Organic farming has a long tradition in Germany, with organic farms already well established in the first half of the 20th century [1
]. The number of farms increased dramatically, following a period of slow growth in the second half of the 20th century, after the implementation of the EU Regulation on Organic Food and Farming in 1992 [2
]. Today, 1,078,000 ha are managed organically, amounting to over 6% of the total usable agricultural area in Germany. This represents 24,340 farms, or about 9% of all farms in the country [3
]. Due to the rising demand for organic food, these numbers will likely increase in future. A high percentage of these are mixed or stockless arable farms that focus mainly on the production of cereals and grain legumes as cash crops. In addition, extensive open field production of vegetables like carrots (Daucus carota
L.), cabbage (Brassica oleracea
L.) and onions (Allium cepa
L.) is done as a part of large-scale arable rotations. These rotations usually include one or two years of a perennial legume, or mixed grass/legume ley if the farm keeps ruminant livestock [4
]. The perennial legume ley provides fodder, an opportunity for weed control because of frequent cutting, and biologically fixed nitrogen for subsequent crops. Stockless farms may include legume ley in rotations because of these benefits. The period for one rotation of German organic farms is approximately five to eight years, depending on farm type [5
A strong driver for the agricultural activities of German organic farmers is the maintenance and increase of soil quality [5
] and, more holistically, soil health [8
]. The EU-Regulation on Organic Food and Farming reflects this and states that organic farming should focus on “the maintenance and enhancement of soil life and natural soil fertility, soil stability and soil biodiversity preventing and combating soil compaction and soil erosion” [9
]. An important step in realizing this aim could be the widespread adoption of RT or NT practices in organic farming. RT encompasses a wide range of practices [10
], even meeting the criterion of conservation tillage if, in accordance to the definition of the CTIC [11
], at least 30% of the soil is covered by a vegetative mulch (e.g., crop residues). A concept which is widely used in Germany to distinguish conventional tillage from RT is whether soil inversion (conventional tillage) vs. non-inversion (RT) occurs, but RT can also indicate less aggressive inversion tillage methods (e.g., strip tillage, reduction in depth of inversion tillage) compared with the moldboard plough. Currently, organic farmers in Germany use different approaches and techniques to reduce tillage: (i) reduction of moldboard plough operations in a rotation; (ii) reduction in tillage depth while maintaining inversion tillage; (iii) non-inversion tillage at shallow soil depths and (iv) NT. For our purposes, RT includes approaches (i) through (iii), even though in some cases (e.g., for ridge systems) mulch cover is not used and our definition is therefore not in line with the one of CTIC.
The basic function of soil tillage—to control weeds and provide a suitable seedbed for rapid germination and development—is limited or eliminated entirely in RT and NT. Weed and volunteer control (e.g., volunteers from perennial legumes) without intensive inversion tillage (and without herbicides in organic farming) is one of the main challenges in RT and NT [12
]. Yield limiting factors such as weed pressure and reduced nitrogen availability [13
], along with environmental benefits [18
] differ strongly between RT and NT on the one hand, and conventional inversion tillage on the other, influencing the level of acceptance by farmers.
There are several long-term trials on RT and NT underway in Germany. Some of these trial results are published in international journals, while others are only available in German language. To the knowledge of the authors, very limited information is available in English on the motives of German farmers who are considering the adoption of RT and NT [12
]; the same is true for farmers who are using RT and NT [19
]. The latter publication gives an interesting insight into the RT practices used in northwestern Europe, but, as the sample size for Germany was very small, it is unclear how this reflects the actual scope and depth of RT and NT in the country. Peigné et al. [19
] detected country-specific differences in terms of peer-to-peer exchange, dissemination and extension of information on RT and NT. The experience and knowledge of German organic farmers could here initiate a novel, bottom-up approach to push the development of RT and NT. Therefore, our paper aims to (i) explore the development of organic RT and NT systems in Germany; (ii) describe the motives of German organic farmers for conversion to RT and NT; (iii) make information on the current cropping systems in RT and NT systems from “grey” non-peer-reviewed literature available to a wider audience; (iv) compile information on the on-going research on no-till and reduced tillage systems in Germany by case studies and (v) discuss the perspectives and challenges for those systems.
2. Status Quo of Reduced Tillage in Germany
According to the last official report on production methods of the German Federal Statistical Office [20
], soil inversion tillage by moldboard plough is still the dominant tillage practice, and was applied in 2009/2010 to approximately 56% of the arable area in Germany (corresponding to 6.6 million ha). This number includes both conventional and organic farming systems, because separate data are not available. Only 12% of the arable farms completely abandoned the moldboard plough, and 34% applied inversion tillage (moldboard ploughing) in some years and non-inversion tillage (chisel ploughing) in other years. All in all, the chisel plough was applied to 38% of the arable land in Germany. No-tillage is not widely used and accounted for approximately 1% of the arable land in 2010 [20
Despite these numbers, among the countries of EU-27, Germany ranks above the European average area under RT, which is one-fifth of the EU-27’s total arable area [21
]. Adoption rates of RT and NT seem to be largely a question of farm size. German farms with an area > 150 ha used RT or NT on more than 60% of cropland in 2010 [21
]. These farms were mainly located in the eastern part of the country: Three out of the five eastern states used conventional tillage on <40% of arable land, reflecting the lowest percentage of conventional tillage use in all of Germany [21
]. In nearly all western federal states, conventional tillage was used on >50% of the arable farmland area. Approximately 30% of the farmers who apply RT or NT practices in Germany grow cereals, oil crops or protein crops, with a third of them practicing NT [21
]. In summary, the relative adoption of RT or NT in Germany increases with farm size more so in eastern Germany, where agricultural cooperatives were very large in the former GDR, and is more common on farms where only a few staple crops are grown and, consequently, crop diversity is limited.
Most regions of Germany, except mountainous regions, belong to a warm, temperate, humid climate with warm summers (Cfb after the classification of Köppen-Geiger; [22
]). While many studies from water limited areas show that yields can be the same or even higher under NT, as compiled by Triplett and Dick [23
] and Derpsch et al. [24
], this effect rarely occurs in humid climates [14
]. Under these conditions, effects of the mulch cover on water saving are not beneficial and can even be counterproductive for yield [26
]. In spite of this constraint, the need for adoption of RT or NT systems in (organic) farming in Germany clearly exists, as about 17% of the agricultural usable area is threatened by water and wind erosion [27
] and drought events are expected to increase due to climate change, especially in eastern and southern parts of Germany [28
6. Crop Rotation and Residue Management
The most important tool to control or prevent weeds, improve soil parameters and provide N in organic farming is rotation design. Crop rotation design is of particular importance in RT and particularly NT systems because it is one of the few tools available for controlling weeds and volunteers. Other non-mechanical weed control measures are limited in terms of efficacy or costs, for example, adjustment of crop density or flaming. Contrasting crop rotations used on three German organic farms employing RT and NT are provided in Figure 1
]. These rotations reflect the practices used on these farms following adjustment to specific site conditions and the constraints and opportunities of the different farm types. In addition, the rotations and the associated machinery and tillage operations represent a sequence from moderate RT to NT/direct seeding. Farm 1 uses shallow inversion tillage by a skimmer plough combined with frequent applications of a rototiller. On farm 2, RT involves only non-inversion methods with fewer passes than those used on farm 1. The direct seeding system on farm 3 reduces tillage to a minimum and operates with a very high amount of soil cover (strip till in living mulches, undersown crops, bi-cropping, and cover crops).
All three rotations start with a grass clover ley, which is typical for cropping sequences in Germany, no matter which tillage system is used. Farmers usually have site-specific experience for the establishment of these mixtures (e.g., underseeding in spring or autumn depending on water availability for germination) and can easily introduce them into their RT and NT systems. This practice seems to frequently be applied by organic farmers using RT and NT over all of northern Europe [19
]. In some cases, the vigorous growth of undersown crops results in harvest problems and reduced yields of the cereal cash crop [34
]. Generally, weed suppression is greater in perennial leys than annual leys, but perennial leys generally are limited to mixed farms with ruminant livestock where forage is needed as feed (farm 1). On arable, stockless farms (e.g., farm 2; Table 3
), this is usually not an option, since no commercial use of the grass clover exists, even though this practice could improve weed control. The weed controlling effect of annual and perennial leys used for forage is based on the frequent cutting (up to four times per year) which directly destroys annual weeds, and which moreover exhausts perennial weeds that re-grow from persistent root systems. A lower share of annual or perennial legume ley, or grass clover, respectively, in the crop rotation can therefore lead to high occurrences of Convolvulus arvensis
L. that can develop into problem weeds on certain fields [42
]. For farm 3, direct seeding of a perennial grass clover ley appears to be the best option to combat perennial weeds by frequent cuttings, because tillage operations that would mix the topsoil for weed control are not applied; the blades of the WEcoDyn cut beneath the soil surface, but the weed controlling effect is limited.
The RT systems used on three contrasting German organic farms create different challenges in terms of crop management and weed control (Table 3
). Farm 1 uses inversion tillage and faces few challenges in breaking the perennial legume (red clover; Trifolium pratense
L.) ley. A different strategy is required to destroy and incorporate the ley biomass on farm 2, which is accomplished with several passes using a chisel plough without the need of a rototiller (Figure 1
). Farmers using RT often break perennial legume leys during dry spells in autumn in order to kill off the plants, but this method can be risky due to weather uncertainties. Moreover, breaking a perennial legume ley in autumn followed by the seeding of winter cereals (which do not develop much before winter) increases N leaching during winter [63
]. Whether or not a farmer really manages to reduce costs by RT partially depends on the number of passes [42
], and in this regard farmer 1 may have room for improvement since he performs several soil inversion passes, though at a comparatively shallow depth.
All three farms use cover crops whenever possible to reduce weed pressure, to reduce erosion during autumn and winter rains and to fix N. Species like buckwheat (Fagopyrum esculentum
Moench), spring types of faba bean and peas, vetch, Phacelia (Phacelia tannacetifolia
Benth.), mustard (Sinapis alba
L.), and Persian clover (Trifolium resupinatum
L.) die off during winter and provide a mulch with a low C/N ratio to cover the soil surface. Farms 1 and 2 use leguminous cover crops, and it can be assumed that this results in high NO3
-N availability in spring. All three farms include winter rye in their rotation, which usually performs well under RT practices [17
]. Alternating summer and winter crops help reduce weeds (Table 3
). Farmer 2 always used a mixture of field beans, peas and vetches as cover crops—together with the clover grass, this might increase the risk of diseases [5
Farm 3 faces unique challenges since direct seeding is done in a NT system. The WEcoDyn machinery allows seeding into thick mulches and even into living mulches. The competitiveness of living mulches can be reduced by intensive cutting of the living mulch prior to seeding and strip tilling of the cash crop into the living mulch. Use of living mulches and of cover crops should be alternated in this rotation. In agricultural practice, this system showed the highest weed pressure and the lowest yields, compared to farm 1 and 2 for several reasons [42
]. As the clover strips (remnants from the prior clover grass ley) were maintained for several years, they allowed the establishment of perennial weeds (e.g., dandelion, Taraxacum officinale
(L.) Weber ex F.H. Wigg). This weed infestation prevented a proper seedbed preparation for the living mulches substituting the initial clover strips. Moreover, after several years of NT, there was a build up of annual weeds (grasses, and Vicia hirsuta
(L.) Gray), which subsequently became a problem after germination of the main crop. The cover crops described above failed to produce enough biomass to suppress weeds in the following cash crops, and management of the living mulches was not optimized. The use of high residue biomass cover crops, prior to seeding spring crops like soybean and maize, could be an option to combat weeds for this farm. Silage maize performed very well in an RT trial in Switzerland despite high weed infestations [65
]. In Germany, for a stockless farmer in favourable climatic conditions, growing grain maize would be a good option in terms of weed control and as a cash crop, in particular with a leguminous cover crop providing additional N (Table 3
). Another option could be the seeding of winter legumes into the mulch of the cover crop as this reduced plant losses resulting from low temperatures [42
The results of the long-term field experiments indicate that RT approaches involving non-inversion tillage and NT presently are not viable options for organic farmers in Germany because of yield depression coupled with yield instability. However, recent studies in Switzerland and other European countries contradict this and suggest that RT methods can result in similar [66
] or even higher yields than inversion tillage methods [65
]. Some of the field experiments used in our evaluation may still be in the transition period from conventional tillage to RT or NT, since this can last for a number of years before new equilibria in soil characteristics and weed populations are established [68
]. In long-term experiments with adapted rotations, yield reductions seem to decline in RT systems over time [69
There are inconsistencies in the impacts of tillage equipment used in RT and NT systems that complicate comparisons with conventional tillage systems. For example, the double-layer plough performed well in reducing weeds and stabilizing cash grain yield in some instances [13
], but not in others. For example, a higher incidence in weeds and subsequent yield reduction was associated with double layer ploughing in a meta-analysis of studies across Europe, Canada, and the USA [69
]. Variations in climate, soils and rotations confound analyses of RT and conventional tillage. It seems that specially tailored RT and NT systems can work in some environments, but we do not yet know under which conditions these systems are most appropriate.
More studies demonstrating the economic profitability of RT and NT are needed before larger numbers of German organic farmers will be motivated to adopt these methods, even if cost savings are not the most important reason for converting [12
]. The ability of cost savings in labor and fuel to off-set yield losses following the adoption of RT is dependent on various factors (e.g., the number of passes, acreage performance of machinery, machinery costs, etc.), but until now, no systematic assessment of these aspects on organic farms has been made.
Reduced tillage systems are very knowledge intensive and demanding and, at the current stage of development in Germany, readily accessible information on these systems is lacking and best-practice examples are still scarce. A step-wise, site-dependent approach encouraged by organic farmers’ associations and farmers’ networks for peer-to-peer extension may be an option for knowledge dissemination. Reducing the number of inversion tillage operations and inversion tillage depth can be the first steps towards adoption of RT systems, and this should be economically feasible for the farmer since they might reduce labor and fuel costs without compromising yields too much [46
]. The farmer can gain experience with the crops for which RT and NT work at a specific location, the optimum placement of those crops in a rotation, and the environmental benefits that result following the adoption of RT and NT.
Current data show that profits for organic farmers in Germany rise while they decrease for conventional farmers due to low commodity prices [3
]. This leads to a growing number of farms converting from conventional to organic farming. As the number of farms applying NT in conventional farming has risen in recent years, we assume that a considerable number of the “organic newcomers” are (i) large in size and (ii) already familiar with NT approaches. Therefore, we assume that these farmers will modify their tillage practices to fit organic systems but, most likely, will not resort to inversion tillage again. For these farmers, “thinking outside the box” may be easier than long-time organic farmers and we anticipate new ideas in cropping system design as well as in the design of adapted tillage equipment as a result of the interaction these groups.
In this context, the role of weeds warrants special attention from an agro-ecological point of view. Farmers may experience increased weed problems following the adoption of RT and NT [12
], but since biodiversity in agro-ecosystems declines despite efforts to stop this tendency [70
], greater weed abundance may lead to greater biodiversity (e.g., pollinators, ground beetles, birds). This enhancement in biodiversity may have financial value in the future due to changes in agricultural policies, even if economic incentives do not presently exist.
In addition to the positive site-related effects on the environment offered by RT and NT, more global benefits may exist. For instance, Cooper et al. [69
] found increasing C-stocks following adoption of shallow inversion tillage accompanied by yield losses of only 5.5% in a meta-study of data from 12 long-term trials from the US and Canada and 28 from Europe, including 6 of the German field trials described previously. Even if it was unclear whether this will really lead to C-sequestration or mere stratification of C in the soil profile [71
], higher C-stocks in the topsoil would have many benefits for soil conservation, in addition to improving soil biological and soil physical parameters [72
]. This would contribute to meeting a central paradigm of organic farming: maintaining or even enhancing soil quality and soil life. As results of field research have demonstrated, hurdles remain, particularly related to weed control, which must be overcome before widespread adoption of RT and NT will occur. In addition, research with models, as done with NDICEA, elsewhere in Europe [73
], should be used to better understand the N dynamics of organic RT and NT systems in German long-term trials.
Climate change will alter rainfall patterns and lead to an increased occurrence of drought in some regions in Germany (e.g., in the North-East), resulting in increased water stress and reduced yields [74
]. As RT and NT have a high potential to improve water infiltration, reduce evaporation and improve soil structure, we assume that acceptance for these systems will rise in the future. With changing climate patterns, yield levels in conventional inversion tillage systems might also decline, leading to greater relative economic profitability of RT and NT. Climate models additionally predict a higher frequency for extreme weather events—lower rainfall during the summer and higher rainfall during the winter for Germany [28
]—suggesting, in this context, that RT and NT may offer a strategy for increasing the resilience of organic farming systems and a means for adaption to climate change. In response to these challenges, a project was launched to develop specific RT and NT solutions for organic farming in an action research approach [75
] in the German federal state of Brandenburg (Northeast Germany), one of the regions where highest impacts of climate change on agriculture are expected [74
]. The increasing annual temperatures in Germany due to climate change, and the anticipated extension in the growing season length, suggest that there may be opportunities to grow crops that could not be grown in the past. For example, it may become possible to grow soybeans in southern Germany, again allowing for new cropping sequences that fit RT or NT systems.