Inclusion of forage legumes in low-input forage mixtures improves herbage production and soil fertility through addition of nitrogen (N) from N₂-fixation. The impact of different grass–legume ...mixtures on the N contribution of the forage mixture has rarely been investigated under comparable soil and climatic conditions. We conducted a field experiment on a sandy soil at two nitrogen levels with seven two-species forage mixtures: alfalfa, bird's-foot trefoil, red clover, or white clover in mixture with perennial ryegrass, and white clover in mixture with meadow fescue, timothy, or hybrid ryegrass. We found high N₂-fixation of more than 300kgNha⁻¹ from both red clover and alfalfa even when the two mixtures received 300kgtotal-Nha⁻¹ in cattle slurry. The addition of cattle slurry N fertilizer lowered N₂-fixation for white clover and red clover as expected, but for bird's-foot trefoil and alfalfa no changes in the proportion of N derived from N₂-fixation was observed. We conclude that the competition for available soil N from perennial ryegrass in mixture was an important factor for the proportion of N in alfalfa, white clover, and bird's-foot trefoil obtained from N₂-fixation. White clover had a high proportion of N derived from atmosphere for all companion grasses despite significant differences in white clover proportion. Although the perennial ryegrass–alfalfa mixture in the grass phase yielded more than twice the N from N₂-fixation compared to white clover in the perennial ryegrass mixture, this did not in the following year lead to higher residual N effects of alfalfa. Both in terms of N yield in the grass phase and N yield in the subsequent spring barley red clover contributed most to the improvement of soil N fertility.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Background
A high use‐efficiency of fertilizer N remains essential to sustain high crop productivity with low environmental impact. However, little is known on the long‐term lability of mineral ...fertilizer N.
Aims
To quantify crop uptake and leaching of 15N‐labelled mineral fertilizer that has been retained in an agricultural soil for 25–30 years in crops with variable growing season.
Methods
A field plot received 15N‐labelled mineral fertilizers over a period of 5 years and was then kept under arable cropping for 12 years. After relocation to 16 lysimeters, the topsoil grew set‐aside grassland for the next 13 years. Then crop uptakes and leaching losses of 15N remaining in soil was tested over a 2‐year period by either converting set‐aside grass to production grassland, or by replacing it with spring barley (+/− autumn cover crop) or vegetation‐free fallow. All treatments received unlabelled mineral N fertilizers.
Results
Crop uptake and leaching of 15N were generally highest in the first test year after termination of the set‐aside. The leaching of residual 15N in soil declined in the order: vegetation‐free soil (4.7%), spring barley (1.9%), spring barley + cover crop (0.7%) and production grassland (0.2%). Corresponding losses for the second leaching period were 2.7%, 0.9%, 0.4% and 0.06%. There was a fixed relationship between leaching losses of 15N and total N.
Conclusions
After residing in soil for 25–30 years, the lability of labelled mineral N fertilizer residues appeared slightly higher than the lability of bulk soil N. Autumn vegetation was crucial for reducing leaching losses.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Background
Legume biological nitrogen (N
2
)-fixation is stimulated by neighbouring non-fixing species, but studies of legume N
2
-fixation in temporary grasslands including non-leguminous forage ...herb (forb) species are rare.
Methodology
We investigated N
2
-fixation, N yield, and total herbage production in a range of species mixtures consisting of three forb species—chicory (
Cichorium intybus
L.), ribwort plantain (
Plantago lanceolata
L.), and caraway (
Carum carvi
L.)—mixed into a traditional red clover (
Trifolium pratense
L.) and perennial ryegrass (
Lolium perenne
L.) mixture at two fertilisation levels.
Results
The percentage of red clover N derived from the atmosphere (%Ndfa) was higher in mixtures containing non-legumes than in pure stand but, did not increase with inclusion of forbs. On a whole-seasonal basis, red clover in mixtures derived 90% or more of its N from fixation even when fertilised with 216 kg total N ha
−1
. Forbs, in particular chicory, reduced the amount of N
2
-fixation and total N yields by affecting the red clover proportion in the harvested biomass.
Conclusions
Generally, inclusion of forbs in red clover-ryegrass mixtures had no negative effect on total herbage production and percentage of legume N
2
-fixation. However, to maintain a high total N and N
2
-fixation yields, mixtures should not include a high seeding proportion of chicory.
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BFBNIB, DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NMLJ, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•The arable-to-grassland conversion caused an annual SOC accrual of 0.30 Mg C/ha.•The accrual was unaffected by pre-conversion soil C level.•A steady state in SOC accrual was not observed during the ...26 years of grassland.
Converting arable land to permanent grassland may favor SOC sequestration and thus climate change mitigation. We studied a field experiment on coarse sand soil that during 1894–1997 was under arable rotation with various nutrient treatments (unfertilized, mineral fertilizer, animal manure), leading to topsoils with different SOC contents. In 1998, the treatments stopped, and a semi-natural grassland has been established with topsoil sampled seven times during the following 26 years. Introduction of grassland increased topsoil SOC content linearly at a rate of 0.30 ± 0.01 Mg C ha−1 yr−1, unaffected by pre-conversion SOC level and with no sign of steady state. By mitigating the loss of SOC associated with continued arable cropping, the overall benefit of this land conversion becomes 0.39 Mg C ha−1 yr−1 during the period 1998 to 2023.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Early harvest of barley did not affect the biomass yield of undersown cover crops.•Incorporation of high stubble of straw in spring reduced the residual N effect.•N supply from root ...biomass was independent of the cover crop shoot yield.•Cover crop root and stubble residues contributed mostly to the residual N effect.
Cover crops (CC) may play an essential role in the recycling of nutrients in organic farming systems with cereals. Harvest time of cereals and management of straw in the field can affect the growth of CC and subsequent nitrogen (N) fertiliser replacement value (NFRV) in the following crop. This study investigates 1) the effect of harvest time, 2) cutting height of straw and 3) straw removal from the main crop on CC growth, composition, uptake and NFRV in the following crop and 4) the effect of CC harvest in autumn on the NFRV in the succeeding crop.
A CC mixture of mainly red clover, with chicory and ryegrass was sown under a spring barley crop in 2017, and replicated in 2018. Four strategies of barley harvest were conducted: 1) early harvest as whole crop or 2) early harvest of the upper parts only, 3) at maturity with straw removed or 4) at maturity with straw left on the field surface. Subsequently, CC and high stubbles of left straw were harvested and removed in autumn in half of the field replicates. The residual effect was measured in spring barley in the succeeding year.
The CC aboveground biomass dominated by the clover had an N uptake for both years of 40−77 kg N ha−1. Variability was significant between years but not caused by the harvest time or by straw management. In the succeeding year, residues from barley and CC could replace 61−85 kg N ha−1 of mineral N fertiliser, which were mostly derived from CC roots and stubble. High straw stubble left (40 cm length) significantly reduced the NFRV of CC shoots by 20%.
Root residues (including barley and CC roots) contributed a substantial N supply to the following crop irrespective of aboveground CC biomass. The availability of N derived from CC shoot mineralisation differed significantly in the two years and was also influenced by straw left from the previous crop.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Residues from hydrogen sulfide (H2S) removal in biogas filters contain sulfur (S) in various forms (sulfate, sulfide, elemental S) that, if properly stored, is potentially valuable as crop ...fertilizer. We investigated 1) the turnover of the S compounds from filter materials during storage in untreated and digested cattle manure (CM), and 2) the S fertilizer replacement value (SFRV) of the filter materials applied in pure form or mixed manure with and without storage. The S filter materials from four H2S removal processes (biological and physical-chemical) containing mostly sulfate and/or elemental S were added to untreated CM or digested CM and stored at 10 °C for six months. Afterwards, a pot experiment was established to assess the S availability in an oil-seed rape (Brassica napus) crop. Microbial reduction of sulfate into sulfide took place rapidly after 69 days storage of untreated CM. A lower reduction rate was observed in digested CM mixtures. After six months, 68% and 32% of the initial sulfate content were still present in mixtures containing the S filter materials from biological desulfurization with digested CM and untreated CM, respectively. Sulfate reduction was inhibited for 120 days when digested CM was mixed with S saturated solution from an ash filter, probably due to high pH (≥8.2) and redox potential (>−100 mV) levels. Oppositely, elemental S was immediately and simultaneously both reduced and oxidized. Relatively low losses of total S were observed during the present storage conditions. Despite S turnover, the SFRV of CM and digested CM significantly increased from 15–19% (of total S applied) to 56–90% when S filter materials were added. The storage of S filter materials in digested manure reduced the risk of sulfide production and potential S volatilization. The S filter materials were a valuable source of plant-available S.
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•Storage of S biogas filter materials is often required prior application to crops.•Storage in manure can induce S loss and reduce the subsequent S fertilizer value.•A high amount of sulfide was formed during storage of filter S in manure.•Sulfate reduction to sulfide was less during storage in digested manure.•S filter materials are valuable fertilizers even after 6 months storage in manure.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
On dairy farms, fertilization of grass-clover swards ensures stable grass yields but may increase the potential for nitrate leaching on light-textured soils. The aim of this study was to quantify the ...N use efficiency and nitrate leaching under fertilized grass-clover leys. The study was conducted over 2 years at two sites, with increasing applications of mineral fertilizer (0–480 kg available N ha
−1
) alone or in combination with a basic application of cattle slurry. For plots fertilized with mineral N, the N soil surface balance was independent of the application rate and in the same range as for unfertilized plots (− 11 to 51 kg N ha
−1
). However, when plots were fertilized with slurry N (+ mineral N), the surplus was substantially increased owing to the fraction of organic N applied in slurry (95–100 kg N ha
−1
) and higher biological N
2
fixation inputs (55–228 kg N ha
−1
). The type of fertilizer had no effect on nitrate leaching across the full range of application rates. Nitrate leaching increased quadratically as a function of application rate, with a range of 3–117 kg N ha
−1
(0.33–17 mg l
−1
in soil solution sampled with suction cups) in the first year and less in the second year, when clover proportion was lower due to the self-regulatory nature of grass-clover mixtures. Importantly, the rate of marginal leaching increased with fertilization level: below 150 kg N ha
−1
there was no additional leaching from fertilization and at 200 kg N ha
−1
around 5% of additional fertilizer-N was leached. This is less than generally found for arable crops and thus even in intensive dairy systems, grass-clover leys are an environmentally favorable crop.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Carbon (C) and nitrogen (N) dynamics in a third production year ryegrass–clover mixture were investigated in the field. Cylinders (diameter 29.7
cm) were installed to depths of 20, 40 and 60
cm and ...equipped with suction cups to collect percolating pore water. Ryegrass and clover leaves were cross-labelled with
14C- and
15N-enriched urea and the fate of the two tracers was studied for 3 months during summer. Transfer of
14C occurred mainly from ryegrass to clover, whereas the largest transfer of
15N was in the opposite direction. The average transfer of N from clover was 40% (SE±3.1,
n=9) of N in ryegrass, whereas the fraction of N in clover donated by ryegrass was 5% (±1.2,
n=9). The amount of
14C transferred from ryegrass to clover was 1.7% (±0.1,
n=9) of the
14C-activity in the total above-ground plant biomass found in the unlabelled clover and with a transfer from clover to ryegrass being 0.4% (±0.1,
n=9).
15N-enriched compounds were not detected in percolating pore water, which may be caused by either dilution from irrigation or low availability of leachable N compounds.
14C was found solely as
14CO
2 in the pore water indicating that dissolved organic carbon (DOC) did not originate from fresh root deposits. Transfer of
14C between the two species in the mixed crop alongside with high transfer of
15N despite a large percolation of pore water indicates that part of the N transfer occurred in non-leachable N-forms. The amount of N transferred between the two species was found to depend on the ratio between dry matter accumulated in the donating and receiving species, the
14C-allocation within the receiving species and the root turnover rate in the soil.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Cover crops varied in chemical composition and nutrient uptake between species.•Release of N, P and S at a low temperature varied between species and plant parts.•Unrecoverable soil pools, such as ...rhizodeposits, contributed substantially to N and P release.•Rumex acetosa, Vicia villosa, Lupinus albus and Raphanus sativus are promising cover crops providing multiple nutrients.
Ecological intensification is crucial for arable organic farmers, in order to partly close the yield gap to conventional yields. One strategy for this is improved management of cover crops, to increase availability of both nitrogen (N), phosphorus (P) and sulfur (S) for the subsequent main crop. However, the potential of cover crops to take up and release nutrients has primarily been determined for aboveground biomass and mostly for N. There have been fewer studies on belowground biomass, and these have focused on recoverable roots. Thus, unrecoverable residues from rhizodeposits and nodules, have been overlooked. The aim of this incubation study was therefore to assess the release of N, P and S from aboveground residues and from intact soil with belowground residues of different cover crop species at low temperature. Shoots and intact soil with roots from seven different cover crops were incubated for 80 days at a temperature of 5 °C.
A comparison of the cover crop species revealed a wide variation in nutrient uptake, chemical composition and release of N, P and S, that also varied between shoot and intact soil with roots. Release of N from shoots showed a marked non-stoichiometric behavior, in contrast to the release of P and S, that correlated well with C:P and C:S ratios. N release (from Vicia villosa) and especially P mobilization (from legumes) in intact soil was much greater than the amounts determined in recoverable roots. This shows that unrecoverable pools such as rhizodeposits and fine roots contributed to nutrient release. Garden sorrel (Rumex acetosa) is a promising cover crop regarding uptake and mobilization of P, but also as a multifunctional cover crop for supplying N, K, S and Mg. Hairy vetch (Vicia villosa) is a promising cover crop for N, oilseed radish (Raphanus sativus) for S, P and K, and white lupin (Lupinus albus) for N, P and Mn supply.
Based on our results, we propose the use of mixtures of cover crops with different N, P and S uptake and release having the potential to supply a more complete suite of nutrients to the subsequent crop.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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