Leaf Senescence Rate Research Articles

Morphophysiology of tropical grasses under different water supply in two growing seasons: II. BRS Massai and BRS Tamani grasses

This study aimed to evaluate the physiological parameters and the biomass flow and structural characteristics of BRS Massai and BRS Tamani grasses under different irrigation conditions. The rating of gas exchange, biomass flow and structural characteristics were performed in dry periods and dry/rainy season, under the water supply of 30; 60; 90 and 120% of the reference evapotranspiration (ETo). The experimental design was completely randomized in a factorial arrangement 4x2 (water supply and grass). The experiment was conducted in pots with capacity for 7.5 dm³, using as substrate layer of 0-0.2 m soil. There was no effect (P < 0.05) between the gas exchange in the dry period, having the largest growing parameters of irrigation schemes. In the transition period of dry/rainy, we observed a reversal behavior in relation to the dry period, showing a rapid recovery of grasses under the minor water supply. It was observed quadratic behavior to concentrations of CO2 in the leaf mesophilic (Ci) with maximum point to the BRS Massai grass and minimum point to the BRS Tamani grass, where the major and minor Ci were 119 and 48 ppm in the water supply of 107 and 35% of ETo, respectively. In relation to the biomass flow, the BRS Tamani grass presented greater stem elongation rate and leaf senescence rate in relation to BRS Massai in both periods assessed. In the dry period, we observed a higher biomass production of green leaf blades in the BRS Tamani grass, while in the transition dry/rainy season, the results for this variable were similar, and at the same time that observed higher accumulation of green culm biomass to the BRS Tamani grass, which certainly affected its structure. It is concluded that the application of a minimum daily water supply of 30% of ETo allows the maintenance of BRS Massai and BRS Tamani grasses without incurring the death of tillers and reduction of regrowth vigor, whereas the water supply of 90% of ETo favors the morphophysiological characteristics, especially of BRS Tamani grass.

Growth of Megathyrsus maximus cv. Mombaça as affected by grazing strategies and environmental seasonality. II. Dynamics of herbage accumulation

For tropical forage grasses, leaves are the main morphological component accumulated at the beginning of regrowth, and as leaf area index increases, plants change their growth pattern, allocating more resources to stem elongation as a means of optimising light capture. We hypothesised that, for Mombaça guineagrass, stem elongation and leaf senescence rate play a major role in determining net herbage accumulation rate (NHAR) and that senescence would be the key factor driving the reduction in NHAR when regrowth is interrupted beyond the critical leaf area index, that is, when canopy light interception (LI) exceeds 95%. Treatments corresponded to all combinations of two levels of pre-grazing canopy LI during regrowth (LI95% and LIMax) and two post-grazing heights (30 and 50 cm), and were allocated to experimental units according to a randomised complete block design with four replications. Measurements were performed throughout contrasting climatic conditions during four seasons from January 2001 to February 2002. Overall, spring and the two summers were the seasons when rates of leaf appearance, leaf elongation and leaf growth rate were higher, and leaf lifespan was smaller; the inverse occurred during autumn–winter. Despite the lack of statistically significant differences in NHAR between LI treatments during some seasons of the year, the ratio of leaf growth rate to NHAR was consistently higher for LI95% than LIMax. The pre-grazing target of LI95% was also efficient for decreasing stem elongation and leaf senescence rate. Increased senescence on individual tillers was the key driver generating modifications in the patterns of variation in NHAR beyond the critical leaf area index, suggesting that there is no advantage in extending the regrowth period when the main objective is to maximise leaf growth rate or NHAR.

Effects of thidiazuron and ethephon on the grain filling and dehydration characteristics of maize in Northeast China

ABSTRACT A mixture of ethephon (ETH) and thidiazuron (TDZ) (called ETTD) has been proven to effectively reduce maize grain moisture content and improve yield and quality of mechanical grain harvesting, but the underlying mechanism is unclear. Field trials were conducted in 852 Farm, Heilongjiang Province, China, in 2017 and 2018, to study the effects of ETH, TDZ and ETTD sprayed on Xianyu335 at 25 days after flowering (appropriate time in the pre-experiment) on grain filling and dehydration characteristics. ETH, TDZ and ETTD significantly accelerated leaf senescence, increased grain, bract, and cob dehydration rates, and decreased grain filling duration and moisture content. TDZ and ETTD significantly increased grain filling rate and auxin (IAA), zeatin riboside (ZR), and abscisic acid (ABA) and decreased gibberellic acid (GA). ETH had no significant effect on ABA and GA, but significantly reduced IAA and ZR in the later period. The grain dehydration rate was significantly negatively correlated with grain filling duration and positively correlated with rates of grain filling and bract and cob dehydration. ETTD significantly decreased the rates of breakage, impurity, and increased mechanical grain harvesting yield. In conclusion, ETTD can be an effective measure to improve yield and quality of maize mechanical grain harvesting.

Effect of seed tuber physiological age on leaf area production of potato cultivars Russet Burbank and Atlantic

A pot trial was conducted to study the effect of seed tuber physiological age on the leaf growth of two potato cultivars. The study was conducted in a controlled stress free environment in a glasshouse at University of Tasmania Horticultural Research Centre. Seed tubers of two cultivars (Atlantic and Russet Burbank) with different physiological ages were used. The trial was set up as a complete randomized block design with four replicates. Some leaf growth characters were observed including the leaf phenology and production. ANOVA on the observed parameters show a significant difference between the physiological ages of the seed tuber used in the leaf growth characters. Higher node or leaf appearance rate was observed in cv. Russet Burbank (39.5 °Cd per leaf) in the plants from older tubers compared to the younger seed tubers (51.2 °Cd per leaf). On the contrary, no significant differences were found for the leaf senescence rate. Seed tuber ages also affected the size of fully expanded leaves in cv. Russet Burbank but not in Atlantic. More branching was found in the plant established from physiologically older seed tubers.

Morphogenic and structural characteristics of Panicum cultivars during the establishment period in the Brazilian Northeast

This study aimed to evaluate the morphogenic and structural characteristics of six Panicum maximum cultivars during the establishment period. A completely randomized block design with four replicates and six treatments (Tamani, Mombaça, Massai, Tanzania, Aruana and Zuri cultivars) was used. Morphogenic (leaf appearance rate, leaf elongation rate e stem elongation rate), structural (final leaf length, tiller population density e number of leaves per tiller) and productive (forage mass, leaf blade mass, stem mass, senescent material mass and leaf:stem ratio) characteristics were evaluated. There was no difference (p > 0.05) between the cultivars in terms of the number of live leaves per tiller (2.95 leaves/tiller). Mombaça cultivar had (p < 0.05) higher canopy height (50.64 cm) compared with other cultivars. The highest (p < 0.05) tiller population density was observed in Tamani (235.90 tillers m-2) and Massai (201.60 tillers m-2) cultivars. Leaf lifespan (54.18 days), phyllochron (17.40 days/leaf) and leaf senescence rate (0.87 cm tiller day-1) were not different (p > 0.05) between cultivars. However, leaf appearance rate was higher (p < 0.05) in Tanzania (0.07 leaves tiller day-1) than in Aruana cultivar (0.05 leaves tiller day-1). Leaf blade mass was higher (p < 0.05) in Mombaça cultivar (1518.31 kg DM ha-1), whereas Massai showed higher (p < 0.05) leaf:stem ratio (9.25). Panicum cultivars Tamani, Tanzania and Massai establishment after 75 days, while the other cultivars establish at 105 days of sowing in the Brazilian Northeast.

Morphogenesis, structure, and dynamics of paiaguas palisadegrass tillering after intercroping with sorghum for the recovery of pasture in different forage systems

The use of pasture is the most economical alternative for feeding ruminants. However, most pastures in Central Brazil are experiencing some degree of degradation. Crop-livestock integration has been shown to be a sustainable and viable alternative for the recovery of these degraded areas. The objective of this study was to evaluate the morphogenic and structural characteristics of Paiaguas palisadegrass and to determine the population dynamics and the survival rate of the tillers, through a stability diagram of the grass, after intercropping with sorghum for the recovery of pastures in different, integrated, crop-livestock forage systems. The experimental design was a randomized block design, with four replications. The treatments were composed of four forage systems: Paiaguas palisadegrass monoculture, sorghum intercropped with Paiaguas palisadegrass in the row, sorghum intercropped with Paiaguas palisadegrass in the interrow, and sorghum intercropped with oversown Paiaguas palisadegrass. The evaluations were performed in the four climatic seasons of the year (winter, spring, summer, and fall) in the same plots during the period of one year in 16 1042 m2 enclosures under a continuous stocking system. No effect was observed for the forage systems and seasons of the year on the leaf elongation rate, leaf senescence rate, and leaf life span. The development of Paiaguas palisadegrass was reduced in the winter relative to the other seasons of the year. However, it presented satisfactory production during this period despite the low rainfall. The results showed that the Paiaguas palisadegrass showed satisfactory production in all forage systems and may be indicated for intercropping with sorghum to promote the recovery and formation of pastures. The use of crop-livestock integration systems is an efficient cultivation technique for the recovery and formation of low-cost pastures to meet the demands of animal production.

Forage yield and morphogenesis of Megathyrsus maximus cultivars in Roraimas’s savannas

In order to evaluate the forage productivity and the morphogenic and structural characteristics of Megathyrsus maximus cultivars (Massai, Mombasa, Kenya, Tamani, Tanzania and Zuri), an experiment was conduct under natural environmental conditions in the savannahs of Roraima. The highest yields of green dry matter (GDM) were found with cultivars Zuri (4,317 kg ha-1) and Mombasa (4,115 kg ha-1), followed by Kenya (3,868 kg ha-1) and Tamani (3,755 kg ha-1), while Massai (3,341 kg ha-1) and Tanzania (3,225 kg ha-1) were the least productive. GDM yield was directly correlated with LAI and inversely proportional to tiller population density (TPD). The cultivars Tanzania and Kenya had the highest number of tiller leaves and leaf appearance rates, while the highest leaf expansion rates were estimate in cultivars Zuri and Kenya. The highest average length of tiller leaves was estimate in the cultivars Zuri and Mombasa. Leaf senescence rates were inversely proportional to TPD and the highest recorded with the cultivars Mombasa and Tamani. The six cultivars of M. maximus showed satisfactory forage yields and can be recommend for cultivation in the edaphoclimatic conditions of the of Roraima’s savannas. The determination of morphogenic and structural characteristics can contribute to the establishment of appropriate and specific management practices for each cultivar, aiming to optimize its productivity and reduce losses due to leaf senescence.

Simulating the Influences of Soil Water Stress on Leaf Expansion and Senescence of Winter Wheat

Current crop models usually need a lot of input information to simulate crop leaf area index and have relatively large simulation errors under soil water stress, which need to be improved. In this study, based on experiments conducted in glass soil columns and field under rainout shelters in four years (2012-2016) in Yangling, Shaanxi Province in China, we attempted to establish a dynamic model for simulating leaf expansion and senescence of winter wheat under soil water stress. First, a temperature response function was established with four cardinal temperatures (base temperature, lower optimum temperature, higher optimum temperature, and maximum temperature). Then two soil water stress functions were established to quantify the effect of soil water stress on the processes of leaf expansion and leaf senescence of main stem per plant. The first order derivative of a logistic function was then modified with the temperature and soil water stress response function and was used to simulate the daily rate of leaf area expansion and senescence of main stem. The parameters of the new model were estimated using the Solver add-in in MS Excel and then validated based on the data of soil column experiments in 2014-2015 growing season. Then the new model was evaluated with another dataset of column experiments conducted in 2015-2016. Furthermore, the influence of soil water stress on wheat tillering was included in the new model based on open field experiments in 2012-2013 growing season. Then, the new leaf area index (LAI) simulation model was further verified with the data of open field experiments under rainout shelter (2013-2014) and rainfed condition (2004-2005, 2005-2006, and 2008-2009) in different sites. A comparison was conducted between new LAI model and the original LAI module of CERES-Wheat. The results showed that the leaf expansion rate was not affected when the relative soil water availability was greater than 0.7; water stress inhibited the leaf expansion when relative soil water availability was between 0.2 and 0.7; leaves withered and yellowed when relative soil water availability was less than 0.2. The overall average root mean square error (RMSE) and residual accumulation coefficient (CRM) were 9.78 cm2 plant−1, -0.03, and 6.51 cm2 plant−1; 0.05 for model calibration and validation, respectively. The RMSE of LAI decreased by an average of 47.89% compared with the original LAI module of CERES-Wheat. The results of this study can help to improve the current CERES-Wheat model for model applications in the arid and semi-arid regions of China.

Special issue in honour of Prof. Reto J. Strasser - Characterization of photosynthetic performance during natural leaf senescence in winter wheat: Multivariate analysis as a tool for phenotypic characterization

In the current research, we used chlorophyll fluorescence measurements and photosynthetic pigment content to evaluate onset and rate of the flag leaf senescence every 7 d beginning at the flowering stage (0 d after flowering, DAF) until late senescence stage (35 DAF) on three winter wheat field-grown varieties (Alka, Žitarka, and Olimpija) with the similar maturation time. OJIP curves implied that flag leaves of variety Alka detained the longest photosynthetic efficiency, while the earliest symptoms of senescence onset were indicated by positive L-band at 7 DAF and K-band at 14 DAF in variety Olimpija. A shift in I-P phase in the wheat flag leaves suggested the reduction of first acceptors in PSI, implying degradation of photosynthetic apparatus. Performance index (PItotal) proved to be the sensitive indicator of senescence; it decreased very early at 7 DAF in the flag leaves of variety Olimpija compared to Alka and Žitarka. Principal component analysis elucidated quantum yield of energy dissipation and dissipated energy flux per reaction centre as the earliest indicators of senescence in wheat flag leaves and thus showed that multivariate approach may be useful in detection of senescence onset. Sustainability indexes (SIs) corroborated the statistical significance results of evaluated parameters implying that SIs can be used as user friendly data analysis for screening purposes. Selection for functional stay-green trait could contribute to increasing crop yields.

Acúmulo de forragem e características morfogênicas e estruturais de Megathyrsus maximus cv. Tamani sob intensidades de desfolhação

Abstract. The effects of defoliation intensity (10, 20, 30 and 40 cm above soil level) on green dry matter (GDM) yield and morphogenetic and structural characteristics of Megathyrsus maximus cv. Tamani were evaluated under field conditions in Roraima´s savannas. The effects of defoliation intensity on the GDM yields, leaf area index and leaf elongation rates was adjusted to the quadratic regression model and maximum values recorded with cutting at 28.2; 33.3 and 21.6 cm above soil level, respectively. The population tiller density, number of leaves tiller-1 and leaf appearance rate was inversely proportional to the defoliation intensity, while the opposite occurred for to average leaf length and leaf senescence rate. Apical meristem removing percentage was higher with increasing defoliation intensity. Regrowth vigor showed close negative correlation with defoliation intensity. Pastures of M. maximus cv. Tamani managed under 25 to 30 cm residue provides higher forage productivity, larger efficiency of forage utilization, greater tissue renewal and canopy structure more favorable to grazing.Keywords: Green dry matter, leaves, tillering, senescence

Morphogenetic and structural characteristics of Megathyrsus maximus cv. Centenário under defoliation intensities

The effect of defoliation intensities (20, 30, 40 and 50 cm above soil level) on green dry matter (GDM) yield and morphogenetic and structural characteristics of Megathyrsus maximus cv. Centenário were evaluated under field conditions in Roraima´s savannas. The effects of defoliation intensities on the GDM yields, leaf area index and leaf elongation rates was adjusted to the quadratic regression model and maximum values recorded with cutting at 35.8; 44.9 and 30.2 cm above soil level, respectively. The tiller population density, number of leaves tiller-1 and leaf appearance rate was inversely proportional to the intensity of defoliation, while the opposite occurred for to average leaf length and leaf senescence rate. Apical meristem removal percentage was higher with increasing defoliation intensity. Vigor regrowth showed close negative correlation with defoliation intensity level. Pastures of M. maximus cv. Centenário managed under 30 to 35 cm residue provides higher forage productivity, larger efficiency of forage utilization, greater tissue renewal and canopy structure more favorable to grazing.

Growth dynamics and senescence of digit grass as a response to several canopy heights

The purpose of this study was to examine the growth and senescence dynamics of Digitaria eriantha cv. Survenola as a response to several canopy heights (25, 35, 45, and 55 cm) of harvests in two seasons of the year (rainy and dry). The experiment was established at the Federal University of Sergipe, in São Cristóvão - SE, Brazil, from 03/26/2015 to 03/28/2016, under a randomized-complete-block design with four replicates. Plots were irrigated, and upon reaching the pre-established canopy heights, they were cut to a 10 cm-residual height. Increasing canopy heights in the dry season led to lower tiller density, for basal and aerial tillers. However, irrespective of tiller type and season, this variable increased after the rest period. Light interception rose with canopy heights (P<0.05) in the dry period and it showed a quadratic response in the rainy season. Greater canopy heights led to a higher (P<0.05) daily leaf senescence rates and daily stem growth rates. Regardless of the season, the total accumulation and net herbage accumulation rates of basal tillers increased as canopy heights did. The greatest canopy height promoted the daily stem production, whereas the lowest height did not allow the grass to express its production potential. The defoliation-height range of 35 to 45 cm is the most recommended, as it favors the control of stem growth and leaf senescence.

Response of Brachiaria brizantha cv. Piatã pastures to nitrogen fertilization

With the objective to evaluate the effects of nitrogen levels (0, 40, 80, 120 and 160 kg of N ha-1) on green dry matter (GDM) yield and morphogenetic and structural characteristics and nitrogen nutrition index (NNI) of Brachiaria brizantha cv. Piatã, was installed an experiment under field conditions in Roraima´s savannas. Nitrogen fertilization increased significantly (P<0.05) GDM yields, number of tillers, number of leaves tiller-1, average leaf size, leaf area index, leaf senescence rate, leaf appearance and elongation rates. Maximum GDM yields, leaf elongation rates, leaf length and number of leaves tiller-1 were obtain with the application of 145.9; 118.2; 108.9 and 133.6 kg of N ha-1, respectively. Nitrogen nutrition index alone with 120 or 160 kg N application was higher than the grass N internal critical level. The NNI, efficiency of utilization and apparent N recovery were inversely proportional to the increased N levels.

Morphogenesis of Cynodon cultivars fertilized with nitrogen

To evaluate the biomass flow of two cultivars of Cynodon (Tifton 85 grass and vaquero grass) fertilized with increasing levels of nitrogen (N) (control – without nitrogen; 200; 400 and 600 mg dm-3) under greenhouse conditions, this study was carried out, in a completely randomized design, with factorial arrangement. Forages were examined during three regrowth cycles, with results presented as mean values of the cycles. In the analysis of the effect of nitrogen fertilization, the Tifton 85 grass showed an increasing response to nitrogen levels for the leaf elongation rate (LER). The vaquero grass had a quadractic response for the LER with increasing levels of N. As for the stem elongation rate, there was an increasing linear response in both grasses according to increasing levels of N. The leaf senescence rate (LSR) of the Tifton 85 grass has been enhanced by nitrogen fertilization. The vaquero grass revealed a quadractic response for this variable LSR with nitrogen fertilization, with a minimum value of 0.96 cm tiller-1 day-1 with nitrogen level of 42.5 mg dm-3. The phyllochron and the total number of leaves of both grasses have been influenced by nitrogen fertilization, with downward and upward linear responses, respectively, with increasing levels of nitrogen. For the final mean leaf length (MLL) of both forages, we verified an increasing response with increasing levels of nitrogen. Tifton 85 grass and vaquero grass presented similar LER in the absence of nitrogen, but higher values were observed for the fertilized Tifton 85 grass. The fertilization using nitrogen leads to positive responses of the biomass flow of Tifton 85 grass and vaquero grass under the conditions of the present study.

The morphogenesis of marandu palisadegrass at fixed or variable heights in different seasons of the year

Height variations in a sward over the year may be efficient for increasing plant growth, compared with maintenance of the sward at a constant height. Thus, this experiment was conducted from February 2013 to May 2014 to characterise the development of Urochloa brizantha syn. Brachiaria brizantha cv. Marandu (marandu palisadegrass), managed under three defoliation strategies: constant height (30 cm during the entire experimental period), increasing height (15 cm in the winter, 30 cm in the spring, and 45 cm in the summer), and decreasing height (45 cm in the winter, 30 cm in the spring, and 15 cm in the summer). The experimental design was completely randomised, in a split-plot arrangement, with four replicates. Phyllochron was higher in the winter, but leaf and stem elongation rates and the number of live leaves per tiller were lower compared with the spring and summer. In the summer, the swards under increasing height displayed a higher phyllochron than those under decreasing and constant height. When comparing seasons, the highest leaf senescence rate occurred in spring. In the winter, the sward with increasing height had shorter leaves and stems, in contrast to the summer. The sward under decreasing height showed a high stem elongation rate in the spring. Marandu palisadegrass has great flexibility in terms of defoliation management and a typical seasonal development pattern. Modifying the sward height results in a gradual change in the development of marandu palisadegrass and generates residual effects on the subsequent season.

GROWTH AND DEVELOPMENT OF MOMBASSA GRASS GROWN IN FULL SUN AND SHADE UNDER NITROGEN LEVELS

The objective of this work was to evaluate the effects promoted by full sun and natural shading (25%) enviroemnts , under the productive components of Panicum maximum cv. Mombasa grown in diferent levels of nitrogen (0, 25, 50, 100 kg ha-1 cycle-1 ). Urea was used as nitrogen source, applied on the surface. This study evaluated the following variables: number of total leaves (NTL), number of green leaves (NGL), number of dead leaves (NDL), leaf lifespan (LLS), sheath length (SL), stem elongation rate (SER), Phyllochron (PHYL), leaf appearance rate (LApR), leaf elongation rate (LElR), leaf senescence rate (LSR), average length of leaf blade (ALLB), leaf area index (LAI) and tiller population density (TPP). The shaded environment provided better conditions for sheath length and leaf elongation rate, however in full sun the tiller density was higher.

Produtividade de forragem e morfogênese de Brachiaria ruziziensis sob níveis de nitrogênio

Com o objetivo de avaliar os efeitos da adubação nitrogenada (0, 60, 120, 180 e 240 kg de N ha-1) sobre a produção de forragem, características morfogênicas e estruturais e índice de nutrição nitrogenada (INN) de Brachiaria ruziziensis foi conduzido um experimento em condições de campo nos cerrados de Roraima. A adubação nitrogenada afetou positiva e significativamente (P<0,05) a produção de matéria seca verde (MSV), número de perfilhos, número de folhas perfilho-1, tamanho médio de folhas, índice de área foliar e taxas de aparecimento, expansão e senescência das folhas. Os maiores rendimentos de MSV, taxa de expansão foliar, tamanho médio de folhas e número de folhas perfilho-1 foram obtidas com a aplicação de 220,6; 238,6; 191,5 e 225,5 kg de N ha-1, respectivamente. O nível crítico de N foi reduzido com o aumento da produtividade de forragem. O INN, para todos os níveis de N avaliados, foi insuficiente para suprir o nível crítico de N da gramínea. Os níveis críticos de N, a eficiência de utilização e sua recuperação aparente foram inversamente proporcionais às doses de N aplicadas.

Morfogênese, características estruturais e acúmulo de forragem do Megathyrsus maximus brs zuri submetido a adubação nitrogenada

A adubação nitrogenada possibilita aumentar a capacidade de suporte das pastagens, entretanto, o uso de elevadas doses pode causar efeitos negativos no crescimento de gramíneas forrageiras. A partir do pressuposto, objetivou-se avaliar a influência de doses crescentes de nitrogênio sob as características morfogênicas e estruturais, acúmulo de biomassa e eficiências de conversão e recuperação do nitrogênio em pastagem de Megathyrsus maximus cv. BRS Zuri. Foram testadas cinco doses de nitrogênio (0, 200, 400, 600 e 800 Kg de nitrogênio/ha) em delineamento experimental de blocos casualizados, com quatro repetições. Foi observado comportamento quadrático para as taxas de alongamento e aparecimento foliar, tempo de vida e o filocrono. Houve aumento no número de perfilhos e na produção de matéria seca quando as plantas foram submetidas à adubação, porém, tanto a eficiência de utilização quanto a recuperação aparente do nitrogênio reduziram linearmente com o aumento do nível de nitrogênio. O uso de fertilizante nitrogenado promoveu melhora nas características morfogênicas (P<0,05) exceto para taxa de alongamento de colmo e taxa de senescência foliar que se mantiveram estáveis. A Adubação com nitrogênio acelera as taxas de crescimento do Megathyrsus maximus cv. BRS Zuri. As respostas máximas nas variáveis morfogênicas, no número de folhas vivas e totais por perfilho são obtidas com doses próximas de 500 kg/ha, enquanto que doses variando de 600 a 647 kg/ha proporcionam maior tamanho de folha por perfilho, densidade populacional de perfilhos e produção de matéria seca. As eficiências de utilização e recuperação do nitrogênio reduzem com o aumento das doses de nitrogênio.

Canopy structure and morphogenesis of Italian ryegrass intercropped with red clover under cutting intervals determined by thermal sum

ABSTRACT: The canopy structure and morphogenesis of ryegrass (Lolium multiflorum Lam.) was investigated after it was over seeded with Tifton 85 (Cynodon spp.) and intercropped with red clover (Trifolium pratense L.). Time intervals between cuts were determined by different thermal sums (125, 250, 375, and 500 degree-days [DD]). Cuts were conducted at a height equivalent to 50% of the average canopy height. Morphogenic and structural data were collected from July to October of 2016 and 2017, from a completely randomized block experimental design. Canopy height, extended tiller height, pseudostem length, and forage mass were fitted to linear equations according to the thermal sums. Interaction of ryegrass with red clover was the highest (12.1%) for longer cut intervals (375 and 500 DD). The leaf appearance rate (0.0080 leaf/DD), phyllochron value (128.8 DD), and senescence rate (0.10 cm/DD) of ryegrass were comparable between the different intervals. The slowest elongation rate (0.06 cm/DD) with the shortest interval duration between cuts (171.6 DD) was observed in the 125 DD interval. According to the findings from this 2-year experiment, the use of a 250 DD cut interval was recommended between grazing events, taking into account the efficiency of forage use, ryegrass leaf, stem ratio, and interactions with red clover in the canopy under rotational stocking.

High-Throughput Phenotyping of Dynamic Canopy Traits Associated with Stay-Green in Grain Sorghum

Drought is a recurring phenomenon that puts crop yields at risk and threatens the livelihoods of many people around the globe. Stay-green is a drought adaption phenotype found in sorghum and other cereals. Plants expressing this phenotype show less drought-induced senescence and maintain functional green leaves for longer when water limitation occurs during grain fill, conferring benefits in both yield per se and harvestability. The physiological causes of the phenotype are postulated to be water saving through mechanisms such as reduced canopy size or access to extra water through mechanisms such as deeper roots. In sorghum breeding programs, stay-green has traditionally been assessed by comparing visual scores of leaf senescence either by identifying final leaf senescence or by estimating rate of leaf senescence. In this study, we compared measurements of canopy dynamics obtained from remote sensing on two sorghum breeding trials to stay-green values (breeding values) obtained from visual leaf senescence ratings in multienvironment breeding trials to determine which components of canopy development were most closely linked to the stay-green phenotype. Surprisingly, canopy size as estimated using preflowering canopy parameters was weakly correlated with stay-green values for leaf senescence while postflowering canopy parameters showed a much stronger association with leaf senescence. Our study suggests that factors other than canopy size have an important role in the expression of a stay-green phenotype in grain sorghum and further that the use of UAVs with multispectral sensors provides an excellent way of measuring canopy traits of hundreds of plots grown in large field trials.