a higher nitrogen import into tillers (r = 0.8⁺). Since an export of N from the main shoots into the tillers was not observed a higher N uptake (≥ 6 %) was calculated from N balances. After a fertilization with ¹⁵N-labelled fertilizers the additional ¹⁵N uptake was 13 % to 20 %.
Possible stress reducing activities caused by EA are discussed.     

Reducing potential gene escape in time by appropriate post-harvest tillage—Evidence from field experiments with oilseed rape at 10 sites in Europe

Persistence of oilseed rapeseed in soil can result in weed problems but also reduce oil quality of following rape crops or result in unwanted gene escape which is particularly relevant in the context of genetically modified oilseed rape. In this paper data from 13 field experiments at sites in England, Austria and Germany are presented where tillage operations were tested that potentially reduce the build-up of a seed bank. In the majority of experiments seed losses were artificially simulated by broadcasting ca. 10,000 freshly ripened rapeseed m⁻² onto cereal stubbles. Oilseed rapeseedlings in autumn, the seed bank in winter–spring and yields of the following crop winter wheat were assessed as a function of tillage regime. During summer and autumn 19–70% of the seeds germinated and emerged. This part of the population was killed by following tillage operations or herbicide applications. However, 0–29%, in moist years 0–5%, of the initially broadcasted seeds developed dormancy and remained ungerminated in the soil until the following winter–spring.

Delaying incorporation of the seeds by leaving the stubble untouched for up to 4 weeks resulted in a reduced seed bank in almost every case. Also, repeated stubble tillage compared to an early single stubble tillage operation resulted in a smaller seed bank. The type of primary tillage (ploughing versus non-inversion cultivation) had no clear effect. No relation was found between the number of seedlings in autumn and the size of the seed bank the following winter–spring. Grain yield of the following crop winter wheat was not adversely affected by delayed stubble tillage.

The results indicate that stubble tillage aiming at a reduced seed bank of oilseed rape should focus on conditions avoiding induction of secondary dormancy rather than improving germination conditions. This means that, under the climatic conditions of central and western Europe, the stubble should be left untouched for several weeks after harvest before starting the usual tillage sequence with stubble tillage and ploughing or a non-inversion tillage sequence.     

Indentification of strong and weak yield determining components of winter oilseed rape compared with winter wheat

Yield formation of winter oilseed rape was compared with that of winter wheat in terms of absorption of PAR, radiation use efficiency and harvest index by means of crop growth simulation. Cumulative incoming PAR from April 15 until maturity, cumulative absorption of PAR, radiation use efficiency and harvest index were lower for winter oilseed rape compared with winter wheat. To improve potential seed yield of winter oilseed rape, a crop type with increased cumulative absorption of PAR, radiation use efficiency and harvest index is desirable.     

Application of pig slurry—First year and residual effects on yield and N balance

Crops generally utilize nitrogen (N) from slurries less efficiently than from mineral fertilizers. In order to compare the effects of slurry and mineral N application on yield and residual fertilization effects, a long-term field trial was established in autumn 1994, where pig slurry was applied to oilseed rape (OSR), winter wheat and winter barley at the same application dates as mineral N fertilizer. N amounts ranged from 0 to 240 kg total N ha⁻¹. The same treatment regimes were applied to the same plots in each year. Starting in 2010 (2011), wheat (barley) received no N fertilization in order to allow for testing residual fertilizer effects. Every year seed yield and N offtake by the seeds were determined.Accounting only for ammonia N of pig slurry, similar seed yields in OSR and slightly higher grain yields in wheat and barley compared to mineral N fertilizer were achieved. This indicates that mineralization of organically bounded slurry N compensated gaseous ammonia losses. In plots without N fertilization, OSR showed no yield trends during the experimental period, whereas wheat (barley) yield started to decrease after 10 (13) years without N fertilization. In the highly fertilized treatments, no significant trend in seed yield or N amount required for maximum yield could be detected. In the subsequent unfertilized wheat crop, accumulated slurry effects increased grain yield more than those of mineral N fertilizer. Barley grown in the second year without N supply remained unaffected by the previous slurry N application.     

Shortening generation times for winter cereals by vernalizing seedlings from young embryos at 10 degree Celsius

Methods allowing quick generation cycles are available for various crop species but are limited to spring genotypes. However, winter types predominate in many crops including wheat and barley. Different from spring ones, winter genotypes need to be treated in low temperature for extended periods to accelerate flowering. Combined with known factors that reduce generation cycles for spring wheat and barley, the generation cycle effects of vernalizing seedlings from young embryos of winter types at 10°C of several crop species were studied. Here, we described how to obtain up to seven generations of winter barley, six generations for winter wheat or five generations for both winter oat and triticale genotypes per annum. This procedure should find wide applications in breeding and other biological studies.     

Crop Management Effects on Pre-and Post-Anthesis Changes in Leaf Area Index and Leaf Area Duration and their Contribution to Grain Yield and Yield Components in Spring Cereals

Seasonal changes in leaf area index (LAI) and leaf area duration (LAD, i.e. LAI integrated over cumulated degree days) have a marked effect on crop productivity. Three case experiments were conducted at Suitia (60°11′N) and Viikki (60°13′N) Experimental Farms, University of Helsinki, Finland, to evaluate the possibilities of accelerating pre-an thesis expansion of leaf area and modifying pre- and post-anthesis LAD in spring cereals through crop management. Effects of time of incorporation of a green manure crop residue into the soil [conventional tillage (autumn ploughing and seed bed preparation in the spring), conservation tillage (sole spring tillage) with and without a green manure crop, common vetch (Vicia saliva I.)]and N fertilizer rate (0, 50, 100kg N ha^?1) on LAI and pre- and post-anthesis LAD in wheat (Triticum aestivum L.) were studied in exp I; green manuring (common vetch) and N fertilizer rate (0,40, 70,110,150kg N ha^?1) in barley (Hordeum vulgare L.), oat (Avena sativa L.), and wheat in exp II; and foliar application of chlormequat chloride (CCC) and ethephon in oat lines (dwarf, naked, modern, landrace) differing in canopy structure in exp III. Time of incorporation of the green manure crop residues into the soil (exp I), green manuring (exp II), N fertilizer rate (exps I and II), and selection for crop growth type (exp III), but not CCC and ethephon, modified LAI and LAD in spring cereals by affecting the rate of pre-anthesis expansion and post-anthesis reduction in leaf area rather than by markedly prolonging the growth period. High rates of N fertilizer accelerated expansion of leaf area, especially prior to stem elongation, and resulted in high pre-anthesis LAD due to enhanced tiller growth (exps I and II) and more tillers per main shoot (exp I). Green manuring increased leaf expansion from the tillering stage most when combined with high N rate, and especially in barley (exp II), but no such effects were found in exp I. Use of a high N fertilizer rate (exps I and II) and green manuring (exp II) also resulted in high post-anthesis LAD. Such modifications enabled higher rates of grain- and head-filling, and in exp I contributed to increased head weight and grain yield. Selection for inherent differences in growth type provided an additional possibility for manipulation of canopy structure and yield formation.     

The influence of crop sequence on fungicide and herbicide use intensities in North German arable farming

The reduction of pesticide use intensity is a societal and political ambition. Crop rotation is one important method to control pests and diseases in arable farming. We investigated the contribution of crop rotation to the variability of herbicide and fungicide use of 60 farms in four regions of Northern Germany. Our study aimed at answering the question: do diverse crop sequences lead to reduced herbicide and fungicide use in arable farming?Ten-year data on chemical plant protection measures and field management were examined for six field crops. We classified crop sequences (triplets of three succeeding crops) according to their susceptibility for weeds and diseases (= ’riskiness’). The Treatment Frequency Index (TFI) of the last crop in the triplet was set in relation to the crop triplet riskiness, additionally also in combination with tillage.In general, herbicide and fungicide use intensities were smaller in more diverse crop sequences. Diversified cereal sequences, involving roots and tubers, maize or spring cereals were less dependent on herbicides. Cultivation of maize in three subsequent years increased herbicide use. Crop sequences including high proportion of winter cereals increased fungicide use in cereals, while roots and tubers, winter oilseed rape and set-aside in the crop sequence decreased it. In winter oilseed rape, sequences with roots and tubers also increased fungicide use. In sugar beets, sequences with maize or a high concentration of sugar beets led to increasing fungicide use. If farmers chose riskier crop sequences tillage by plough decreased the need for herbicide and fungicide use.To reduce herbicide and fungicide use intensities we recommend increasing the diversity of crop rotations, including a higher number of crops per rotation together with ploughing. Simplifying both crop sequence diversity and tillage intensity implies higher use of herbicides and fungicides. Results will be useful for convincing farmers to diversify crop sequences.     

Assessing non-chemical weeding strategies through mechanistic modelling of blackgrass (Alopecurus myosuroides Huds.) dynamics

Because of environmental and health safety issues, it is necessary to develop strategies that do not rely on herbicides to manage weeds. Introducing temporary grassland into annual crop rotations and mechanical weeding are the two main features that are frequently used in integrated and organic cropping systems for this purpose. To evaluate the contribution of these two factors in interaction with other cropping system components and environmental conditions, the present study updated an existing biophysical model (i.e. AlomySys) that quantifies the effects of cropping system on weed dynamics. Based on previous experiments, new sub-models were built to describe the effects on plant survival and growth reduction of mechanical weeding resulting from weed seedling uprooting and covering by soil, and those of grassland mowing resulting from tiller destruction. Additional modifications described the effect of the multi-year crop canopy of grassland on weed survival, growth, development and seed return to the soil. The improved model was used to evaluate the weed dynamics over 27 years in the conventional herbicide-based cropping system most frequently observed in farm surveys (i.e. oilseed rape/winter wheat/winter barley rotation with superficial tillage) and then to test prospective non-chemical scenarios. Preliminary simulations tested a large range of mechanical weeding and mowing strategies, varying operation frequencies, dates and, in the case of mechanical weeding, characteristics (i.e. tool, working depth, tractor speed). For mechanical weeding soon after sowing, harrowing was better than hoeing for controlling weed seed production. The later the operation, the more efficient the hoeing and the less efficient the harrowing. Tractor speed had little influence. Increasing tilling depth increased plant mortality but increased weed seed production because of additional seed germination triggering by the weeding tool. Decreasing the interrow width for hoeing was nefarious for weed control. The best combinations were triple hoeing in oilseed rape and sextuple harrowing in cereals. The best mowing strategy was mowing thrice, every 4–6 weeks, starting in mid-May. The best individual options were combined, simulated over 27 years and compared to the herbicide-based reference system. If herbicide applications were replaced solely by mechanical weeding, blackgrass infestation could not be satisfactorily controlled. If a three-year lucerne was introduced into the rotation, weed infestations were divided by ten. Replacing chisel by mouldboard ploughing before winter wheat reduced weed infestations at short, medium and long term to a level comparable to the herbicide-based reference system.     

Can Leaf Chlorophyll Measures at Differing Growth Stages be used as an Indicator of Winter Wheat and Spring Barley Nitrogen Requirements in Eastern Canada?

Plant need-based N management approaches may increase the efficiency of N fertilizer application in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). The leaf chlorophyll concentration estimated through the SPAD-502 meter gives a relative assessment of N status in crop. Field trials were conducted near St John's, Newfoundland, between 1997 and 2000 to describe the relationship between winter wheat and spring barley grain yield, protein content, protein yield and SPAD measurements, as affected by differential stage of crop growth, seeding rate and topdress N fertilizer. Grain yield, protein content, and protein yield of winter wheat and spring barley exhibited linear responses to increasing N topdress application rate. SPAD-502 values were moderately to highly positively correlated with grain yield, protein content, and protein yield as a result of increasing topdress N fertilization, and moderately negatively correlated as a result of increasing seeding rate. It may be difficult to make an N-application rate recommendation based on SPAD measurements, as a critical SPAD value may vary among years, locations, cultivars and soil characters.     

Effect of Foliar Applications of Glycinebetaine on Stress Tolerance, Growth, and Yield of Spring Cereals and Summer Turnip Rape in Finland

Crop losses caused by environmental stresses might be reduced by applying osmoprotectans to crop canopies. Glycinebetaine is endogenously accumulated by some halophytes under stress conditions and represents such a compound. Glycinebetaine was applied exogenously to barley ( Hordeum vulgare L.), oat ( Avena sativa L.), spring wheat ( Triticum aestwum L.), and summer turnip rape ( Brassica rapa ssp. oleifera DC.) canopies and its optimal concentration was monitored in the greenhouse. In field experiments the response of crop plants to betaine applications was assessed by measuring accumulation of above ground biomass, leaf area index (LAI), leaf chlorophyll, and yield. The optimum betaine concentration producing advantageous effects on growth and crop physiology in turnip rape was close to 0.1 M and for wheat 0.3 M. Such concentrations promoted accumulation of betaine similar to that of halophytes under stress conditions [ca. 200 μmol (g DM)⁻¹]. In the 1993 field experiment peak LAIs were recorded in irrigated wheat and barley treated with 17.5 kg ha⁻¹ betaine applied at 300 1 ha⁻¹. Green leaf area was slightly more persistent in wheat treated twice with 1 kg ha⁻¹ betaine applied at 200 1 ha⁻¹ in 1994, although it was not associated with increased grain yield. Our results indicated that betaine has no actual potential in Finland for the principal grain crops but further studies are needed in stress prone environments to assess the potential of betaine treatments for preventing crop failures.     

Effect of Different Preceding Crops and Crop Rotations on Yield of Winter Oil-seed Rape (Brassica napus L.)

To determine the effect of different preceding crops and crop rotations on the grain yield of oil-seed rape, a long-term rotation experiment was conducted at the Hohenschulen experimental station in Kiel, NW Germany. Additional factors included the nitrogen fertilization and the fungicide application. The results reported herein are based upon the harvest years 1988 to 1993. Averaged over the different rotations and husbandry treatments, the grain yields in the 6 experimental years varied between 2.71 t ha^?1 and 3.99 t ha^?1. In contrast, the effect of the different husbandry treatments was smaller and non significant. Averaged over 6 years, only the fungicide application caused small yield increase of 0.2 t ha^?1. The highest grain yields of 3.77 t ha^?1 or 3.65 t ha^?1 occurred when oil-seed rape was directly following peas. Low yields between 3.15 tha^?1 and 3.33 tha^?1 were obtained when oil-seed rape was grown after oilseed rape. The lowest grain yield of 3.13 t ha^?1 was produced with oil-seed rape grown in monoculture only. In rotations with oil-seed rape following a preceding cereal crop (wheat or barley), the grain yields averaged between 3.22 tha^?1 in a two course rotation and up to 3.44 tha^?1 in a four course rotation. In general, the yields of oil-seed rape increase with the length of the rotation and the length of the break between two oilseed rape crops. The yield component number of seeds per m² was affected by the previous cropping accordingly, whereas the thousand seed weight did not respond to the cropping history. Based upon disease assessments in the first years of this experiment, we argue that an increase in the incidence of fungal diseases has considerably contributed to the yield decrease of oil-seed rape in short rotations.     

Einfluß langjähriger Winterweizen-Monokultur auf Ertragsbildung, Krankheitsbefall und Nematodenbesatz im Vergleich zum Winterweizenanbau in der Fruchtfolge

Influence of winter wheat grown continuously on grain yield, foot rot infection and nematodes compared with winter wheat in rotation
The field trial, started in 1968 at the experimental-station in Rauischholzhausen, was intended to give informations about winter wheat in continuous cultivation. The question was if intensification of growing culture enables monoculture wheat to yield as high as winter wheat in rotation (sugar-beet, winter wheat, spring barley). Influence of green manuring with additional nitrogen, straw manuring with additional nitrogen, straw burning and fungicid treatment against eyespot was investigated.
The following results have been obtained in the years 1969 to 1985:
1. In the 17 years average winter wheat in rotation yielded with 50.1 dt/ha a higher amount of grain dry weight than wheat in monoculture (43.6 dt/ha). Only in 3 years wheat in monoculture reaches the grain yield level of wheat in rotation.
2. The incidence of Pseudocercosporella herpotrichoides was in wheat after wheat about 10% higher than in wheat after sugar-beets.
3. The use of fungicides against culm base diseases caused in monoculture an increase in yield of about 2.7 dt/ha which was not higher than in rotation (+2.5 dt/ha).
4. The first 12 years indicated a decline-effect with continuously decreasing differences in the yield of wheat in monoculture compared with rotation. But until the 17th year of the trial grain yield differences were as high as in the beginning.
It is not possible either by means of intensification of fertilizing or chemical plant protection treatment to reach the grain yield level of winter wheat in rotation with winter wheat in monoculture. Even the use of modern agronomical methodes remains crop rotation as a central part of an effective plant culture.     

不同冬季覆盖作物轮作对农田土壤碳氮影响

风蚀是干旱区农田生态系统中土壤质量降低的关键因素,冬季作物覆盖可有效减少农田的土壤风蚀。通过探究河西灌区不同冬季覆盖作物轮作复种绿肥对农田土壤碳氮影响,以期为构建合理的周年覆盖轮作模式提供理论依据。本研究在热量一熟有余两熟不足的河西灌区春小麦种植区把冬小麦、冬油菜两种冬季覆盖作物和绿肥还田处理嵌套种植形成：（1）春小麦—冬油菜—箭筈豌豆(WCP)、（2）春小麦—冬小麦—箭筈豌豆(WWP)、（3）春小麦—箭筈豌豆(WP)、(4)春小麦—春小麦(W,CK)不同种植模式,在360 kg/hm² (N2)、270 kg/hm² (N1)、0 kg/hm² (N0) 3个施氮水平下,研究不同轮作模式对农田土壤碳、氮含量的提升效应。结果表明：在同一种植模式下土壤有机碳、土壤可溶性有机碳、热提取态有机碳、硝态氮、氨态氮、微生物量碳氮含量随施氮量的增加而增加,但在氮肥减量(N1)的条件下,与常规施氮(N2)相比较WCP轮作模式土壤有机碳、土壤可溶性有机碳、热提取态有机碳含量及微生物量氮无显著降低。相同施氮条件下,轮作模式间差异不显著,但与CK间差异显著;其中,0~10 cm土层,WCP轮作模式土壤有机碳、土壤可溶性有机碳、土壤热提取态有机碳、硝态氮、氨态氮、微生物量碳氮含量平均较CK提高5.42%、9.78%、10.96%、20.51%、15.76%、18.94%;10~30 cm土层,提高9.54%、7.06%、12.99%、20.12%、16.51%、18.16%。因此,春小麦轮作冬油菜复种绿肥模式在氮肥减量条件下仍对农田土壤碳氮有明显的提升效应,为河西灌区良好的周年覆盖作物轮作模式。