Legume Cover Crops Research Articles

No‐till with Stylosanthes guianensis cover crop affects weed community and improves weed management in upland rainfed rice in Madagascar

AbstractIn Madagascar, upland rainfed rice is traditionally grown on tilled soil without transplanting. Weed infestation by annual species is a serious issue in such a system. Stylosanthes guianensis, a legume cover crop, can be grown with rice as a living mulch but its effect on the weed community and rice yield was not yet well studied. Therefore, a field experiment was conducted in Mid‐West Madagascar from 2016 to 2018. A no‐till system with stylosanthes (NT) managed as a living mulch was compared to the conventional tilled (CT) system. Two fertilisation regimes were included: organic manure (F1) and organic manure combined with mineral fertiliser (F2). Weed floristic surveys were performed, and weed harmfulness evaluated by comparing weedy and weed‐free plots. The living mulch harmfulness was evaluated using weed‐stylosanthes‐free plots. Results showed that NT suppressed dominant grass weeds Digitaria spp. and Eleusine indica leading to a decrease in total weed biomass. Rice yield was significantly higher in NT than in CT; in weed‐free condition, it was 2.4 versus 2 t ha−1 in NT and CT, respectively, and 1.5 versus 0.6 t ha−1 in NT and CT, respectively, in weedy condition. The living mulch reduced rice yield by 14% but it remained significantly higher in NT than in CT. The addition of mineral fertiliser to the organic manure had a positive effect on rice yield but only in weed‐free conditions. This study showed that a no‐till system with a living mulch can help to control the most competitive weeds without undermining rice production.

Combining Zeolites with Early-Maturing Annual Legume Cover Crops in Rainfed Orchards: Effects on Yield, Fatty Acid Composition and Polyphenolic Profile of Olives and Olive Oil

Under climate change threats, there is a growing need to adapt the conventional agronomic practices used in rainfed olive orchards by sustainable practices, in order to ensure adequate crop yield and olive oil quality and to preserve soil health. Therefore, for two years, the effects of conventional tillage practice (T) and two sustainable soil management strategies, a leguminous cover crop (LC) and its combination with natural zeolites (ZL), on the yield, fatty acid composition, polyphenolic profile and quality indices of olive fruits and oil were evaluated. Crop yield was significantly increased by LC and ZL in the first year. Although in the second year no significant differences were verified, the cumulative yield increased significantly by 31.6% and 35.5% in LC and ZL trees, respectively. LC enhanced the moisture and size of olives, while ZL increased, in general, the concentrations of oleuropein, verbascoside, caffeic acid and epicatechin, as well the oleic/linoleic ratio in fruits and the levels of 3,4-dihydroxyphenylglycol, tyrosol, verbascoside and caffeic acid in olive oil. Despite the higher concentration of total phenols in the fruits and oil from T trees in the warmer and dryer year, the quality of the oil decreased, mainly when compared with ZL, as evidenced by the peroxide value and K232 and K270 coefficients. In short, both sustainable soil management strategies appear to be promising practices to implement in olive orchards under rainfed conditions, but the innovative strategy of combining zeolites with legume cover crops, first reported in the present study, confers advantages from a nutritional and technological point of view. Nevertheless, studies subjected to the long-term use of these practices should be conducted to ensure the sustainability of the crop yield and olive oil quality.

A grass–legume cover crop maintains nitrogen inputs and nitrous oxide fluxes from an organic agroecosystem

AbstractLegume cover crops are central to an ecological nutrient management approach that can reduce nitrogen (N) losses from agriculture. Diversifying cropping systems with a legume–grass cover crop mixture could further reduce N losses by increasing soil N assimilation and synchronizing N mineralization with N uptake by the following crop. We established four winter cover crop treatments (crimson clover, cereal rye, clover–rye mixture, and weedy fallow control) in an organic grain agroecosystem that had been managed for 30 years with a legume cover crop as the only external N source. We hypothesized that the legume–grass mixture would provide similar inputs of biologically fixed N2 compared with the sole legume, while reducing N2O emissions during decomposition following tillage. We measured cover crop aboveground biomass C:N and clover N2 fixation, soil inorganic N and N2O fluxes throughout the corn growing season following cover crop tillage, and corn N assimilation at harvest. Even with a reduced clover seeding rate in mixture, the clover and mixture treatments had similar fixed N inputs, litter N and C:N, and no differences in cumulative N2O emissions. During the first peak flux, N2O emissions were 2–5 times higher in clover and mixture relative to rye and fallow, with no differences between clover and mixture. There were no treatment differences at the second N2O peak, which followed the first major rain event. We contextualized these findings by calculating a 6‐year partial N mass balance for this agroecosystem, which was slightly negative (−6.8 ± 0.8 kg N ha−1 year−1) when accounting for historical mean annual N2O emissions and nitrate leaching. Overall, N inputs and harvested N exports were approximately in balance for this legume‐based crop rotation, suggesting that the legacy of ecological nutrient management has promoted efficient N cycling. However, results from our field experiment indicate that short‐term N2O flux rates following cover crop incorporation can be high even for a legume–grass mixture. Additional strategies to reduce soil disturbance are therefore needed to further tighten N cycling in organic grain agroecosystems.

Strip-tillage and Zonal Cover Cropping Effects on Organic Squash Production

Zonal management of cereal–legume cover crop mixtures may help address weed and nitrogen management challenges common in organic reduced tillage systems. During a field study conducted over 3 years in Michigan, we evaluated the effects of cover crop management, tillage, and supplemental mulch on organically produced acorn squash (Cucurbita pepo). During the fall season before squash production, rye (Secale cereale L.) and vetch (Vicia villosa Roth) cover crop mixtures were sown in two distinct spatial arrangements: a “mixed planting,” in which seeds were sown in the same rows, and a “zonal planting,” in which vetch was planted only in the in-row zone and rye was planted only in the between-row zone of the subsequent squash crop. During the following spring season, cover crops were mowed, and four tillage and cover crop management combinations were established: full-width tillage with the mixed planting of rye–vetch (full-till mixed); strip-till with the same mixed planting (strip-till mixed); strip-till with the rye–vetch zonal planting (strip-till zonal); and strip-till with the zonal planting and additional rye mulch added between crop rows immediately after crop establishment (strip-till zonal plus rye). The strip-till mixed treatment resulted in yields equivalent to those of the full-till mixed treatment despite lower available nitrogen and greater early weed competition in some cases. Within strip-till treatments, zonal planting of rye–vetch provided no benefits relative to full-width planting (treatment 2 vs 3) and resulted in lower total cover crop biomass, a higher density of escaped weeds, and lower squash yields during 1 of 3 years. Supplemental rye mulch improved weed suppression and yields in strip-till zonal treatments and resulted in yields equivalent to those of the full-till mixed treatment in all years, but it provided no benefits relative to strip-till mixed. Our results demonstrate that strip-till organic squash production can produce yields equivalent to full-till production in Northern climates, but that zonal planting and supplemental mulch have limited benefits for addressing ongoing weed and nitrogen management challenges. Growers must weigh costs associated with these challenges against potential benefits for soil and pest regulating ecosystem services before adopting these agricultural conservation practices.

Penyuluhan Mengenai Beberapa Teknik Untuk Menginduksi Pembungaan Pada Tanaman Mucuna Bracteata Di Desa Kampung Padang Kecamatan Pangkata Kabupaten Labuhanbatu

Most of Kampung Padang resident is a farmer especially as a oil palm and rubber farmer. In the cultivation of oil palm and rubber, there are still a few villagers from Kampung Padang who plant Mucuna between plants as a ground cover crop or Legume Cover Crop, even though Mucuna has many benefits, especially for suppressing weed growth and improving soil chemical properties. The difficulty of obtaining seeds makes people rarely use Mucuna. Some techniques that can be done to induce flowering in plants are using a growth regulator (ZPT) paclobutrazol. Several research results regarding the use of paclobutrazol have succeeded in shortening the length of plant tendrils. Other techniques that can be used to induce flowering in plants are providing water stress, ringing the plants, and pruning the roots of the plants. The response from the people of the Padang village population was very enthusiastic, seen from the many people who asked questions during the event.

Impacts of summer-seeded legume cover crops and termination-tillage method on nitrogen availability to corn in rotation

Summer-seeding legume cover crops can reduce erosion, mitigate nitrate leaching losses during the non-growing season, and provide bio-accumulated nitrogen (N) to the following crop. Very little information is available, however, on the most effective methods for terminating summer-seeded cover crops, or on the amount of N they can provide to subsequent crops. We therefore evaluated the impacts of selected legume cover crops and cover crop termination-tillage methods on corn (Zea mays L.) N credit and grain yield in a soybean (Glycine max Merr.) - winter wheat (Triticum aestivum L.)/cover crop - corn rotation over 3 consecutive years on a clay loam soil in southwestern Ontario. The cover crops were summer-seeded after wheat harvest, and included hairy vetch (Vicia villosa L. Roth), red clover (Trifolium pratense L.), white clover plus crimson clover mix (incarnatum and Trifolium alba L.), and a no cover crop control (CK). The cover crops were nested within termination-tillage method, including moldboard plow-down in fall, and herbicide spray-down in spring under strip-tillage or no-tillage then corn planting. Nitrogen fertilizer to corn was applied via side-dress at 200 kg N ha-1 to the CKs, and at 100 kg N ha-1 to the cover crops. Averaged over 3 years, above-ground biomass N level followed the pattern: hairy vetch > white clover plus crimson clover mix > red clover for fall plow-down termination. There were no significant differences in cover crop biomass N levels for spring termination. Corn response to cover crop was significantly affected by termination-tillage method and cover crop species, with poor corn stands after no-tillage, red clover and white plus crimson clover. Fall plow-down termination provided a range in N credit of 80-85 kg N ha-1, which was significantly greater than the N credit under herbicide spray-down in spring. Under spring strip-tillage and no-tillage, hairy vetch produced significantly greater corn grain yields than red clover and white plus crimson clover mix.

Long-term C and N sequestration under no-till is governed by biomass production of cover crops rather than differences in grass vs. legume biomass quality

Agricultural activities through conventional and intensive practices contribute to climate change by increasing emission of reactive carbon (C) and nitrogen (N) from soils to the atmosphere. Minimum soil disturbance, appropriate residue management and cover cropping as conservation practices are perceived as key strategies to limit GHGs emissions by increasing soil C and N sequestration as soil organic matter (SOM), thus promoting soil aggregation and enhancing soil fertility. Yet, the actual contribution of conservation practices to C and N sequestration, as well as mechanisms behind chemical and biochemical stabilization of SOM in the long-term are still controversial. In the present 9-year field study on a wheat-maize-soybean rotation we investigated the effect of no-till (NT) coupled with grass vs. legume cover crop (i.e., rye [Secale cereale L., NT-R] or hairy vetch [Vicia villosa Roth, NT-V]) on main crop yields, C and N input by cover and main crops, soil aggregation and C and N sequestration rates, in comparison with conventional tillage (CT). We hypothesized that NT-R may lead to higher biomass input, C sequestration and comparable yield to CT, while NT-V may increase N input, N sequestration and lead to comparable yield to CT. We found that yield of winter wheat, maize, and soybean were never reduced under both NT treatments, neither during the transition phase, nor afterwards. Rye and hairy vetch provided the same amount of biomass and C input, although vetch doubled N input compared with rye. Moreover NT-V increased cumulative biomass and C input from main crop residues compared with NT-R. Both NT-R and NT-V promoted C (+0.4 Mg ha−1 y−1 and +0.6 Mg ha−1 y−1, respectively) and N (+88 kg ha−1 y−1 and +145 kg ha−1 y−1, respectively) soil sequestration, mainly due to the increase of macroaggregate-associated C and N, thus corroborating a major role of NT for macroaggregates formation and SOM stabilization within macroaggregates. Since no difference was found between cover crops in terms of biomass input, and C and N sequestration potential, we concluded that cover crop biomass production (rather than biomass quality) and retention onto the soil as residue were the main drivers of soil C and N sequestration. Therefore, both rye and hairy vetch may be combined with NT and promise significant potential as effective C farming practices.

Assessing the Impact of Agricultural Practices on Nitrogen Emission and Environmental Sustainability

Nitrogen emissions from agricultural activities have garnered increasing attention due to their implications for environmental sustainability. Field studies conducted throughout a month is needed to improve flux estimates for the greenhouse gas nitrous oxide (N2O). In this study, we reported N2O emissions measured using gas chromatograph equipped with an electron capture detector. The soil at the experimental site was loamy. N2O emissions were significantly higher from the root systems of nodulating soybeans compared to non-nodulating soybeans during the late growth period. To mitigate nitrogen emissions in soybean cultivation, optimize fertilizer application, promote biological nitrogen fixation through inoculation and legume cover cropping, implement crop rotation, use cover crops, reduce nitrogen loss through erosion control, manage irrigation efficiently, employ precision agriculture, educate on nutrient stewardship, utilize biofertilizers, conduct environmental monitoring, invest in legume breeding, and enact government regulations and incentives for sustainable nitrogen management practices. Therefore, this study significantly advances our knowledge of sustainable soybean cultivation and the pivotal role and means in mitigating environmental challenges linked to nitrogen emissions.

Application of legume cover crop and various vermicompost dosages on young cinchona in the marginal area

AbstractCinchona (Cinchona ledgeriana Moens) is one of the important medicinal plants that have the potential to cultivate as herbal medicine. This plant grows well in highland areas. Developing cinchona plants in the marginal area needs effort and modification techniques such as planting legume cover crop (LCC) to maintain the humidity and supply nutrition by fertilizing. Vermicompost is one of the organic fertilizers with rich nutrition to support plant growth. This research aimed to observe the effect of a combination of Mucuna bracteata as LCC and vermicompost dosage on young cinchona growth in a marginal area. This research was carried out from September 2019 to March 2020 at the Ciparanje Experimental Station, Faculty of Agriculture, Universitas Padjadjaran. The experimental research was conducted using a Randomized Block Design (RBD) method, which consisted of 12 treatments which were a combination of legume cover crop (Mucuna bracteata) and vermicompost dosages (0 g, 200 g, 400 g, 600 g, 800 g, and 1000 g per plant), with four replications. The result showed that the doses of vermicompost fertilizer of 400 g per plant combined with M. bracteata as cover crop gave the highest value on the leaf number and stem diameter. In contrast, the best treatment for leaf chlorophyll content was 200 g per plant vermicompost without LCC planting. Thus, the application of vermicompost combined with the planting of Mucuna bracteata cover crop on young cinchona plants is strongly recommended.Keywords: Cinchona ledgeriana, Mucuna bracteata, organic fertilizer, plant growth. AbstrakTanaman kina (Cinchona ledgeriana Moens) merupakan tanaman obat-obatan penting yang sangat berpotensi untuk dikembangkan sebagai obat bahan alam. Tanaman ini dapat tumbuh baik di dataran tinggi. Penanaman kina di wilayah marjinal memerlukan berbagai modifikasi seperti pemberian tanaman penutup tanah (LCC) untuk mempertahankan kelembaban tanah dan pemenuhan nutrisi melalui pemupukan. Tujuan dari penelitian ini untuk melihat pengaruh kombinasi dari penggunaan Mucuna bracteata sebagai LCC dan dosis pupuk kascing pada pertumbuhan tanaman kina belum menghasilkan di wilayah marjinal. Penelitian ini dilakukan sejak September 2019 hingga Maret 2020 di kebun percobaan Ciparanje, Fakultas Pertanian, Universitas Padjadjaran. Rancangan percobaan menggunakan rancangan acak kelompok (RAK) dengan 12 perlakuan yang terdiri dari kombinasi tanaman penutup tanah (LCC) yaitu Mucuna bracteata dan pupuk kascing (0 g, 200 g, 400 g, 600 g, 800 g and 1000 g) per tanaman yang diulang empat kali. Hasil penelitian menunjukkan dosis pupuk kascing 400 g/tanaman yang dikombinasikan dengan Mucuna bracteate menghasilkan jumlah daun dan diameter batang tertinggi dibandingkan perlakuan lainnya. Sedangkan 200 g pupuk kascing tanpa LCC merupakan perlakuan dengan nilai klorofil daun tertinggi. Berdasarkan hasil tersebut, penggunaan pupuk kascing yang dikombinasikan dengan Mucuna bracteate sebagai LCC dapat meningkatkan pertumbuhan tanaman kina belum menghasilkan.Kata Kunci: Cinchona ledgeriana, Mucuna bracteata, pupuk organik, pertumbuhan tanaman.

Native Rhizobia Improve Plant Growth, Fix N2, and Reduce Greenhouse Emissions of Sunnhemp More than Commercial Rhizobia Inoculants in Florida Citrus Orchards.

Sunnhemp (Crotalaria juncea L.) is an important legume cover crop used in tree cropping systems, where there is increased interest by growers to identify rhizobia to maximize soil nitrogen (N) inputs. We aimed to isolate and identify native rhizobia and compare their capabilities with non-native rhizobia from commercial inoculants to fix atmospheric dinitrogen (N2), produce and reduce nitrous oxide (N2O), and improve plant growth. Phylogenetic analyses of sequences of the 16S rRNA and recA, atpD, and glnII genes showed native rhizobial strains belonged to Rhizobium tropici and the non-native strain to Bradyrhizobium japonicum. Plant nodulation tests, sequencing of nodC and nifH genes, and the acetylene-dependent ethylene production assay confirmed the capacity of all strains to nodulate sunnhemp and fix N2. Inoculation with native rhizobial strains resulted in significant increases in root and shoot weight and total C and N contents in the shoots, and showed greater N2-fixation rates and lower emissions of N2O compared to the non-native rhizobium. Our results suggest that native rhizobia improve plant growth, fix N2, and reduce greenhouse emissions of sunnhemp more than commercial rhizobia inoculants in Florida citrus orchards.

Potential Nitrogen Contributions by Tropical Legume Summer Cover Crops in Mediterranean-Type Cropping Systems

Legume cover crops in temperate cropping systems can fix substantial amounts of nitrogen (N) and reduce N fertiliser requirements for subsequent crops. However, little is known about potential biological N2 fixation by summer cover crop legumes in the short summer fallow in Mediterranean-type cropping systems. Six legume species (balansa clover, barrel medic, mung bean, sunn hemp, lablab and cowpea) were grown for 8–9 weeks in the field in semi-arid southern Australia during the summer fallow, and in a glasshouse experiment, to estimate N2 fixation using the 15N natural abundance method. Cowpea, sunn hemp and lablab produced 1.2–3.0 t ha−1 biomass in the field while balansa clover and barrel medic produced < 1.0 t ha−1. The percent of N derived from the atmosphere (%Ndfa) in the field ranged from 39% in barrel medic to 73% in sunn hemp, but only 15% (balansa clover) to 33% (sunn hemp) in the glasshouse experiment, likely due to higher soil mineral N availability in the glasshouse study. Biological N2 fixation of cowpea and sunn hemp in the field was 46–55 kg N ha−1, while N2 fixation in lablab and mung bean was lower (around 26 kg N ha−1). The N2 fixation in cowpea and sunn hemp of around 50 kg N ha−1 with supplementary irrigation in the field trial likely represents the upper limit of N contributions in the field in typically hot, dry summer conditions in Mediterranean-type climates. Given that any increase in summer cover crop biomass will have implications for water balances and subsequent cash crop growth, maximising N benefits of legume cover crops will rely on increasing the %Ndfa through improved rhizobium strains or inoculation technologies. This study provides the first known estimates of biological N2 fixation by legume cover crops in the summer fallow period in cropping systems in Mediterranean-type environments, providing a benchmark for further studies.

Effect of Different Cover Crops on Suppression of the Weed Oxalis pes-caprae L., Soil Nutrient Availability, and the Performance of Table Olive Trees ‘Kalamon’ cv. in Crete, Greece

Winter cover crops are used in organic olive production to increase N-supply and yields, and to reduce weed competition. However, there is limited information on the effect of different cover crops on weed suppression, soil fertility and productivity of organic olive orchards. Here, we compared the relative effect of four contrasting cover crops established from (i) untreated vetch seed, (ii) vetch seed inoculated with a commercial Rhizobium seed inoculum, (iii) an untreated vetch/barley/pea seed mixture and (iv) untreated seed of Medicago polymorpha L. (a native legume species which establishes naturally in olive orchards in Crete) in a 35-year-old experimental table olive orchard. The use of a vetch/barley/pea mixture resulted in the greatest suppression of the dominant weed species Oxalis pes-caprae. Rhizobium inoculation of vetch seed resulted in significantly lower vetch establishment and significantly higher Oxalis suppression but had no significant effect on the root nodulation of vetch plants. There was no significant difference in fruit yield between cover crop treatments, but the fruit weight was significantly higher when cover crops were established from un-treated vetch seeds and the vetch/barley/pea seed mixture compared with the cover crops based on inoculated vetch or Medicago seed. However, although Medicago establishment was very low (<10 plants/m2), fruit yields were numerically 20% higher in the Medicago plots. These findings suggests that, overall, legume cover crops had no effect on fruit yields. This conclusion is supported by the results of the olive leaf analyses which detected no significant differences in nitrogen and other mineral macro- and micronutrient concentration between treatments, except for B (highest in olive leaves from Medicago and lowest in untreated vetch plots) and Mo (highest in olive leaves from Medicago and lowest in vetch/barley/pea mixture plots). Overall, our results suggest that the current recommendation to establish legume-based cover crops in organic olive orchards every year, may need to be revised and that establishing cover crops every 2–4 years may reduce costs without affecting olive fruit yields.

Impact of cover crop and mulching on soil physical properties and soil nutrients in a citrus orchard.

BackgroundCover crops and mulching can ameliorate soil porosity and nutrient availability, but their effects on the physical characteristics and nutrients in the raised bed soils are unclear.MethodsThe field experiment was conducted in a pomelo orchard from 2019 to 2021, with an area of 1,500 m2. The treatments included control (no cover crop), non-legume cover crop (Commelina communis L.), legume cover crop (Arachis pintoi Krabov & W.C. Gregory), and rice straw mulching (Oryza sativa L.). At the end of each year (2019, 2020, and 2021), soil samples were collected at four different layers (0–10, 10–20, 20–30, and 30–40 cm) in each treatment. Soil bulk density, soil porosity, and the concentration of nutrients in the soil were investigated.ResultsThe results revealed that soil bulk density at two depths, 0–10 and 10–20 cm, was reduced by 0.07 and 0.08 g cm−3 by rice straw mulch and a leguminous cover crop, thus, increasing soil porosity by ~2.74% and ~3.01%, respectively. Soil nutrients (Ca, K, Fe, and Zn) at topsoil (0–10 cm) and subsoil (10–20 cm) layers were not significantly different in the first year, but those nutrients (Ca, K, Fe, and Zn) improved greatly in the second and third years.ConclusionsLegume cover crops and straw mulch enhanced soil porosity and plant nutrient availability (Ca, K, Fe, and Zn). These conservation practices best benefit fruit orchards cultivated in the raised bed soils.

Can Organic P Inputs Alleviate P Limitation Effects on Nutrient Uptake and Biological N2-Fixing Capacity of Hairy Vetch (Vicia villosa)?

Phosphorus (P) is a limiting nutrient in many agroecosystems and, apart from affecting plant growth, can also limit biological N2 fixation (BNF) by leguminous plants. Thus, increasing P supply can have a positive effect on BNF particularly in P-deficient soils. Here, we provide new insights into the response of hairy vetch (Vicia villosa), widely adopted as a legume cover crop, to P limitations, by comparing the effects of inorganic (Pi) and organic (Po) P supply on plant growth and BNF capacity. This was achieved by means of a greenhouse experiment in which rhizobia-inoculated hairy vetch was grown in a P-limited agricultural soil and changes in plant growth, nitrogen (N) and P uptake, BNF capacity, and soil phosphatases activities were evaluated as a function of Pi and Po inputs, in the form of orthophosphate or phytic acid, respectively. When compared to P-deficient conditions where BNF was primarily limited by plant growth rather than directly due to the high P costs of symbiotic N fixation, Pi addition substantially enhanced plant growth (threefold), nodule formation (16-fold), P acquisition (sixfold), and BNF efficiency (sevenfold). In contrast, even with the addition of the highest dose of Po, the increase in plant growth, nodule formation, P acquisition, and BNF capacity (1.7, 3.5, 2.4 and 2.1-fold, respectively) was much less expressed, indicating that hairy vetch could only minimally access Po sources over the growth period in order to alleviate the P limitation effect on N2 fixation in under P-deficient conditions. These findings suggest that hairy vetch will not be able to provide sufficient BNF for improving soil N inputs in low-fertility cropping systems that rely on organic inputs.

Legume winter cover crop (Persian clover) reduces nitrogen requirement and increases grain yield in specialized irrigated hybrid rice system

In high-yield irrigated rice systems, options for legume cover crops with the capacity for biological nitrogen (N) fixation in the period between harvest have been sought. However, options are limited due to excess water and low oxygen level in the soil. The persian clover (Trifolium resupinatum) is an exception as it is a promising species due to its adaptation to waterlogged soils. Thus, the objective of this work was to evaluate accumulated nitrogen in the legume, soil mineral and microbial N levels and the response of a rice hybrid established in succession to persian clover during four growing seasons in subtropical conditions in southern Brazil. The field experiment was carried out during four crop seasons in a 2 × 4 factorial, with two conditions of soil cover, fallow and legume (persian clover) under four levels of N (0, 60, 120 and 180 kg N ha−1). It was observed that the cultivation of Persian clover increased the availability of mineral and microbial N in the soil by 35% and 6.5%, respectively. There was a 14.1% reduction in the optimal nitrogen rate in the rice hybrid. The grain yield of rice grains using persian clover in winter is 7.8% higher in relation to fallow, with the greatest difference between clover and fallow at the lowest N rates (0 e 60 kg ha−1). Thus, persian clover is a promising legume to be used in the period between harvest in hydromorphic soils cultivated with irrigated rice in subtropical conditions.

Cover crops and N fertilization affect soil ammonia volatilization and N2O emission by regulating the soil labile carbon and nitrogen fractions

Introducing cover crops in monocropping systems to improve soil health has been broadly adopted worldwide. However, the impacts of different cover cropping systems on soil emissions and related soil fractions and their regulatory mechanism remain elusive. In this study, four cropping systems, i.e., relay intercropping with Orychophragmus violaceus L./cotton (OvC), Vicia villosa Roth/cotton (VvC), a cover crop mixture (Ov and Vv)/cotton (MSC) and a fallow field–cotton (FFC) system, were combined with four N application rates in a two-rotation cycle (2019–2021) to evaluate the effects on soil greenhouse gases (GHGs) emission, ammonia (NH3) volatilization, and labile carbon (C) and nitrogen (N) fractions and their relationships. Compared with the FFC system, the cumulative NH3 volatilization and nitrous oxide (N2O) emissions of OvC are noticeably reduced 13% and 58%, respectively, and those of VvC are comparable, while those of MSC are markedly increased by 15% and 24%, respectively. N fertilization significantly affects soil NH3 volatilization and N2O emissions, and a higher N rate results in more gaseous N emissions. In addition, NH3 volatilization and N2O emission are positively correlated with the soil microbial biomass N (MBN), dissolved organic N (DON), NH4+-N and NO3--N but negatively correlated with microbial biomass C (MBC) and dissolved organic C (DOC). OvC system decreased gaseous N emission by high soil MBC/MBN ratio, Vv as cover crop indirectly promote soil N2O emission through increased soil MBN, DON and MBC content, while cover crop mixtures increase soil labile C and N fractions and enhance gaseous N emission ultimately. Overall, application of N fertilizer and cover crop mixture both promoted soil NH3 and N2O emissions; the relay intercropping nonlegume cover crop Ov noticeably mitigates N2O and NH3 emissions through an increase in the soil MBC and reduce in the labile N, while introduction of the legume cover crop Vv increases N2O emissions but reduces soil NH3 volatilization due to a lower soil MBC/MBN ratio.

Cold stress reduces nodulation and symbiotic nitrogen fixation in winter annual legume cover crops

Cold stress reduces nodulation and symbiotic nitrogen fixation in winter annual legume cover crops

Carbon saturation deficit and litter quality drive the stabilization of litter-derived C in mineral-associated organic matter in long-term no-till soil

Long-term no-till cropping systems can induce significant differences in the mineral associated organic matter (MAOM) saturation levels but little is known on the effect of MAOM saturation on “new” C stabilization from added litter in different fractions of soil organic matter (SOM). We assessed the effect of C saturation deficit (Csd) in the MAOM on C stabilization in different SOM fractions in the surface layers of a sandy clay loam Acrisol under five no-till cropping systems adopted over 36 years in a field experiment. The cropping systems with varying C inputs led to a range of C content and Csd in the MAOM (<20 µm) in a thin soil layer (0–5 cm). In each field plot with different Csd levels, 13C-labeled litter from shoot biomass of black oat (grass) and vetch (legume) was added at a rate equivalent to 4.5 Mg ha-1C in PVC collars. After 15-month field incubation, soil was sampled and physically fractionated. Higher C stabilization in MAOM was observed for legume than grass-derived C in the top 0–2.5 cm layer, but only for soils with higher C stabilization capacity. When litter-derived C stabilization in MAOM was limited by its previous C level close to saturation, C incorporation was greater in the intra- and inter-aggregate SOM fractions. Our findings revealed that Csd and litter quality affect C stabilization in surface soil layers of no-till soils, and when C stabilization in MAOM is low due to saturation of the MAOM fraction, the C accrual occurs preferentially in labile and intra-aggregate fractions in long-term no-till soils. Therefore, sustainable management practices that promote continuous and diversified C inputs involving legume cover crops are crucial to sustain C incorporation in relatively stable forms in long-term no-till soils.

Sustainable intensification through double-cropping and plant-based fertilization: production and plant-soil nitrogen interactions in a 5-year crop rotation of organic vegetables

ABSTRACT A sustainably intensified (SI) organic vegetable rotation, employing plant-based fertilizers, more crops, reduced tillage, and cover crops was compared to common practice (CP) where plants were fertilized with animal manure, typically one crop was grown per season, soil was plowed and often left bare over winter. Second and third-year results are presented. Nitrogen (N) input obtained within the rotation from N2 fixed by legume cover crops was higher under SI (34% potential self-sufficiency) than CP (5%). Marketable yields of cabbage, celeriac, leek, lettuce, and onion were similar, and aboveground dry matter increased by 16% under SI (8.6 Mg ha−1) compared to CP (7.5 Mg ha−1). Nitrogen use efficiency (N output/ N input) was 8–16% higher under SI compared to CP, mainly due to the full year clover. Nitrogen surface balance (N input – N output) was higher for SI compared to CP, indicating increased N leaching risk under SI. Short season and shallow-rooted crops under SI left more mineral N to 2.5 m depth in autumn than deeper-rooted crops under CP. Cover crops indicated to mitigate N leaching risk. Vegetable production can be intensified sustainably using more yielding crops, cover crops, reduced tillage, and plant-based fertilizers.

Effect of grafting and cover crop quality on nitrogen uptake from different pools by drip irrigated heirloom tomatoes in an open field trial

Fresh-market tomatoes (Lycopersicon esculentum Mill.) are increasingly produced with subsurface drip irrigation in California, as growers adapt to decreased water availability. Drip irrigation improves water use efficiency, but may reduce the soil volume where conditions are optimal for microbial and root activity. This poses complications for organic growers, whose cropping systems are dependent on microorganisms to convert the nitrogen (N) from organic sources into plant-available N. To investigate grafting as a potential practice to increase access to N, grafted and non-grafted “Brandywine” heirloom tomatoes were grown with drip irrigation in a two-year field trial. The three rootstocks were “Maxifort,” “Fortamino,” and “DRO138TX.” Prior to each growing season, a legume cover crop mix was grown and labeled with 15N ammonium sulfate to track tomato N uptake from cover crop residues. There were no significant differences in yield, N uptake and N partitioning in the plants due to rootstock treatments. Leaf analyses suggested that the tomato plants were not N deficient in either year. However, there was a significant difference in total N uptake from cover crop residues between years. This was caused by large differences in N concentration in the cover crop. Plants responded to a lower N availability by producing less vine biomass, while producing the same fruit yield. A budget revealed that the tomato plants accessed a considerable amount of N from the soil below 60 cm of the profile to cover their demand.