Canopy Ground Cover Research Articles

Architectural Responses of Cashew to Intercropping and Nutritional Amendments in Nigerian Guinea Savanna Agro Ecology

Field experiment was conducted at Cocoa Research Institute of Nigeria sub-station Ochaja, to evaluate the impact of manure and intercrops on cashew tree growth, canopy development and yield. Treatments consisted of Bambara and Sesame intercrops and manuring using Cocoa pod husk (CPH) and NPK fertilizer applied at the rate of 0, 1,713kg and 400kg/ha respectively. The experiment was laid out in a split-split plot design with three replications and monitored within the two years of study. Data collected includes: Plant height, Stem girth and canopy North-South/East-West direction. These was used to calculate: crown diameter, canopy spread, canopy volume, canopy ground cover and canopy ground cover percentage. The results showed that the growth characters of Cashew were positively influenced by alley crops of Sesame and Bambara nut and manuring. Manuring with CPH exerted differences in the responses of cashew to alley crops, in particular, canopy development. Intercropping with a combination of bambara-sesame and the application of NPK fertilizer proved to have the highest Cashew growth development but showed no significant differences on the yield and yield attribute. The GGE biplot results identified the best intercrop system for each of the three-fertilizer type treatment. Within the two years of the experiment, Cashew development was not hampered by the introduction of the different intercropping systems.

A one – source model to estimate sensible heat flux in agricultural landscapes

A one-source model type that combines surface renewal (SR) and similarity theories to estimate the sensible heat flux (H) involving the land surface temperature (LST) and low-frequency measurements, HSR-LST, was tested over agricultural surfaces with fractions of ground canopy cover that ranged from 39% up to 97% and canopy heights ranging from 0.2 to 1.8 m. The performance was tested under clear sky conditions and for stable and unstable cases during the day. The sensible heat flux was estimated using in situ LST measurements over a homogenous canopy (wheat) under stable conditions. Unstable conditions were met for two growing crops (rain-fed soybean and corn) where HSR-LST was tested using LST retrieved from Landsat 5 to 7. The sensible heat flux taken as a reference for soybean and corn was determined using the eddy covariance (EC) method and for wheat it was determined using the residual method (the evapotranspiration was measured using a large weighing lysimeter). For wheat HSR-LST performed slightly better than a calibrated one-source model. For soybean and corn, it performed similarly to one-source and two-source model types. The one-source models included two types, one requiring calibration and the other one self-calibrating, using ‘hot’ and ‘cold’ spots in the surroundings. Further testing for sparse canopies is suggested prior to the development of a two-source model in the framework of SR-LST because HSR-LST performed similarly to the other models. For corn, HSR-LST had the closest performance to HEC and for soybean the two-source model (the best) was slightly closer to HEC than HSR-LST. The root mean square differences (RMSD) comparing HSR-LST against the reference were in the range 26 (corn) – 46 (wheat) Wm−2. Therefore, HSR-LST is an alternative to consider for estimating H because it was competitive and simpler to apply than other thermal remote sensing-based methods.

Development and Validation of Methodology for Estimating Potato Canopy Structure for Field Crop Phenotyping and Improved Breeding.

Traditional phenotyping techniques have long been a bottleneck in breeding programs and genotype- phenotype association studies in potato, as these methods are labor-intensive and time consuming. In addition, depending on the trait measured and metric adopted, they suffer from varying degrees of user bias and inaccuracy, and hence these challenges have effectively prevented the execution of large-scale population-based field studies. This is true not only for commercial traits (e.g., yield, tuber size, and shape), but also for traits strongly associated with plant performance (e.g., canopy development, canopy architecture, and growth rates). This study demonstrates how the use of point cloud data obtained from low-cost UAV imaging can be used to create 3D surface models of the plant canopy, from which detailed and accurate data on plant height and its distribution, canopy ground cover and canopy volume can be obtained over the growing season. Comparison of the canopy datasets at different temporal points enabled the identification of distinct patterns of canopy development, including different patterns of growth, plant lodging, maturity and senescence. Three varieties are presented as exemplars. Variety Nadine presented the growth pattern of an early maturing variety, showing rapid initial growth followed by rapid onset of senescence and plant death. Varieties Bonnie and Bounty presented the pattern of intermediate to late maturing varieties, with Bonnie also showing early canopy lodging. The methodological approach used in this study may alleviate one of the current bottlenecks in the study of plant development, paving the way for an expansion in the scale of future genotype-phenotype association studies.

Impact of Varying Light and Dew on Ground Cover Estimates from Active NDVI, RGB, and LiDAR.

Canopy ground cover (GC) is an important agronomic measure for evaluating crop establishment and early growth. This study evaluates the reliability of GC estimates, in the presence of varying light and dew on leaves, from three different ground-based sensors: (1) normalized difference vegetation index (NDVI) from the commercially available GreenSeeker®; (2) RGB images from a digital camera, where GC was determined as the portion of pixels from each image meeting a greenness criterion (i.e., (Green − Red)/(Green + Red) > 0); and (3) LiDAR using two separate approaches: (a) GC from LiDAR red reflectance (whereby red reflectance less than five was classified as vegetation) and (b) GC from LiDAR height (whereby height greater than 10 cm was classified as vegetation). Hourly measurements were made early in the season at two different growth stages (tillering and stem elongation), among wheat genotypes highly diverse for canopy characteristics. The active NDVI showed the least variation through time and was particularly stable, regardless of the available light or the presence of dew. In addition, between-sample-time Pearson correlations for NDVI were consistently high and significant (P < 0.0001), ranging from 0.89 to 0.98. In comparison, GC from LiDAR and RGB showed greater variation across sampling times, and LiDAR red reflectance was strongly influenced by the presence of dew. Excluding times when the light was exceedingly low, correlations between GC from RGB and NDVI were consistently high (ranging from 0.79 to 0.92). The high reliability of the active NDVI sensor potentially affords a high degree of flexibility for users by enabling sampling across a broad range of acceptable light conditions.

Cashew Growth and Canopy Dynamics as Influenced by Manuring in a Guinea Savanna Agro-Ecology of Nigeria

A two-year experiment was conducted to study the response of manuring on growth and canopy development on three-year-old Cashew trees. The experiment was laid in a randomized complete block design, with three replications. Soil characteristics including the chemical and physical properties were analyzed before and after the experiments. Fecti-plus organic pelletized fertilizer was applied at different rates of 0,750.6 and 1,501.2 kg/ha-1 respectively around the circumference of the tree. Before the application, the fertilizer sample was also analyzed. Data collected were plant height, stem girth, canopy dynamics which includes: Canopy diameter, canopy radius, canopy spread (North-South and East-West directions), canopy volume, canopy ground cover and percentage ground cover. The results from the pre soil sample show a relatively low status but were significantly enhanced after the application of the pelletized organic fertilizer (Ferti-plus). The soil nutrient composition of Oc, Om, N, K, Na, Ca and Mg+ was significantly highest in the plots having 1,501.2 kg/ha-1 treatments. Generally, there was a significant increase in the soil nutrient with the addition of pelletized fertilizer in respective of the rate of application. Also the results on the canopy dynamic in terms of canopy volume, spread and diameter revealed better development with the use of 1501.2 kg/ha-1 pelletized fertilizer and significantly different to 750.6 kg/ha-1 and those in the no-manure (control)plots. Meanwhile, the use of pelletized organic fertilizer gave superior growth and canopy development. It also influenced the growth of the Cashew plants, as well as the physical and chemical properties of the soil status.

Sorghum best practice management recommendations based on AquaCrop modeling scenario analysis in various agro-ecologies of KwaZulu Natal, South Africa

Nationally recommended sorghum planting dates in South Africa are inaccurate since they are similar for all sorghum growing regions, irrespective of climatic and soil variations within agro-ecological regions The objective was to apply a well–calibrated and tested AquaCrop model to formulate optimal planting dates and best practice management recommendations for rainfed sorghum production in three different agro–ecologies of KwaZulu–Natal, South Africa (Ukulinga, Deepdale, and Richards Bay). The FAO AquaCrop model was used to generate 10 planting dates for the different agro–ecologies. Crop files for two sorghum genotypes Ujiba (landrace) and PAN8816 (hybrid) were used for model simulations, where 10 year historical climate data was considered. Seasonal rainfall, amount of soil evaporation, crop transpired water, and ground canopy cover were identified as key parameters influencing sorghum biomass, yield and water productivity. The following optimal dates were identified at Ukulinga (7 September - 24 November), Richards Bay (23 December - 3 January), and Deepdale (21 December - 3 January). These were recommended to update generic national recommendations for sorghum for agro-ecologies represented by the respective sites. High soil evaporation relative to transpiration in all agro-ecologies indicated that the low hanging fruit in improving sorghum yields was strategies use of strategies that reduce soil evaporation and increase soil water retention. Further research can look at calibrating and validating AquaCrop for best practice management recommendations suggested in this study to predict with accuracy the impact of such strategies on yield and water productivity of sorghum in various agro-ecologies.

Optimizing Nitrogen Fertigation Rates for Young Southern Highbush Blueberry

The commercial blueberry industry in Florida has expanded significantly in both acreage and value in the past several years. The southern highbush blueberry (SHB, Vaccinium corymbosum L. interspecific hybrid) is the major blueberry type grown in Florida. The nitrogen (N) demand of young SHB differs from the northern highbush blueberry (NHB, V. corymbosum L.) and from mature blueberry plants. The objective of this study was to optimize fertigated N rates for the growth and yield of young SHB plants. One-year-old ‘Emerald’ and ‘Farthing’ plants were fertilized with 32N-0P-0K through drip irrigation at annual rates of 0, 42, 84, 168, and 336 kg N ha−1. Soil nitrate levels at multiple depths were measured along with leaf nutrient concentration, percent canopy ground cover, fruit yield and fruit quality. The results indicated that N rates had no significant effect on leaf nutrient concentrations. Greater N rates advanced bloom and harvest, increased percentage of ground cover (an indicator of canopy size), fruit yield and berry numbers per plant, but decreased mean berry diameter and weight. The soil nitrate results from both ‘Emerald’ and ‘Farthing’ revealed that the 336 kg N ha−1 treatment had a significantly greater risk for nitrate leaching than the lower N treatments in spring. The effect of N rates on fruit quality varied with cultivar and harvest season. The linear plateau regression of fruit yield and N rates indicated that the maximum yield reached at the annual N fertigation rate of 222 kg ha−1 for ‘Emerald’ and 206 kg ha−1 for ‘Farthing’.

A survey of ground beetles (Coleoptera: Carabidae) in Ahuriri Scenic Reserve, Banks Peninsula, and comparisons with a previous survey performed 30 years earlier

ABSTRACTCarabidae (Coleoptera) are commonly used as indicators of ecosystem health due to their high diversity, conservation value and relative ease of identification. Carabids were monitored at Ahuriri Scenic Reserve, Port Hills, Canterbury, from August 2007 to September 2008 using pitfall traps. Carabid captures, species richness and distribution across the reserve were compared with those found in a similar study in 1977–1978. Monthly carabid captures were highly correlated with average temperature in both studies. There was little evidence of carabids responding to habitat factors, such as leaf litter depth, pH or ground cover. However, Megadromus antarcticus was positively associated with canopy openness and ground cover, whereas Holcaspis angustula was more abundant where canopy cover was extensive and there was a relatively high incidence of bare rock. Thirteen species of carabid were recorded in 1977–1978, of which six were absent, four had decreased, one was stable and two species increased in abundance from collections made in 2007–2008. The loss of one Banks Peninsula and five New Zealand endemic beetle species from this reserve is of concern, and future work should aim to gain more detailed information on the habitat requirements of these species to assist conservation management strategies.

Drought response in field grown potatoes and the interactions between canopy growth and yield

Potato is an important food crop with high yields. However when exposed to drought it suffers major yield losses. Considering its global importance and the increasing incidence of drought due to climate change, research toward drought tolerance in potato remains imperative. We have studied a set of 103 commercial cultivars representing the genetic diversity in the European potato market. The cultivars were grown in different field locations in three subsequent years (2013–2015). Our aim was to understand how different field drought regimes affect canopy growth in potato, and how these effects translate to tuber yield. The field environmental conditions were monitored, and pictures of canopy ground cover during the growing season were taken. Canopy growth parameters were extracted by an iterative method using the beta sigmoid growth function to model canopy growth. At harvest, tuber yield was scored and tuber size was graded. The GGE (Genotype and Genotype-by-Environment) bi-plot and Finlay Wilkinson’s Regression were used to investigate Genotype x Environment interactions. We observed that the timing of the drought occurrence differentially affected canopy growth and tuber yield. Under drought stress, fast attainment of exponential growth and maximum canopy cover had negative effects on tuber formation and tuber bulking. Growth rate, maximum canopy cover, and area under the canopy curve (photosynthetic capacity over the growth season) were more important for tuber bulking than they were for tuber formation under drought stress. Cultivars with high yield were identified as potential material for improvement to drought tolerance. These findings will contribute to the breeding for drought-tolerant potato amidst the threats of climate change.

Estimation of ground canopy cover in agricultural crops using downward-looking photography

Fast and accurate estimates of canopy cover are central for a wide range of agricultural applications and studies. Visual assessment is a traditionally employed method to estimate canopy cover in the field, but it is limited by the costs, subjectivity and non-reproducibility of the produced estimates. Digital photography is a low-cost alternative method. In this study we tested two automated image classification methods, the first one based on a histogram-analysis method (Rosin), the second one based on a combination of a visible vegetation index and the L*a*b* colour space conversion (LAB2), which have both been previously tested in forestry, and a supervised image classification method (Winscanopy), to estimate canopy cover from downward-looking images of agricultural crops. These methods were tested using artificial images with known cover; this allowed exploring the influence of canopy density and object size on canopy cover estimation from photography. The Rosin method provided the best estimates of canopy cover in artificial images, whose accuracy was largely unaffected by variation in canopy density and object size. By contrast, LAB2 systematically overestimated canopy cover, because of the sensitivity of the method to small variations of chromaticity in artificial images. Winscanopy showed good performance when at least two regions per class were manually selected from a representative image. The results were replicated in real images of cultivated aromatic crops. The main findings indicate that digital photography is an effective method to obtain rapid, robust and reproducible measures of canopy cover in downward-looking images of agricultural crops, including aromatic plants.

High-Throughput Phenotyping of Canopy Cover and Senescence in Maize Field Trials Using Aerial Digital Canopy Imaging.

In the crop breeding process, the use of data collection methods that allow reliable assessment of crop adaptation traits, faster and cheaper than those currently in use, can significantly improve resource use efficiency by reducing selection cost and can contribute to increased genetic gain through improved selection efficiency. Current methods to estimate crop growth (ground canopy cover) and leaf senescence are essentially manual and/or by visual scoring, and are therefore often subjective, time consuming, and expensive. Aerial sensing technologies offer radically new perspectives for assessing these traits at low cost, faster, and in a more objective manner. We report the use of an unmanned aerial vehicle (UAV) equipped with an RGB camera for crop cover and canopy senescence assessment in maize field trials. Aerial-imaging-derived data showed a moderately high heritability for both traits with a significant genetic correlation with grain yield. In addition, in some cases, the correlation between the visual assessment (prone to subjectivity) of crop senescence and the senescence index, calculated from aerial imaging data, was significant. We concluded that the UAV-based aerial sensing platforms have great potential for monitoring the dynamics of crop canopy characteristics like crop vigor through ground canopy cover and canopy senescence in breeding trial plots. This is anticipated to assist in improving selection efficiency through higher accuracy and precision, as well as reduced time and cost of data collection.

Biophysical response of young pomegranate trees to surface and sub-surface drip irrigation and deficit irrigation

Due to recurring agricultural water shortages, many farmers are looking for crops such as pomegranate that have both some degree of drought resistance and a higher economic value. To manage limited water effectively, it is necessary to know how pomegranate trees respond to varying levels of applied water and the type of irrigation system used. This study was conducted in experimental orchards located at the University of California Kearney Agricultural Research and Extension (UC KARE) Center and the USDA-ARS San Joaquin Valley Agricultural Sciences Center in Parlier, California. The impact of surface drip (DI) and subsurface drip irrigation (SDI) at the UC KARE orchard and irrigation levels (35, 50, 75, 100% of crop water use) at the USDA-ARS orchard on tree canopy size [fractional canopy ground cover (f c), normalized difference vegetation index (NDVI), normalized difference infrared index (NDII)], canopy-to-air temperature difference, and fruit yield was determined during the 2012–2014 growing seasons. There was no difference in tree canopy size between the DI and SDI systems at the UC KARE site; but trees under SDI produced larger fruit in 2013 and higher yield whilst saving about 10% of water application. The difference in water application highlights an advantage of SDI over DI systems to conserve water without creating negative impacts on tree size or yield. At the USDA-ARS site, the 35 and 50% irrigation treatments significantly reduced tree canopy size in 2013 and 2014, compared to the 75 and 100% irrigation treatments. In 2014, trees irrigated with 75% of crop water use produced more yield than trees irrigated at 35% of crop water use. Furthermore, NDVI and NDII were correlated to f c. The relationships between NDVI to f c and f c to pomegranate crop coefficient were established. The derived crop coefficient from ground-based remotely sensed data may potentially be used as a tool by farmers and water managers to estimate pomegranate tree water use on a field or regional scale using aerial or satellite imagery.

Evaluation of Land Restoration Practices on Northern Bobwhite Productivity in North-Central Texas: Preliminary Results

The decades long decline in grassland avian populations is ultimately attributed to changing land use throughout the United States. Due to their economic importance and status as a healthy grassland indicator species, attention focused towards land management for northern bobwhite (Colinus virginianus) benefits other grassland vertebrate and invertebrate species. Land restoration practices offer opportunities to mitigate the declines in northern bobwhite populations. While several studies focus on restoring land for northern bobwhite, this study addressed the effectiveness of such restoration practices. We radio-marked female bobwhite from April to July 2016 and located the birds every three to five days to gather land use information at female diurnal locations. We also placed infrared, time-lapse video cameras within 5m of a nesting site in addition to daily nest checks to identify potential nest predators. We measured vegetation characteristics including visual obstruction, herbaceous, grass, litter, woody material, and canopy ground cover at each nest site and female diurnal location. We built nest survival models using AICc model selection to determine the influence of vegetation characteristics and camera. Of the 31 captured birds, 12 attempted nesting, resulting in four successful nests. We calculated that the nests have a 95% chance of survival the day after and a 32% chance of overall success. Our AICc models found no interactions among nest success and vegetation characteristics. Following nest termination of successful broods, all four broods were abandoned. Two females were radio-marked during their brood-rearing period and both broods lasted longer than 30 days of dependence. We compared the means of vegetation measurements of female diurnal locations between treated and non-treated areas and found no significant differences (p > 0.05). Further assessments of breeding success between treated and non-treated areas are needed to better understand the effects of restoration practices.

Growth, Development, and Water Consumption of Irrigated Bean Crop Related to Growing Degree-Days on Different Soil Tillage Systems in Southeast Brazil

Degree-days may be an alternative for predicting the influence of temperature on physiological aspects of plants in a changing climate. The objective of this research was to evaluate the relation between cumulative degree-days index (∑G) and the development, growth, and water consumption of irrigated bean under different soil tillage systems (STS). We developed an experiment in Southeast Brazil in plots managed with the following STS: chisel ploughing (CP), disk ploughing (DP), and revolving hoe (RH). The treatments did not influence the crop phenology when correlated to∑G. The parameters of canopy ground cover, leaf area index, total dry matter, and the plant height presented a highly significant relationship with∑G(P&lt;0.05). We also compared the results of field water balance with a simulation developed between the crop coefficient and∑Gand found a strong relationship (R2= 0.93∗∗; ∗∗: high statistical significance (P&lt;0.01)) between these measurements and the model. The total water consumption measured at the irrigated bean crop reached 383 mm, 386 mm, and 375 mm while that simulated from dual crop coefficient approach based on∑Greached 378 mm, 373 mm, and 349 mm to CP, DP, and RH, respectively, representing a mean difference of 4.2%.

Satellite-based crop coefficient and regional water use estimates for Hawaiian sugarcane

Water availability is a major limiting factor for sustainable production of potential biofuel crops in Maui, Hawaii, USA. It is essential to improve regional, near-real time estimates of crop water use to facilitate optimal water management. Satellite remote-sensing offers multiple methods to estimate water management, however, most approaches assume a spatially homogeneous regional meteorology, which does not apply in Hawaii due to strong orographically-induced variations in climate. Canopy ground cover (fc) and spectral reflectance were measured over two sugarcane fields on the satellite Landsat 7 overpass dates. A strong linear relationship between satellite-based Normalized Difference Vegetation Index (NDVI) values and fc was found (R2=0.97). Canopy ground cover was also found to be highly correlated to crop coefficient (Kc) which was calculated from reference evapotranspiration (ET0) and sugarcane crop evapotranspiration (ETc) observations from the Eddy Covariance towers. Spatial ET0 for the entire sugarcane plantation was determined from an automated weather station network previously installed by the commercial grower of the plantation. Regressions were used to convert the satellite NDVI to Kc maps, and then the satellite-based ETc maps were created from the satellite-based Kc maps and ET0 values computed and interpolated from the weather station network. To compare with the satellite-based crop coefficient/reference ET method, ETc and Kc were also estimated using a satellite-based surface energy balance technique, the METRIC model. These two satellite-based methods were correlated fairly well (R2=0.84 for Kc and 0.81 for ETc). Compared to the METRIC model, the satellite-based crop coefficient/reference ET method may be more practicable for estimating crop water use in Maui, where ground-based ET0 measurements are available through the on-site automated weather station network with right choice of reference ET equation.

Hourly and Daily Single and Basal Evapotranspiration Crop Coefficients as a Function of Growing Degree Days, Days After Emergence, Leaf Area Index, Fractional Green Canopy Cover, and Plant Phenology for Soybean

<abstract><title><italic>Abstract.</italic></title> Hourly evapotranspiration (ET) crop coefficients (K_c) are needed to optimize the effectiveness and efficiency of high-frequency micro- and sprinkler irrigation practices involving the application of water multiple times a day. However, not much is known about the daily and seasonal patterns and magnitudes in hourly K_c values for soybean. In addition, locally developed K_c values are necessary for more robust within-season irrigation management, crop ET estimation, and water balance analyses. Hourly and daily K_c functions were developed for soybean in south-central Nebraska through extensive field research. Actual crop evapotranspiration (ET_a) was measured using a Bowen ratio energy balance system. Daily crop coefficients were calculated as K_c = ET_a/ET_ref, wherein reference (potential) evapotranspiration (ET_ref) was calculated using the Penman-Monteith equation with a fixed canopy resistance for both alfalfa-reference (ET_r) and grass-reference (ET_o) surfaces. The K_c values were derived in two forms: (1) a single (normal or average K_c) K_cr based on ET_r, and K_co based on ET_o; and (2) a basal coefficient (K_cbr) based on ET_r, and K_cbo based on ET_o. The seasonal patterns of variation of K_cr, K_co, K_cbr, and K_cbo were examined on five different temporal base scales: days after emergence (DAE), cumulative growing degree days (GDD), leaf area index (LAI), fractional green canopy groundcover (CC), and plant phenology (V and R stages). The 2007 and 2008 growing season ET_a totals were 535 and 514 mm, respectively. Extreme hourly K_c values were frequently observed in the early morning and late afternoon hours when ET_a was very low relative to ET_r and ET_o. Daily means of the 10 to 13 hourly values computed for K_cr ranged from 0.25 to 1.06 in 2007 and from 0.15 to 1.02 in 2008, whereas those computed for K_co ranged from 0.39 to 1.37 in 2007 and from 0.22 to 1.29 in 2008. Daily K_cr and K_co values calculated based on daily data ranged from 0.20 to 1.12 and from 0.27 to 1.47, respectively. Comparison of all daily means of hourly coefficients with the corresponding daily coefficients in one-to-one graphs and zero-origin based regression of the former on the latter revealed linear regression coefficients of 0.92 (2007 K_cr), 0.95 (2008 K_cr), 0.96 (2007 K_co), and 0.97 (2008 K_co), with R² values of 0.78 or better. On average, hourly K_c values were about 4% to 8% lower that the corresponding daily values. Substantial diurnal variability was observed in K_co and K_cr measured during daylight hours (ranging from 0.1-0.2 to 1.5-1.6) from early morning to late afternoon (8:00 to 18:00), and the range of variability was substantially dependent on the coincident V and R stages. The relationship between K_c and LAI was best represented by two regression trend lines: one representing crop development from its beginning up to the start of senescence, and the other representing crop development thereafter. A similar break in the regression trend line was observed in the relationship between basal K_c and GDD. In contrast, the relationship between K_c and fractional CC was not biphasic and could be modeled with one regression trend line. The FAO-56 tabulated K_co values and those measured in this research were significantly different (p < 0.05). Thus, the FAO-56 values, if used for south-central Nebraska soil, climate, and management practices or similar conditions, would not be able to provide accurate ET_a and crop water requirement estimates. Because this research proved that K_co and K_cr values are not constant during the day from dawn to dusk, using daily average K_co or K_cr values would not be able to provide robust and precise determination of crop irrigation requirements for irrigation practices delivered more than once per day. The crop coefficients developed in this research as a function of several base scales should provide crop consultants, extension service personnel, agronomists, irrigation practitioners, and other irrigation and water management professionals with robust and accurate methods for choosing and applying crop coefficients to be used for more precise determination of ET_a and water requirements, thus leading to more efficient and effective seasonal soybean irrigation management.

Consumptive water use and crop coefficients of irrigated sunflower

In semi-arid environments, the use of irrigation is necessary for sunflower production to reach its maximum potential. The aim of this study was to quantify the consumptive water use and crop coefficients of irrigated sunflower (Helianthus annuus L.) without soil water limitations during two growing seasons. The experimental work was conducted in the lysimeter facilities located in Albacete (Central Spain). A weighing lysimeter with an overall resolution of 250 g was used to measure the daily sunflower evapotranspiration throughout the growing season under sprinkler irrigation. The lysimeter container was 2.3 m × 2.7 m × 1.7 m deep, with an approximate total weight of 14.5 Mg. Daily ET c values were calculated as the difference between lysimeter mass losses and lysimeter mass gains divided by the lysimeter area. In the lysimeter, sprinkler irrigation was applied to replace cumulative ET c, thus maintaining non-limiting soil water conditions. Seasonal lysimeter ET c was 619 mm in 2009 and 576 mm in 2011. The higher ET c value in 2009 was due to earlier planting and a longer growing season with the maximum cover coinciding with the maximum ET o period. For the two study years, maximum average K c values reached values of approximately 1.10 and 1.20, respectively, during mid-season stage and coincided with maximum ground cover values of 75 and 88 %, respectively. The dual crop coefficient approach was used to separate crop transpiration (K cb) from soil evaporation (K e). As the crop canopy expanded, K cb values increased while the K e values decreased. The seasonal evaporation component was estimated to be about 25 % of ET c. Linear relationships were found between the lysimeter K cb and the canopy ground cover (f c) for the each season, and a single relationship that related K cb to growing degree-days was established allowing extrapolation of our results to other environments.

AquaCrop—The FAO Crop Model to Simulate Yield Response to Water: I. Concepts and Underlying Principles

This article introduces the FAO crop model AquaCrop. It simulates attainable yields of major herbaceous crops as a function of water consumption under rainfed, supplemental, deficit, and full irrigation conditions. The growth engine of AquaCrop is water‐driven, in that transpiration is calculated first and translated into biomass using a conservative, crop‐specific parameter: the biomass water productivity, normalized for atmospheric evaporative demand and air CO2 concentration. The normalization is to make AquaCrop applicable to diverse locations and seasons. Simulations are performed on thermal time, but can be on calendar time, in daily time‐steps. The model uses canopy ground cover instead of leaf area index (LAI) as the basis to calculate transpiration and to separate out soil evaporation from transpiration. Crop yield is calculated as the product of biomass and harvest index (HI). At the start of yield formation period, HI increases linearly with time after a lag phase, until near physiological maturity. Other than for the yield, there is no biomass partitioning into the various organs. Crop responses to water deficits are simulated with four modifiers that are functions of fractional available soil water modulated by evaporative demand, based on the differential sensitivity to water stress of four key plant processes: canopy expansion, stomatal control of transpiration, canopy senescence, and HI. The HI can be modified negatively or positively, depending on stress level, timing, and canopy duration. AquaCrop uses a relatively small number of parameters (explicit and mostly intuitive) and attempts to balance simplicity, accuracy, and robustness. The model is aimed mainly at practitioner‐type end‐users such as those working for extension services, consulting engineers, governmental agencies, nongovernmental organizations, and various kinds of farmers associations. It is also designed to fit the need of economists and policy specialists who use simple models for planning and scenario analysis.

Gas exchange rates of potato stands for bioregenerative life support

Plants can provide a means for removing carbon dioxide (CO 2) while generating oxygen (O 2) and clean water for life support systems in space. To study this, 20 m 2 stands of potato ( Solanum tuberosum L.) plants were grown in a large (113 m 3 vol.), atmospherically closed chamber. Photosynthetic uptake of CO 2 by the stands was detected about 10 DAP (days after planting), after which photosynthetic rates rose rapidly as stand ground cover and total light interception increased. Photosynthetic rates peaked ca. 50 DAP near 45 μmol CO 2 m −2 s −1 under 865 μmol m −2 s −1 PPF (average photosynthetic photon flux), and near 35 μmol CO 2 m −2 s −1 under 655 μmol m −2 s −1 PPF. Short term changes in PPF caused a linear response in stand photosynthetic rates up to 1100 μmol m −2 s −1 PPF, with a light compensation point of 185 μmol m −2 s −1 PPF. Comparisons of stand photosynthetic rates at different CO 2 concentrations showed a classic C 3 response, with saturation occurring near 1200 μmol mol −1 CO 2 and compensation near 100 μmol mol −1 CO 2. In one study, the photoperiod was changed from 12 h light/12 h dark to continuous light at 58 DAP. This caused a decrease in net photosynthetic rates within 48 h and eventual damage (scorching) of upper canopy leaves, suggesting the abrupt change stressed the plants and/or caused feedback effects on photosynthesis. Dark period (night) respiration rates increased during early growth as standing biomass increased and peaked near 9 μmol CO 2 m −2 s −1 ca. 50 DAP, after which rates declined gradually with age. Stand transpiration showed a rapid rise with canopy ground cover and peaked ca. 50 DAP near 8.9 L m −2 d −1 under 860 μmol m −2 s −1 PPF and near 6.3 L m −2 d −1 under 650 μmol m −2 s −1 PPF. Based on the best photosynthetic rates from these studies, approximately 25 m 2 of potato plants under continuous cultivation would be required to support the CO 2 removal and O 2 requirements for one person.

Hemispherical digital photographs offer advantages over conventional methods for quantifying pathogen-mediated changes caused by infestation ofPhytophthora cinnamomi

Estimates of canopy closure using hemispherical digital images, canopy cover using a point-intercept method, ground cover, number of plant species and total plant species cover were used to quantify the impact of Phytophthora cinnamomi in disease centres in Banksia shrubland, Banksia woodland and Eucalyptus marginata forest biomes of the South-West Botanical Province of Western Australia. Estimates of the time required to capture and analyse data and correlations were used to contrast the five methods. For canopy closure or cover, hemispherical digital images were on average, seven times faster to capture and analyse than the point-intercept method. For both canopy closure and ground cover, mean values from three point samples were not significantly different to mean values from transects across the disease front. Differences in canopy closure and ground cover between biomes and disease obtained from point sampling showed the same trends as transects. Canopy closure differed significantly between biome, being greatest for E. marginata forest, least for Banksia shrubland and intermediate for Banksia woodland. Ground cover was greatest for Banksia shrubland, least for E. marginata forest and intermediate for Banksia woodland. For all biomes there was significantly less canopy closure in diseased than adjoining healthy areas. There was no significant difference in ground cover between diseased and adjoining healthy areas of Banksia shrubland, but significantly less ground cover in diseased than adjoining healthy areas in the Banksia woodland and E. marginata forest. Canopy closure and ground cover are likely measuring different aspects of the impact of P. cinnamomi and, therefore, both should be measured when determining pathogen-mediated changes. Advantages of using hemispherical digital images over the other methods for determining temporal and spatial changes associated with P. cinnamomi infestation are discussed.