Samson Øpstad

Research Scientist

(+47) 406 21 871
samson.opstad@nibio.no

Place
Fureneset

Visiting address
Fure, 6967 Hellevik i fjaler

Abstract

More than 2/3rds of Norway’s agricultural area are grassland, and more than half of it is over 5 years old. Renewing old grassland increases annual yield but causes yield loss during renewal. Parts of the increased yield is due to replacement of low-productive species with high production species and cultivars, replacing biodiversity with productivity. Finding the optimal rate of renewal requires long term experiments to compare the sustainability of different strategies. Therefore, three field experiments were established to investigate the effect of difference renewal and harvest strategies on grass yield and quality, on similar mineral soil at Særheim (58.5°N, 5.6°E) in 1968 and Fureneset (61.3°N,5.0°E) in 1974, and on peat soil at Svanhovd (69.5°N,30.0°E) in 1968. Until 1991, the experiment included non-renewed treatments, and renewal every 3rd or 6th year. It was cut either two or three times a year, with autumn grazing on parts of the two-cut regime. The experiment was simplified in 1992, with the establishment of another non-renewed treatment, all treatments being cut 3 times a year (2 at Svanhovd), no grazing but contrasting slurry and compound fertilizer applications. This phase lasted until 2011, followed by period with no renewal and minimal registration. The third phase started in 2016, with renewal of all treatments at Fureneset and Særheim, except the permanent grassland from 1968/1974. Duration between renewals was doubled, and fertilizer applications revised. Presenting results from the third phase, we show that five to six years are required to recoup and significantly over-yield the non-renewed grassland. We will use soil chemical and physical properties, fertilizer application and yield gaps as well as ecological succession from sown seed mixture in 2017 till 2022 grassland to discuss the why we needed six years for all renewed treatments to over-yield permanent grassland from 1974.

Abstract

In Norway, the effect of drainage on grassland yields has received little attention for decades. Low level of drainage may be a reason for low grassland production. Therefore, a drainage experiment was established in a western Norwegian ley, on a sandy silt soil with a high capacity for water storage. The plots had six and twelve meters drain spacing, as well as undrained. There were two or three cuts, and fertilization of 190 or 290 kg N yr-1 ha-1. Drainage intensity gave a small significant increase in yield. N loss in drainage water increased with drainage intensity. The yield increase is likely too small to justify drainage, but the intervention might still be worthwhile due to increased N efficiency and a more manageable risk of compaction. A precise quantification of the hydrological effects is hard due to inherent soil variability.

Abstract

In Norway, the effect of drainage on grassland yields has received little attention for decades. Low levels of drainage may be a reason for low grassland production. Therefore, a drainage experiment was established in a western Norwegian ley, on a sandy silt soil with a high capacity for water storage. The plots had six- and twelve-metres drain spacing, as well as an undrained treatment. For each drainage treatment there were two or three cuts per year, and fertilization of 190 or 290 kg N yr-1 ha-1. Drainage intensity gave a small significant increase in yield. N loss in drainage water increased with drainage intensity. The small herbage yield increase is unlikely by itself to justify drainage, but the drainage installation might still be worthwhile due to increased N efficiency and a more manageable risk of compaction. Precise quantification of the hydrological effects is hard to make due to the inherent soil variability.

Abstract

Several studies conclude that permanent and temporary swards are equally productive, given equal management. In Norway, one experimental field trial has been maintained since 1974 (Fureneset; 61°18’N, 5°4’E). This ongoing experiment includes long-term/permanent ley (no-tillage over 25 and 45 years) next to temporary leys reseeded regularly. The objective of the study was to test reseeding/ renovation methods that may maintain long-term forage productivity. We hypothesized that sod seeding after chemical fallowing improves grassland productivity equally to that from reseeding after ploughing. In 2017, the frequently ploughed treatments, and half of the 25-year-old sward, were renewed by ploughing and reseeding with grass-clover seed mixtures. The second half of the 25-year-old sward was chemically fallowed and sod-seeded. The treatments included three different fertilizer strategies: mineral fertilizer (210 N kg ha-1) and cattle slurry in combination with mineral fertilizer (210 and 340 kg total-N kg ha-1). On average for four production years (2018-2021) the dry matter yield (DMY) of permanent sod-seeded 25-year-old ley was about 11 t ha-1, and these yields were equal to swards renewed by ploughing and reseeding.

Abstract

Current forage production on tile drained peat soil is challenged by low drainage efficiency and large GHG emissions. Alternative methods need to be evaluated to sustain agricultural usage while protecting peat C and N stocks. Peat inversion is a valid method when the peat layer is less than 1.5 m deep and lies on top of a self-draining mineral soil. The peat body is covered by the underlying mineral soil while maintaining connectivity to the self-draining subsoil through tilted mineral soil layers. We studied the effect of inversion of previously tile drained peat with forage production on dry matter yield (DMY), methane (CH4) and nitrous oxide (N2O) emissions and peat degradation. The field experiment was carried out in adjacent fields with inverted and tile drained nutrient poor peat in Western Norway during 2014-2018. At both fields the surface was slightly graded towards open ditches surrounding the field. The thickness of the mineral cover layer of the inverted peat varied between 80-100 cm on top of the graded surface (upper site) and 40-50 cm closer to the ditches (lower site). Coarse silt and fine sand dominated the texture of the cover layer and content of organic matter was very low (0.5 % tot. C). The texture was finer (higher content of silt and clay) at the lower site compared to the upper site. Mean DMY for 4 ley years at the inverted (upper site) and tile drained peat was 12.2 and 10.3 t ha-1 y-1, respectively. Mean methane emissions in tile drained peat were 200, 140, 209 and 55 kg CH4-C ha-1 in 2015, 2016, 2017 and 2018, respectively, whereas the CH4 exchange in inverted peat was small. In inverted peat, we found up to 50 vol% CH4 in the soil air close to the buried peat, which strongly decreased towards the soil surface at both inverted sites. Nitrous oxide emissions in fertilized tile drained peat were 4.3, 9.5, 9.8 and 5.3 kg N2O-N ha-1 in 2015-2018, respectively. In inverted peat (upper site) N2O emissions were 3.6, 3.6, 8.5 and 2.7 kg N2O-N ha-1 these years. In lower site, measured in 2017 and 2018, the emissions were 10.3 and 4.5 kg N2O-N ha-1, respectively for the two years. N2O-emissions were small in unfertilized plots both at tile drained and inverted peat. Depth profiles of N2O in soil air indicated that N2O is produced in the mineral layer and not in the buried peat. Continuously monitored O2 profiles showed O2-concentrations of 0-5 vol% in the top of the buried peat and much higher concentrations (5-20 vol %) in the tile drained peat. Dark chamber measurements in 2018 showed a CO2-flux of 1.43, 1.49 and 2.35 kg ha-1 h-1 CO2-C after 1.st cut and 1.4, 1.25 and 2.01 kg ha-1 h-1 CO2-C after 2.cut in inverted upper site, inverted lower site and tile drained peat, respectively. The larger respiration measured at tile drained peat most probably derives from larger heterotrophic respiration, as the mass of roots was lower in tile drained than in inverted peat. Results from this field experiment suggest that inversion of tile drained peat reduces the CH4 emissions and degradation of the peat. N2O emissions is fertilizer induced in both tile drained and inverted nutrient poor peat, and is determined by soil and weather conditions at the time of fertilization. The large variation in emissions between years can be explained by different weather conditions. 2017 was a wet year and 2018 a very dry year.

Abstract

Perennial versus short term (<3 years) grass vegetation cover is likely to have considerable differences in root density and thus carbon (C) inputs to soil. Carbon inputs are important to maintain soil organic carbon (SOC) and may even increase it. In Norway and Scandinavia, the SOC content in soil is often higher than in other parts of Europe, due to the cold climate and high precipitation (i.e. slower turnover rates for soil organic matter) and a dominance of animal production systems with a large amount of grassland. Here we aimed to evaluate differences in SOC content, down to 60 cm depth, of a long-term grassland (without ploughing for decades) and a short-term grassland (frequently renewed by ploughing) under contrasting climate, soil and management conditions. Quantification of SOC was carried out on three long-term experimental sites on an extended latitude gradient in West and North Norway. The samples were taken from 4 depth increments (0-5, 5-20, 20-40 and 40-60 cm) in treatments that have not been ploughed for at least 43 years, and in treatments that were ploughed every third year until 2011. Preliminary results suggest that there is no significant difference in SOC storage down to 60 cm between long-term and short-term grasslands.

Abstract

The abundance of Juncus effusus (soft rush) and Juncus conglomeratus (compact rush) has increased in coastal grasslands in Norway over recent decades, and their spread has coincided with increased precipitation in the region. Especially in water‐saturated, peaty soils, it appears from field observations that productive grasses cannot compete effectively with such rapidly growing rush plants. In autumn–winters of 2012–2013 and 2013–2014, a four‐factor, randomised block greenhouse experiment was performed to investigate the effect of different soil moisture regimes and organic matter contents on competition between these rush species and smooth meadow‐grass (Poa pratensis). The rush species were grown in monoculture and in competition with the meadow‐grass, using the equivalent of full and half the recommended seed rate for the latter. After about three months, above‐ and below‐ground dry matter was measured. J. effusus had more vigorous growth, producing on average 23–40% greater biomass in both fractions than J. conglomeratus. The competitive ability of both rush species declined with decreasing soil moisture; at the lowest levels of soil moisture, growth reductions were up to 93% in J. conglomeratus and 74% in J. effusus. Increasing water level in peat–sand mixture decreased competivitiveness of meadow‐grass, while pure peat, when moist, completely impeded its below‐ground development. These results show that control of rush plants through management may only be achieved if basic soil limitations have been resolved.