Entire Crop Cycle Research Articles

Soybean fallow and nitrification inhibitors: Strategies to reduce N2O emission intensities and N losses in Australian sugarcane cropping systems

The Australian sugar industry is facing mounting pressure to reduce the nitrogen (N) losses and nitrous oxide (N2O) emissions associated with N fertiliser use. Research has shown that N2O emissions from sugarcane (Saccharum officinarum L.) cropping systems can be reduced with the use of fertilisers coated with nitrification inhibitors, or by sowing legume crops in the fallows between sugarcane crop cycles. However, the efficacy of these two N management strategies across different climatic zones is still unclear, as results from field studies have been contradictory. The objectives of this study were therefore to use the DayCent model to assess the long-term effects of the two strategies (separately or in combination) on N2O emissions, N losses and yields. The model was parameterised using data from eight field experiments (39 treatments) conducted across four of the five main districts of the Australian sugarcane industry. A series of long-term scenarios embracing a range of N fertiliser rates (0−160 kg N ha−1 applied as urea), climatic regions (Tropics and Subtropics), soil textures (fine- and coarse-textured soils) and N-loss risk scenarios (crop fertilised well before or close to the on-set of the wet season) were tested for both N management strategies. Simulations identified that the combined use of soybean (Glycine max L.) fallows and N fertiliser coated with the 3,4-dimethylpyrazole phosphate (DMPP) nitrification inhibitor was the most effective strategy to maintain or even increase current yields while significantly reducing N2O and cumulative N (mainly due to nitrate) losses. When used alone, the soybean fallow strategy on average reduced N losses over the entire crop cycle by 29 % compared with current industry best practice. However, this strategy showed a limited capacity to reduce N2O emissions over the entire cane crop cycle (median: -3% compared with current industry best practice), or even increased them in scenarios at high-risk of N losses in the Tropics. The use of urea coated with DMPP alone allowed current fertiliser N rates to be reduced by 30 % without any substantial yield penalty. In environments prone to high N losses, DMPP urea abated overall N losses and N2O emissions by 41 % and 30 %, respectively. This was the first study to use such an extensive dataset to parameterise a biogeochemical model for yields, N2O emissions and N losses in sugarcane cropping systems. The findings will be instrumental in guiding future research and policies designed to improve the profitability and environmental sustainability of this industry.

Sustainable Protected Cropping: A Case Study of Seasonal Impacts on Greenhouse Energy Consumption during Capsicum Production

Sustainable food production in protected cropping is increasing rapidly in response to global climate change and population growth. However, there are significant knowledge gaps regarding energy consumption while achieving optimum environmental conditions for greenhouse crop production. A capsicum crop cultivated in a high-tech greenhouse facility in Australia was analysed in terms of relationships between key environmental variables and the comparative analysis of energy consumption during different seasons. We showed that daily energy consumption varied due to the seasonal nature of the external environment and maintenance of optimal growing temperatures. Total power consumption reported throughout the entire crop cycle for heating (gas hot water system) and cooling (pad and fan) was 12,503 and 5183 kWh, respectively; hence, heating consumed ca. 70% of the total energy requirement over the 8-month growing period (early spring to late autumn) in the greenhouse facility. Regressions of daily energy consumption within each season, designated either predominantly for heating or cooling, indicated that energy consumption was 14.62 kWh per 1 °C heating and 2.23 kWh per 1 °C cooling. Therefore, changing the planting date to late spring is likely to significantly reduce heating energy costs for greenhouse capsicum growers in Australia. The findings will provide useful guidelines to maximise the greenhouse production of capsicum with better economic return by taking into consideration the potential optimal energy saving strategy during different external environment conditions and seasons.

Plastochron and yield of Physalis peruviana L. grown in different environments and transplanting dates

This study aimed to estimate plastochron, leaf area, and yield of Physalis peruviana seedlings grown in different environments and transplanted on different dates. The experiment was carried out in a completely randomized design, arranged in a 2 x 3 factorial scheme, namely: two cultivation environments (protected and field) and three transplanting dates (10/27/2013, 12/15/2013, and 02/11/2014). Four replicates of eight plants were used per plot, and the four central plants composed the useful area. Based on mathematical models and temperature data, plastochron was estimated for the entire crop cycle and vegetative and reproductive phases separately. Leaf area and node number were measured, and their relationship established at the end of the study. Other variables assessed were fruit number, mass, and yield per plant. Our results showed that the higher temperatures in the protected environment anticipated phenological timings. Plastochron values of 60.0 and 16.5 °C day-1 can be used during vegetative and reproductive stages, respectively. The protected environment increased vegetative growth and development, as well as yield of P. peruviana seedlings. In the Guarapuava-PR region, P. peruviana seedlings should be transplanted during the spring so that higher fruit yield and quality could be achieved.

Breeding effects on the genotype × environment interaction for yield of durum wheat grown after the Green Revolution: The case of Spain

This study evaluates the changes caused by breeding in the genotype by environment (G × E) interaction of the durum wheat varieties most widely cultivated in Spain after the Green Revolution. A set of 12 cultivars was tested in 27 environments, which are understood as the combination of different sites, years, and treatments (water regime and planting dates), representative of the durum wheat growing conditions in Spain with average grain yields (GY) ranging between 2.8 and 9.1 Mg ha−1. The most important environmental factors affecting the G × E interaction for yield were themaximum and the mean temperature during the entire crop cycle. An improvement in genetic yield was observed in warm environments and under optimal water conditions that resemble those where the germplasm originated (essentially as advanced lines) before its release in Spain. Therefore, the adaptation of semi-dwarf durum in Spain has shown a tendency to specific adaptation rather than large-scale adaptation. Two different patterns of selection have been reported due the G × E interaction and changes in the ranking of genotypes: in the high yielding environments (GY > 5 Mg ha−1), plants favor increased water uptake, with higher levels of transpiration and more open stomata (more negative values of carbon isotope composition, δ13C, and higher canopy temperature depression, CTD), whereas, in low yielding environments (GY < 5 Mg ha−1) plants close their stomata and favor greater water use efficiency (less negative δ13C values and lower CTD values).

Nitrogen loading of Eucalyptus globulus seedlings: nutritional dynamics and influence on morphology and root growth potential

Achieving successful outplanting of trees on increasingly harsher sites is a global concern. In Chile, for example, new Eucalyptus globulus plantations are being targeted to poorer, low fertility sites where additional stresses often negatively affect seedling performance during the first field season. Nitrogen-loading during the later stages of nursery production can, however, significantly improve seedling physiological performance on harsher sites by increasing plant growth and nutrient storage reserves for subsequent root growth after outplanting. Maximizing these benefits, and applying the concept of loading throughout the entire crop cycle, requires a better understanding of nitrogen (N) dynamics. Thus, for container E. globulus, considered one of the most important plantation species worldwide, we evaluated the effects of increasing N supply (50 to 600 mg N L−1) on seedling morphological traits, biomass production, root growth potential, and foliar N. After 15 weeks of N application, seedlings showed an increase in all growth variables evaluated up to 300 mg N L−1, whereas higher rates allowed luxury consumption. Modeling growth responses revealed, however, an apparent ammonium antagonism with other macronutrient cations suggests that high rates of this N-form may negate the potential benefits of N-loading, or that other modifications to the fertilizer solution may promote additional growth at higher N rates. Foliar N concentration, which was easily and accurately measured with a leaf chlorophyll meter, showed a gradient from basal to apical leaves suggesting a strong translocation of N in E. globulus seedlings. Our results suggest nursery management that supplies 300 mg L−1 of N through the entire growing season could improve seedling nutritional status, morphological attributes, and growth of new roots, attributes that may improve establishment on low fertility sites.

Decision Support Tool for Operational Planning of Field Operations

Precision Farming (PF) and Controlled Traffic Farming (CTF) are well known concepts within agriculture, but the adoption rate of these practices by farmers is still very low, because farmers lack the needed skills or fail to see the benefits of using these practices. If farmers want to reap the full benefits, operational planning must be carried out in advance for the entire crop cycle, before the crop season begins. However, operational planning across the entire crop cycle is a non-trivial task, since the efficiency of each operation is determined by a range of selected operational features (e.g., wayline direction, operational speed, vehicle capacity, wayline sequence, and turn type). To that end, we present, in this paper, an application that can support farmers with operational planning of field operations with CTF, by automating the process. It provides the farmer with an overview of all his field operations, and acts as a decision support tool during the operational planning process. The application allows farmers to store and manage field and equipment information, which is used as input, when setting up CTF and generating way lines and route plans for the individual fields. One of the key benefits of the application is the provided comparison feature, where farmers can compare alternative solutions, based on Key Performance Indicators (KPIs). Results from an example field, for operations with different machine setups, are presented to illustrate how KPIs and visualisations can support farmers during the decision process.

Agronomical valuation of a drip irrigation system in a commercial mushroom farm

Optimal mushroom growth is dependent on continuous water supply. Usually water is occasionally added by spraying on the casing layer. Drip irrigation system was developed in order to keep the optimal water contents in compost and casing during entire crop cycle. In this study, the use of drip irrigation system was compared to spray watering. The system (Netafim & Migal) is based on a unique dripper – Uniraam CNL 0.7 L/h that enables a very accurate and uniform water distribution in the substrates. Drip irrigation system led to more productive water use: yield of mushrooms was found to be higher (29.5 kg m−2 vs 27.6 kg m-2 for drip and spraying system, respectively) and higher mushroom quality was also found, with a higher percentage of “categorie I” mushrooms, that reduced picking costs. All of that helps to improve profitability of the mushroom crop.

Effects of deficit irrigation on the yield and irrigation water use efficiency of drip-irrigated sweet pepper (Capsicum annuum L.) under Mediterranean conditions

Water scarcity is seriously affecting agricultural production, especially in arid and semi-arid areas. Therefore, there is increasing interest in improving water productivity in agriculture. This research aims to study the effects of deficit irrigation on the productive response of sweet pepper plants. Nine deficit irrigation strategies were assayed during two seasons (2017 and 2018) in a randomised complete block design with three replicates. These irrigation strategies consisted of applying 100%, 75% and 50% of the irrigation water requirement (IWR) during the entire growing period (continued deficit irrigation) or applying 75% or 50% of the IWR during one of the following stages (regulated deficit irrigation): vegetative growth, fruit setting, and harvesting. Pepper plants cultivated under deficit irrigation reduced fruit biomass and indicators of plant water status. Applying water deficits during the vegetative growth and fruit-setting stages had minimal effects on the marketable yield but with minimal water savings. Irrigating pepper plants with 75% or 50% of the IWR during the entire crop cycle or with 50% of the IWR during harvesting resulted in a high incidence of fruits affected by blossom end rot, which in turn, led to a drastic reduction of the marketable yield in relation to fully irrigated plants (− 36%, − 55% and − 44%, respectively). These strategies also recorded the highest soluble solid and phenolic contents. Reducing the water applied to 75% of the IWR at harvesting led to a yield reduction (− 19%) but with important water savings (21%) and acceptable levels of soluble fruit solids and phenolic compounds.

Strategic timing and rate of sulphur fertilization improves sulphur use efficiency in subirrigated greenhouse-grown chrysanthemums

Industry standards for nutrient delivery to greenhouse-grown ornamentals are typically in excess of the plant’s needs and can be reduced without causing adverse effects. Previous studies have reduced the level of specific nutrients or suite of nutrients over the entire crop cycle or at the onset of reproductive growth. Here, two split-plot experiments (four blocks each) were conducted with subirrigated, potted, disbudded chrysanthemums (Chrysanthemum morifolium Ramat.) grown under greenhouse conditions with sulphate treatment (2.25 mmol L−1 S supplied continuously over the crop cycle in experiment 2 only and 2.25, 1.125, or 0.5625 mmol L−1 S interrupted at inflorescence emergence) as the main plot and cultivar (‘Olympia’ and ‘Covington’) as the sub-plot. Morphological characteristics of plants with fully-expanded inflorescences were unaffected by decreasing S delivery over the crop cycle. Dry mass (DM) yields and S budgets revealed that supply-based S use and S uptake efficiencies increased markedly in both cultivars with decreasing S delivery. Minor amounts of reduced-S, rather than sulphate, were lost from leaves of ‘Covington’ during inflorescence development. High quality chrysanthemums had sufficient leaf-S (0.17%–0.23% DM) at inflorescence emergence even with the lowest S supply, which would deliver an approximate 87.5% reduction in S over the crop cycle compared with industry standards. The primary mechanism to obtain sufficient S for the growth of chrysanthemums in these studies was increased uptake efficiency.

Nitrogen limitation in high-yield soybean: Seed yield, N accumulation, and N-use efficiency

Recent reviews about soybean nitrogen (N) requirement have speculated about a possible N limitation in high-yield environments (>4.5 Mg ha−1). However, these studies did not provide definitive experimental data to test that hypothesis and results from the literature are conflicting. To fill this knowledge gap, we evaluated N limitation across 13 high-yield soybean environments in Argentina and USA. Each experiment included a ‘zero-N’ treatment, which forced the crop to rely on biological N2 fixation and indigenous soil N, and a ‘full-N’ treatment, which provided an ample fertilizer N supply during the entire crop cycle based on site-specific yield potential. Accumulated N in aboveground dry matter (ADM) measured in a N-omission maize plot grown adjacent to the soybean experiments was used to determine indigenous soil N supply. Soybean seed yield, protein and oil concentration, ADM, harvest index (HI), accumulated N in ADM, N harvest index (NHI), and seed N were measured in both treatments at physiological maturity. A simple conceptual framework relating ADM with accumulated N was used to assess treatment differences in ADM, accumulated N, and N-use efficiency (NUE). To account for treatment differences in seed biomass composition, mass-based ADM was expressed in glucose equivalents (ADMe). Seed yield ranged from 4.6 to 6.7 Mg ha−1 (full-N) and 4 to 5.8 Mg ha−1 (zero-N), with the full-N treatment averaging 12% (0.6 Mg ha−1) and 3% (9 g kg−1) higher seed yield and protein concentration, respectively. The full-N treatment exhibited 18% (70 kg N ha−1) and 14% (1.6 Mg ha−1) greater accumulated N and ADM, respectively, compared with the zero N treatment, without changes in HI and NHI, but slightly lower NUE (29 versus 30 kg ADM kg−1 N in full and zero-N, respectively). However, NUE differences between treatments became indistinguishable when ADM was expressed as ADMe (45 kg glucose kg−1 N). The (full-N minus zero-N) seed yield difference and the indigenous soil N supply were negatively associated. This research documented (i) the existence of N limitation in high-yield soybean, (ii) that seed yield and protein concentration increases were physiologically associated with changes in accumulated N (but not in NUE and/or NHI), and (iii) that the degree of N limitation is modulated by indigenous soil N supply. Findings from this study can serve as a basis to identify environments with the largest N limitation and thus guide N management in soybean.

Gas exchanges and production of watermelon plant under salinity management and nitrogen fertilization

ABSTRACT In the Brazilian semi-arid region, the occurrence of water with high salt concentrations is common, making it a limiting factor for the agricultural production. The water-use salinity management strategies are an alternative capable of minimizing the deleterious effects of the stress on plants. This study aimed to evaluate the gas exchanges and production of ‘Sugar Baby’ watermelon plants under strategies of irrigation with saline water and nitrogen fertilization. The experiment was conducted in a randomized block design, arranged in a 6 x 2 factorial scheme, with five replicates, corresponding to six irrigation strategies with saline water applied at different phenological stages of the crop (control - irrigation with low-salinity water throughout the entire crop cycle, and salt stress at the vegetative stage, vegetative/flowering stage, flowering, fruiting and fruit maturation) and two nitrogen rates (50 % and 100 %, equivalent to 50 mg and 100 mg of N kg-1 of soil). Two levels of water salinity were studied: one with a low and the other with a high level of electrical conductivity (0.8 dS m-1 and 3.2 dS m-1, respectively). The salinity of 3.2 dS m-1 in the vegetative/flowering and fruit maturation phases decreases the stomatal opening, transpiration and CO2 assimilation rate. The level with 50 % of N provides a higher assimilation rate of CO2 and fresh fruit mass. The watermelon plant expresses a greater sensitivity to saline stress in the vegetative and flowering phases, a situation that results in a decreased fruit size.

SUGARCANE CROPS WITH CONTROLLED WATER DEFICIT IN THE SUB-MIDDLE SÃO FRANCISCO VALLEY, BRAZIL

ABSTRACT Sugarcane is one of the most affected crops by water scarcity. The efficient use of the irrigation water is an alternative to minimize this problem. The objective of this work was to evaluate biometric parameters, yield, and technological quality of sugarcane plants subjected to different controlled water deficit regimes in the sub-middle São Francisco Valley, Brazil. The experiment was conducted in a randomized block design, in two crop cycles, with three replications, with ten treatments consisted of three controlled water deficits (15%, 30%, and 45% of the crop evapotranspiration - ETc), applied at three development stages of the plant - sprouting and tillering (Stage I), grand growth (Stage II), and maturation (Stage III) - and a control with 100% of the ETc throughout the entire crop cycle. The controlled water deficit did not affect the technological quality of the sugarcane in any development stage. The sugarcane yield was higher when using a controlled water deficit of 30% of ETc in the sprouting and tillering stages of the plants. The water deficit of 15% of ETc is recommended for the grand growth, or maturation stages of the sugarcane plants for a greater water use efficiency of the production system.

Assessment of a non-destructive method to estimate the leaf area of Armoracia rusticana

The aim of the study was to analyze horseradish growth for developing a mathematical model to estimate the leaf area based on linear measurements of the leaf surface. Leaf area (LA), number, and morphometric characteristics of the leaves including lamina length (L) and width (W) were evaluated on two horseradish accessions (Cor and Mon) throughout a 2 year growing cycle. In both accessions, increased values of LA and leaf number were found by comparing the second with the first-growing season. Leaf development occurs along with variations in size and not in shape during the plant growth. The leaves are elliptical in shape but tend to be wider and bigger in Cor accession and tapered and similar to narrow ellipses in Mon showing different length/width relationship. Consequently, several regression models relating to the LA and L, W, L2, and W2 individually or in combination were fitted for each accession based on a set of 1000 leaves. The horseradish LA can be predicted based on either length or width alone. However, the regression linear model LA = aLW + b (LA = 0.71LW − 0.27 and LA = 0.76LW − 3.22 for Cor and Mon, respectively) provided the best LA estimation (R2 > 0.95). The validation of this latter model showed high correlation between LA measured and LA predicted in both accessions (R2 = 0.98). Considering the type of foliage of horseradish, the proposed model can be used to estimate the leaf area throughout the entire crop cycle.

N2O and CO2 emissions, nitrogen use efficiency under biogas slurry irrigation: A field study of two consecutive wheat-maize rotation cycles in the North China Plain

Reuse of biogas slurry (BGS) could reduce fertilizer application rate because this material is an alternative source of nutrients and irrigation that could replace some of applied fertilizer. However, the environmental impacts of BGS irrigation, such as greenhouse gas emissions (GHG) are poorly understood. We investigated the global warming potential (GWP) and greenhouse gas intensity (GHGI) of BGS irrigation by quantifying the nitrous oxide (N2O) and carbon dioxide (CO2) emissions under different BGS irrigation rates in a two-year wheat-maize rotation field in the North China Plain. We found BGS irrigation did not change the patterns and fluxes of CO2 and N2O emission during the entire wheat-maize cropping cycle. In addition, there were no significant difference between BGS treatments (BSL, BSM, and BSH) and conventional fertilizer treatment (CF) in GWP. Further, no significant difference occurred in GHGI between BSM (33% BGS and 67% groundwater were mixed and irrigated during the wintering period and joining stage of wheat and after maize sowing, 315 kg·N·hm−1), BSH (50% BGS and 50% groundwater were mixed and irrigated during the wintering period and joining stage of wheat and after maize sowing, 477 kg·N·hm−1) and CF (conventional NPK fertilizer, 420 kg·N·ha−1), despite a higher value BSL (33% BGS and 67% groundwater were mixed and irrigated during the wintering period of wheat and after maize sowing, 210 kg·N·hm−1).The BSL and BSM treatments significantly increased the nitrogen use efficiency (NUE) compared to the CF treatment (11.3% for BSL and 15.3% for BSM). Despite the lower NUE in the BSH treatment relative to CF, it was not statistically significant. Therefore, BGS reuse can increase NUE and does not cause environmental impacts. According to the results of GHGI and NUE, it can be concluded that BSM should be recommended as an improved recycling management practice for the wheat-maize rotation systems.

Soil Moisture Sensor-based Systems are Suitable for Monitoring and Controlling Irrigation of Greenhouse Crops

Sensor-based feedback control irrigation systems have been increasingly explored for greenhouse applications. However, the relationships between microclimate variation, plant water usage, and growth are not well understood. A series of trials were conducted to investigate the microclimate variations in different greenhouses and whether a soil moisture sensor-based system can be used in monitoring and controlling irrigation in greenhouse crop productions. Ocimum basilicum ‘Genovese Gigante’ basil and Campanula portenschlagiana ‘Get Mee’ bellflowers were monitored using soil moisture sensors for an entire crop cycle at two commercial greenhouses. Significant variations in greenhouse microclimates were observed within the two commercial greenhouses and within an older research greenhouse. Evaporation rates were measured and used as an integrated indicator of greenhouse microclimate conditions. Evaporation rates varied within all three greenhouses and were almost double the lowest rates within one of the greenhouses, suggesting microclimates within a range of greenhouses. Although these microclimate variations caused large variations in the growing substrate water contents of containers within the greenhouses, the growth and quality of the plants were unaffected. For example, no significant correlations were observed between the growth of bellflower plants and the average volumetric water content (VWC), minimum VWC, or maximum VWC of the growing substrate. The change in VWC at each irrigation (ΔVWC), however, was positively correlated with the fresh weight, dry weight, and growth index (GI) of the bellflowers. For basil, no significant correlations were observed between plant growth and ΔVWC. This suggests that sensor-based feedback irrigation systems can be used for greenhouse crop production when considerations are given to factors such as the magnitude of microclimate variation, crop species and its sensitivity to water stress, and growing substrate.

Fungicides in second harvest corn: cercosporiose control and blotch, productivity, economic return and grain quality

Os objetivos desse trabalho foram avaliar a eficiencia de The aim of this study was evaluate efficacy fungicides to control cercospora leaf spot ( Cercospora zeae-maydis ) and helminthosporium leaf blight ( Exserohilumturcicum ), productivity, economic returns and quality of grain of corn culture of second crop in Farm Bandeirantes at Feliz Natal/MT. The treatments evaluated were: pyraclostrobina+epoxiconazol (0,7 L ha -1 ), trifloxistrobina+protioconazol (0,3L ha -1 ), azoxistrobina+cyproconazol (0,3 L ha -1 ), azoxystrobina (0,25 L ha -1 ), trifloxistrobina+ciproconazol (0,2 L ha -1 ) and control. Theapplicationof products occurred when corn was with 55 days, with a high propelled sprayer. The experimental design was a randomized block, with 6 treatments and 3 replications. The severity of each disease was visually determined through periodic analyses and ten plants were marked in each repetition, which were evaluated during the entire crop cycle. The data of severity obtained were used to calculate the area under disease progress curve (AUDPC). It was also obtained the production per ha, the economic return (R$ ha-1) and physiological quality of grain was evaluated by germination tests and accelerated aging of the grains. All treatments had significant difference compared to the control sample in controlling cercospora leaf spot about the control of helminthosporiumleat blight, the fungicides trifloxystrobin+prothioconazol and trifloxystrobin+cyproconazol were not efficient, and the fungicides pyraclostrobina+epoxiconazol , azoxystrobina , azoxistrobina+cyproconazol were efficient. The treatments that had major production are from the group of triazoles+strobilurine and the fungicide pyraclostrobin+epoxyconazol showed greater economic viability. Not were differences among fungicides, and neither of the treatments compared to control, in germination and accelerated aging tests, showing that the grains have good quality characteristics

Root growth and yield of sugarcane as a function of increasing gypsum doses

ABSTRACT Sugarcane plays an important role in the Brazilian agribusiness. However, poor rainfall distribution and soil acidity directly affect its production in the Northeast Brazil. Gypsum improves the soil physical and chemical properties, attenuating the effects of water stress and acidity in the edaphic environment. This study aimed at determining the effect of gypsum doses on sugarcane growth and yield. A field experiment was conducted using a 3 x 5 factorial arrangement organized in a randomized block design, with four replications. Treatments consisted of a combination of three sugarcane varieties (RB011941, RB92579 and RB991536) with five gypsum doses (0 Mg ha-1, 2.5 Mg ha-1, 5.0 Mg ha-1, 10.0 Mg ha-1 and 20.0 Mg ha-1). RB92579 exhibited the highest stalk (157.90 Mg ha-1) and sugar (24.10 Mg ha-1) yield. Gypsum did not influence the sugarcane yield or plant growth in the vegetative growth stage, but, in the maturation phase, the leaf area declined and the number of shoots increased with the rise in gypsum doses. Applying gypsum increased the roots density along the soil profile, with a rise of around 1.10 g dm-3 at the most technically efficient dose (12.5 Mg ha-1), however, yield was not influenced, maybe due to the effect of high rainfall during the entire crop cycle. Thus, higher gypsum doses are recommended during periods of drought to benefit from the resulting increased root system.

Meteorological limits to winter wheat productivity in the U.S. southern Great Plains

Although the U.S. southern Great Plains accounts for approximately 30% of total U.S. wheat (Triticum aestivum L.) production, yields in the region have rarely surpassed 3.0Mgha−1 and quantification of the wheat yield gap (YG) and meteorological factors associated with potential wheat productivity are scarce. Our objectives were to identify spatial gradients in key weather variables and to assess the meteorological drivers of wheat productivity and resource-use efficiency, and to quantify the wheat YG across Texas, Oklahoma, Colorado, and Kansas. Water-limited wheat grain yield (Yw) was simulated for 30 consecutive years at 68 locations across the southern Great Plains using Simple Simulation Modeling-Wheat (SSM-Wheat), and actual soil and weather data, sowing date, and population density. Regional gradients in meteorological variables were determined for (i) the entire crop cycle, (ii) pre- and post-anthesis, or (iii) jointing-anthesis interval, and Yw were related back to these variables using linear and stepwise multiple-regression. Boundary function analysis determined water productivity (WP) and transpiration-use efficiency (TE). Strong latitudinal gradients occurred for temperatures and longitudinal gradients for precipitation (P), evapotranspirative demand (ETo), and solar radiation (Rs). Wheat Yw averaged 5.2Mgha−1 and followed the longitudinal P gradient increasing from west (3.6Mgha−1) to east (6.9Mgha−1). Interannual Yw variability was large with coefficient of variation (CV) increasing from 13 to 51% east to west. Meteorological variables accounting for major portions of the Yw variability were water supply (P+PAWs) in the west [82% of regression sums of squares (SS)] and cumulative solar radiation (Rs) during the anthesis − physiological maturity in the east (73% of SS). Temperatures during the anthesis-physiological maturity phase negatively affected grain yields across all locations and years (7% of SS). Wheat WP (17.2kgha−1mm−1) and TE (20.8kgha−1mm−1) benchmarks derived in this study align well with values reported for wheat grown in other regions of the world.

Tolerance to Salinity of Sesame Genotypes in Different Phenological Stages

The sesame crop is usually avoided in salt-affected areas because of the various effects of saline stress on plants. Besides varying between species, salinity effects are known to vary for genotypes of the same species as well as plant development stages. Thus, through the irrigation of plants with saline water, this study evaluates tolerance to saline stress of new sesame genotypes in different phenological stages. Three experiments were carried out under greenhouse conditions, using the sesame genotypes BRS Seda, LAG-927561 and LAG-26514. Water with different levels of electrical conductivity (ECw = 0.6, 1.6, 2.6, 3.6 and 4.6 dS m-1) was used to irrigate plants during germination and initial growth stages, as well as the entire crop cycle. Tolerance to saline stress (3.6 dS m-1) during growth and production stages was also studied. Salinity did not affect sesame germination, but seedling growth was hindered from the ECw of 1.6 dS m-1 onwards, and plant height was the most affected growth variable. Seed production is affected by salinity, regardless of the phenological stage in which plants are exposed to salinity. The strains LAG-927561 and LAG-26514 show promising signs in studies on adaptation to saline stress.

Determination of sufficiency values of canopy reflectance vegetation indices for maximum growth and yield of cucumber

Large nitrogen (N) fertilizer applications are a feature of intensive vegetable production systems, and optimal N management is required to maximize N use efficiency and minimize N losses. Vegetation indices (VIs) of canopy reflectance, measured with proximal sensors, are generally strongly related to crop N status. For practical application, sufficiency values that distinguish between N deficiency and sufficiency are required. In this work, sufficiency values of VIs for maximum crop growth and for yield were determined for two cucumber crops grown in contrasting seasons (Autumn and Spring). Canopy reflectance was measured with a Crop Circle ACS-470 sensor. Sufficiency values for maximum growth were based on the relationships of VIs with the Nitrogen Nutrition Index (NNI), i.e. the ratio between actual and critical crop N contents. Sufficiency values for maximum yield were based on linear-plateau relationships of yield with VIs. Strong relationships were obtained between all VIs and both NNI and yield for most of the weekly measurements during both crops. For NNI, best-fit relationships were linear, quadratic, power or exponential, and had coefficients of determination (R2) of 0.61–0.98. For yield, most linear-plateau relationships between yield and VIs had R2 values of 0.47–0.89. VIs based on reflectance in green and red edge had slightly better relationships with NNI and yield than VIs in the red, with the Green Normalized Difference Vegetation Index (GNDVI) and the Green Ratio Vegetation Index (GRVI) being the most sensitive and consistent indices for estimating both crop NNI and yield. Relationships between VIs and NNI and yield for all weekly measurements of each crop, and for the two crops combined, were also analyzed to provide unique sufficiency values for maximum growth and yield that applied to the entire crop cycle of each crop and of both crops considered together. Overall, there were slight differences between sufficiency values for maximum growth and for maximum yield and the unique sufficiency values were generally intermediate to the weekly sufficiency values. This study demonstrated the potential for using VIs for monitoring crop N nutrition and yield in cucumber. The calculated sufficiency values of VIs may facilitate the use of proximal optical sensors in farming practice for optimal N management through periodic monitoring for deviation from sufficiency values.