Drainage impact on ley productivity, soil physical properties, gas emission and profitability in forage production in Western Norway.

An experimental field with three drainage intensities (high: 6 m between tile drains, low: 12 m between tile drains, no tile drains) was established on mineral soil in Askvoll. The design consisted of two grass leys (2 and 3 cuts/year) with two levels of nitrogen fertilization (190 or 290 kg N/ha). Precipitation, soil temperature, ground water level, soil moisture, and drainage runoff were monitored continuously, while methane (CH4) and nitrous oxide (N2O) emissions were monitored weekly. At a peat site in Fræna, we compared drainage by ?peat inversion? with an adjacent tile drained peat. The inverted peat was covered with a 0.5 ? 1m layer of mineral soil taken from beneath the peat, while maintaining contact to the self-draining mineral subsoil through ditches filled with mineral soil. Also here we compared two levels of N-fertilization (180 or 260 kg/ha). Mean dry matter yield (DMY) at Askvoll for three ley years (2015-2017) was 8.01, 8.58 and 8.80 t/ha/y with no, low and high drainage intensity, respectively. Cutting twice per year gave somewhat higher yields (8.95 t/ha/y) than cutting three times per year (7.99 t/ha/y). Increased fertilization increased yields from 7.90 to 9.04 t/ha/y. At Fræna, mean DMY for the ley years (2015-2017) was 12.63 and 10.75 t/ha/y on inverted and tile drained peat, respectively. Increased fertilization at the inverted peat increased DMY from 10.68 to 12.63 t/ha/y. The soil at Askvoll had low air capacity (8.2-11.3 vol%) and low saturated hydraulic conductivity (0.3-4.0 cm/h). Because of high spatial variability, we did not find significant effects of drainage intensity or cutting regime on soil physical parameters. The mineral material cover above the inverted peat had a high proportion of coarse silt and fine sand and was low in organic matter. Bulk density and air capacity were higher, and plant available soil moisture was smaller in inverted than in tile-drained peat. Inversion gave better drainage and trafficability, while increasing the risk for summer drought. At Askvoll emissions of N2O and CH4 were measured at high and low drainage intensity in the highly N-fertilized, 2-cut system from 01.05.2014 to 14.12.2016. Mean annual N2O emissions were 0.94, 4.24 and 2.90 kg N/ha for 2014, 2015 and 2016, respectively, corresponding to 1% of the applied fertilizer N. Throughout the entire measurement period, 9.2 and 6.9 kg/ha N2O-N was emitted at high and low drainage intensity, respectively, whereas cumulative emissions of CH4 were -0.2 and 14.9 kg C/ha. High soil moisture and periods of waterlogging in parts of the field with low drainage intensity likely stimulated reduction of N2O to N2, thus reducing N2O-emissions. Total N2O and CH4 based emissions at high and low drainage intensity accounted for 370 and 410 kg CO2 eq/tonne grass DM (mean of 2014-2016), respectively. At Fræna, measurements from spring to late autumn in 2015 (27.04-14.10) and 2016 (05.04-20.11) showed CH4 emissions of 200 and 140 kg C/ha in tile-drained peat and 4 og 23 kg C/ha in pristine peat. In inverted peat, the emissions were 1 kg/ha in 2015 and -1 C/ha in 2016. In inverted peat, we observed high CH4 concentrations in the soil air just above the buried peat, indicating substantial CH4-oxidization in the mineral layer above the peat. N2O emissions were 4.3 and 9.5 kg N/ha in fertilized tile drained peat in 2015 and 2016, respectively, whereas 3.6 kg/ha N was emitted in fertilized inverted peat both years. In tile-drained peat, the N2O emission factor for applied N was 1.6 and 3.4% in 2015 and 2016, respectively, whereas it was 1.3 and 0.9% in inverted peat. N2O emission in unfertilized plots (tile drained, inverted and uncultivated peat) was negligible. Total emissions of N2O and CH4 in tile drained and inverted peat corresponded to 720 and 390 kg CO2 eq/tonne grass DM (mean of 2015 and 2016). Data from Askvoll are used to investigate the effect of drainage intensity on water table, soil moisture, soil temperature, N-leaching and to calibrate DRAINMOD. Water balance calculations suggest that considerable amounts of water flow to the groundwater without being intercepted by the newly installed tile drains. The amount is however smaller at the higher drainage intensity. The results also suggest that both drainage intensities have the capacity to react fast to precipitation-induced rise in groundwater level. N-leaching increased with increased fertilization and drainage intensity. Investment costs for drainage were updated and compared to potential yield increase based on data from the Farm Business Survey in western Norway. Yields at Askvoll and Fræna were used to make budgets based on different levels of investment, interest rates and longevity of drainage. Due to small yield differences between the drainage intensities, the drainage investments at Askvoll was not profitable. At Fræna, the large yield increase following peat inversion made inversion profitable despite high costs.

"Drainage impact on ley productivity, soil physical properties, gas emission, and profitability in forage production in Western Norway" is a 4.5 year project aiming to increase the effort on drainage within Norwegian research, education and advise. Norweg ian grassland has experienced a decrease in yields during the last 10 years despite better cultivars and agronomic knowledge. Poor drainage, suboptimal physical properties, and increased size of farms and weight of agricultural machinery are pointed out a s possible reasons. More rainfall is expected which will worsen this situation. Drainage, soil compaction and fertilization have been listed as research areas to reduce N2O emission from agriculture and better drainage and reduced soil compaction to incre ase yield. The project focuses on practical farming conditions by testing two different drainage methods; subsoil drainage system on mineral soil and inverted peat soil with tilted layers on top of peat soil. On both field types two management intensities and two N-fertilization levels will be established and the effect of dry matter yield and N-loss will be investigated, as well as the impact of soil compaction on soil physical conditions. Emission of greenhouse gases (N2O, CH4) related to drainage inten sity will mainly be observed during the growing season but also during autumn and early spring and with episodes of freezing-thawing during winter. Existing drainage recommendations are based on old and outdated knowledge, and new drainage criteria will b e defined from the data obtained in the project. The profitability of drainage will be quantified on farm level. The project will launch a new knowledge base focusing on advising and passing on knowledge to the farming community, advisory system and publi c administration bodies, and master students will be invited to have their education within drainage, soil physics or greenhouse emission to increase the number of persons with competence within soil physical issue