Climate change challenges water protection in agriculture
Liisa Pietola,
Head of Environmental Affairs,
Central Union of Agricultural Producers and Forest Owners MTK,
Finland
Farmers and forest owners around the Baltic Sea experience climate change in their livelihoods. In Nordic conditions, the warming climate causes delayed winters and frosty days. Milder winters increase precipitation and discharge of nutrients from soils. Without climate change, the soil would be frozen for longer time, and excess runoff would be less frequent. Similarly, frosty days would be needed for restoring aggregated soil structure of erosion sensitive fine-textured farmlands, which can be compacted after field traffic of cultivation. Consequently, frosty winters are crucial for maintaining soil fertility, and keeping soil particles and nutrients on the ground, thus controlling eutrophication.
Erosion sensitive clay soils on focus
In Finland, over 90 % of the phosphorus and nitrogen load occurs outside the growing season. Due to the increase of heavy rains and water saturated soil conditions this number is even higher. Particularly in the erosion sensitive clayey area in South-Western Finland, close to the Archipelago Sea, climate change complicates farming, agricultural water management, and water protection.
The primary cause of erosion is degradation of aggregate structure of clays, after prolonged water saturated conditions. Tiny soil particles disperse, and the crumbed structure is lost. Soil particles are transported by soil surface runoffs to rivers, and to the sea. Soil freezing would be essential, as it causes drying and strengthens stability of soil aggregates. Good soil aggregate structure, in turn, promotes good soil aeration and water availability, thus enhancing plant growth and nutrient uptake.
Thus, due to the climate warming, clay soils need special care and management for erosion and nutrient leakage control. The crop monoculture, and intensive tillage with bare soil conditions, cannot continue like past decades. Instead, we need to keep soil covered by crops all year round. Catch crops should be utilized together with spring-sown crops, or winter crops sown after harvested crop. Today, the minimum tillage is common, and many fields are left untilled before spring sowing. This may, however, challenge seedbed conditions for successful plant emergence and growth in the following season, thus risking nutrient uptake by crops.
Grasses role increasing
35 years ago, my professor in soil science, late Dr. Reijo Heinonen (www.slu.se) predicted that if climate warming eliminates frozen soil profiles, cultivated clay soils need to be transformed to grasslands. Otherwise the aggregated soil structure will not be maintained. In grasslands, the root growth would substitute the positive effect of freezing on soil aggregates, and the crop cover would control erosion, like on mountainous regions.
We have witnessed his prediction. Fortunately, the modern technology allows us to continue cropping along with additional soil improver crops, like deep rooting catch crops. To adapt climate change, crop rotation by perennial grasses seems to be, however, an additional requirement.
The essential part of water protection and nutrient discharge control is biomass harvest, i.e., nutrient uptake from soil reservoirs, mobilized by microbes, or by fertilizers. The yield needs to be harvested and taken away. Otherwise we cause leakage of dissolved nutrients from decaying plants on the ground. Perennial grasslands take phosphorus up deeper from the soils by their roots. Thus, if above-ground biomass is not harvested, algae available dissolved phosphorus accumulates on soil surface, and risk of nutrient runoff is obvious.
Markets for grass biomass needed
Harvested biomass needs markets. A big question of water protection is how to find those markets. Two options are animal feeds or biogas production. In the costal clayey area, there is not enough cattle to utilize grasses for valuable protein production. The sensible mixt of cropping and livestock would be most beneficial for water protection.
Similarly, high yielding grasses are essential for carbon sequestration by soils, while thriving for climate neutral future and food. We need to diversify cropping and land use, but also utilize the potential of grass-based cattle farming, as described by MTK-SLC Climate Roadmap for Agriculture.
Willingness to act
Farmers and forest owners have strong a will to protect waters. This was well documented by the inquiry for MTK members, carried out in 2018 and 2020. These results, and all the efforts, challenges and opportunities are described in the new MTK-SLC Water program: Towards a good status of waters – through 1) agricultural and forestry practices that reduce loads; 2) using cost-effective and well-targeted water protection solutions; 3) through catchment area-specific planning; 4) by applying more precise research data and by increasing know-how.
Email: liisa.pietola@mtk.fi
Expert article 2869
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