•N leaching was positively correlated to N surplus at the rotation level.•Catch crops reduced N leaching by about 20 kg N ha−1 at the rotation level.•Legume-based catch crops reduced N leaching and ...increased N yield.•Catch crop biomass had to reach a threshold level to achieve low N leaching.
Components of the field nitrogen (N) balance (input and surplus) are often used to predict nitrate leaching from agricultural lands. However, management factors, such as use of catch crops, greatly affect the actual loss and are a key to reduce N leaching. The present study is based on the 4th cycle of a long-term crop rotation experiment in Denmark, and it aims to quantify, from a crop rotation perspective, the influence on N leaching from N input and surplus or management factors. The experiment included three cropping systems (two organic and one conventional) with or without use of animal manure and catch crops. N leaching was calculated from measurements of nitrate in soil water sampled with ceramic suction cups installed at 1 m depth in all plots. At the rotation level, over a four years period, N leaching was positively related to N input and surplus. However, the overall effect of N input and surplus on N leaching was lower than the effect of use of catch crops. The response rates of N leaching to increasing N inputs and N surplus were about 0.08 and 0.19–0.25, respectively. Catch crops reduced N leaching by 23 kg N ha−1, irrespective of conventional and organic management system, with legume-based catch crops being as effective as non-legumes. Animal manure increased N leaching in one of the organic systems. The organic system with two years of green manure per rotation cycle was the one at highest risk of N leaching, especially from crops following green manure incorporation. Spring wheat and potatoes were the two crops with highest N leaching, and a stable low level of N leaching was only achieved above a crop-specific threshold in catch crop biomass.
The contribution of large molecular size organic nitrogen (N) to plant N uptake is unclear.
Soils with and without maize, at three pH levels, were treated with (carbon-14 and -13 (14C, 13C), 15N) ...triple-labelled > 100 kDa organic N. After 48 h, soil and maize were sampled for bulk and compound specific isotope analysis to study the turnover in soil and plant 13C and 15N uptake.
Mineralization of > 100 kDa organic N increased with higher pH only in soil without maize. The > 100 kDa organic N disappeared rapidly in soils with and without maize, but surprisingly more > 100 kDa organic N derived amino acids remained in soil with than without maize – most likely in the microbial biomass. Total 15N uptake in maize increased with higher soil pH. The organic N uptake was estimated to account for 20–30% of the total 15N uptake. Organic N uptake was confirmed by the presence of 13C-labelled amino acids in maize roots.
The study suggests that the importance of plant organic N uptake increases when N is derived from complex molecules such as proteins compared to studies using single amino acids as N source, and that rhizosphere microorganisms increase anabolic utilization of organic N compared to microorganisms in the bulk soil.
► Aboveground and root biomass was significantly affected by the age of grasslands. ► CO2 emissions showed no difference with slurry application and age of grasslands. ► There was no difference in ...the CO2 emissions between grazed and cut grasslands. ► A potential for net storage of C in systems with grassland cultivation was indicated. ► C sequestration to a greater extent depends upon the age of the grassland.
Grasslands are potential carbon sinks to reduce unprecedented increase in atmospheric CO2. Effect of age (1–4-year-old) and management (slurry, grazing multispecies mixture) of a grass phase mixed crop rotation on carbon sequestration and emissions upon cultivation was compared with 17-year-old grassland and a pea field as reference. Aboveground and root biomass were determined and soils were incubated to study CO2 emissions after soil disturbance. Aboveground biomass was highest in 1-year-old grassland with slurry application and lowest in 4-year-old grassland without slurry application. Root biomass was highest in 4-year-old grassland, but all 1–4-year-old grasslands were in between the pea field (0.81±0.094gkg−1 soil) and the 17-year-old grassland (3.17±0.22gkg−1 soil). Grazed grasslands had significantly higher root biomass than cut grasslands. There was no significant difference in the CO2 emissions within 1–4-year-old grasslands. Only the 17-year-old grassland showed markedly higher CO2 emissions (4.9±1.1gCO2kg−1 soil). Differences in aboveground and root biomass did not affect CO2 emissions, and slurry application did not either. The substantial increase in root biomass with age but indifference in CO2 emissions across the age and management in temporary grasslands, thus, indicates potential for long-term sequestration of soil C.
Secondary metabolites secreted by microbes and plants act as mediators in plant-microbe interactions including nutrient uptake. However, until now very little is known about their role in nutrient ...assimilation, particularly amino acids, which are important compounds due to their high N content. Here we show that the addition of flavonoid secondary metabolites, derived from clover, to soil changed the bacterial diversity, enhanced the flux of asparagine, and increased the pools of glutamine/glutamate in the soil. This indicates that flavonoids are functionally important qualitative and quantitative components of clover root exudates. Furthermore, the addition of microbial secondary metabolites negatively affected clover uptake of asparagine and plant performance, which demonstrates that microbial competition for nutrients may have multiple physiological targets in the plant. Finally, the detection of intact asparagine in clover roots confirms that amino acid uptake is significant to the plant in agricultural soil. In conclusion, amino-acid flow in the clover rhizosphere can be modified by the effects of clover-derived flavonoids on the bacterial community structure, which affects the flux and pools of amino acids; microbial secondary metabolites, which reduce clover uptake of asparagine; and direct recapture of amino acids by clover.
•The effect of white clover and microbial secondary metabolites on the amino acid cycling in the clover rhizosphere is shown.•The addition of clover flavonoids to soil changed bacterial diversity and enhanced temporal flux and pools of amino acids.•The addition of microbial secondary metabolites negatively affected clover uptake of asparagine and plant performance.•Amino acid uptake from soil is of importance to the white clover.
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.
Comprehensive climate change mitigation necessitates soil carbon (C) storage in cultivated terrestrial ecosystems. Deep-rooted perennial crops may help to turn agricultural soils into efficient C ...sinks, especially in deeper soil layers. Here, we compared C allocation and potential stabilization to 150 cm depth from two functionally distinct deep-rooted perennials, i.e., lucerne (Medicago sativa L.) and intermediate wheatgrass (kernza; Thinopyrum intermedium), representing legume and non-legume crops, respectively. Belowground C input and stabilization was decoupled from nitrogen (N) fertilizer rate in kernza (100 and 200 kg mineral N ha
), with no direct link between increasing mineral N fertilization, rhizodeposited C, and microbial C stabilization. Further, both crops displayed a high ability to bring C to deeper soil layers and remarkably, the N
-fixing lucerne showed greater potential to induce microbial C stabilization than the non-legume kernza. Lucerne stimulated greater microbial biomass and abundance of N cycling genes in rhizosphere soil, likely linked to greater amino acid rhizodeposition, hence underlining the importance of coupled C and N for microbial C stabilization efficiency. Inclusion of legumes in perennial cropping systems is not only key for improved productivity at low fertilizer N inputs, but also appears critical for enhancing soil C stabilization, in particular in N limited deep subsoils.
Aim This study was conducted to answer the question of whether clover can absorb asparagine in the presence and absence of inorganic nitrogen, as well as to determine the resulting concentration of ...post-uptake compounds closely involved in asparagine metabolism. Methods Clover was grown at two asparagine concentrations (10 μM and 1 mM) supplied in both the absence and presence of ammonium nitrate. Using dual-labeled ¹³C ¹⁵N-asparagine, the uptake rate was analyzed via bulk ¹⁵N and ¹³C excess and the detection of intact ¹³C ¹⁵N-asparagine in white clover. Results The results from the two methods indicated greater utilization of ¹³C ¹⁵N-asparagine in the 10 μM treatment than in the 1 mM treatment. The ¹³C ¹⁵Nasparagine uptake rate was higher when ¹³C ¹⁵N-asparagine was provided alone than when it was supplemented with inorganic nitrogen. Up to nine times lower uptake rates were obtained when intact ¹³C ¹⁵N-asparagine was measured than when bulk ¹⁵N and ¹³C excess were analyzed. The labeled amino acids that are closely related to ¹³C ¹⁵N-asparagine metabolism (aspartic acid, glutamic acid and glutamine) were detected in clover roots and shoots. Conclusions Using two different methods, white clover's potential to absorb intact asparagine, even in the presence of inorganic nitrogen, was confirmed. The dual-methodology approach employed in this study demonstrates how the post-uptake metabolism can affect quantification of amino acid uptake.
Crop mixtures are often beneficial in crop rotations to enhance resource utilization and yield stability. While targeted management, dependent on the local species composition, has the potential to ...increase the crop value, it comes at a higher expense in terms of field surveys. As fine-grained species distribution mapping of within-field variation is typically unfeasible, the potential of targeted management remains an open research area. In this work, we propose a new method for determining the biomass species composition from high resolution color images using a DeepLabv3+ based convolutional neural network. Data collection has been performed at four separate experimental plot trial sites over three growing seasons. The method is thoroughly evaluated by predicting the biomass composition of different grass clover mixtures using only an image of the canopy. With a relative biomass clover content prediction of R
= 0.91, we present new state-of-the-art results across the largely varying sites. Combining the algorithm with an all terrain vehicle (ATV)-mounted image acquisition system, we demonstrate a feasible method for robust coverage and species distribution mapping of 225 ha of mixed crops at a median capacity of 17 ha per hour at 173 images per hectare.
Intensively managed grasslands are dominated by highly productive grass-clover mixtures. Increasing crop diversity by inclusion of competitive forbs may enhance biomass production and sustainable ...biofuel production. Here we examined if one or all of three forbs (chicory, Cichorium intybus L.; caraway, Carum carvi L.; plantain, Plantago lanceolata L.) included in ryegrass-red clover mixtures enhanced above- and below-ground productivity, and assessed their biofuel potentials, based on a three-year experiment with and without fertilisation as cattle slurry. We determined herbage yield, standing root biomass, and estimated methane energy output and greenhouse gas (GHG) emissions per energy unit using life cycle assessment. Results showed that plantain-containing grass-clover mixtures significantly increased herbage yield, while chicory- or caraway-containing mixtures maintained similar yields to the grass-clover mixture. Standing root biomass of the grass-clover mixture was enhanced by inclusion of caraway and plantain, with that of plantain further enhanced by fertilisation. The highest methane energy output was achieved in plantain-containing grass-clover mixtures. All unfertilised mixtures achieved the 60% reduction in GHG emissions compared to fossil fuel, whereas all fertilised mixtures did not meet the 60% reduction target. These findings suggest that including competitive forbs such as plantain in grass-clover mixtures enhances productivity, supporting low-carbon footprint bioenergy production.
In agricultural production, intercropping is a widely used system with many benefits. Lupin (Lupinus angustifolius L.) is a legume that contains a large variety of plant secondary metabolites, which ...have multiple functions in the plant, e.g. signalling, nodulation and stress response. An untargeted metabolomics approach was applied to investigate how the metabolome of lupin was affected by intercropped barley (Hordeum vulgare L.). The only primary metabolite of lupin affected by intercropping was tryptophan. Several secondary metabolites were affected by intercropping in lupin, and five flavonoids were annotated hereof. The flavonoid levels were increased, and tryptophan levels decreased in lupin when intercropped. Two flavonoids are prenylated, and prenylated flavonoids are believed to play a role in the plant's stress response. Furthermore, flavonoids are involved in plant defence and the nodulation process. Thus the present flavonoids may affect regulation of lupin N
2
-fixation activity.
Highlights
Intercropping caused a change in the secondary metabolites of Lupinus angustifolius L.
Prenylated flavonoids were generated in Lupinus angustifolius L. as a response to intercropping
Tryptophan was the only identified primary metabolite affected by intercropping
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