Climate-friendly practices applied: optimized crop rotations
In order to reduce greenhouse gas emissions on the farms, SOLMACC farmers implement different changes in their crop rotation systems, including an increased share of grain legumes and increasing forage legumes/grass-legume leys.
Find out more details on how some SOLMACC farmers implement this practice and which challenges they are facing.
A closer look at the crop rotation at the Pfänder farm
Johann, Johannes and Florian Pfänder, who grow field vegetables on relatively heavy soils with an irrigation system, use a method on their farm which might best be called temporary mixed cropping of broad bean (Vicia faba) and field vegetables. Their strategy pursues multiple objectives:
- N-fertilisation for the vegetables
- improved soil condition through revegetation and increased carbon-sequestration due to higher amounts of organic matter and root exudates of the bean plant
- rapid soil cover and shadowing between the vegetable rows with weed-suppressive effect, which considerably reduces time pressure of mechanical weed-control
- extraction of surplus water from heavy wet soils due to higher evaporation rate and therefore better soil aeration and improved conditions for mechanical cultivation
- improved preceding crop effect on the field bean rows
The technical realization is as follows: In general the working width of all field vegetable machinery on the farm is standardized to 3 meters. A simple mechanical seed-drill machine with 12,5 cm row spacing is used to seed 4 rows of field bean with a seed placement depth of 3, maximum 4 cm, then 2 rows are blocked, then again 4 rows of field beans, 2 rows blocked etc.. The maximum of 4 cm seed placement depth is more shallow than usual in order to ensure the safe mechanical killing of the bean plant later on. Approximately 2 weeks after seeding the beans, when the ground has settled again the vegetable rows are planted in the free space (blocked rows) between the field beans. Along the vegetable rows the mechanical hoe is used while the field beans grow without any mechanical hoe.
At 20-30 cm plant height the field bean rows are treated with a rotary hiller (Comeb). The tines of the rotovator are adjusted to 5-6 cm working depth to ensure that the seed grain of the bean plant is definitely captured in order to safely prevent regrowth. From then on the vegetables continue growing without interrow-crop. The field bean should not be higher than 30 cm in order to enable the rotary hiller to work well. This method is used in cabbage, celery, leek, broccoli and cauliflower. Onions reacted very sensitive to the cutting of their fine roots, so the described method is no longer used in this culture.
So far there have been no negative experiences. What was recognized positively is that the cabbage which grows on fields with preceding broad been as temporary mixed crop is less damaged by cabbage flea beetles (Phyllotreta spp.) compared to the cabbage that has no beans on the field in the previous year. Generally speaking the results of the described procedure with respect to the above described objectives has proven so positive that the farmers have used it since they developed it in 2007 and intend to keep it in their future tool-box as a practically tested and approved innovation.
An overview of the crop rotation with legumes at Trägsta, Hånsta Östergärde and Körslätts gård
Up in the north, our SOLMACC farm Trägsta grows ley in four out of six years. Even in the fifth year, they grow a combination of legumes and cereal, e.g. peas with barley. Everything is harvested as green fodder for the farms dairy cows.
At Hånsta Östergärde the animal density is lower than at Trägsta. Here they normally grow two years out of seven with ley. Some of the leys are used for fodder and grazing, others for clover seed and grass seed production (which could also be grazed in the autumn). Other legumes like peas or field beans are also grown once in every rotation. During the SOLMACC project, Hånsta Östergärde have also successfully tried a new winter peas variety (EFB 33) which is grown together with triticale. Winter peas are normally not grown in Sweden.
In the very south of Sweden, Magnus Bengtsson at Körslätts gård has no use for ley fodder. Unfortunately there are not any suitable farms in the region for him to trade ley fodder with. Instead Magnus grows nitrogen fixing red clover for seed production and lupin beans which is used as feed for his outdoor chickens.
An overview of the crop rotation at the Caramadre farm
The Caramadre farm performs different crop rotation systems. In 2016, it cultivated the following crops: early brassica, field bean (leguminous), pumpkin, chicory and Sudan Grass (green manure).
With the beginning of the SOLMACC project, the farmers decided to include also leguminous components into the crop rotation. They included field bean in the arable crops and “crotalaria” mainly in the greenhouses. Both of these species increase the nitrogen fixation, which promotes a fertile soil and functions as a substitute for other (synthetic) fertilizer treatments.
The farmer is very satisfied of yields of the products obtained and the improvement of soil fertility, they are getting better with the new rotations implemented. However, agriculture production is a continuous learning process and thus at this point, the farmers consider to make changes in the summer green manure management.
The utilization of green manure in crop rotation to precedes the summer-autumn (Brassicaceae, Umbelliferae, Compositae, etc.) involves the use of essences that have high-speed growth, such as Sudan grass. This grass produced a high amount of biomass and may help to build up further soil humus on the fields. The transformation processes of fresh biomass into soil humus is a complex process, depending on the local soil types, the soil management, the climate and weather patterns. In order to achieve a good transformation of fresh biomass in humus, it takes time. The microbiological activity of the soil are constantly dynamic (between formation and degradation), all this is governed by a matrix which is known and stable, such as the soil, and an unstable element such as the weather. Once the green mass is in contact with the soil, the flora and fauna of the terrestrial attacks and degrades it to build stable organic compounds (humification) or mineralization, therefore releasing nutrients. The transformation process is speeded up by leaving the soil undisturbed, meaning that the farmer should reduce tillage or other management activities. However, these may be necessary to reduce weed pressures on the field and thus allow arable cropping. Therefore, the farmer needs to balance the necessity of leaving the soil undisturbed to enhance soil humus and thus soil fertility, while assuring that further crop cultivation is not hindered by increased weed pressure.