Stubble Height Research Articles

An ANSYS/LS-DYNA Simulation and Experimental Study of Sectional Hob Type Laver Harvesting Device

To solve the problems of low net harvesting rate, high loss rate, and uneven stubble height during the harvest of laver, the laver (Porphyra yezoensis) was selected as the research object, the analysis of the cultivation mode, biomechanical characteristics, harvesting trajectory and force of laver were carried out. A sectional hob type harvesting device was designed. A rigid-flexible coupling model related to the interaction between the cutting mechanism and the laver was constructed based on ANSYS/LS-DYNA. The Box–Behnken design method was used to simulate the effects of different structural parameters and process parameters on the force of laver cutting, and the bench test of the laver harvesting device was carried out. The simulation results showed that the four factors that significantly affect the force exerted on the laver during cutting in proper order were cutter revolving speed, knife extension length, knife inclination angle and forward velocity. When the combination of the forward velocity, the cutter revolving speed, the knife extension length and inclination angle was 0.77 m/s, 900 r/min, 40 mm, and 110°, respectively, the cutting force on laver was the smallest, which was 4.21 N. The bench test of harvesting performance showed that the cutter revolving speed has a significant impact on the recovery rate, and the forward velocity has a significant impact on the loss rate. When the harvesting speed ratio was λ4 (the cutter revolving speed was 900 r/min and the forward velocity was 0.77 m/s), the net harvesting rate and the loss rate were 97.45% and 3.38%, respectively, and the cutting proportion of laver can reach 77.5%. The results of the study provide a theoretical basis for the development of harvesting for laver.

Bison influences on composition and diversity of riparian plant communities in Yellowstone National Park

AbstractRiparian zones are among the most biologically diverse ecosystems in the Intermountain West, USA, and provide valuable ecosystem services, including high rates of biotic productivity, nutrient processing, and carbon storage. Thus, their sustainability is a high priority for land managers. Large ungulates affect composition and structure of riparian/stream ecosystems through herbivory and physical effects, via trailing and trampling. Bison (Bison bison) in Yellowstone National Park (YNP) have been characterized as “ecosystem engineers” because of their demonstrated effects on phenology, aboveground productivity of grasses, and woody vegetation structure. Bison have greatly increased in numbers during the last two decades and spend large periods of time in the broad open floodplains of the Northern Range of the Park, where they are hypothesized to have multiple effects on plant species composition and diversity. We sampled indicators of bison use as well as riparian vegetation composition, diversity, and structure along eight headwater streams within YNP's Northern Range. Total fecal density ranged from 333 to 1833 fecal chips and/or piles/ha, stubble heights ranged from 7 to 49 cm, and streambank disturbance ranged from 9% to 62%. High levels of bison use were positively correlated with exotic species dominance and negatively correlated with species richness, native species diversity, willow (Salix spp.) cover, and wetland species dominance. At three sites, the intensity of bison use exceeded recommended utilization thresholds to avoid degradation of streams and riparian zones on public lands. The influences of large herbivores, principally bison, on vegetation composition and structure suggest the cumulative effects of the current densities on the Northern Range are contributing to biotic impoverishment, representing the loss of ecosystem services that are provided by native riparian plant communities. In addition, contemporary levels of bison use may be exacerbating climate change effects as observed through ungulate‐related shifts in composition toward plant assemblages adapted to warmer and drier conditions. However, the resilience of native riparian vegetation suggests that sites currently heavily utilized by bison would have the potential for recovery with a reduction in pressure by this herbivore.

Design and Experiment of Feeding Device for Hairy Vetch Harvesting

In order to solve the problem of low mechanization level of hairy vetch harvesting, a feeding device for an anti-winding hairy vetch harvester was designed. Firstly, the physical properties of hairy vetch stalk were studied. According to the mechanical properties of hairy vetch stalk, the key components of the feeding device were designed and analyzed, the structure and working principle of the feeding device were described. Secondly, the discrete element method was used to simulate and analyze the movement performance of the feeding device. On this basis, the ternary quadratic regression orthogonal rotation combination test was established with the vertical drum, the machine forward speed, and the spiral conveyor speed as the test factors and the stem loss rate as the test index. The simulation results showed that when the vertical drum was 1037.5 r/min, the machine forward speed was 2.76 m/s, the spiral conveyor speed was 348.88 r/min, and the straw loss rate was 2.38%, and the feeding device performs best at this time. Finally, the on-site performance test of the feeding device was carried out. The results showed that: all the test indicators met the requirements of the national standard; the actual cutting width was 1.66 m; the cutting stubble height was 6.41 mm; the over stubble loss rate was 0.45%; the missed cutting loss rate was 0.20%; and the stem loss rate was 3.00%, which verified the rationality of the design of the feeding device. In order to solve the problem of low mechanization level of hairy vetch, which easily becomes entangled in the working process, an anti-winding feeding device for hairy vetch harvesting was designed.

Co-Harvest and Anaerobic Co-Storage of Corn Grain and Stover as Biomass Feedstocks

Highlights Cutting height and harvest date were used to alter stover moisture content, yield, and composition. Anaerobic co-storage of grain and stover limited losses to less than 6% of dry matter. Extent of fermentation was greater for higher moisture stover than grain, but total acids were less than 5 g kg-1. Reducing the harvester cutter head rotational speed resulted in a greater fraction of whole corn kernels. Abstract. This research investigated the utility of co-harvesting and anaerobic co-storage of corn grain and stover to positively influence their physical and chemical characteristics as a biomass feedstock. Corn grain and stover were harvested in 2019 and 2020 with a self-propelled forage harvester. Stover yield, moisture content, and composition were altered by the harvest date, stubble height, and header configuration. Harvest date had the utility of varying the stover moisture content (p < 0.001) from 42.3% to 53.5% (w.b.) and 43.1% to 53.9% (w.b.) for the 2019 and 2020 harvest years, respectively. Stubble height was also utilized to vary stover moisture content. A negative linear relationship was established between stubble height and stover moisture content for the early (R2 = 0.76) and late harvest (R2 = 0.91) dates for both years. Stover yield also showed a negative linear relationship (R2 = 0.76) with stubble height over both years. Regardless of the stubble height, the row-crop header collected more stover (p < 0.001) than the ear-snapper header. In 2020, harvested stover ranged from 5.0 to 10.5 Mg ha-1, with ha-1 representing 41% to 85% of the total available stover. In both years, stover ash content was less than 64 g kg-1. Material stored in pilot-scale silos (19 L) was well conserved during anaerobic storage, with average DM losses of 4.8% and 3.4% in 2019 and 2020, respectively. Grain moisture content averaged 23.6% (w.b.) at harvest, and 31.0% (w.b.) after storage as moisture migrated from the moist stover to the drier grain. Harvesting whole-plant corn with a forage harvester had the unwanted effect of reducing the particle size of the grain fraction, which would complicate downstream utilization. However, reducing the harvester cutterhead speed increased the fraction of intact kernels from 47% to 85% by mass. The studied system was a viable alternative to conventional corn grain and stover systems for producing feedstocks for biochemical conversion. Keywords: Ash, Ensiling, Ethanol, Maize.

Experimental Studies on the Operation of Agricultural Crops Mowing Unit with Simultaneous Chopping and Incorporation of Stubble Into the Soil

Abstract For harvesting crops, one-phase and two-phase methods are most often used. When implementing the second one, mounted and trailed units are used. The latter is becoming less and less used due to the problems with movement stability in the horizontal plane because of the asymmetric layout. A stubble background, which is susceptible to solar and wind influences, is formed as a consequence of application of the mounted harvesting unit, As a result, the field’s soil in the inter-swath space intensively loses moisture. A harvesting unit based on a tractor with rear steerable wheels has been designed to eliminate this shortcoming. A header is mounted on its front hitch linkage system, and a disc harrow is mounted on the rear one. During the working movement, such a harvesting unit mows the crop into swaths, chops the stubble in the inter-swath space, and simultaneously incorporates it into the soil. This article presents the operation results of such a unit for harvesting winter wheat, oats, and sudan grass. Research has established that oscillations in the deviations of the mowed crops’ swaths from a straight line are of low frequency. The variances spectra of this process, as follows from the Analysis of normalized spectral densities, are concentrated in the frequency range of 0-0.5 m−1. The mean value velocities of the harvesting unit are 2.13-2.61 m·s−1, which is 0.17-0.21 Hz. The variances of oscillations in the header operating width, the cut crop’s swath width, and the disc harrow’s width are concentrated in approximately the same low-frequency range, the maximum value of which is small and does not exceed 0.9 m−1 or 0.37 Hz. The oscillation processes of the mowed crops’ stubble height have a higher frequency. The cutoff frequency of their normalized spectral densities is at the level of 3.0 m−1. In terms of time, considering the harvesting unit movement velocity of 2.13-2.61 m·s−1, this is 1.02-1.25 Hz. At the same time, oscillations in the stubble height of mowed crops are characterized by small variances, the maximum value of which does not exceed 11 cm2.

Impact of Stubble Heights on Native Hay Meadows in Southeast Kansas

Management practices affect hay production in native meadows. The objective of this study was to evaluate how stubble heights affect forage yield and quality in a native meadow. Prescribed spring burns contribute to improving forage quality. Setting the stubble height at 3 inches resulted in high forage quality and had a low yield impact.

On-farm evaluation of growth performance and nutritional values of Brachiaria hybrid and Pennisetum purpureum cultivars in Southern Highlands, Tanzania

Abstract Improved cultivars (cvs.) of Brachiaria hybrid and Pennisetum purpureum forages have been studied extensively in research settings but still there is a paucity of information about their on-farm performance. This study was therefore set to evaluate the on-farm performance of Brachiaria hybrid cvs. Cayman and Cobra, and Pennisetum purpureum cvs. ILRI 16835 and Ouma in the Southern Highlands of Tanzania. A total of 30 smallholder dairy farmers who cultivated these improved forage grasses were involved in this study. A 2 m × 2 m sub-plot was marked in established pasture plots and a standardised cut at a 5–7 cm stubble height was done at the beginning of this study. The forage growth performance was conducted from April–July, 2021 (dry period) in two phases of 6 weeks each. These cultivars were evaluated for their above-ground growth performance and nutritional values at the end of each phase. Plant height, leaf length, leaf widths, and number of tillers per plant among cultivars varied significantly (p < 0.05) while above-ground forage biomass did not vary among cultivars (p > 0.05). Crude protein values did not vary significantly among cultivars (p > 0.05), they were 131–141 g kg−1 dry matter (DM). These values were not able to meet the nutritional requirements of the lactating dairy cow. Brachiaria hybrid cv. Cayman had the lowest (p < 0.05) neutral detergent fibre (NDF, 539 g kg−1 DM) compared to other cultivars (545–571 g kg−1 DM), hence high digestibility. It was concluded that Cayman was the best cultivar for forage production in the Southern Highlands, Tanzania due to its low NDF content. However, lower biomass warrants mixing of Cayman with other feeds to meet the daily requirements of a lactating dairy cow.

Early harvesting and increasing stubble-cutting height enhance ratoon rice yield

Summary To clarify the combined effects of the cutting time and cutting height on ratooning ability and rice grain yield of the ratoon crop in the novel ratoon rice cropping, a field experiment was carried out to investigate the combined effects of harvesting time and the stubble-cutting height of the main crop on the growth duration, ratooning ability and grain yield of the ratoon crop. The growth period was shortened by 3.5 days on average when the harvesting time was 10 days ahead of time. On average, the growth duration was prolonged by 7 days per each decrease of 10 cm stubble height. Early harvesting and increasing stubble-cutting height greatly increased the grain yield of the ratoon crop. The highest grain yield was achieved at 10 days after flowering stage and a stubble height of 30 cm, which were 6916 kg·hm−2 for XLY900 and 7262 kg·hm−2 for YY4149, averaged across years. High rice yield of the ratoon crop was mainly depended on panicle numbers and grain-filling percentage, rather than spikelets per panicle. Increasing cutting height and the cutting time of the main crop ahead maintain more stubble biomass and nitrogen content. A significant positive correlation was observed between stubble nitrogen content and tillers-to-stubble ratio (TSR), as well as a significant positive relation was found between panicle-to-stubble ratio and TSR. Therefore, cutting 10 days after flowering stage of the main crop with 30 cm stubble-cutting height enhances ratooning ability due to higher stubble biomass and nitrogen content, and then increases rice yield of the ratoon crop.

Responses of grassland productivity to mowing intensity and precipitation variability in a temperate steppe.

Mowing for hay is an important land use in grasslands that is affected by precipitation variability, due to the water-limited nature of these ecosystems. Past land use and precipitation conditions can have legacy effects on ecosystem functions, potentially altering responses to both mowing and precipitation. Nonetheless, it is still unclear how natural variation in precipitation will affect plant responses to changes in mowing intensity. We conducted a seven-year field experiment with three mowing intensity treatments compared to the traditional mowing intensity (5cm stubble height) as a control: increased mowing (2cm stubble), decreased mowing (8cm stubble) and ceased mowing. Decreased mowing increased both plant aboveground net primary productivity [ANPP] and forage yield across the whole community, driven by increases in graminoids, mainly owing to the positive response of plants to precipitation. Both mowing disturbance and precipitation variability had legacy effects on plant ANPP; however, these responses differed among the whole community, graminoid, and forb levels. Current-year community-wide ANPP [ANPPn] was positively associated with current-year precipitation [PPTn] in all mowing treatments, driven by positive precipitation responses of the dominant graminoids. For forbs, however, ANPPn was negatively associated with prior-year growing season precipitation [PPTn-1] across mowing treatments, potentially due to lagged competition with the dominant graminoids. Our results suggest that the response of the dominant graminoids is the primary factor determining the response of ANPP to mowing and precipitation variability in these grassland ecosystems, and highlight that decreasing mowing intensity may maximize both herder's income and grassland sustainability.

Legume proportion affects bahiagrass–rhizoma peanut mixture production and nutritive value and legume composition of cattle diets

Our objectives were to (1) quantify the effects of legume proportion on herbage accumulation (HA) and nutritive value of pasture mixtures compared with grass monocultures receiving typical or no N fertilizer application and (2) compare animal selection measures in legume–grass mixed pastures using microhistological and δ13C techniques applied to fecal samples. We evaluated HA and nutritive value in 2 grazing systems: (1) mixtures of Florigraze rhizoma peanut (Arachis glabrata Benth.) and Pensacola bahiagrass (Paspalum notatum Flügge) (MIX-SYS; 6 to 78% legume, grazed to a 15-cm stubble height at 42-d grazing intervals and ~7-d residence periods) and (2) bahiagrass monocultures receiving no N or 50 kg of N/ha per year (BG-SYS and BGN-SYS, grazed to 10-cm stubble height at 21-d grazing intervals with ~7-d residence periods) over 2 yr. Animal [~220 kg, 12-mo-old Brahman (Bos indicus) × Angus (Bos taurus) heifers] diet selection in MIX-SYS was quantified using microhistological and δ13C techniques applied to fecal samples. Herbage in vitro digestible OM (IVDOM) and CP concentrations increased linearly with increasing legume proportion in MIX-SYS up to ~45%, but MIX-SYS HA decreased linearly with increasing legume proportion. Treatment MIX-SYS had greater average HA [5,920 ± 271 (SE) kg/ha vs. 4,890 ± 236 kg/ ha for monocultures] and nutritive value than BG-SYS and BGN-SYS (CP of 12.9 ± 0.7% and IVDOM of 55.8 ± 1.0% for MIX-SYS vs. 9.1 ± 0.4% and 50.7 ± 1.5%, respectively, for monocultures). Results of microhistological and δ13C techniques applied to fecal samples were highly and positively correlated with sward canopy legume proportion, but fecal δ13C tracked legume proportion in the pasture more closely than the microhistological technique. Benefits of legumes to HA and nutritive value were observed at low legume participation, but they did not increase proportionally as legume percentage increased above ~45%. These results support a conclusion that relatively small proportions of legumes have measurable positive effects on important grassland characteristics.

Morphological and productivity responses of Buffel grass (Cenchrus ciliaris) and Guinea grass (Panicum maximum) ecotypes to simulated grazing in a semi‐arid environment

AbstractBackgroundLivestock production is an economically significant activity in grassland‐based production systems with herbivory, a critical process in modifying plant structure and regulating biomass dynamics in these areas.MethodsA grazing simulation experiment was undertaken in a semi‐arid environment in Kenya to determine the effects of clipping frequency and intensity on the morphology and productivity of Cenchrus ciliaris and Panicum maximum grass ecotypes. The ecotypes were clipped at different frequencies (every 2, 4, and 12 weeks) and different intensities (5, 10, and 15 cm clipping heights). The morphological responses of the grass ecotypes and biomass yields were determined.ResultsThe grass ecotypes showed significantly (p < 0.05) varied responses to cutting frequency and intensity. Morphological parameters, tillering, and biomass production were all affected by clipping frequency and intensity. The highest dry matter (DM) yields were recorded under low frequency (LF) clipping, followed by moderate frequency (MF) clipping and high frequency (HF) clipping. LF clipping in C. ciliaris ecotype Kilifi was 20% and 31% more compared to MF and HF clipping. No significant difference in yields was found by cutting the C. ciliaris ecotype Magadi at 4‐ and 12‐week intervals, even though clipping at 2‐week intervals cumulatively yielded less biomass. There was a biomass yield reduction in P. maximum ecotype Taveta of 23% and 25% for MF and HF clipping, respectively, while for ecotype Isinya, the reduction was 13% and 15% for MF and HF, respectively. Clipping intensity had a significant (p < 0.05) effect on cumulative yields in C. ciliaris ecotypes, but not P. maximum. Ecotypic differences were apparent in both C. ciliaris and P. maximum ecotype DM yields.ConclusionsThe results in this study suggest that clipping range grass ecotypes less frequently (4‐ and 12‐week intervals) and at 10 and 15 cm stubble heights results in higher biomass yields. Generally, LF and MF grazing and cutting strategies are advantageous for semi‐arid lands. Combinations of frequent and high‐intensity utilization grazing strategies should be discouraged as they are likely to lead to reduced biomass yields and negative effects both on grasses and on the environment.

Improving Fodder Yields and Nutritive Value of Some Forage Grasses as Animal Feeds through Intercropping with Egyptian Clover (Trifolium alexandrinum L.)

The present study aimed to evaluate the potential of improving the feeding value of Egyptian clover (EC), ryegrass (R), triticale (T), barley (B), and oats (O) monoculture, or Egyptian clover mixed with ryegrass (EC+R), oats (EC+O), barely (EC+B), and triticale (EC+T) at 75:25% seeding rate, respectively, during two successive winter seasons of 2018/19 and 2019/20. Harvesting of plots was carried out at 5 cm stubble height after 60, 100, and 140 days from sowing. The in vitro nutritive value and ruminal fermentation of the monoculture and intercropping containing EC were evaluated. Green forage yield of EC was higher than other plants with about 160% of fresh forage compared with T, O, or EC+T intercropping. The highest crude protein (CP) concentration was noted in EC, while the lowest (p < 0.001) concentration was observed in T, which had the highest fiber fractions content. Ryegrass had the highest net in vitro gas production (GP), while EC+R had the lowest GP (p < 0.05). The EC increased dry matter and organic matter degradability. EC and R reduced protozoal count, while total volatile fatty acids (VFA), acetate, and propionate were increased with B and EC+T intercropping (p < 0.05). Overall, intercropping of EC with grass of triticale or ryegrass at mixing rates of 75:25% resulted in improving fresh and dry forage yields. The legume–grass intercropping improved the protozoa count partitioning factor as an index of microbial protein synthesis and total VFA concentration.

FORAGE YIELD AND COMPOSITION OF BLACK OAT IN MONOCULTURE AND IN ASSOCIATION WITH WINTER VETCH

Associated grass-legume pastures have advantages over grass monoculture; in order to evaluate them the association of black oat (Avena strigosa Schreb) with winter vetch (Vicia villosa Roth) was analysed. The objective of the study was to evaluate forage yield, the botanical, morphological, and chemical composition of black oat in monoculture and in association with winter vetch, at different crop heights and residual stubble heights. Eighteen treatments were evaluated in randomized complete blocks with divided plots. In large plots, the culture type (monoculture or association); and in small plots, nine harvest management options (combinations) of three crop heights (Ch: 40, 50 and 60 cm) and three residual stubble heights (Rsh: 8, 14 and 20 cm). Forage yield was higher (p ≤ 0.05) in Ch50-Rsh8, Ch60-Rsh8 and Ch60-Rsh14 during the second crop cycle, with an average 8555 kg DM ha-1. In monoculture and in association, more cuts were made (three to four) with Ch40-Rsh14 and Ch40-Rsh20 and fewer cuts (one to two) with Ch60-Rsh8, Ch60-Rsh14 and Ch60-Rsh20. Crude protein concentration was 19 % higher (p ≤ 0.05) in monoculture than in association (19.2 and 16.2 %); the highest concentrations (p ≤ 0.05) of crude protein were obtained in Ch40-Rsh8, Ch40-Rsh14 and Ch40-Rsh20 (average 20.5 %), and the lowest was recorded in Ch60-Rsh8 (13.2 %). The forage with the least neutral detergent fibre (p ≤ 0.05) was harvested in Ch40-Rsh8, Ch40-Rsh14 and Ch50-Rsh14 (average 43.4 %), and the highest (49.3 %) was obtained in Ch60-Rsh20. In monoculture and in association, a greater amount of forage was harvested, distributed in at least two harvests, with Ch of 50 and 60 cm in combination with 8 and 14 cm of Rsh. However, the forage did not have the best composition, due to higher concentrations of neutral detergent fibre and lower crude protein concentration.

Intensification of disturbance destabilizes productivity through effects on dominant species

• Both intensification and cessation of disturbance destabilized plant productivity. • Community stability was mainly driven by the stability of dominant species. • Maintaining disturbance may be an appropriate strategy for community stability. Disturbances, including anthropogenic disturbances, are integral to the maintenance of grassland ecosystems. Most research on anthropogenic disturbances focuses on the effects of intensification, yet cessation of disturbance can have equally important effects on grassland biodiversity and ecosystem functioning. Natural disturbances have largely been replaced by anthropogenic disturbance, which has pronounced effects on community function and structure in grassland ecosystems. It is still unclear how changing disturbance intensity affects community stability and its mechanisms. We examined the temporal stability of above-ground net primary productivity (ANPP) in a seven-year field mowing experiment which included normal disturbance (control, mowing annually at 5 cm stubble height), increasing disturbance (mowing annually at 2 cm stubble height) and ceasing disturbance (no mowing) in a typical steppe in Inner Mongolia. Overall, ceasing disturbance increased ANPP of whole community but increasing disturbance had no significant effect on community ANPP, which was driven by ANPP of dominant species; and species richness and asynchrony were independent of changing disturbance. Despite having no effect on species richness, both intensification and cessation of disturbance destabilized plant community productivity, primarily through effects on the stability of the dominant species. This highlights the importance of dominant species in driving community dynamics. Maintaining disturbance intensity is an appropriate strategy to maintain hay production and community stability in typical steppe in Inner Mongolia, and may be beneficial to the development of sustainable utilization of grassland and may ensure the income of resident population.

Influence of plant population density of <i>Chamaecrista rotundifolia</i> on its value for hay making in the Eastern Amazon, Brazil

Chamaecrista rotundifolia is a forage legume little used with Brazilian livestock; however, it has been studied for this purpose for over 40 years in Australia. The aim of this study was to characterize the influence of plant densities of approximately 444,400, 111,100 and 27,800 plants/ha (equivalent to spacings of 0.15 × 0.15; 0.30 × 0.30 and 0.60 × 0.60 m) on quantitative and qualitative parameters of C. rotundifolia grown in pure stands as forage under exclusive cropping for hay. While leaf dry matter yields in the first 93 days after planting ranged from 1.48 to 9.32 t DM/ha, declining to 0.71–4.92 t DM/ha in the subsequent 83 days, crude protein concentration of the material was only 7–8%. Since this species tends to lose leaf during periods of stress, larger paddock studies are needed to determine how well leaf material is retained under conventional hay-making conditions. Optimal stubble height following harvesting should be investigated in an endeavor to increase DM yields at second harvest along with improved survival of plants.

Design and Experiment with a Double-Roller Sweet Potato Vine Harvester

The yield of sweet potato vines is large, making it a good source of food. However, it is difficult to harvest sweet potato vines due to creeping and intertwining. Therefore, according to the domestic sweet potato planting model, this paper designed a double roll sweet potato vine harvester which can complete the operations of vine picking, vine killing, conveying and header harvesting at one time. The machine adopts the process of front roll vine picking, rear roll vine killing and rod bar lifting. The key components of the vine picking device, vine killing device and lifting device were designed and calculated. A numerical simulation test of the vine harvesting process was carried out by using the discrete element numerical simulation method. It was determined that the length of the vine picking rod from the outside to the inside is 175 mm, 150 mm and 105 mm, respectively, and the inclination angle of the end is 160°. There are six vine killing knives on each vine killing knife plate. The inclination of the lifting device is 50°and the conveying speed is 3 m/s. Using the box Behnken experimental design method, taking the vine picking roller speed, vine killing roller speed and ground clearance as the experimental factors, and taking the sweet potato vine harvest rate, stubble height and potato injury rate as the evaluation indexes, a quadratic regression orthogonal test was carried out, the effects of various factors on the evaluation indexes were analyzed, and the experimental factors were optimized and verified. The experimental results showed that the optimal parameter combination is as follows: the rotation speed of vine picking roller should be 716 r/min, the rotation speed of vine killing roller should be 1960 r/min and the ground clearance should be 16 mm. With these parameters, the harvest rate of sweet potato vines is 93.1%, the stubble height is 29.5 mm and the potato injury rate is 0.174%. As such, the harvester meets the requirements for the mechanized harvesting of sweet potato vines and is of great significance as a light and simplified product for the sweet potato industry.

190 Effects of Flooding on Grazed Pastures: Forage Quality, GHG Emissions and C Stocks

Abstract Manure creates hot spots of nutrients concentration, and consequently nutrient losses to air and water. In flood-prone areas these losses represent a major concern for environment. However, there is a gap on the understanding of the effects of recurring, short-term flooding on environmental and forage characteristics. This study evaluated the effects flooding on soil carbon (C) stock; and greenhouse gas (GHG) emissions (methane, CH4; nitrous oxide, N2O; and carbon dioxide, CO2) from soil; and forage dry matter and quality in flooded and non-flooded grazed pastures during four sampling periods (spring, early summer, late summer, and fall) of 2021. Soil samples were collected from 0-100cm, forage samples were cut at stubble height and soil greenhouse gases (GHG) emissions were monitored using the static chamber methodology. Preliminary results show trends of reduced forage digestibility in flooded pastures. No differences were observed on forage dry matter. Overall, there was no differences between CO2 emission from soil in flooded and non-flooded areas. Soil CH4 fluxes were primarily negative, and flooding seems to reduce the sink potential for CH4 from soil, except during early summer. For N2O the effects of season were very pronounced, increased emissions from spring to early summer and throughout fall in both flooded and non-flooded pastures. We did not observe any N2O sinks, and no difference between treatments. Flood-prone pastures had decreased C stock in comparison with non-flood pastures. Preliminary results show that forage production may represent a good option for flooded areas, since no effects were observed on mass and few effects on quality. However, flooding reduced C stock potential and CH4 sinks. A second sampling season will be performed in 2022 to further observe these results and allow for C-equivalent flux calculations. The balance between productivity and environmental impacts of flood-prone pastures will then be assessed.

PSI-3 Balance between Productivity and Environmental Impacts of Grazed and hay Fields

Abstract Animal production has been associated with environmental impacts, but meat and dairy demand continuously increases. Grazed and hayfields have been responsible for enteric methane emissions, but also identified as great C stocks. Sustainable intensification, or balance between sustainability and productivity, is sought and we need to better understand the trade-offs to design appropriate management strategies. This study evaluated effects of grazed pastures and hayfields on carbon (C) stocks; and on soil GHG emissions (methane, CH4; nitrous oxide, N2O; and carbon dioxide, CO2), and forage dry matter and quality during four sampling periods (spring, early summer, late summer, and fall) of 2021. Forage samples were cut at stubble height, soil GHG emissions were monitored using static chamber methodology, and soil samples were collected from 0-100 cm. During the growing season, hayfields presented higher forage quality and lower forage production than grazed pastures. In addition, grazed pastures presented higher soil C stocks than hayfields. Hayfields presented lower CO2 emissions from soil in comparison to grazed pastures, suggesting slower decomposition of organic matter, which could be associated to lower C stocks. On the other hand, hayfields presented lower GHG emissions in comparison to grazed pastures, when considering CH4 and N2O emissions. Overall, a clear trade-off between the two types of fields is observed. Grazed pastures seem to be adding more C stocks over time, but also emitting more GHG emissions. Forage quality was also reduced. Hayfields had lower GHG emissions, but also lower C stocks. Forage quality was greater. In terms of long-term ecosystems' resilience and climate change mitigation, C addition from grazed pastures is more beneficial. In an eventual C market development, where C credits could be used or sold, grazing systems would be in advantage, again due to greater C stocks even if emitting slightly higher GHG emissions.

Experiments on the Influence of Corn Straw Morphological Combinations on Timely No-Tillage Sowing Soil Temperature and Moisture in Cold Regions

After corn mechanical harvest in autumn in the cold region of northeast China, straw mulching leads to high soil topsoil water content and slow ground temperature rise in the spring sowing season, which may result in a no-tillage planter being unable to operate in time, delayed sowing date, poor seedling emergence quality, and low grain yield. Based on the problems of high moisture content and low temperature in soil topsoil in the spring sowing season in conservation tillage with straw mulching, an experimental study on timely sowing in the spring sowing season was carried out from the perspective of combination optimization of attribute parameters of straw mechanical treatment. Taking the four mechanical treatment attributes as experimental factors, including straw length, straw shape, mulching form (surface covering, inter-ridge covering, and inter-ridge mixed soil covering), and stubble height after corn harvest in autumn of 2019 as experimental factors, and soil topsoil moisture content and temperature during spring sowing in 2020 as evaluation indexes, a field plot experiment was carried out by four factors and three levels of orthogonal combination test method. The results showed that all the factors had significant influence on soil topsoil moisture content and soil topsoil temperature (p < 0.05). It is helpful to reduce the moisture content of soil topsoil and increase the temperature of soil topsoil by increasing the length of corn stalk, breaking the stalk moderately, covering the stalk between ridges, and increasing the stubble height of stalk. Design-Expert software was used to optimize the parameters. The results showed that when the length of straw was 150 mm, the shape of straw was half-cut (dividing straw into two parts evenly along the axis), the mulch was between ridges, and the stubble height was 600 mm, the moisture content of soil topsoil was 22~24% and the temperature of soil topsoil was higher than 8 °C during spring sowing. After corn harvest in autumn of 2021, corn stalks were treated in that year according to the results of parameter optimization combination. The soil topsoil moisture content and temperature were measured to be 24.4% and 8.2 °C, respectively, in the spring sowing season of 2022, which proved that the optimization results in this experiment were credible. The experimental results provide a technical reference for the implementation of conservation tillage with straw surface mulching in the cold region of northeast China.

Mowing mitigated the sensitivity of ecosystem carbon fluxes responses to heat waves in a Eurasian meadow steppe

The heat waves (HW) will be more frequent and intense in the future with increased human activity and uncertain implications for ecosystem carbon fluxes. The semi-arid Eurasian grassland is sensitive to climate change and under frequent HWs attacks. Mowing as one of the most common human practices in this region, combining with HW can have comprehensive effects on plant communities, biomass, and nutrient cycling. Hence, a 3-year (2019–2021) field manipulation experiment was conducted to assess how mowing influenced the carbon cycling under HWs, and the interactions between HWs and mowing on carbon fluxes at the community and ecosystem levels in a Eurasian meadow steppe. Over the three years, HW significantly reduced net ecosystem CO2 exchange (NEE) and gross ecosystem production (GEP) by 28 % and 8 % (P < 0.05), respectively, whereas ecosystem respiration (Re) did not show significant changes. Moderate mowing (stubble height was set at 6–8 cm) for harvest effectively mitigated ecosystem sensitivity to HWs and significantly increased ecosystem carbon fluxes (NEE, Re, and GEP), biomass and the number of species. Mowing reduced the negative impact of HWs on ecosystem carbon fluxes by about 15 % compared to HWs alone, contributing to the invasion of species such as Thalictrum squarrosum and Vicia amoena, and increased the indirect effect of HW on NEE in the structural equation model. In addition, the higher soil water content (SWC) was another effective way to reduce the impact of HWs. Therefore, mowing and higher SWC would be effective ways to counteract the negative effects of HWs on carbon fluxes in future grassland management.