Abstract
The potential new oil crop Lepidium campestre (field cress) was undersown with long and short row distances in spring barley in three-year trials with eight replications. Plots with no undersowing were used as controls. The purpose was to assess the effect on barley-grain yield of the oil crop and its seed-yield potential. In the plots without undersowing, with long and short row distance of undersown L. campestre the barley-grain yields in the three years were, on average, 5069, 5130, and 5330 kg/ha, respectively. The trials showed a statistically significant positive effect on barley yield of undersowing with short row distance. The average seed yields of L. campestre in the following years were 4697 and 5000 kg/ha for plots with long and short row distance, respectively. The results are positive in relation to possibilities to domesticate this species as a new undersown oil crop for an energy-saving and environmentally friendly cropping system.
Introduction
In plant production the cropping system to a large extent determines energy inputs and environmental effects. Present cropping systems with only annual species in, e.g., cereals, oil crops, and pulses are energy demanding through annual sowing and tilling. These systems also leach plant nutrients, which instead of benefiting crop growth pollute the ambient aquatic environment (Bergström & Brink, Citation1986; Gustafsson, Citation1987). Despite an extensive accumulation of research and knowledge in this field during the last few decades, no significant reduction of leaching of plant nutrients from Swedish agriculture has been recorded (Johnsson & Mårtensson, Citation2002). Production systems where spring cereals are undersown are more efficient in reducing leaching than are those with spring- or autumn-sown annuals (Jensen, Citation1991; Lemola et al., Citation2000; Känkänena & Eriksson, 2007). A production system with undersowing of an overwintering oil crop in a spring cereal would save energy by sowing two crops at the same time without tilling in between. Leaching of nutrients would also be reduced by absence of tilling and by accumulation of biomass of the oil crop after harvest of the cereal. The oil crop then overwinters and is harvested the next season. If it is perennial these positive effects are increased. The system will have many of the energy and environmental advantages of ley production.
Fossil fuels are today exploited to a degree where there is a serious concern that we will run out of these relatively cheap sources of energy relatively soon. Increasing concerns about carbon dioxide emissions and their effect on climatic change and high crop yields per unit area with relatively low world market prices have initiated the quest for alternatives. Production of fuel in the form of ethanol and bio-diesel and of industrial raw materials has the potential to cover substantial areas of arable land. Oil crops for production of special industrial oil qualities to substitute for petroleum oils (Princen, Citation1983; Dyer et al., Citation2008) are especially attractive. They are a renewable source of raw materials and reduce the direct use of fossil sources.
A project at the Swedish University of Agricultural Sciences (SLU) aiming at domesticating the wild biennial cress Lepidium campestre L. of the Brassicaceae family has its starting point in the problem complexes referred to above. It aims at developing an oil crop that is undersown in a spring cereal. It will be furnished with an industrial oil quality. This species has been selected among a number of earlier investigated candidates (Merker & Nilsson, Citation1995). It has several advantages in the proposed production system. It has a good agronomic plant type with branching only in the upper part of the upright stems. It is a spring-germinating biennial with closely related perennials. Its life cycle is hence pre-adapted to undersowing. It has a winter hardiness far better than that of the Brassica oil crops, a suitable seed size, a high seed yield, and resistance to the pollen beetle (Merker & Nilsson, Citation1995). It also has an oil quality with high content of linolenic acid, which is an industrial quality as such (Nilsson et al., Citation1998). Self-fertilisation and diploidy are other important advantages enabling simple pure-breeding of characters in a domestication project. Investigations on cultivation and effects on yield of different sowing densities and nitrogen supply were presented by Börjesdotter (Citation1999a, Citation1999b).
Shattering resistance and higher oil content are key properties in the efforts to make L. campestre a useful oil crop (Merker & Nilsson, Citation1995; Andersson et al., 1998). These are characters determined by few or single genes, while winter hardiness, yield, life cycle, and adaptation to the cropping system or the environment generally, are properties with complex inheritance. Hence from a plant-breeding point of view it should be easier to domesticate L. campestre for the new cropping system and end use than to adapt established oil crops (Merker & Nilsson, Citation1995). Content of glucosinolates and protein and other characters affecting feeding value need not to be addressed to start with, since a purely industrial crop is the goal.
In establishing L. campestre as a new undersown oil crop its seed yield and its effect on the yield of the spring cereal are crucial. The present study was designed to elucidate these two aspects. Three-year trials with barley plots with L. campestre undersown at two different row distances and without undersowing allowed the analysis of interactions between the factors year, barley yield, and undersowing at two row distances to be made. The seed-yield potential of L. campestre and its interactions with year and row distance were also analysed. The yield factors thousand-grain weight (TGW) and thousand-seed weight (TSW) were also studied in the trials.
Materials and methods
Trials were sown in 2004, 2005, and 2006 in sandy loam soil at the Lönnstorp experimental station at Global Positioning System (GPS) coordinates N 55o40′9′′, E 13o6′10′′ near Alnarp, Sweden. Sowing dates were 2004-04-14, 2005-04-13, and 2006-05-03. The spring barley variety Prestige was sown with a 16-drill Öyord machine in four rows of six plots of the size 187.5 cm×300 cm at a density of 150 kg/ha. A block design was used with three treatments randomised in eight blocks. Each of the four rows of six plots hence contained two blocks. The three treatments were no undersowing (none), undersowing with 25-cm row distance (25 cm), and undersowing with 12.5-cm row distance (12.5 cm) of L. campestre accession NO94-6 collected in Arild, Sweden.
The undersowing with a plot size of 2.75 m2 (137.5 cm×200 cm with 9 rows 25 cm apart or 17 rows 12.5 cm apart) was made by hand by marking each row as a furrow at right angles to the barley rows by means of pressing into the ground a wooden frame of triangular rods. Furrows were covered after sowing. This gave a seed depth of 1–2 cm. The density of undersowing was 90 seeds per row.
The trials were given 100 kg N/ha for the barley before sowing and another 80 kg N/ha in early spring the following year for the L. campestre. Since herbicides could not be used in the trials, plots and paths between them were weeded by hand three times each season. This eliminated most weeds from the trials.
The trials were harvested with a combine harvester with a 1.6-m-wide header. This gave a harvested plot size of 4.8 m2 and 2.75 m2 for barley and L. campestre, respectively. Barley borders left after harvest were removed with the combine. All barley straw from the combine harvester was removed from the trial. Plot yields of the two species were weighed by the combine directly and a sample (700–1000 g) of each plot was taken and weighed manually. Samples were dried and the plot yields, TGW, and TSW were calculated on a 15%-moisture basis. Harvest dates were 2004-08-11, 2005-08-22, and 2006-08-12 for the barley and 2005-07-26, 2006-08-01, and 2007-07-18 for the L. campestre.
Besides yield the following parameters were recorded for each plot: stand of the barley (full stand = 100%), heading date of the barley, straw stiffness of the barley (standing upright = 100%), stand of the L. campestre (percentage of the total row length covered with plants) in the autumn and in the spring of the following year (full stand = 100%), date of initiation and termination of flowering of L. campestre, stalk stiffness of L. campestre (standing upright = 100%), and plant height of L. campestre in cm. TGW and TSW were determined on all dried plot samples.
Weather conditions were close to the average for the region in 2004, 2005, and 2007. 2006 was deviating and was dry after sowing with some precipitation in late May and early June. Then a very dry summer followed in June and July. August and September had high precipitation. Weather conditions in 2006 affected agricultural yields negatively in the whole region.
The data were analysed as a split-plot experiment with the GLM procedure of the software Statgraphics Plus (Manugistics Inc.), with year as main factor and treatments as sub-factors. Year was tested against year (repetition) and treatment against the residual variance. Barley yield and TSW data were log transformed before analysis as the variances differed between years. A 2-way analysis of variance (ANOVA) was done on separate year data with treatment (undersowing or row distance) and replications as factors. The means were tested for significant differences at 95% with the Duncan test.
Results
Barley grain yield varied both with year (P=0.0000) and undersowing (P=0.0038). However, the treatment effects on grain yield differed between years, but within limits for nonsignificance (P=0.0635). The main difference was a stronger positive effect of the shorter row distance of undersowing in 2006 (P=0.0949) and also a positive effect of the longer row distance in 2005 (P=0.1113). Over the three years undersown L. campestre with 25-cm row distance had no significant effect on barley grain yield. With a row distance of 12.5 cm, however, it had P=0.0038. The effects of treatments on TGW were all small and not significant ().
Table I. Barley grain yield and thousand-grain weight (TGW) without undersown L. campestre, with 25-cm row distance and with 12.5-cm row distance of undersown L. campestre 2004–2006. Different letters in each column denote significant differences according to the Duncan test at 95% significance level.
Seed yield of L. campestre the year after the barley crop was as high as 4848 kg/ha on average, but differed between years, with the highest yield in 2005 and lowest in 2006 (P=0.0001). There was no effect of different row distances over the three years (P=0.0871). However, in 2006 the 12.5-cm row distance out-yielded the 25-cm one (P=0.0140). This difference between years is also indicated by a significant year×row distance interaction (P=0.0431). The effect on TSW was different between years and row distance (P=0.0001 and P=0.0071, respectively). On average a short row distance resulted in smaller seeds. This effect was observed in all years, but was only significant for the high yielding year of 2005 (P=0.0261) ().
Table II. L. campestre seed yield and thousand-seed weight (TSW) with 25-cm and 12.5-cm row distance 2005–2007. Different letters in each column denote significant differences according to the Duncan test at 95% significance level.
No differences were observed in the barley plots between the three different treatments for stand of the plots, heading date, and straw stiffness. The stands were uniformly full (100%). Heading dates were 2004-06-24, 2005-06-23, and 2006-06-20 for the three years. The barley was standing upright (100%) in all plots over the three years.
The stands of the undersown L. campestre did not differ between row distances. In 2004/2005 there were good stands with an average score of 99%. In 2005/2006 the stands varied between 75 and 85% with an average for long and short row distances of 79 and 81%. In 2006/2007 the stands were again dense with averages of 98 and 99% for short and long row distances respectively. Stands in the spring were in all three years equal to those in the autumn.
The L. campestre plots started flowering in the first half of May (05-11, 05-07, and 05-12) and terminated flowering three weeks later. Flowering was between one and two days later for the plots with long row distances. All the L. campestre plots were standing upright in all three years. Plant height did not differ between row distances. Plant heights for the three years were 80, 75, and 75 cm, respectively. The L. campestre plots were harvested on 2005-07-26, 2006-08-01, and 2007-07-18 in the three years, respectively.
Discussion
The competition between the barley and the undersown species is crucial for the economic success and applicability of cropping systems with undersowing. Känkänen & Eriksson (Citation2007) reported neutral or significantly negative effects on barley grain yield by undersowing of different legume and grass species. Spaner & Todd (Citation2003), in barley trials with undersown forage mixtures, reported no effects of undersowing on barley-grain yields. In this light the present results are quite interesting. There seems to be a positive effect of undersowing of L. campestre on the barley yield. Different statistical treatments gave the same result. Although the present experiments give no direct explanation, the reasons can be sought in, e.g., water and nitrogen balance or in other indirect or direct interactions between the crops. The fact that the dry year 2006 showed the largest difference between plots without undersowing and plots with undersowing with short row distance could speak in favour of this possibility. Whatever the reasons are, it is interesting and promising for the cropping system with undersown L. campestre in barley that the two species function well together and that there may even be a yield advantage from the co-cultivation.
Another notable finding of this series of trials is the high seed yield of L. campestre with an average yield of over 4800 kg/ha. Border effects in the relatively small plots call for some caution in drawing conclusions from these results. On the other hand quite some shattering of seeds took place before and in connection with harvest. The measured seed-yield levels are anyhow surprisingly high, taking in account that we are dealing with a wild plant not affected by domestication and plant breeding. They are comparable with seed yields in southern Sweden of winter oilseed rape, Brassica napus. From trials in Uppsala, Merker & Nilsson (Citation1995) reported yields up to 3700 kg/ha, and Börjesdotter (1999a, 1999b) recorded values of over 2000 kg/ha. The present much higher yields could be explained with, e.g., a different location of the trials, more plant nutrients available, and higher border effect in the smaller plots. The accession of L. campestre used in the present experiments was collected not far from the trial site and should hence have a good general adaptation at the trial site. The present trials, with eight replications per year during three years, safely reflect the very high seed-yield potential of the species.
The yield of L. campestre seeds was not significantly different between the two row distances over the three years. Looking at the years individually this difference was statistically significant in 2006. This can be explained by the stands not being full in that year. They were on average 80% full as a result of incomplete emergence. This is in line with results of Börjesdotter (Citation1999a) who, in trials with Barbarea species and L. Campestre, found significant effects on seed yield of density of stands. Absence of plants in 20% of the total row length of the plots in 2006 had more severe effects in the plots with long row distance. The short row distance had a better ability to compensate for uneven emergence and stand. Taking in account also the effect of undersowing on the barley yield the short row distance is preferable in this cropping system, unless there are special reasons for a longer row distance, like, e.g., mechanical weeding.
The potential of using L. campestre as an effective oil crop is, however, influenced not only by the seed yield but also by the chemical composition of the seeds. Andersson et al. (Citation1999) as well as Nilsson et al. (Citation1998) in thorough analyses of seed composition of five accessions reported around 20% fat, 20% protein, and 40% dietary fibre. The high content of fibre is a result of a thick seed coat. With the present seed composition the species at a seed-yield level of 4 tons/ha produces the modest quantity of 800 kg oil/ha. This is comparable to the oil yield in southern Sweden of the relatively low yielding oil turnip rape, Brassica rapa. The isolation of mutants with a thin seed coat could improve this situation. It is known from the Brassica oil-crops that such mutants increase the oil content (Chen et al., Citation1988).
The numerical tendency of increasing TGW with undersowing is not statistically significant. The probable stimulation of barley grain yield by undersowing reported here is hence to be looked for mainly in other yield components. TSW of L. campestre plots with long row distance is statistically significantly higher than for short-row-distance plots. A compensation for fewer plants per plot by higher TSW seems to play a role, together with compensation also in other yield components.
The results presented here on possible positive effects of the undersowing on barley grain yield and the high seed yield of L. campestre seem promising for attempts to domesticate it as a new oil crop for a beneficial cropping system. In order to draw more precise conclusions on the interactions between the two crops further experimental work is needed. Field trials drawing also water and nitrogen balance as well as weeds and insects into focus would be informative, as would different laboratory experiments on allelopathic effects.
Acknowledgements
Financial support for this study was received from The Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas). Anders Engberg, Eskil Kempe, and Erik Rasmusson of the Lönnstorp experimental station are gratefully acknowledged for skilful handling of the trials, and Ann-Sofie Fält and Maria-Luisa Prieto-Linde for valuable technical assistance.
References
- Andersson , A.A.M. , Merker , A. , Nilsson , P. , Sörensen , H. and Åman , P. 1999 . Chemical composition of the potential new oilseed crops Barbarea vulgaris, Barbarea verna and Lepidium campestre . Journal of the Science of Food and Agriculture , 79 : 179 – 186 .
- Bergström , L. and Brink , N. 1986 . Effects of differentiated applications of fertilizer N on leaching losses and distribution of organic N in the soil . Plant and Soil , 93 : 333 – 345 .
- Börjesdotter , D. 1999a . Influence of plant density on stand development and seed yield of Barbarea verna, Barbarea vulgaris and Lepidium campestre . In : Börjesdotter , D. (1999) . Potential oil crops: Cultivation of Barbarea verna, Barbarea vulgaris and Lepidium campestre . Doctoral dissertation at the Swedish University of Agricultural Sciences, Department of Ecology and Crop Production Science. ISSN 1401-6249, ISBN 91-576-5746-7 .
- Börjesdotter , D. 1999b . Effects of nitrogen supply and seed rate on plant stand and seed yield of Barbarea verna, Barbarea vulgaris and Lepidium campestre . In : Börjesdotter , D. (1999) . Potential oil crops: Cultivation of Barbarea verna, Barbarea vulgaris and Lepidium campestre . Doctoral dissertation at the Swedish University of Agricultural Sciences, Department of Ecology and Crop Production Science. ISSN 1401-6249, ISBN 91-576-5746-7 .
- Chen , B.Y. , Heneen , W.K. and Jönsson , R. 1988 . Inheritance of seed colour in Brassica campestris L. and breeding for yellow-seeded . B. napus L. Euphytica , 59 : 157 – 163 .
- Dyer , J.M. , Stymne , S. , Green , A.G. and Carlsson , A.S. 2008 . High value oils from plants . Plant Journal , 54 : 640 – 655 .
- Gustafsson , A. 1987 . Nitrate leaching from arable land in Sweden under four cropping systems . Swedish Journal of Agricultural Research , 17 : 169 – 177 .
- Jensen , E.S. 1991 . Nitrogen accumulation and residual effects of nitrogen catch crops . Acta Agriculturae Scandinavica , 41 : 333 – 344 .
- Johnsson , H. , & Mårtensson , K. 2002 . Kväveläckage från svensk åkermark Rapport 5248, Naturvårdsverket .
- Känkänen , H. and Eriksson , C. 2007 . Effects of undersown crops on soil mineral N and grain yield of spring barley . European Journal of Agronomy , 27 : 25 – 34 .
- Lemola , R. , Turtola , E. and Eriksson , C. 2000 . Undersowing Italian ryegrass diminishes nitrogen leaching from spring barley . Agricultural and Food Science in Finland , 9 : 201 – 216 .
- Merker , A. and Nilsson , P. 1995 . Some oil crop properties in wild Barbarea and Lepidium species . Swedish Journal of Agricultural Research , 25 : 173 – 178 .
- Nilsson , P. , Johansson , S.Å. and Merker , A. 1998 . Variation of oil composition of species from the genera Barbarea and Lepidium . Acta Agriculturae Scandinavica, Section B. Soil and Plant Science , 48 : 159 – 164 .
- Princen , L.H. 1983 . New oilseed crops on the horizon . Economic Botany , 37 : 487 – 492 .
- Spaner , D. and Todd , A.G. 2003 . The impact of underseeding forage mixtures on barley grain production in northern North America . Canadian Journal of Plant Science , 83 : 351 – 355 .