A new approach to soil tillage for organic vegetable production: permanent beds
Védie H., Berry D., Leclerc B., Grébert D. , Lhôte J.M. 
Key words : organic vegetable production, soil tillage, permanent beds, soil fertility
Abstract
The effect of controlled traffic with permanent crop beds was compared to mouldboard ploughing in France for organic vegetable production. Four trials were carried out over a period of three to seven years at four sites with different pedo-climatic conditions. Variable results were obtained, depending on soil type (susceptibility to compaction), tillage machinery type, vegetable type (root or not, grown from seed or transplant) and weed development. However, permanent crop beds with controlled traffic generally improved biological activity and reduced labour demand.
Introduction
In vegetable production, rapid succession of several crops during the year leads to intensive vehicle traffic, sometimes on wet soils, and therefore to soil compaction. Reduced tillage technique developed for vegetable crops by Wenz and Mussler in Germany (Deveyer et al., 2001) offers a new type of tillage management with permanent beds: no mouldboard ploughing, permanent wheel tracks and preferential use of tine machines. A national network was created in France in 2005 to study new approaches of tillage in organic farming, associating several trials on arable farms (results reported in these proceedings by Peigné et al.) and four trials in vegetable production. We studied the feasibility of permanent crop beds under various soil, climate and crop rotation conditions. The aim was to answer the following questions : is it possible to avoid ploughing in vegetable crops ? What are the requirements for the successful adoption of a permanent bed system ? What are the consequences on soil fertility, crop development and weed control ?
Materials and methods
Four trial plots are included in this study with two soil tillage treatments on a randomised block design with 2 or 3 replicates : controlled traffic tillage with Permanent Beds ("PB") compared with Conventional tillage ("C"). Sites conditions are shown in table 1. Permanent Beds (PB) : wheel tracks were the same from the beginning of the trials, regardless of the cultural practice. The crop bed (1.2 m to 1.5 m wide depending on the site) was free from any compaction due to vehicle traffic. Tine machines were preferentially used for this treatment with "Actisol" and some specific equipment developed at each site (Berry D., Taulet A., 2006). Conventional tillage (C) : wheel tracks were not controlled. Mouldboard ploughing was the reference at three sites, with use of rotary equipment. Same fertilisation as in PB.
Measurements and observations were the same for the four experimental sites : evolution of the physical (cultivated soil profile (Roger-Estrade J. et al., 2004)), chemical (organic matter, nitrogen, phosphorus, potassium, magnesium), and biological fertility (microbial biomass (Chaussod et al., 1988) and activity, earthworm activity); crop performance (yield and quality); weed pressure and labour times.
Table 1 : main characteristics for the four experimental sites
Site	A
Rhône-Alpes	B
Nord	C
Charentes	D
Provence	
Beginning	2001	2003	2005	2005	
Soil texture (% clay/silt/sand)	
26 / 47 / 27	
27 / 49 / 24	
28 / 42 / 30	
22 / 62 / 16	
Rainfall (mm/nb days)	1000 mm / 86 days	680 mm / 120 days	716 mm / 77 days	660 mm / 45 days	
Crop rotation	2001 : leek +  GM*
2002 : lettuce
2003 : carrot +  GM
2004 : cabbage
2005 : GM + spinach
2006 : leek	2003 : turnip
2004 : carrot
2005 : pea + GM
2006 : onion
2007 : turnip	2005 : carrot
2006 : leek
2007 : potato	2005 : squash
2006 : melon + GM
2007 : onion & Japanese radish	
* GM : Green Manure
Results 
Physical, chemical and biological fertility :
- The reduced tillage with permanent bed system tended to increase soil compaction, especially in the 10-30 cm layer. The proportion of non-compacted clods (with internal structural state ) was higher for PB in the surface layer (0-10cm) and lower underneath. This observation was very clear for the most recent sites (C and D), but not for the oldest one (site A), where PB had been used for seven years. Compaction under the PB can also affect the culture bed on the sides (lateral compaction); this effect seemed to decrease with time (sites A and B).
- Cultivation using permanent beds had little impact on organic matter, except for a slight increase of the labile organic carbon (diameter > 50 µm). On the contrary, it enhanced the microbial activity, which can be measured through potential mineralisations of carbon (C) and nitrogen (N) (Table 2). For site D, the different measurements were not in favour of PB compared to conventional tillage because of the soil compaction problems.
- After three to six years of cultivation using PB, macrofauna activity did not significantly increase (data not shown). Nevertheless, structure from biological activity is higher in less compacted cultivated soil profiles.
Crop performance : The permanent bed tillage system did not affect the yield of the main vegetable crops measured on crop bed, but the quality of root vegetables decreased. Carrot and Japanese radish roots harvested at three of the four trials were deformed, because of the more compacted soil. Weed control was a real problem for one site only (site B), where perennial weed (Sonchus spp.) development affected some crops yield such as peas.
Labour time : The implements used on the permanent beds that are not driven by the tractor's power take-off allow faster cultivation speeds and thus reduce the labour time for soil preparation. In the seven-year study at trial site A, the average cultivation time using a tractor was reduced by 30% (Table 3). 
Table 2 : Evolution of organic matter, microbial biomass and potential mineralisation (C : conventional tillage – PB : Permanent Beds)
Site	A (0-25 cm)	B (0-25 cm) 	C (0-12 cm)	D (0-25 cm)	
Treatment	C	PB	C	PB	C	PB	C	PB	
Total org.C (g/kg)	13.6	15.3	15	14.8	17.1	18.6	15.1	14.3	
Labile org. C 1 (%total C)	18.1	20.2	21	23	24.4	31.1	24	22	
Microbial Biomass (mgC/kg)	462 (b)	506 (a)	442 (b)	554 (a)	352	410	285	209	
C Mineralisation (mg/kg/28days)	240 (b)	297 (a)	288	369	403	381	398	360	
N Mineralisation (mg/kg/28days)	21.1	22.2	20.2 (b)	29 (a)	22.1	20.7	42.4 (a)	32.2 (b)	
1 labile organic carbon : diameter > 50 µm - a,b : significant for P<0,05
Table 3: Compared labour time at site A (minute/70-m long crop bed)
	Conventional tillage (plough)	Permanent beds	Time reduction (%)	
Leek 2001	47 min	21 min	55 %	
Lettuce 2002	42 min	32 min	24 %	
Carrot 2003	68 min	48 min	30 %	
Cabbage 2004	78 min	59 min	31 %	
Spinach 2005	40 min	34 min	18 %	
Leek 2006	64 min	49 min	23 %	
Average decrease of labour time	- 30 %	
Discussion
The different consequences of soil tillage with permanent beds, depending on the pedo-climatic and crop conditions, are summed up in Figure 1 :
- Cultivation time with permanent beds has a strong impact on the results : mixed or poor results are obtained at the three-year-old sites, whereas all parameters (biological and physical soil properties, crop results, time savings) positively evolve at the seven-year-old site. As with any emerging technology, many years are needed before obtaining satisfactory results : adapting the cultivation techniques and using adapted custom-built tillage equipment (there is very little reduced tillage equipment available for vegetables). Soil texture is an essential factor: in soils with poor structural stability, such as the silty soil on site D with 66 % silt, "deep" soil tillage down to 25 cm is essential for permanent beds to compensate for self-compressing.
- Weed pressure (perennial weeds), can seriously hinder the elimination of ploughing. 
- Finally, for sown vegetables, a particular attention must be paid to the careful preparation of the seedbed, which is difficult without rotary equipments.
Figure 1 : Permanent bed impact on soil fertility and crop performances in terms of implementation conditions and time, in comparison to conventional tillage
Conclusions
The results show that it is possible to eliminate ploughing for the cultivation of organic vegetable crops. There are very few references with conservation tillage with vegetable crops, and almost none with a permanent bed system. Our study shows that it is an interesting alternative that improves soil biological activity and decreases labour time using tractor, leading to significant energy savings. However, this method has limitations depending on pedo-climatic conditions and the lack of suitable equipment, which lead to various results.
Further researches are required to specify the soil tillage techniques according to pedological conditions (silty soils, for instance), to improve weed control and to ensure the incorporation of fresh organic matter (crop residues and green manure).
References
Berry D., Taulet A., 2006 : Les atouts des planches permanentes, Biofil n°44, janv.fév.2006
Chaussod R., Houot S., Guiraud G., Hetier JM., 1988 : Size and turnover of the microbial biomass in agricultural soils : laboratory and field measurements. In D.S Jenkinson and K.A. Smith (ed.), Nitrogen efficiency in agricultural soils. Elsevier. p. 323-338
Deveyer L. & al (2001) : Travail du sol en maraîchage biologique : méthode classique / Méthode Wenz-Mussler, ISARA / SERAIL, 28p.
Roger-Estrade J., Richard G., Caneill J., Boizard H., Coquet Y., Défossez P., Manichon H., 2004. Morphological characterisation of soil structure in tilled fields : from a diagnosis method to the modelling of stuctural changes over time. Soil and Tillage Research. 79(1) : 33-49