Lukas Bender1, 6Sabine Gruber2, 7Wilhelm Claupein2, Sabine Zikeli1
Key words: Intercropping, mineralization, competition, vegetables, weeds
Abstract
The use of living mulch for erosion control is discussed in organic vegetable production. Supposed challenges are competition between crop and mulch, and sufficient weed control. A two-factorial field trial was conducted in 2015 in SW Germany to test effects of living mulch on yield and weeds
in cabbage. White cabbage (Brassica oleracea convar capitata var. alba; both a round and a pointed
variety) was intercropped with perennial ryegrass (Lolium perenne; RG) or white clover (Trifolium
repens L.; C), or grown without living mulch (control). Total head yield was 38.8 > 2.8 > 2.1 t ha-1 fresh mass (control > C > RG) across varieties. Up to 11 times more weed plants than in the control were recorded in living mulches. The share of marketable heads of pointed cabbage ranged from 88%>18%>0.9% and for round cabbage from 72%>5%>0.5% (both control>RG>C). Competition early in the year and low mineralization due to reduced soil disturbance are assumed to be the main reasons for the low yields.
Acknowledgments
We thank Oliver Hübner and our other colleagues from the research station for organic farming Kleinhohenheim for their invaluable support at any time.
Introduction
The production of vegetables is frequently linked to soil erosion caused by wide row spacing during early stages of development, poor soil cover for long periods of time, intensive tillage before transplanting or sowing, and mechanical weed control. Fertile soils, which are most suitable for vegetable production, are often prone to erosion due to their texture, e.g. a high percentage of silt. Intercropping with living mulch (LM) might reduce soil erosion when the soil surface is covered by the leaves of LM, and when the root network stabilizes and maintains the soil structure. On the other hand, disadvantages such as competition between mulch and crop, and difficulties in weed control are expected. To understand the issue, and to define problems and solutions associated with the LM system, we set up a field trial with cabbage in 2015. The aim of the study was to determine yield and weeds of cabbage-LM intercropping, and to develop improvements and adaptations of the cropping system.
Material and methods
The University of Hohenheim experimental station for organic farming, Kleinhohenheim, is located in South-West Germany, at 435 m above sea level, with an average mean temperature of 9.7 °C and an average annual precipitation of 736 mm. The soils are Luvisols developed from loess, with soil depths of up to 2m. The farm is certified by the organic farming associations Demeter e.V., Bioland e. V., and Naturland e.V. and has been managed organically since 1994. Crops preceding white
16
Institute of Crop Science, co-ordination for organic farming and consumer protection, University of Hohenheim, Germany, www.uni-hohenheim.de, eMail: [email protected]
27
Institute of Crop Science (Agronomy, 340a), University of Hohenheim, Germany, www.uni-hohenheim.de, eMail: [email protected] (corresponding author)
cabbage (Brassica oleracea convar capitata var. alba) were grass clover ley (Trifolium pratense, T.
repens, Lolium perenne; 2014), emmer (Triticum dicoccum; 2013), onions/carrots (Allium
cepa/Daucus carota; 2012), and spring wheat (Triticum aestivum; 2011). The trial was a two-
factorial row-column design (due to a slope in two directions) with cabbage variety (pointed: “Filderkraut”; round: “Dottenfelder Dauer”) being factor one, and living mulch being factor two in three levels: white clover (Trifolium repens cv. Riesling; “C”); perennial ryegrass (Lolium perenne
cv. Leon; “RG”), and control (bare soil). Plot size was 7.0 × 4.5 m with six rows of cabbage per plot and inter-row spacing of 0.75m. The intra-row spacing was 0.65m for pointed cabbage and 0.35 m for round cabbage, i.e. 65 and 120 plants per plot or about 2.1 (pointed) and 3.8 (round) plants m-2. Cabbage was transplanted in strips 0.25m wide tilled by a rotary harrow into the mulch when the plantlets had 3–5 foliage leaves at the end of May 2015 (Table 1). No additional fertilizer was applied. Before primary tillage in spring, mineral nitrogen (Nmin) content was 30 kg ha-1 (0– 90cm depth), while Corg was 1.24% in the topsoil (0-30cm). To control competition during the growing season, the living mulch plots were mown twice with a hand mower, and the cut material remained on the area (Table 1). On July 14 a strip of 10cm alongside each cabbage row was tilled with a goosefoot-shaped chisel to reduce competition from the mulch strips. Cabbage was hand weeded in the rows. The trial was irrigated several times using sprinkler irrigation with about 75 mm in total, independent of the treatment.
Table 1: Actions before and during the cabbage growing season on the experimental field in Kleinhohenheim in the year 2015 (dd/mm), for mixed cropping of cabbage with living mulch (LM).
Operation Date Operation (continued) Date
Soil tillage by chisel plough 01/04, 15/04, 29/04 Irrigation approx. 15 l m-² per date 04/06, 13/07, 17/07, 21/07, 11/09 Sampling Nmin (0-90 cm) 30/04, 27/10 Mowing of LM close to the ground 18/06, 08/07 Sowing of LM (white clover: 10 kg ha-1, ryegrass: 30 kg ha-1 30/04 Tillage by goosefoot chisel close to the cabbage rows
14/07
Tillage by rotary harrow (control plots)
25/05 Hand weeding and hoeing in rows (control)
15/07 Cabbage transplanting 26/05 Sampling of living mulch
and weeds
19/08, 15/10
Weed record 03/06, 03/07,
11/08
Harvest of cabbage 20/10 Hoeing of the control 17/06, 26/06,
14/07
Weeds were counted five times per plot in an area of 0.05 m² between the rows. An area of 4 x 0.125 m² was cut twice to determine the biomass of living mulch and weeds. At harvest, three cabbage heads per plot were taken randomly to determine average head weight. The cabbage yield of the four inner rows (21 m²) was measured by hand-harvesting mature heads. Threshold for marketability was a head weight of about 0.4 kg (round cabbage) and about 0.6 kg (pointed cabbage).
Results
The year 2015 was exceptionally dry and hot for long periods during the growing season. There were no major losses recorded through insects and fungi (data not shown). During the season, the number of weeds was significantly higher when cabbage was intercropped with living mulch
“Innovative Research for Organic Agriculture 3.0”,
Organic World Congress 2017 in New Delhi, India, November 9-11, 2017
compared to the control, particularly at the beginning of the season (Figure 1). Chenopodium album
and Matricariaspp. were the dominant weeds. Less abundant weeds were grouped under “other”.
These were Galium aparine, Cirsium arvense, Capsella bursa-pastoris, Thlaspi arvense, Sonchus
arvensis, and Echinochloa crus-galli.
Figure 1: Weed numbers m-² between cabbage rows (across varieties) with or without living mulch (control: bare soil, RG: perennial ryegrass, C: white clover) at three dates, experimental station Kleinhohenheim, 2015. Different letters indicate significant differences (P<0.05) between treatments, comparison only within the same date. SEM 3rd June: ± 13.32; 3rd July: ± 14.11; 11th August: ± 3.29. Persicaria spp.: P. maculosa and P. lapathifolia
Weed numbers converged over time (Figure 1) and weed biomass was relatively equal among the three treatments at the time of harvest in mid-October (Figure 2). The total biomass (fresh mass of cabbage, mulch and weeds) was two to three times higher in the control than in the living mulch treatments when recorded at harvest. At that time, cabbage contributed 93% and weeds 7% of the total fresh biomass in the control, while cabbage represented only 22% and 16% of the total biomass in mixed cropping with RG and C, respectively (Figure 2). Weeds represented 38% (RG) or 11% (C), and living mulch had a share of 40% and 73% in RG and C, respectively.
The individual mean head mass of pointed cabbage was higher than that of round cabbage (Figure 2). The pointed cabbage yielded 18.3 t ha-1 compared to 10.4 t ha-1 for round cabbage across treatments (not shown). Approximately 90% of the pointed, and 70% of the round cabbage met the standards for marketable heads when grown in the control. In the living mulch, however, the marketable yield was below 20%, and below 1% in white clover living mulch (Figure 2).
0 20 40 60 80 100 120 140 160
Control RG C Control RG C Control RG C
3rd June 3rd July 11th August
N u m b e r o f w e e d s m -² other Persicaria spp. Stellaria media Matricaria spp. Chenopodium album a b b b a b a b ab
Figure 2: Total fresh biomass (FM) of vegetation (cabbage, living mulch weeds) at harvesting in October 2015, *significant at P<0.05 (A), and FM of cabbage heads (B) when intercropped with living mulch (ryegrass, clover), Kleinhohenheim, Germany. No statistics for cabbage yield due to inhomogeneity of variance. Top of the columns in B: share of marketable heads.
Discussion
The low marketable yields clearly indicate that intercropping cabbage with living mulch did not work in 2015. We assume three reasons: reason 1 being that the low mineralisation and associated reduction in nutrient uptake in the mulch plots had a high impact, while the side-effect of common (but not performed) mechanical weed control by a hoe – stimulating N mineralisation – was very low. This effect might have been strengthened by reason 2: the unusual drought period from May to July, which may have further reduced mineralisation and limited nutrient uptake by soil water, leading to an increased competition for water and nutrients between the living mulch and the crop (Pfeiffer et al. 2016). The amount of irrigation water has not been adapted to the treatments, but this would be an option for following years and in practical farming. Reason 3 was likely an unsuitable match between mulch variety and/or the time and the method of establishing and transplanting of mulch or cabbage (Montemurro et al. 2016).
Suggestions for tackling future challenges
In principle, we still believe in the value of living mulch systems, and suggest (i) to use mulch with a very low competition capacity, (ii) to maintain the tillage using a chisel tine close to the cabbage row, (iii) to reduce the width of the mulch strip compared to ours, (iv) to adapt the amount of irrigation to the water-use of the living mulch, (v) to consider dead mulch from a non-frost-tolerant species such as annual clovers (e.g. Trifolium subterraneum), and (vi) to apply organic fertiliser to minimize competition for nutrients.