Adaptation strategies for increased cereal production under a wetter future climate

Increasing precipitation, combined with increasing farm machinery size and poor drainage, will potentially have serious implications for Norwegian cereal production in the future. OPTIKORN has contributed to the knowledge-base needed for adaptation strategies that reduce soil compaction, waterlogging and nutrient loss. Good soil structure with high infiltration rate is necessary to avoid the accumulation of water and oxygen depletion in the root zone. Mechanical subsoiling has been used for many years to alleviate compaction, with varying results. We have combined mechanical subsoiling with biological soil loosening, and various species were studied for their ability to loosen soil. Also, mechanical subsoiling was combined with either biological soil loosening or liming. Results show that the effect of mechanical loosening is only temporary, mainly due to recompression. Liming stabilized the soil in the upper layer but had no stabilization effect in deeper layers. Results indicate that liming may have a positive effect in the long-term. Plant roots alone did not loosen the subsoil. The combination of mechanical subsoiling and roots of deep growing plants could improve soil structure, reduce re-compaction and conserve the loosening effect. In this study, none of the measures to loosen compacted soil had an overall positive effect. Economic calculations indicate that the profitability of mechanical and biological loosening is poor. In cases of severely compacted areas, the most economical option for loosening is the plough with plough pan breaker. It is easier and cheaper to avoid soil compaction than trying to repair it. The majority of drainage systems in Norway were constructed between 1960-85, and although many of these systems suffer from deterioration, the investment in new drainage systems is low. Experimental data as well the model-based scenario analyses indicated that poor drainage conditions can lead to increased runoff and more frequent flash floods, reduced soil trafficability, reduced crop yields and increased soil and nutrient losses via surface and subsurface water pathways. Without mitigation measures, climate change will most likely cause further negative impacts on these processes. The only exception is soil trafficability, that can improve with warming climate, thus, the soil may become trafficable earlier in the spring. Measurements showed that subsurface drainage systems are a highway for nitrogen (N) transport and significant amounts of suspended solids (SS) and phosphorus (P) can also be transported. Model-based scenario analyses of water regime that accounted for topsoil and subsoil compaction, changes in drainage design (space and depth) and choice of crops under future climate conditions indicate that i) soil compaction will lead to increase in surface runoff in the future; ii) the unfavorable effect of soil compaction on plant development and water regime will increase; iii) drainage design has somewhat stronger effect on soil water regime than soil compaction; iv) reduced distance between the drainpipes can partly mitigate the effects of soil compaction by increasing drainage outflow and reducing surface runoff, but might lead to increase in nutrient losses; v) winter crops, due to increased transpiration can improve soil water regime under present and future conditions and vi) with changing climate, the soil can become trafficable earlier in the spring in the future then today. Fertilizer must be applied in the correct amount and at the right time to utilize yield potential. Increased precipitation and more extreme downpours increase the risk of nutrient losses. Split application of N in wheat has been recommended for many years, where as one spring application has been the dominate practice in barley. An extra N application is often recommended following heavy rainfalls to compensate for leaching losses. In field trials we have studies the effect of split N applications in barley, compared to one spring application. Results show that yield is not affected by fertilizer timing. Lowering the amount of N applied at sowing reduces the soil N concentration, thereby reducing the risk of losses. The practice of applying extra N following leaching periods can be replaced by a planed split application that can be adjusted according to the growing season. Economic studies show that it is more profitable to split apply N compared to one application at sowing. A planed split application is therefore the best strategy with respects to both economics and the environment. The question of how much N has been leached out of the root zone following exessive rainfall is often posed. In this project a new N calculator has been developed. The calculator take N dynamics in the soil into consideration, and is based on the Danish model «Daisy». A test version of the calculator is complete, and quality control must be assured before the calculator can be made publically available.

The results emphasize that soil structure is easily damaged, but more difficult to repair. As such, the results underline the need for strategies to (a) increase soil stability and (b) avoid (sub-) soil compaction. Furthermore, the results show the challenges in using lime to stabilize subsoil. Plant roots may a have a potential to (I) loosen compacted subsoil over time, and (II) stabilize subsoil loosening effect, but more research is needed on (a) establishment strategies for different types of soil loosening plants, (b) how these could be integrated into a crop rotation that generates income and (c) long term effect. The results from OPTIKORN will help farmers decision making process in terms of avoiding of soil compaction, soil structure improvement and subsoil loosening. For society and decision makers these results illustrate (a) the need for better strategies to improve soil structure and stability, (b) necessity to avoid soil compaction. The information gathered on drainage activity and profitability analyses will be useful for government with respect to developing effective grant programs. This knowledge will also be beneficial for farmers and advisors. Results of the economic analysis can result in increased drainage activity, which is positive for production, farmer’s economy, the environment and the climate. The model-based scenario analysis applied in the project is a complex approach that can account for the – sometimes contradictory- effect of various management practices and mitigation measures in an integrated way. The key message to the society, farmers and decision-makers is that complex strategies are needed to maintain cereal production without increasing the pressure on the environment under changing climatic conditions. These would include i) site-specific soil conserving practices to avoid soil compaction; ii) split and precision fertilization for reducing nutrient losses that might occur due to increased surface runoff and drainage outflow in the future and iii) new crop rotation schemes. As changing the drainage system is an expensive measure, further studies are needed for optimizing and adapting i) soil management, ii) crop rotation, including winter crops and iii) fertilizer strategies to future climate conditions. The presented method could also be used in decision making, to decide, i) whether drainage pipes should be established in a certain area; ii) how the drainage system should be designed to maintain future hydrological conditions; iii) what would be the benefit from reduced soil compaction and optimized fertilizer strategy, etc. Results from the study of fertilization strategies will be very useful for Norwegian agriculture as well as for the environment. A planned split fertilization is more profitable than applying all fertilizer at sowing. Split application reduces the loss of nutrients to the air and water as it is possible to adjust fertilizer application more precisely to the needs of the plants.

Increasing precipitation, combined with ever-increasing farm machinery size and poor drainage conditions in many locations challenge our stewardship of the soil and will have serious implications for Norwegian cereal production. These challenges must be mitigated if the anticipated future increase in production potential due to a warmer climate is to be realized. Strategies that reduce the risk of soil compaction and waterlogging, thereby reducing the loss of nutrients to water and air, are essential. A good soil structure with a high infiltration rate is necessary in order to avoid the accumulation of excess water and oxygen depletion in the root zone over prolonged periods. Mechanical subsoiling has been used for many years to alleviate compaction, however positive results are far from guaranteed. The impact of combining mechanical subsoiling with biological soil loosening species or structure liming on soil loosening effect and longevity will be explored. The majority of drainage systems in Norway were constructed between 1960-85, and although many of these systems now suffer from deterioration, the investment in new drainage systems is low. A better documentation of drainage profitability is required in order to stimulate drainage investments and new guidelines must be developed. More knowledge on plant responses to waterlogging, ability to recover, and the impact of N fertilization for plant recovery, is also needed. Adapted fertilization strategies that minimize loss of nutrients to air and water and reduce yield loss under conditions with excessive precipitation will be developed. The economic impact of management options drives the rate of adoption at farm level, and hence an overall evaluation of the profitability, agronomy and environmental impact of adaptation strategies is necessary. This will be a key step in interpreting the results, to ensure practical and effective strategies that reduce the risk of yield loss under increasingly wetter conditions.