Agronomic,nutritive value,reproductive, cytogenetic,and molecular aspects of Paspalum accessions: Contribution to the development of new forage cultivars

This study investigated the agronomic, nutritive value, cytogenetic, molecular, and reproductive aspects of twenty-five Paspalum accessions to support breeding programs. The agronomic aspects and the nutritive value were evaluated in a randomized block experimental design with four replications, and with monthly repeated measures for 2 years. For the molecular characterization 16 microsatellite markers developed for different Paspalum species in previous works were used. The number of chromosomes was determined by visualizing the meiotic cells and the DNA content was determined by flow cytometry. The embryo sac clarification technique was used to characterize the reproductive system. T he results indicated genetic variability for all the variables related to yield and nutritive value. For almost all variables, the values of Paspalum accessions were higher than those of the commercial cultivars Megathyrsus maximus cv. Tanzania and Urochloa brizantha cv. Marandu, used as references. However, the accessions showed in vitro dry matter digestibility values lower than the mean value presented by the references. The groups formed in the molecular analysis showed correspondence to the groups observed in the principal components analysis, considering the variables related to yield and nutritive value. Most accessions were revealed to be tetraploid with 40 chromosomes and most accessions belonging to the Virgata group displayed a sexual embryo sac structure . Some crosses can be indicated for genetic breeding, due to a superior genomic affinity between the accessions and the higher probability of heterosis in the progeny. These results provide subsidies to genetic plant breeding programs that use these accessions.     

Mixtures of grasses: An alternative to traditional pasture monocultures in the tropics

A two-year experiment assessed herbage production and above- and below-ground characteristics of a highly productive monoculture (‘BRS Zuri’ guineagrass [Panicum maximum Jacq.]) and two mixtures of three grasses (Mixture 1: ‘BRS Zuri’ guineagrass, ‘BRS Xaraés’ palisadegrass [Brachiaria brizantha Stapf.], and ‘Basilisk’ signalgrass [Brachiaria decumbens Stapf.]; Mixture 2: ‘BRS Quênia’ guineagrass [Panicum maximum Jacq.], ‘Marandu’ palisadegrass [Brachiaria brizantha Stapf.], and ‘BRS Paiaguás’ palisadegrass [Brachiaria brizantha Stapf.]), cultivated in the Brazilian tropical savanna. Mixtures 1 and 2 were subjected to two grazing intensities (removal of 40 or 60% of pre-grazing height) and ‘BRS Zuri’ guineagrass monoculture was defoliated to a single grazing intensity of 50%. Treatments were randomly assigned to fifteen 0.25-ha plots and managed under intermittent stocking by cattle. Herbage accumulation rate was similar among pastures and years (p > .1). The root mass in the tussocks did not differ (p > .1), with mean values ranging between 0.62 to 1.81 kg DM m⁻². Root density in the tussock interspaces was greater in the mixtures (p < .001), regardless of seasons (p = .405) and years (p = .292). The mixtures were dominated by guineagrass (70%) and palisadegrass (30%) at the end of the experiment, with the population of ‘Basilisk’ and ‘BRS Paiaguás’ being completely suppressed throughout the experimental period. Mixing guineagrass and brachiariagrasses can be an alternative to the traditional pastoral systems in the tropics, as it does not compromise herbage production and presents a capacity to produce more roots than a very productive monoculture of ‘BRS Zuri’ guineagrass.     

Production of beef cattle grazing on Brachiaria brizantha (Marandu grass)—Arachis pintoi (forage peanut cv. Belomonte) mixtures exceeded that on grass monocultures fertilized with 120 kg N/ha

Mixed grass/legume pastures are an alternative to grass monocultures for increased beef cattle production in tropical climates. The objective of this study was to evaluate the productivity of beef cattle grazing either a mixed pasture of Brachiaria brizantha cv. Marandu grass and Arachis pintoi (forage peanut) cv. Belomonte or a Marandu monoculture, under rotational stocking. Five trials were conducted over a period of nine years in north-eastern Brazil where the sward structure (forage, grass and legume mass) and animal performance were compared for a mixed Marandu grass/forage peanut pasture, and a Marandu grass monoculture with 120 kg N ha⁻¹ y⁻¹. Stocking rate was adjusted to maintain forage allowance at 4% body weight/day. A block design was used with four replicates, and warm and cool seasons within each trial were considered, using repeated measurements over time. In the warm season, the forage mass in the mixed pastures was 17% greater than in the monoculture (p = .049), and the stocking rate, average daily gain and liveweight gain per ha were 16.4%, 20.0% and 28.7% greater (p = .004, p < .001 and p < .001 respectively). The average daily gain showed a positive linear relationship with the legume proportion in the sward (p < .001). The mixed forage peanut/Marandu pasture sustained significantly greater beef cattle production (789 kg ha⁻¹ y⁻¹) compared to the N-fertilized grass monoculture (655 kg ha⁻¹ y⁻¹). Appropriately managed, mixed pastures of forage peanut/Brachiaria pastures are sustainable and have high potential for use in the humid tropics.     

Productivity of beef cattle grazing Brachiaria brizantha cv. Marandu with and without nitrogen fertilizer application or mixed pastures with the legume Desmodium ovalifolium

The use of forage legumes to contribute biologically fixed nitrogen (N) to pastures is an alternative to increase beef cattle production in tropical regions. The objective was to compare the impact of the introduction of a legume with that of N fertilizer application on forage and animal production in Brachiaria pastures. This two-year study assessed three pasture treatments: (1) mixed Marandu palisadegrass (Brachiaria brizantha [syn. Urochloa brizantha] cv. Marandu) and the legume “ovalifolium” (Desmodium ovalifolium) cv. Itabela (Mixed), (2) Marandu palisadegrass pastures with 150 kg N ha⁻¹ (Fertilized), and (3) Marandu palisadegrass without N fertilizer (Unfertilized). Rotational stocking with a variable stocking rate was used with a target herbage allowance of 1.0 kg forage kg body weight⁻¹. The pre-grazing green herbage mass was similar for Fertilized and Mixed pastures, with 54% and 63% more mass than Unfertilized pasture, respectively (p < .001). Cattle that grazed the fertilized pasture had the greatest average daily gain (ADG; p = .017). The stocking rate and liveweight gain per area were greatest for the Fertilized and Mixed pastures (p < .001 and p < .001, respectively). No differences between treatments were found for DM forage intake (p = .555). Organic matter digestibility was lowest (p < .001) for the Mixed pasture. The inclusion of the ovalifolium legume in the Marandu pasture had the same impact on beef cattle production as annual fertilization with 150 kg N ha⁻¹. The potential and environmental benefits of ovalifolium are discussed.     

Light and plant growth‐promoting rhizobacteria effects on Brachiaria brizantha growth and phenotypic plasticity to shade

This is the first report on the effect of light intensity and plant growth‐promoting rhizobacteria (PGPR) on the growth of a tropical forage grass, being a relevant study to improve pasture management in conventional farming and integrated crop‐livestock‐forestry systems. In this study, our aim was to evaluate the effects of light intensity and Burkholderia pyrrocinia and Pseudomonas fluorescens inoculation on Brachiaria brizantha cv. BRS Piatã growth, and phenotypic plasticity to shade. The experiment was conducted in a semi‐controlled environment. Seedlings of B. brizantha were allocated to full sun and shade. P. fluorescens and B. pyrrocinia were inoculated individually or co‐inoculated by soil drench, 14 days after seedling emergence. We evaluated morphogenesis, structural and growth parameters. Irrespective of the light regime, co‐inoculated plants had greater leaf area and SPAD index (chlorophyll content). Increase in total biomass production in co‐inoculated plants was over 100% and 300%, under full sun and shade respectively. Co‐inoculated P. fluorescens and B. pyrrocinia increased shade tolerance in B. brizantha, improving plant performance. Co‐inoculation promoted growth in B. brizantha under both sun and shade, indicating its potential as a bio‐fertilizer in conventional and integrated systems, especially in silvopastoral systems, where light availability to pasture growth may be limited.     

Bio‐agronomic characterization and implications on the potential use as forage of Bituminaria bituminosa and B. morisiana accessions

Perennial forage legumes may be pivotal for improving the sustainability of Mediterranean rainfed farming systems. This study summarizes the outcomes of a study aimed at characterizing morphological and agronomic traits of new germplasm of Bituminaria bituminosa and B. morisiana in Mediterranean environments. Five B. morisiana and three B. bituminosa native populations were evaluated in a small‐plot field experiment in Sardinia (Italy) and compared with seven Spanish accessions of B. bituminosa. The two Bituminaria species differed greatly in morphological traits and the beginning of the flowering stage, and remarkable variations between species were found for forage production and its seasonal distribution, seed yield and persistence. Average cumulative dry‐matter yield was higher in B. bituminosa than in B. morisiana (+7.6%; 297 vs. 276 g per plant). Average 3‐year seed production varied greatly between accessions (from 0.3 to 141 g per plant). Differences for these traits were also found between Sardinian and Spanish germplasm of B. bituminosa. Four clusters were generated by K‐means clustering. Accessions included in cluster III exhibited a positive combination of favourable forage production, high seed yield and satisfactory persistence. Nonetheless, the cluster analysis did not highlight a sharp discrimination between Bituminaria species. The overall results revealed the potential role of Sardinian accessions of B. bituminosa and B. morisiana in extending the forage season and for increased resilience of grasslands in Sardinia and other Mediterranean regions under rainfed conditions.     

Liveweight gain of beef cattle in Brachiaria brizantha pastures and mixtures with Stylosanthes guianensis in the Brazilian savannah

The use of stylosanthes in mixed grass-legume pastures may minimize the decline in forage quality and quantity that occurs in monoculture grass pastures, even though the availability of commercial cultivars in Brazil is still limited. The objective of the study was to evaluate the liveweight (LW) gain of young Nellore bulls in a mixed pasture of Brachiaria brizantha (cv. Paiaguás) with the latest release Stylosanthes guianensis cv. Bela. The study was conducted in Planaltina, FD, Brazil, from September to August in two consecutive years, right after seeding. The experimental design was a randomized complete block design with two treatments (mixed or monoculture Paiaguás pastures) and three replicates. The average daily gain (ADG) was on average greater in mixed pastures (0.436 vs. 0.350 kg head⁻¹ day⁻¹ in mixed and grass pastures respectively), particularly in the dry period (0.344 vs. 0.183 kg head⁻¹ day⁻¹). The benefit of mixed over monoculture grass pastures throughout the year was 22 kg LW/head and 55 kg LW/ha. The presence of stylosanthes increased the crude protein (CP) concentration in mixed pastures (120 g/kg) when compared to monoculture grass pastures (109 g/kg), probably influencing the ADG of bulls. The increase of liveweight gain, predominantly in the dry season, makes the high-protein stylosanthes cv. Bela an alternative to buffer the seasonal deficit of forage quality in newly seeded grass pastures.     

Grazing intensity affects forage accumulation and persistence of Marandu palisadegrass in the Brazilian savannah

This 3‐year study evaluated the effects of grazing intensity on herbage and steer responses in continuously stocked Brachiaria brizantha cv. Marandu pasture in the Brazilian savanna. Treatments consisted of three grazing intensity levels, characterized by canopy heights of 15, 30 and 45 cm, measured twice per week. Responses variables included tiller population density (TPD), herbage accumulation rate (HAR) and body weight gain per area (WGA). A decline in TPD (1,237 vs. 767 tillers/m²) was observed from the first to the third grazing years, which influenced the HAR from the first to the third years (90.1 vs. 52.4 kg ha^?1 day^?1). A marked decline in body WGA (541 vs. 276 kg ha^?1 year^?1) was observed along the three years in pastures managed at a height of 15 cm, indicating that this is an unstable condition for Marandu palisadegrass pasture. HAR was similar for pastures managed at 30 or 45 cm and was relatively stable during the experimental period, averaging 91.8 and 99.1 kg ha^?1 day^?1 respectively. Body WGA was similar and constant throughout the experimental period for pastures managed at 30 (596 kg ha^?1 year^?1) and 45 cm (566 kg ha^?1 year^?1). Maintaining continuously stocked Marandu palisadegrass pastures at a 15 cm canopy height should be avoided due to long‐term decreases in plant persistence and animal body WGA, particularly when soil P is below critical levels at pasture establishment and during pasture utilization.     

Forage biomass,soil cover,stability and competition in perennial grass–legume pastures with different Paspalum species

The short life span, irregular forage production and susceptibility to weed colonization of cool‐season grass–legume pastures are serious problems in grazing dairy systems in warm‐temperate regions. The inclusion of warm‐season species has the potential to mitigate these problems. In this study, we evaluated the effect of the inclusion of two warm‐season grasses with different growth habits on seasonal forage biomass, soil cover and weed colonization. Three different pasture mixtures were evaluated under grazing: conventional pasture (CP) [tall fescue (Festuca arundinacea), white clover (Trifolium repens) and birdsfoot trefoil (Lotus corniculatus)], CP with Paspalum dilatatum and CP with Paspalum notatum (CP + Pn). Forage biomass and soil cover were sampled thirteen times during a 3‐year trial, and sampling times were grouped by season for the analyses. The mixtures with Paspalum showed higher soil cover in the autumn, while in the winter CP had higher soil cover than CP + Pn. Competition with tall fescue was similar between mixtures with Paspalum, when considering biomass, but it was higher in CP + Pn when considering soil cover. The inclusion of P. notatum increased biomass during the autumn but decreased the mixture performance during winter by reducing tall fescue soil cover. The addition of a warm‐season grass species with a moderate competing ability like P. dilatatum is likely to avoid a negative impact on the cool‐season component of the pasture.     

Combining ability among apomictic and sexual parents of Urochloa humidicola

The diallel cross constitutes an informative genetic design for choosing genitors and crosses in breeding programmes since it provides estimates of general (GCA) and specific (SCA) combining abilities. Because the breeding programme for Urochloa humidicola ([Rendle] Morrone & Zuloaga; syn. Brachiaria humidicola [Rendle] Schweick) at Embrapa Beef Cattle is recent, these estimates are still unknown. Thus, the aim of this study was to obtain the estimates of GCA and SCA from the partial diallel cross design between sexual and apomictic parents. The crosses involved nine sexual and ten apomictic parents. Seventy‐one full‐sib progenies were obtained and evaluated in an incomplete block design, using all parents and the cv. BRS Tupi as a check. The agronomic and forage quality traits were evaluated using seven harvests. Statistical analysis was performed using the mixed model approach. Significant variations were associated with GCA among sexual parents for biomass yield and forage quality traits. However, this cannot be observed for apomictic parents for GCA. The SCA effect was not significant for the assessed traits. These results showed the predominance of additive effects. Sexual parents SEX3 and SEX4 presented the highest potential for contributing favourable alleles in hybrid combinations. The absence of GCA among apomictic parents and SCA suggests the need to increase genetic variability for the generation of breeding populations of U. humidicola.     

Effectiveness of saccharin and ulvan as resistance inducers against rust and angular leaf spot in bean plants (Phaseolus vulgaris)

The present work aimed to study the effect of saccharin and ulvan against rust in artificially inoculated plants and against both rust and angular leaf spot (ALS) in naturally infected bean plants. In the greenhouse, bean plants of cv. Guará (susceptible) and FT-line (rust resistant) at first trifoliate leaf stage were sprayed with saccharin (0.24 mg mL⁻¹) or ulvan (1 or 10 mg mL⁻¹), and inoculated with Uromyces appendiculatus six days after spray. Both compounds provided an intermediary level of protection. They reduced at a similar extent the number, diameter and particularly sporulation of rust pustules in susceptible plants, suggesting that mechanisms of resistance operate at latter stages of fungus colonization. Three follow-up experiments were carried out under natural infection conditions during the spring 2009 and 2010, and summer/autumn 2010. ALS was observed during all three outdoor pot experiments, whereas rust occurred only during the spring 2009 and 2010. Saccharin sprayed every 14 days was able to protect bean plants against rust during the three experiments, whereas significantly reduced ALS only during summer/autumn and spring 2010. On the other hand, ulvan at a reduced dose rate (1 mg mL⁻¹) did not affect significantly the epidemiological development of both diseases. Increase in seed weight was observed when saccharin-treated plants were infected after pre-flowering, but not when rust infection occurred earlier. Possible reasons why such trade-offs can be obtained in certain circumstances are discussed.     

Spatial analysis of genetic diversity in a comprehensive collection of the native grass Bromus auleticus Trinius (ex Nees) in Uruguay

Bromus auleticus Trinius (ex Nees) is a perennial allogamous C3 grass native to the Campos grasslands. It has potential to play a key role in restoration of both abandoned agricultural and overgrazed lands. We aim to reveal the existence of local adaptation and to assess whether phenotypes could be differentiated in relation to their ecogeographic region of origin. Previous reports estimated significant levels of variability among and within populations, but as yet there is no evidence of local adaptation and phenotypic relations with ecogeographic regions for this species. Indeed, there is a lack of knowledge about the spatial distribution of diversity, which limits the possibilities of using B. auleticus in ecological restoration and plant breeding. A comprehensive collection of 82 accessions of B. auleticus from eight ecogeographic regions within Uruguay was used to characterize diversity by measuring phenologic, morphologic, productive and reproductive traits. We found high diversity among B. auleticus accessions, and the spatial distribution of this diversity follows a pattern accounted by ecogeographic regions to a large extent. Our results also indicate large genotype × environment interaction, confirming local adaptation. Phenotypic values permitted, with a 3.7% error rate, discrimination of accessions according to their ecogeographic region of origin, suggesting the existence of differentiated ecotypes. We consider that the diversity observed should be conserved and used for breeding cultivars of this species and for the restoration of degraded grasslands by considering ecogeographic regions when selecting seed sources.     

Application of infrared thermography to assess cassava physiology under water deficit condition

ABSTRACT

Water deficit stress is a major factor that inhibits the overall growth and development in cassava (Manihot esculenta), leading to decreased storage root yield. We conducted a study to investigate whether thermal sensing could be used to indicate water deficit stress and the health and yield of cassava crops in field. The objective of the study was to use thermal imaging to determine relationship between crop water stress index (CWSI) and physiological changes, and to identify the critical CWSI point in fields of cassava cv. Rayong 9 under well-irrigated and water-deficit conditions. At the time of storage root initiation (85 DAP [day after planting]), thermal imagery was collected and the physiological changes and growth characters were measured prior to storage root harvesting (162 DAP). Thermal infrared imager was used to measure the canopy temperature and CWSI of cassava plants. Net photosynthetic rate (P_n), stomatal conductance (g_s) and transpiration rates (T_r) of cassava plants under water deficit conditions for 29 d (114 DAP) were significantly decreased, leading to delayed plant growth as compared to those under well-irrigated conditions. In contrast, air vapor pressure deficit (VPD_air) and CWSI in drought-stressed plants were higher than well irrigated plants. High correlations between T_r/g_s/P_n and CWSI were observed. The study concludes that CWSI is a sensitive indicator of water deficit stress caused due to stomatal function.

Abbreviations: CWSI: crop water stress index; DAP: day after planting; Pn: net photosynthetic rate; gs: stomatal conductance; Tr: transpiration rate; VPDair: air vapor pressure; RMSE: root mean square error     

Forage and animal production on palisadegrass pastures growing in monoculture or as a component of integrated crop–livestock–forestry systems

To meet the global demand for animal protein, sustainable intensification of existing livestock systems may be possible, especially through integration of livestock with crops or forestry. Thus, our objective was to compare forage production and animal performance in grass monoculture and integrated systems in the Brazilian Amazon biome. The four systems were (a) livestock (L) with Marandu palisadegrass {Brachiaria brizantha (Hochst. ex A. Rich.) R. D. Webster} as monoculture, (b) palisadegrass pastures integrated with eucalyptus trees (Eucalyptus urograndis; hybrid of Eucalyptus grandis W. Hill ex Maiden and Eucalyptus urophylla S. T. Blake) arranged in three‐row groves with groves spaced 30 m apart (livestock–forestry; LF), (c) palisadegrass after two years of crops (crop–livestock; CL) and (d) palisadegrass after two years of crops with single rows of eucalyptus trees spaced 37 m apart (crop–livestock–forestry; CLF). From July 2016 to July 2017, all experimental units were continuously stocked using a variable stocking rate. Greater herbage accumulation (HA) occurred in CL and CLF in comparison with L and LF (21,310, 24,050, 19,500 and 18,890 kg DM/ha respectively). The gain per hectare of L, LF and CL (average of 932 kg ha^–1) was less than CLF (1,190 kg ha^–1). Average daily gain was similar among systems (0.69 kg/day). We conclude that integrated systems can support similar (LF or CL) or greater (CLF) levels of animal production than palisadegrass monocultures while increasing diversity of outputs, thereby providing a greater range of viable systems for livestock production in the Brazilian Amazon biome.     

The Role of Active and Passive Water Uptake in Maintaining Leaf Water Status and Photosynthesis in Tomato under Water Deficit

Abstract

Tomato (Lycopersicon esculentum Mill. cv. Know-You 301) shoots were grafted onto the rootstock of the same species or Solanum mammosum and grown in nutrient solution. After the grafted tomato plants developed 4–5 leaves, the uppermost fully expanded leaves were used to determine net photosynthetic rate (P_N) , transpiration rate and leaf water potential (Ψ_L) under control (unstressed) and —0.5 MPa water deficit (mannitol was added to nutrient solution). Both PN and leaf conductance (G_L) were reduced under water deficit. However, tomato plants grafted onto S. mammosum rootstock had higher Ψ_L, P_N and G_L than those grafted onto tomato rootstock under water deficit. This result demonstrates that S. mammosum roots had a greater ability in water uptake under water deficit. Under +0.2 MPa pressure, the root of S. mammosum showed a higher exudation rate than that of tomato. However, the former showed a lower exudation rate than the latter under –0.5 MPa water deficit. It was concluded that the greater ability of water uptake in S. mammosum rootstock under water deficit is related to a lower hydraulic conductivity, which promotes passive, rather than active water uptake.     

Genetic and morphological characterization of Acroceras macrum Stapf

Acroceras macrum is a warm‐season grass used for pastures, and it has high nutritive value. The scarce genetic and reproductive information about this grass is limiting its breeding for forage. The objective of this research was to determine the number of genotypes and cytotypes present in a collection established in Argentina, and to estimate the diversity of this species based on molecular markers, and morphological and agronomic characteristics. The number of genotypes among forty‐seven accessions was determined using ISSR markers. The identified genotypes were further characterized for ploidy levels. In addition, the genetic distances among them were estimated with ISSR markers. They were also propagated and planted into the field following a randomized complete block design with four replications, and a group of sixteen morphological and agronomic variables were evaluated. A total of twenty‐seven genotypes were identified in this collection; twenty‐two genotypes were tetraploid (2n = 4x = 36) and five were hexaploid (2n = 6x = 54). These two cytotypes were found clearly separated by both genetic and phenotypic characteristics. Above‐ground biomass, internode length, initial growth and number of spikelets per inflorescence were the most variable traits. The high diversity present in this collection will allow for the initiation of a breeding programme for A. macrum.     

Effects of nitrogen fertilization and cutting intensity on the agronomic performance of warm‐season grasses

Responses of grasses to N fertilization are affected by cutting intensity although little is known regarding the interactions of these factors in warm‐season grasses. Pre‐cutting canopy height, herbage accumulation and changes in the nutritive value of warm‐season grasses in response to four different management strategies were assessed from October 2011 to September 2014. Treatments included two cutting intensities (70 vs. 50% depletion of canopy height set by 95% light interception), two N fertilization levels (zero vs. 300 kg N ha^?1 year^?1) and six perennial C₄ grass species (Axonopus catharinensis; Cynodon spp. hybrid Tifton 85; Hemarthria altissima cv. Flórida; Megathyrsus maximus cv. Aruana; Paspalum notatum cv. Pensacola; and Urochloa brizantha cv. Marandu) grown in monoculture in a factorial experimental design. Canopy height varied among grass species, cutting intensity and N treatments, mainly among seasons, indicating that more than one management target (i.e. canopy height) existed throughout the plant growth cycle for each species. The largest herbage accumulation occurred in the N fertilization treatments for most species, regardless of cutting intensity. Nitrogen fertilization and 50% depletion of canopy height increased the leaf proportion and decreased the neutral detergent fibre content. Overall, N fertilization had a stronger positive impact than cutting intensity on the acid detergent fibre content, dry‐matter digestibility and crude protein content, but the magnitudes of the responses were species‐specific.     

Critical water content and water stress coefficient of soybean (Glycine max [L.] Merr.) under deficit irrigation

The objective of this research was to investigate the critical water content (θ _c) and water stress coefficient (K _s) of soybean plant under deficit irrigation. This research was conducted in a plastic house at the University of Lampung, Sumatra in Indonesia from June to September 2000. The water deficit levels were 0–20%, 20–40%, 40–60%, 60–80%, and 80–100% of available water (AW) deficit, arranged in Randomized Completely Block (RCB) design with four replications. The results showed that the soybean plant started to experience stress from week IV within 40–60% of AW deficit. The fraction of total available water (TAW) that the crop can extract from the root zone without suffering water stress (p) was 0.5 and θ_c was 0.305 m³ m⁻³. The values of K _s at p=0.5 were 0.78, 0.86, 0.78, and 0.71 from week IV to week VII, respectively. The optimum yield of soybean plant with the highest yield efficiency was reached at 40–60% of AW deficit with an average K _s value of 0.78; this level of deficit irrigation could conserve about 10% of the irrigation. The optimum yield of soybean plant was 7.9 g/pot and crop water requirement was 372 mm.     

旱涝急转对不同花生品种生理生化指标的影响

为探讨旱涝急转对花生生理生化的影响,以不同旱涝耐性的3个花生品种中花8号（抗旱）、豫花15（耐涝）和湘花2008（旱涝兼耐）为材料,进行不同梯度的先旱、后涝连续处理,比较不同花生品种的叶片相对含水量,过氧化物酶（POD）、过氧化氢酶（CAT）、超氧化物歧化酶（SOD）、谷胱甘肽还原酶（GR）活性,以及丙二醛（MDA）含量的变化情况。结果表明,在旱、涝急转的胁迫过程中,干旱对叶片相对含水量的影响甚于湿涝。一定强度的旱或涝胁迫总体上均可使花生叶片的4种抗氧化酶POD、SOD、CAT、GR活性提高,随着胁迫的加深活性降低,复水后活性回落至对照水平,且旱甚于涝。MDA含量总体变化趋势是干旱胁迫下各品种花生叶片中MDA含量有所升高,并于复水解除干旱胁迫后恢复至对照水平;而湿涝处理阶段,MDA含量呈直线上升趋势,在胁迫解除后有所降低。中花8号、豫花15、湘花2008等3个花生品种具有显著不同的水分适应性,中花8号抗旱性更强而耐涝性较弱,豫花15抗旱性较弱而耐涝性强,湘花2008抗旱性中等而耐涝性更强,为水分广适性品种。     

Effect of sward height on the fermentability coefficient and chemical composition of Guinea grass silage

There is a high correlation between sward height and pasture sward structure. Therefore, in tropical grasslands, taking sward height into account has been a much better strategy in rotational stocking management than considering pre‐defined days of growth. Similarly, sward height could be used to determine the moment when tropical grasses present the best ensilability parameters. This study aimed to identify the sward height at which Panicum maximum cv. Mombaça (Guinea grass) provides the highest fermentability coefficient (FC) and to define the combination of additives that best improves the chemical composition of silage. Two trials were carried out in Selvíria, MS, Brazil, from 2015 to 2016. The first year was used to identify the highest FC, and the second year was used to identify the best combination of eight additives (citrus pulp [CIP], homofermentative and heterofermentative LAB, their combinations and control). Statistical analyses were performed using SAS (p < .05), and one contrast was defined as silage with CIP vs. silage without CIP. The height of 130 cm resulted in the highest FC (31.01). Silages inoculated with CIP had better quality than silages without CIP, due to the high crude protein (8.3 vs. 7.3% DM), DM recovery (98.6 vs. 93.3% DM), low pH (3.92 vs. 4.91) and NH₃‐N values (2.49 vs. 14.73% total N). Sward height is a consistent parameter for determining the time of ensiling Guinea grass, and the inclusion of CIP is necessary to raise the silage quality.