Accumulation Of Growing Degree Days Research Articles

Climate change impact assessment of growing degree days and thermal growing period of cotton in north-west India

ABSTRACT Temperature is an indispensable necessity of plant growth, which explains the 95% variability in plant development. Accumulated temperature, i.e. growing degree day (GDD) is a useful agro-climatic indicator that translates raw climatic data into meaningful decisions. In this study, the GDD concept is used to analyze spatio-temporal variability of accumulated growing degree days (AGDD) and thermal growing period of cotton for the past and future climates in the three different zones (north-east, central and south-west) of Punjab. During the baseline period, higher AGDD were accumulated in the south-western (2,441 °C day), followed by central (2,276.8 °C day) and north-eastern (2,073.8 °C day) zones. During the end of mid-century, AGDD of the central zone was increased by 4–11%, 3–27% for north-eastern, and 3–7% for south-western zones in contrast to the baseline period. This increase in AGDD of cotton might decrease the thermal growing period by 6–14%, 8–25%, and 4–8% for central, north-east and south-western zones, clearly indicating the thermal stress over the cotton crop. This study provides quantitative information for crop breeders and cotton scientists to develop new genetically modified cultivars and improved agronomic practices to mitigate the adverse effect of climate change.

Climate change impact on Spodoptera frugiperda (Lepidoptera: Noctuidae) life cycle in Mozambique

Although different seasonal cues are important for fall armyworm (FAW, Spodoptera frugiperda J.E. Smith) survival, it is known that the life cycle of this insect is strongly dependent on air temperature, means that its development rate proceeds faster when the weather is warm. To develops the insect needs to accumulate an amount of thermal units, as known as Growing Degree-Days (GDD). However, with the climate change driven by global warming, the GDD pattern must be changed and therefore, the life cycle of this new bug in Mozambique may be different from that observed in its native region. In the present study it is estimated the possible changes of FAW life cycle by applying the GDD method over Mozambique, under two representative scenarios of climate changes, RCP4.5 and RCP8.5 for 2070–2099 relative to present climate (1971–2000). For this purpose, dynamical downscaling process through the regional model RegCM4, nested to global model HadGEM2 were used. The outputs of air temperature dataset from the simulations were used to compute the accumulated GDD and hence the FAW number of generations (NG) during the summer-season over the study domain. The findings indicate that there is a bipolar pattern of GDD accumulation, being negative over most of central and restricted areas in southern region, and positive in northern region, altitude-modified climate areas over central region, and over southernmost areas for both representative climate scenarios, relative to present climate. Meanwhile, there is an increase (decrease) in NG in the areas of higher (lower) increase in air temperature for both future scenarios relative to present climate.

Citizen science data reveal regional heterogeneity in phenological response to climate in the large milkweed bug, Oncopeltus fasciatus

AbstractRegional populations of geographically widespread species may respond to different environmental factors across the species' range, generating divergent effects of climate change on life‐history phenology. Using thousands of citizen science observations extracted from iNaturalist and associated with corresponding temperature, precipitation, elevation, and daylength information, we examined the drivers of adult mating and of nymphal phenology, development, and group size for populations of the large milkweed bug, Oncopeltus fasciatus, in different ecoregions. Research‐grade iNaturalist images were correctly identified 98.3% of the time and yielded more than 3000 observations of nymphal groups and 1000 observations of mating adults spanning 18 years. Mating phenology showed distinct regional patterns, ranging from year‐round mating in California to temporally restricted mating in the Great Lakes Northeastern Coast ecoregion. Relative temperature increases of 1°C for a given daylength expanded the mating season by more than a week in western ecoregions. While increases in relative temperature delayed mating phenology in all ecoregions, greater winter precipitation advanced mating in the California ecoregion. In the eastern ecoregions, nymphal phenology was delayed by increases in summer rainfall but was advanced by relative temperature increases, whereas in western regions, relative temperature increases delayed nymphal phenology. Furthermore, accumulated growing degree days (AGDD) was a poor predictor of developmental progression, as we found a positive but weak correlation between AGDD and age structure only for the Appalachian Southeast North America and the Great Lakes Northern Coast ecoregions. These complex phenological responses of O. fasciatus are just one example of how populations may be differentially susceptible to a diversity of climatic effects; using data across a species' whole distribution is critical for exposing regional variations, especially for species with large, continental‐scale ranges. This study demonstrates the potential of photodocumented biodiversity data to aid in the monitoring of life history, host plant–insect interactions, and climate responsiveness.

Effects of Sowing Date and N Management on Growth And Yield of Green Gram (Vigna Radiata L.) Of Assam, India

The field experiment was conducted at Tinsukia in Assam of India during kharif seasons of 2016-17 and 2017-18 to investigate the effect of sowing date and nitrogen (N) management practices on the growth and yield of green gram (Vigna radiata L.). Results indicate that the sowing date, S2 (1st September) showed superiority in respect of the growth and yield of the crop, compared to other sowing dates for both years. Amongst the N management treatments, a significantly higher value of the growth parameters, yield attributes, and yields was observed in the treatment receiving 50% N as inorganic fertilizer along with vermi-compost @ 1.0 t/ha. Among the sowing dates, late sown crop (1st October) accumulated the lower heat units (GDD) and higher thermal time (HTU) at 50% flowering and maturity compared to the early sown crop (15th August or 1st September) causing a reduction in seed yield of green gram. The relationship between accumulated growing degree days (AGDD) and yield was positive for all the phenophases with a statistically significant result during PP2 (flowering to maturity). On the contrary, the correlation between AHTU and yield was negative for all the phenophases. The regression models for different phenophases of the crop indicate 86 - 98% of yield variation which can be explained by accumulated agrometeorological variables. Bangladesh J. Bot. 52(2): 323-329, 2023 (June)

Evaluating the seasonal accumulation of Heat units as an agroclimatic indicator on Baby corn (Zea mays L.) under different sowing windows

Temperature determines the plant's growth and development, which decides the onset of different phenophasic stages of the Baby corn. This study aimed to evaluate the phenological behaviour and yield of Baby corn (Zea mays L.) influenced by sowing windows and heat units with the field investigations carried out during winter (January – April) and kharif (June – September) 2022 at Eastern Block Farm of Tamil Nadu Agricultural University, Coimbatore. Growing Degree Days (GDD), Photo Thermal Units (PTU), Helio Thermal Units (HTU), Relative Temperature Disparity (RTD), Heat Unit Efficiency (HUE) and seasonal efficiency were calculated at different phenological stages. The results revealed that early attainment of phenophases was noticed during winter (62.5 days - January 21st to 27th April) than kharif (77.1 days – 15th June to 4th October). Among seasons, higher accumulation of GDD (1553) and PTU (19099) was observed during kharif 2022, whereas maximum accumulation of HTU (9923) and RTD (2146) was observed in winter 2022. Seasonal efficiency was higher during kharif (118) than during the winter season (81). The sowing windows significantly influenced the higher accumulation of heat units and yield attributes. Hence, higher yield (11922.7 kg ha-1) and HUE (7.3) were obtained during kharif than in winter 2022 (yield – 7849 kg ha-1 and HUE – 5.8). Weather parameters showed a negative correlation except RH-I, WS, SR and HUE during winter 2022 (R2=0.802) and RH-II, WS, RF, Daylength, HUE during kharif 2022, which had a positive correlation (R2=0.795). Baby corn is highly sensitive to increasing temperature. Hence, the study expresses the effect of varying ambient temperature on the duration between the phenological stages and yield.

Effects of seeding date on grain and biomass yield of intermediate wheatgrass

AbstractIntermediate wheatgrass (Thinopyrum intermedium) (IWG) is a perennial grass being domesticated for grain production with potential to provide economic return and ecosystem services across a broad geographic range in North America, yet optimum seeding dates for grain and biomass yield are unknown. Our objective was to determine the effect of late‐summer, fall, and spring seeding dates on grain and biomass yield of a grain‐type IWG population. Trials were conducted at St. Paul and Roseau, MN, Kalispell, MT, and Salina, KS. Seeding dates ranged from August to June of the following year. Grain and biomass yields were highest when seeded at the earliest late‐summer date for all environments except for Kansas, where a September 29 seeding date produced the greatest grain and biomass yields. Little to no grain was produced from spring seedings in the first production year, substantiating that photoperiod and vernalization requirements are needed for seed head induction. Grain and biomass yields were positively correlated to cumulative growing degree days (GDD) from seeding date to winter dormancy. A quadratic response was observed at Salina, KS, where seed yields maximized when GDD accumulation reached 912. Accumulation of vernalization units throughout fall, winter, and spring after seeding was also positively correlated with grain yield. The minimum vernalization units for grain production varied from 50 to 87 across sites. Results highlight important associations between thermal units and IWG grain yield when seeded in late summer; however, other variables affecting IWG seed head induction (e.g., photoperiod, snow cover) require further study.

Maize Leaf Appearance Rates: A Synthesis From the United States Corn Belt.

The relationship between collared leaf number and growing degree days (GDD) is crucial for predicting maize phenology. Biophysical crop models convert GDD accumulation to leaf numbers by using a constant parameter termed phyllochron (°C-day leaf−1) or leaf appearance rate (LAR; leaf oC-day−1). However, such important parameter values are rarely estimated for modern maize hybrids. To fill this gap, we sourced and analyzed experimental datasets from the United States Corn Belt with the objective to (i) determine phyllochron values for two types of models: linear (1-parameter) and bilinear (3-parameters; phase I and II phyllochron, and transition point) and (ii) explore whether environmental factors such as photoperiod and radiation, and physiological variables such as plant growth rate can explain variability in phyllochron and improve predictability of maize phenology. The datasets included different locations (latitudes between 48° N and 41° N), years (2009–2019), hybrids, and management settings. Results indicated that the bilinear model represented the leaf number vs. GDD relationship more accurately than the linear model (R2 = 0.99 vs. 0.95, n = 4,694). Across datasets, first phase phyllochron, transition leaf number, and second phase phyllochron averaged 57.9 ± 7.5°C-day, 9.8 ± 1.2 leaves, and 30.9 ± 5.7°C-day, respectively. Correlation analysis revealed that radiation from the V3 to the V9 developmental stages had a positive relationship with phyllochron (r = 0.69), while photoperiod was positively related to days to flowering or total leaf number (r = 0.89). Additionally, a positive nonlinear relationship between maize LAR and plant growth rate was found. Present findings provide important parameter values for calibration and optimization of maize crop models in the United States Corn Belt, as well as new insights to enhance mechanisms in crop models.

Impact of climate change on Helicoverpa armigera voltinism in different Agro-Climatic Zones of India

The Gram pod borer, Helicoverpa armigera (Noctuidae: Lepidoptera) is a cosmopolitan agricultural insect pest that prefers to feed on plant’s protein biomolecules. Out of different density-independent factors, surface air temperature majorly affects the incidence and damage of the H. armigera on the crops. Early prediction of H. armigera generations (voltinism) in future climate years perhaps prevent additional damage in various crops and improve the farmers preparedness. In this study, future climate data that is temperature obtained for eleven Agro-Climatic Zones (ACZs) of India under four Representative Concentration Pathways (RCPs) scenarios in different climate years (2010, 2030, 2050, 2070, 2090) using weather file generator MarkSim web application. The accumulation of Growing Degree-days (GDD) by H. armigera at eleven ACZs in each climate year under different RCP scenarios was estimated using temperature data. The mean surface air temperature is predicted to 0.51 °C, 1.03 °C, 1.57 °C and 2.1 °C in climate years 2030, 2050, 2070 and 2090, which escalated annual H. armigera Gen. to 12.88, 13.33, 13.79 and 14.23, respectively over the baseline climate year 2010. Likewise, under RCP 2.6, RCP 4.5, RCP 6.0 and RCP 8.5 scenarios H. armigera Gen. is predicted to 12.86, 13.29, 13.23 and 13.97 per annum with mean surface air temperatures 27.4 °C, 27.92 °C, 27.86 °C and 28.72 °C, respectively. The Eastern Coastal Plains and Hills Zone (ACZ 11) across climate years and RCPs has experienced a considerable increase in mean surface air temperature minimum (25.22 °C) and maximum (34.61 °C), which likely favor the GDD accumulation (6319.91) and the Genrations (14.97) in H. armigera. Therefore, the Eastern Coastal Plains and Hills Zone of India could be identified as H. armigera risk zone in near future. The present predictions in various ACZs of India may be significant in planning H. armigera management.

Smooth Brome (Bromus inermis) Phenological Variability under Controlled Greenhouse Conditions

Smooth brome (Bromus inermis Leyss.) has been planted widely for use as a forage grass and erosion control. Its competitive nature and rapid growth have allowed smooth brome to become an invasive species throughout the Northern Great Plains. Prescribed burning is commonly employed to control smooth brome in the region's remaining native grasslands. Burning at the initiation of elongation, when smooth brome populations are most vulnerable, destroys the carbohydrate reserves that allow the plants to recover. Identifying the five-leaf stage in phenological development has been recommended to signal the start of elongation in order to time prescribed burning to be most detrimental to smooth brome. Unfortunately, in a recent field survey of 27 sites in the Northern Great Plains, less than 1% of smooth brome tillers were observed to achieve the five-leaf stage prior to elongation, calling the tying of prescribed burning to identification of the five-leaf developmental stage into question. Accumulated growing degree days (AGDD) provides a more reliable indicator of smooth brome's vulnerability to control efforts through prescribed burning than reliance on the observance of the five-leaf stage. This study was designed to monitor phenological development of smooth brome in a controlled greenhouse environment to determine whether the correlation between AGDD and phenological development was exhibited in greenhouse populations across a gradient of nitrogen conditions encountered throughout the Northern Great Plains. It was determined that, while nitrogen treatment did affect the biomass and number of tillers produced, it did not affect the phenological progression of development. The greenhouse population reached 50% elongation at an average of 2287 AGDD.

Using field hyperspectral data to predict cotton yield reduction after hail damage

Rapid and accurate prediction of yield reduction after a hailstorm is essential for insurance companies for developing compensation standards and farmers to take appropriate post-damage management measures. Here, six (I-VI) hail damage simulation treatments with four damage levels (0%, 30%, 60%, and 90%) each time (for modeling) and natural hailstorm tracking experiment (for model verification) were conducted between 2018 and 2019 to explore the feasibility of yield prediction at field scale in different damage stages according to the reflectance of spectral characteristic bands (RSCB). The performance of models was analyzed with three regression methods (partial least squares regression (PLSR), support vector regression, and backpropagation neural network) based on RSCB and vegetation indices. The model developed at different damage stages showed higher accuracy in predicting yield reduction than a general model developed over the whole vegetation period. The yield prediction model based on RSCB showed better performance compared to that based on the vegetation indices, and overall, PLSR performed the best. A general model was developed for pre-bloom hail damage, whereas three models were developed for damage stage IV (accumulated growing degree days (AGDD) ranging between 975.9 °C·d and 1291.6 °C·d), V (AGDD ranging between 1291.6 °C·d and 1550.0 °C·d) and VI (AGDD greater than 1550.0 °C·d), respectively for post-bloom hail damage. Employing RSCB at different damage stages is a viable approach to predicting cotton yield reduction ascribed to hail damage.

Decreasing Defoliation Frequency Enhances Bromus valdivianus Phil. Growth under Low Soil Water Levels and Interspecific Competition

Bromus valdivianus Phil. (Bv) is a water stress-tolerant species, but its competitiveness in a diverse pasture may depend on defoliation management and soil moisture levels. This glasshouse study examined the effect of three defoliation frequencies, based on accumulated growing degree days (AGDD) (250, 500, and 1000 AGDD), and two soil water levels (80–85% of field capacity (FC) and 20–25% FC) on Bv growth as monoculture and as a mixture with Lolium perenne L. (Lp). The treatments were applied in a completely randomised block design with four blocks. The above-ground biomass of Bv was lower in the mixture than in the monoculture (p ≤ 0.001). The Bv plants in the mixture defoliated more infrequently (1000 AGDD) showed an increase in root biomass under 20–25% FC compared to 80–85% FC, with no differences measured between soil water levels in the monoculture. Total root length was highest in the mixture with the combination of infrequent defoliation and 20–25% FC. Conversely, frequent defoliation treatments resulted in reduced water-soluble carbohydrate reserves in the tiller bases of plants (p ≤ 0.001), as they allocated assimilates mainly to foliage growth. These results provide evidence that B. valdivianus can increase its competitiveness relative to Lp through the enhancement of the root growth and the energy reserve in the tiller base under drought conditions and infrequent defoliation in a mixture.

Phenological Changes of Mongolian Oak Depending on the Micro-Climate Changes Due to Urbanization

Urbanization and the resulting increase in development areas and populations cause micro-climate changes such as the urban heat island (UHI) effect. This micro-climate change can affect vegetation phenology. It can advance leaf unfolding and flowering and delay the timing of fallen leaves. This study was carried out to clarify the impact of urbanization on the leaf unfolding of Mongolian oak. The survey sites for this study were established in the urban center (Mts. Nam, Mido, and Umyeon in Seoul), suburbs (Mts. Cheonggye and Buram in Seoul), a rural area (Gwangneung, Mt. Sori in Gyeonggi-do), and a natural area (Mt. Jeombong in Gangwon-do). Green-up dates derived from the analyses of digital camera images and MODIS satellite images were the earliest in the urban center and delayed through the suburbs and rural area to the natural area. The difference in the observed green-up date compared to the expected one, which was determined by regarding the Mt. Jeombong site located in the natural area as the reference site, was the biggest in the urban center and decreased through the suburbs and rural area to the natural area. Green-up dates in the rural area, suburbs, and urban center were earlier by 11.0, 14.5, and 16.3 days than the expected ones. If these results are transformed into the air temperature based on previous research results, it could be deduced that the air temperature in the urban center, suburbs, and rural area rose by 3.8 to 4.6 °C, 3.3 to 4.1 °C, and 2.5 to 3.1 °C, respectively. Green-up dates derived based on the accumulated growing degree days (AGDD) showed the same trend as those derived from the image interpretation. Green-up dates derived from the change in sap flow as a physiological response of the plant showed a difference within one day from the green-up dates derived from digital camera and MODIS satellite image analyses. The change trajectory of the curvature K value derived from the sap flow also showed a very similar trend to that of the curvature K value derived from the vegetation phenology. From these results, we confirm the availability of AGDD and sap flow as tools predicting changes in ecosystems due to climate change including phenology. Meanwhile, the green-up dates in survey sites were advanced in proportion to the land use intensity of each survey site. Green-up dates derived based on AGDD were also negatively correlated with the land use intensity of the survey site. This result implies that differences in green-up dates among the survey sites and between the expected and observed green-up dates in the urban center, suburbs, and rural area were due to the increased temperature due to land use in the survey sites. Based on these results, we propose conservation and restoration of nature as measures to reduce the impact of climate change.

Base temperatures affect accuracy of growing degree day model to predict emergence of bermudagrasses

AbstractThe germination of bermudagrass [Cynodon dactylon (L.) Pers.] under different temperature regimes has been extensively investigated, but a discrepancy remains between laboratory studies and field results. Thermal requirements calculated in growing degree days (GDD) have been found to differ within the same species depending on the location of the study. The accumulation of GDD may vary under different thermal conditions from seeding to seedling emergence and could depend on TBASE used in the calculation. The most widely used TBASE for bermudagrass is 5 °C. However, laboratory studies have suggested that a base temperature of 15 °C would more accurately predict seedling emergence. In this field study, we investigated the effect of using TBASE 5 °C vs. TBASE 15 °C on the estimation of GDD required by bermudagrass to emerge. Ten cultivars were seeded in northeastern Italy on three dates between 10 March and the end of April in 2013 and 2014. Number of emerged seedlings was counted weekly and soil temperature at 1‐cm depth was recorded significant differences in seedling emergence between bermudagrass genotypes were found. Results demonstrated that the algorithm used to calculate GDD is strongly influenced by the TBASE used and to include a TBASE of 15 °C explains germination and emergence more accurately than a TBASE of 5 °C.

The Use of Thermal Time to Describe and Predict the Growth and Nutritive Value of Lolium perenne L. and Bromus valdivianus Phil

The thermal time, expressed in accumulated growing degree-days (AGDD), was used as a predictor to describe and simulate the independent growth of two pasture crops, Lolium perenne L. and Bromus valdivianus Phil. Two sinusoidal models (four-parameter Logistic and Gompertz) were applied to the growth variables (total leaf blade length per tiller—LBL, and accumulated herbage mass—AHM). The nutritive value of pastures was predicted and modeled using regression equations (linear and quadratic), depending on each nutrient. Data for modeling were collected from a two-year study, in which LBL, AHM, and nutritive value variables for L. perenne and B. valdivianus pastures were measured at three-day intervals. Defoliation was determined according to the AGDD, such that the swards were defoliated at 90, 180, 270, 360, and 450 AGDD. The Logistic and Gompertz models presented similar values for the growth rate (GR) parameters, superior asymptote (Asup), inferior asymptote (Ainf), and point of maximum growth (Pmax). In both species, the maximum growth was 260 AGDD. The GR was similar for both species in different seasons of the year, but the maximum AHM varied, with B. valdivianus presenting a higher value (+1500 kg DM ha−1) than L. perenne during the spring. The regressions accurately described the nutritive value, demonstrating a positive linear relationship between the AGDD and concentrations of neutral and acid detergent fiber (NDF, ADF), an inverse linear relationship with crude protein (CP), and a quadratic relationship with metabolizable energy (ME) and water-soluble carbohydrate (WSC) concentration.

The Effect of Polyethylene Film and Polypropylene Non-Woven Fabric Cover on Cobs Parameters and Nutritional Value of Two Sweet Maize (Zea mays L. var. saccharata Bailey) Hybrids

In 2012–2014, at the Research and Didactic Station of the Department of Horticulture at Wroclaw University of Environmental and Life Sciences (51°19′06″ N, 17°03′49″ E), field studies were conducted to evaluate the responses of two sweet maize hybrids to sowing dates (early and optimum) and five methods of maize plant coverings—polyethylene film: perforated (PE), red (PER), green (PEG), polypropylene non-woven fabric (PP), and control (C), with non-irrigation systems. Total yield and morphological characteristics of cobs were compared. In 2012 soluble sugars and carotenoids content were measured. The use of maize cover at the beginning of growth (PE and PER) significantly influenced the number of rows, while PE and PEG increased the number of grains per cob. Covering maize sown at a later date, with polyethylene film and non-woven fabric, ensured better production effects than using such covers after earlier sowing. Signet F1 hybrid was charact0erized by significantly higher sugar content and Rustler F1 by higher lutein and zeaxanthin levels. The application of the optimum sowing date resulted in a significantly higher yield of cobs, by 11.3%, than after early sowing. The yield increase as a result of the applied covers was higher after sowing at a later date. The content of dry matter in grains was positively correlated with the content of sucrose, glucose, and fructose. The change in carotenoids content also depended on the accumulation of dry matter in the kernels. The study confirmed the correlation of sweet maize accumulated growing degree days (AGDD), and revealed dependence of grain quality on dry matter content in the grain.

Examining Relationships between Heat Requirement of Remotely Sensed Green-Up Date and Meteorological Indicators in the Hulun Buir Grassland

The accumulation of heat and moderate precipitation are the primary factors that are used by grasslands to trigger a green-up date. The accumulated growing degree-days (AGDD) requirement over the preseason is an important indicator of the response of grassland spring phenology to climate change. This study adopted the Normalized Difference Phenology Index (NDPI), which derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), to extract annual green-up dates in the Hulun Buir grassland in China between 2001–2015. Our analysis indicated that the range (standard deviation) and trend for the green-up date were DOY (day of year) 104 to DOY 144 (10.6 days) and −2.0 days per decade. Nine point two percent of the study area had significant (p < 0.05) changes in AGDD requirements. The partial correlations between the AGDD requirements and chilling days (67.04%, pixels proportion) were negative and significant (p < 0.05). The partial correlations between the AGDD requirement and precipitation (28.87%) were positive and significant (p < 0.05). Finally, the partial correlation between the AGDD requirement and insolation (97.65%) were positive and significant (p < 0.05). The results of this study could reveal the response of vegetation to climate warming and contribute to improving the phenological mechanism model of different grassland types in future research.

The Growth Response of Pasture Brome (Bromus valdivianus Phil.) to Defoliation Frequency under Two Soil-Water Restriction Levels

Pasture brome (Bromus valdivianus Phil.) has the potential to increase current levels of herbage production and pasture persistence in New Zealand dryland, well-drained soils. However, there is little literature on the effect of defoliation management on growth of this grass under contrasting soil-water restriction levels. The growth physiology and performance of pasture brome were evaluated in pots in a glasshouse. Defoliation frequency (DF) treatments were applied based on three different accumulated growing degree-days (AGDD): 250, 500 and 1000 AGDD (high, medium, and low DF). At end of the first growing cycle (1000 AGDD), water availability was restricted to 20–25% of field capacity (FC) in half of the pots, while the other pots were maintained between 80–85% FC. Total accumulated herbage mass was positively related with the low DF and well-watered conditions (p < 0.05). At the final harvest, plants subjected to low DF had greater root mass than high and medium DF (p < 0.05). At each harvest, the leaf regrowth stage (LS) for low DF was 3.5, while for high and medium DF, the LS was 1.5 and 2.0; respectively. Tiller water-soluble carbohydrates were highest at the low DF and under 20–25% FC. Regardless of soil-water conditions, defoliation at 3.5 LS supports production, enhancing survival during a drought.

BASE GROWTH TEMPERATURE AND PHYLLOCHRON FOR KIKUYU GRASS (Cenchrus clandestinus; Poaceae)

In order to estimate the base temperature (Bt) of growth through the appearance of leaves and calculate the phyllochron for kikuyu grass, three plots were established on three farms in the Provincia of Ubaté (Cundinamarca, Colombia) located at different altitudes (2560, 2640, 3143 m. a. s. l.). Measurements were made in four cycles in a period of eight months. The Bt was estimated by the least coefficient of variation method using a second order regression model and the model obtained was validated by the cross-validation method. The Bt values for the first, second, third and fourth leaf were 4.02, 3.68, 3.93, and 3.62 ° C, respectively. For the appearance of the first leaf, the kikuyu required more thermal time (TT) (97.5 accumulated growing degree days (AGDD)) than for the second (74.2 AGDD), third (73.8 AGDD) and fourth leaf (76.0 AGDD) (p<0.05). There were no differences in TT among farms (p> 0.05). There was a tendency to a greater number of days required to reach each leaf stage in the farm located at higher altitude and with lower mean temperature. The validation showed an adequate adjustment (r2 = 0.94) and a substantial concordance (CCC = 0.97) between the observed values and the predicted values for the estimated TT with the Bt value obtained for each leaf stage. The results of Bt for kikuyu grass obtained, will allow to make more precise predictions about the phyllochron and generate growth models close to reality.

Estimating of Wheat Water Requirement Using Remote Sensing at El-Menia Governorate Desert Fringe-Egypt

In hyper-arid and arid zones, the crop water requirement management is considered the vital component for sustaining the crop production particularly under drought condition. As such, further investigation is needed to determine optimal water requirements to avoid wasting water in zones already facing water shortages.Further, estimating reference Evapotranspiration(ET0)and Crop Coefficient(Kc)is fundamental requirement of agricultural water management. Thus, the aim of this study is determining an actual crop coefficient(Kc)for winter wheat using remote sensing tools [Normalized Difference Vegetation Index(NDVI)and Soil-Adjusted Vegetation Index(SAVI)] - obtained from Sentinel-2A satellite images, as well as the influence of Accumulated Growing Degree Days(AGDD)for wheat on NDVI and SAVI. Consequently,data were obtained during winter wheat season(November 2019 - April 2020)on El-Menia Governorate Desert Fringe.Data analysis indicated that the total amount of AGDD required to obtain was 1408.37 C°/season for wheat to develop in its life cycle. Moreover, SAVI value recorded the highest value(0.77)in January when the NDVI obtained 0.53 at the same period. Values of NDVI increased dynamically and acquired was 0.53 which was the highest value after wheat obtained 863.79 C°/days(heat unit)in January. Furthermore, there is a linear relation between NDVI and actual Kc which reflect a strong correlation between them for all of the growing stage. Finally, the actual water requirement was 2532.68 m3/fed/season, which is a less than value (2791 m3/fed/season)calculated FAO method. Actual crop coefficients[Kc (actual)]estimated from remote sensing(RS)using NDVI, SAVI with the AGDD equation is beneficial for irrigation scheduling, evaluation of irrigation, water use efficiency and project performance and agricultural water budgets.

Water-Soluble Carbohydrate Recovery in Pastures of Perennial Ryegrass (Lolium perenne L.) and Pasture Brome (Bromus valdivianus Phil.) Under Two Defoliation Frequencies Determined by Thermal Time

The objectives of the experiment were to (i) examine the dynamics of WSC use and the recovery of leaf sheaths and blades of Bromus valdivianus Phil. and Lolium perenne L. subjected to two defoliation frequencies (DFs) determined by thermal time (TT); (ii) evaluate how DF influenced regrowth and accumulated herbage mass (AHM) during fall. Defoliation was carried out at frequencies of 135 and 270 accumulated growing degree days (AGDDs) for both species. Twelve plots were arranged in a three-block design. All plots had a conditioning period to establish the assigned DF prior to sampling. From the start of the experiment, “cores” were collected from each plot every three days until the DF was reached. Every core was separated into leaf and sheath material before measuring the WSC concentration. Lolium perenne had concentrated more WSCs than B. valdivianus. Both species adapted their WSC recovery according to the DF. The recovery of WSC was faster under a DF of 135 AGDDs than that of 270 AGDDs. Leaf sheaths contained more WSCs than leaf blades and were identified as WSC storage organs. This period can be used as the optimal defoliation interval in B. valdivianus and L. perenne grazing systems.