Search

A compreensão da dinâmica entre evapotranspiração de referência (ETo), evapotranspiração de cultura (ETc) e coeficiente de cultura (Kc) e fundamental em irrigação. O objetivo deste trabalho foi analisar a relação entre uma base de dados de ETc da cana-de-açúcar medidos por um lisímetro de pesagem eletrônico de grande porte e Kc e ETo calculados. O lisímetro está instalado em uma área localizada na cidade de Piracicaba, SP, em um cultivo de cana-planta da cultivar RB867515. Para a análise, estimou-se a ETo pelo método de Penman-Monteith e, para a seleção dos dados de ETc, fez-se a seleção de ETo, ETc e Kc baseando-se nos dias em que o Kc foi igual ou inferior a quatro. Posteriormente, excluiu-se os dados em que os dias apresentaram déficit hídrico superiores a zero e agrupou-se todos aqueles próximos entre si anteriores a 201 dias (grupo 1) e todos os próximos entre si posteriores a 385 dias (grupo 2). A ETc média no período de crescimento considerando os grupos 1 e 2 foi de 3,38 mm dia-1 e o Kc médio obtido nestes grupos foi de 1,39. O resultado obtido pode auxiliar no cálculo correto da lâmina de irrigação na cultura.

The decoupling factor (Ω) reflects the leading mechanisms responsible for canopy transpiration and allows to know the relevance of the control of stomatal or canopy conductance on transpiration (T). The Ω is strongly dependent on water availability and can be a good approach to describe how plants minimize excessive water loss by increasing the dominance of biotic factors that controls evapotranspiration under water deficit conditions. We provided an overview of how the Ω concept can be broadly used and applied for studying the sensitivity of evapotranspiration and water conservation potential of canopies under water deficit conditions. A decoupling condition indicates that, under water deficit, the increase of canopy resistance will not have control over the transpiration. Therefore, a structural context of the canopy in which predominantly uncoupled regions will have a lower capacity to reduce evapotranspiration and avoid water losses. Furthermore, because of the water deficit, stomatal closure restricts photosynthesis more than transpiration, and water use efficiency can be lower in decoupled canopies compared to more coupled ones. Yet, we summarized the characteristics that depict structural context predisposing coupled or decoupled conditions that can indicate the capacity of canopy/crop to reduce excessive water losses and maintain a high assimilation/transpiration relation under water deficit.e farmers to design disease management programs accordingly to avert yield losses.

The objective of this study was to evaluate the technical and economic feasibility of installing central pivot irrigation systems in current days (Scenario A) and in two future scenarios, one with a 10% increase in rainfall (Scenario B1) and the other with 10% reduction in rainfall (Scenario B2). For both future scenarios, an increase of 2ºC in the global temperature and the concentration of atmospheric carbon dioxide (CO2) increasing to 528 ppm (parts per million) were considered. For the study, the recommendation for an area of clayey soil and with the sugarcane cycle was evaluated on three different planting dates: May 15, August 15 and November 15. The DSSAT/CANEGRO model was used, and under the current conditions, the simulations indicated greater yield for planting in May, both for rainfed and irrigated. For scenario B1, there was an increase in yield of 22% for rainfed and 33% for irrigated. In addition, irrigation provided yield gains in the two future scenarios of 13% and 14% for B1 and B2, respectively. Based on the results obtained, central pivot irrigation proved economically viable in the simulated climatic conditions. Therefore, the increase in sugarcane production provided by irrigation in agronomic management was sufficient to make investment in the region in question feasible. It is suggested to repeat the study in other regions, since the existing synergy between the factors that define agricultural yield can change the decision making about the implantation of irrigation systems in the production environment.

Brazil is the largest sugarcane producing country in the world. Mills usually operate nine months to process the sugarcane produced in the country. Here we investigated the effect of harvest time on the on-farm sugarcane yield and yield components (stalk fresh yield [SFY], sucrose yield [SY], and sucrose concentration [POL%]). We used a large database collected from commercial sugarcane blocks to assess the effect of harvest time on SY and yield components. Blocks were first clustered based on similarity of climate and soil, referred as environments, and the effect of harvest season on SY, SFY, and POL%, as influenced by the environment and the number of harvests, was evaluated using analysis of variance. Harvest season strongly influenced POL% and SY but had a comparably smaller effect on SFY. Although relatively smaller compared with other sources of variation, there was a statistically significant interactive effect of harvest number and harvest season on SY, with highest SY when harvest occurred during the mid-season or late season in old ratoons and during the mid-season in the case of young ratoons. Closing the yield gap due to sub-optimal harvest time by concentrating the harvest around the productivity peak would increase national sucrose production by 8%, but this is not possible due to logistic and milling constrains. In contrast, our findings suggested room to extend the harvest period to 10 months, which will free up milling capacity by 8% with no yield penalty. The extra milling capacity could serve as a motivation to increase productivity via agronomic practices to fully exploit the milling processing capacity.

Irrigation is necessary to help meet the high demand for water by sugarcane in several countries including Brazil and Australia. The crop irrigation requirements are typically estimated using the crop coefficient-reference evapotranspiration (Kc-ETo) procedure. Sugarcane evapotranspiration rates were measured in three different sugarcane-producing regions of the world, and crop coefficients (Kc) were derived for those diverse environments, irrigation methods, and farming systems, therefore representing a robust basis for irrigation management. We also verified the occurrence of the inverse relation between Kc and ETo found in previous studies. Two experiments in Brazil and one in Australia were used for the analysis. Our data showed that Kc for a full canopy cover was lower than 1.0 in the three experimental sites and that sugarcane evapotranspiration (ETc) seems to be limited and exceeds ETo only when this is below 4 mm day−1. In one of the Brazilian experiments, Kc declined at higher rates than in the other two experiments, and for the three sites, average Kc was 0.77 and 0.87, respectively, for initial and full cover phase when ETo > 6 mm day−1. The increase of aerodynamic and other upstream resistances to water transport of plants appears to be one of the reasons for Kc to decrease at high levels of ETo. Based on our data and the literature, the Kc values provided by Allen et al. (1998) could overestimate the irrigation needs of sugarcane under high evaporative demand conditions. Irrigation management based on Kc should use the average ETo from the preceding 3 days before irrigating to save water and energy while maintaining high yield levels.

CONTEXT Limited land availability and an increasing global population are challenges faced by the agricultural sector in the coming decades. The silvopastoral system is an efficient alternative to full sun pastures that could be used to sustainably intensify animal and crop production. However, the adoption of this system is being held back by a lack of knowledge on how the trees in such a system should be arranged in order to avoid detrimental effects on pasture growth. OBJECTIVE The aim of this study was to test different arrangements of trees in the Eucalyptus-Marandu palisade grass silvopastoral system and to evaluate its performance in different regions of Brazil. METHODS A functional-structural plant model was developed to simulate radiation interception by trees and was then coupled to the CROPGRO-Perennial Forage model to simulate the production of forage biomass. Considering solar radiation as the main resource under competition, water interactions that occur under-ground between Eucalyptus and Maranu palisade grass were not considered. The models were calibrated with experimental data collected in silvopastoral systems in Brazil. The silvopastoral systems were selected according to a combination of tree row spacing (15, 30, and 45 m), two row orientations (north-south and east-west), and single or triple rows. Simulations were replicated for different tree ages (2, 4, 6, 8, 10 and 12 years) representing different levels of shading. RESULTS AND CONCLUSIONS Our simulations show that the tree arrangement has a significant effect on the incidence of radiation on the pasture, resulting in different levels of forage production. Row spacing of 30 and 45 m is suitable for providing forage for the animals for several years. In contrast, tree arrangements with a row spacing of 15 m or triple lines demand more careful planning and management, taking into account the soil and climatic characteristics of each region. Lower declines in the forage production were observed in arrangements of 45 m, varying from 1000 and 3000 kg ha−1 after 6 years of system establishment. In this period, the annual production level was lower than 14,000 kg ha−1 for arrangments with row spacing of 15 and 30 m, being recommend pruning and thinning practices aiming to increase the radiation incidence within the system. SIGNIFICANCE The approach used in this study can be extended to other combinations of species and environments to aid the planning and management of this kind of system.

It was evaluated how straw management modifies the development, growth, nutrient cycling and crop water productivity of sugarcane in the semiarid region of Brazil. The experiment was carried out using two plots with 5 ha each, being one without straw on the soil surface and one with 27.2 Mg·ha−1 covering the soil. Sugarcane growth and development and straw decomposition coefficient were evaluated, whereas the industrial yield, juice quality, dry matter partitioning, and crop water productivity were determined at harvesting. The straw decomposition coefficient was 0.0049 Mg·ha−1·day−1, and the remaining dry mass was equal to 24%. The straw affected the sugarcane growth and development until the first 100 days. The individual internode volume can be adopted as an indicator of the effect of straw on sugarcane growth because the internode volumes up to the sixth position in the with-straw treatment crop were lower than in the no-straw treatment, which was not observed in other variables of the stalks. Keeping straw on the soil surface reduced the crop lodging. Yield and juice quality were not affected, but crop water productivity was increased by keeping sugarcane straw in the field. Made available in DSpace on 2021-02-18T12:20:04Z (GMT). No. of bitstreams: 1 Straw-management-effects-on-sugarcane-growth-2020.pdf: 299525 bytes, checksum: b3d1b6af75f44912ded85e65bd2b7014 (MD5) Previous issue date: 2020

Sugarcane is the most important sugar crop worldwide, with Brazil accounting for 38% of global production. Recent slowdown in sugarcane annual yield gains in Brazil has been attributed to longer replanting time and associated higher number of ratoon harvests. However, little is known about changes in on-farm sugarcane yield and its components as influenced by number of harvests. In this study, we used a large database collected from commercial sugarcane fields (‘blocks’) to assess the influence of number of harvests on variation in sugar yield and its components: stalk fresh yield (SFY) and sucrose concentration (POL%). Blocks were first clustered based on similarity of climate and soil (hereafter referred as ‘environments’). Influence of number of harvests on sugar yield, SFY, and POL% was evaluated across environments using analysis of variance and quantile and least square regressions. On-farm SFY versus number of harvests trends were compared against existing data collected from well-managed experiments. Variation in sucrose yield across block-years was mostly explained by changes in SFY and, in much lesser degree, by POL%. There was a decline in SFY with number of harvests in all cases; however, rate and magnitude of decline was different across climate-soil domains, with faster yield decline in poor soils and larger yield penalty in the region with relatively short sugarcane cropping history. Still, there was large variation in on-farm yield at any environment x harvest number combination, highlighting the importance of management at explaining current yield gap. Conversely, POL% was not affected by number of harvests and varied little across environments. Analysis of data from well-managed experiments showed no detectable yield decline with increasing number of harvests, suggesting that observed on-farm yield decline is attributable to sub-optimal management in commercial blocks. Findings from this study can help inform policy and management associated with replanting decisions.

The lack of base information on crop water requirements under tropical conditions is one of the causes for inefficient water use and inadequate irrigation management. The crop coefficient (Kc) approach is universally adopted for scheduling and quantifying the water management and, recently, its relation with the evaporative atmosphere demand has been included in this approach to improve the decision-making on irrigation management. In this paper, we measured crop evapotranspiration (ETc) in two experiments as evaporative heat flux from a centre pivot-irrigated soybean plantations in tropical Brazil to quantify the crop water needs. Irrigation requirements were determined by comparing ETc with reference evapotranspiration (ETo), derived from FAO-56 (Allen et al., 1998). In this study, the average Kc value obtained was 0.92, which is nearly 20% lower than those recommended by the FAO-56 ( Allen et al., 1998 ) and varied inversely as a function of ETo. Based on aerodynamic and leaf diffusive resistance (rs) data, Ω was computed and presented values relatively high compared to other crops, which means a relatively poor coupling of soybean canopies to the atmosphere. Throughout both experiments, the Kc value decreased by up to 44.8% when the ETo increased from 2 to 4 mm d−1, depending on the phenological phase, indicating the need for taking into account the ETo values when selection the Kc values for improving the irrigation management in tropical soybean.

Studies of the anticipated consequences of climate change suggest that among all economic sectors, agriculture would be the most affected. In Brazil, this issue is particularly relevant, since the agricultural sector and its related activities account for a significant share of the country’s GDP and employment. Using a fixed effects panel model and data from 1990 through 2012, this paper empirically analyzes the vulnerability of agriculture to climate variables in Brazil’s ten main agricultural states and the possible resulting loss of agricultural value in the face of future climate change. Our work is differentiated from prior studies in that it employs state level annual data series, which allows the aggregation of a great deal of relevant current information to the analysis. The results indicate that climate variables have a significant impact on most of these states’ agricultural production, especially air temperature, whose effects showed higher estimated magnitude than those from rainfall. Considering the estimated elasticities and climatic projections, the most severe damage to agriculture is expected in Espirito Santo, Minas Gerais, and Rio Grande do Sul.

This study compares the performance of Global Ensemble Forecast System (GEFS) and European Centre for Medium-Range Weather Forecasts (ECMWF) precipitation ensemble forecasts in Brazil and evaluates different analog-based methods and a logistic regression method for postprocessing the GEFS forecasts. The numerical weather prediction (NWP) forecasts were evaluated against the Physical Science Division South America Daily Gridded Precipitation dataset using both deterministic and probabilistic forecasting evaluation metrics. The results show that the ensemble precipitation forecasts performed commonly well in the east and poorly in the northwest of Brazil, independent of the models and the postprocessing methods. While the raw ECMWF forecasts performed better than the raw GEFS forecasts, analog-based GEFS forecasts were more skillful and reliable than both raw ECMWF and GEFS forecasts. The choice of a specific postprocessing strategy had less impact on the performance than the postprocessing itself. Nonetheless, forecasts produced with different analog-based postprocessing strategies were significantly different and were more skillful and as reliable and sharp as forecasts produced with the logistic regression method. The approach considering the logarithm of current and past reforecasts as the measure of closeness between analogs was identified as the best strategy. The results also indicate that the postprocessing using analog methods with long-term reforecast archive improved raw GEFS precipitation forecasting skill more than using logistic regression with short-term reforecast archive. In particular, the postprocessing dramatically improves the GEFS precipitation forecasts when the forecasting skill is low or below zero.

O Brasil possui uma agricultura de grande demanda hídrica, necessitando de pesquisas nesse segmento. Quantificar a umidade do solo tem grande importância no manejo da irrigação e consequentemente na otimização dos recursos hídricos. Uma maneira de se mensurar essa variável é através da modelagem de sistemas agrícolas, que podem ser realizadas através de modernas plataformas como o DSSAT/CROPGRO. Com a finalidade de estudar a dinâmica da água no solo realizou-se um experimento em Piracicaba-SP na Fazenda Areão na área de pesquisa do Departamento de Engenharia de Biossistemas da Escola Superior de Agricultura “Luiz de Queiroz” (ESALQ/USP), em uma lavoura de soja. Uma estação meteorológica foi instalada na área experimental para a coleta de dados de entrada para a simulação do teor de água através do módulo Soil Water Balance (SWBM) do modelo DSSAT/CROPGRO. A curva de simulação obtida pela modelagem foi correlacionada com dados medidos pelo sensor GS3 Decagon nas profundidades de 0,2m e 0,5m. As entradas e saídas de água do sistema, assumidas nesse trabalho foram a precipitação e evapotranspiração diária, pelo método da Razão de Bowen. A hipótese levantada no presente estudo é que o módulo SWBM do DSSAT é capaz de simular com precisão e acurácia o teor de umidade volumétrica do solo. O modelo obteve uma precisão mediana e boa acurácia para as duas profundidades estudadas.

Continuous monitoring of soil water content is a crucial element for sustainable agricultural water management. The goal of this study was to use the Cropping System Model (CSM)-CROPGRO-Soybean model in conjunction with field data to determine the impact of different irrigation regimes, soil texture, and tillage practices on soybean [Glycine max (L.) Merr.] growth, development, and yield for tropical conditions. Field experiments were conducted at two sites: (i) Piracicaba with conventional tillage (PI-1, season 2016–2017), and no-tillage practices (PI-2, season 2017–2018), where the experiments were irrigated with full water requirements; and (ii) Teresina under conventional tillage (season 2019) with two irrigation treatments of full (TE-1) and 50% (TE-2) water requirements. Soil water content was measured for all experiments using an electromagnetic probe installed at several depths. The results showed that the model was able to simulate soybean growth and development for the different sites, with a very good agreement ( D -statistic > 0.8) between the simulated and observed data. In addition, the soil water content was simulated with satisfactory accuracy ( D -statistic > 0.5). Following model evaluation, long-term hypothetical scenarios for different soil tillage practices and water management regimes were simulated for Piracicaba and Teresina sites. The results showed that the use of no-tillage could reduce the average amount of irrigation in Piracicaba by 30% and in Teresina by 17%, achieving the same yield level as conventional tillage. Thus, the CSM-CROPGRO-Soybean can be used as a tool for determining optimum water management practices for tropical environments.

Climate and soil databases can be used for delineating homogenous environmental zones over large areas of agricultural land to support agricultural research planning and spatial extrapolation of the results of field experiments. In other countries, such framework has proven useful to improve the efficiency and impact of investments in agricultural research. Furthermore, this approach can also contribute to identify key locations with the greatest potential for spatial extrapolation in terms of crop production area with similar climate and soils. In this paper, soil and weather databases covering the main agricultural land in Brazil were developed, and crop-specific technology extrapolation domains (TEDs) were identified for maize, soybean, and sugarcane crops. These databases were useful and viable option for the generation of homogeneous zones maps for different crops and regions. Given the spatial scale of the database applied, it was possible to represent a large area in few TEDs, without losing information regarding climate and soil variability, facilitating the spatial extrapolation of technologies throughout Brazil. Few TEDs are needed to represent a large part of the area of sugarcane (32 TEDs to cover 51% of the area), maize (21 TEDs for 51% of the area), and soybean (17 TEDs for 50% of the total area). Such information may help several areas of the agricultural sector, such as supporting new research that works on areas with large scales, or areas not explored yet.

The semiarid lands of Northeast Brazil represent one of the most densely populated regions of the country. Rainfall variability together with land degradation and large-scale poverty in rural areas makes this region vulnerable to droughts. Most of the agriculture in this region is rainfed and deficient rainfall leads to severe drought impacts. In this review, we examine different short- and long-term strategies directed to cope with possible impacts of droughts proposed by the government, farmers, civil society, and the private sector. These are approaches to adaptation to drought in the Northeast of Brazil, and among them, we have agricultural management and soil conservation and better management of water resources. Other actions include seasonal climate forecasts and funds transfer and credits to affected small-scale farmers. Although some of these actions are for the short term and may help to survive the drought situation, they may be only postdisaster mitigation options that do not improve adaptive capacity. They favor maladaptation and create dependency of farmers to government actions. Some experiences such as AdaptaSertao show potential benefits for small-scale farmers. We identify key challenges for moving toward a more holistic risk management approach and highlight the need to integrate actions and tools for adaptation, combining technology-based solutions with in-depth knowledge of local and regional social, economic, and cultural aspects, among them seasonal climate forecasts and drought impacts studies, among some other proactive predisaster ways, rather than reactive postdisaster actions. Adaptation strategies must increase long-term resilience of food production in the Brazilian Northeast, going beyond an individual drought event.

Carqueja (Baccharis crispa Spreng.) has been primarily used as a medicinal plant around the world. Commercially, the essential oil content of carqueja leaves is the most valuable crop productivity variable. We evaluated the effect of irrigation management in different growing seasons on the essential oil content of carqueja leaves using gas chromatography coupled with mass spectrometry. The experiment was conducted in a greenhouse located in Southern Brazil, where the crop was cultivated for two years in different growing seasons under six irrigation regimes: 25%, 50%, 75%, 100%, 125%, and 150% of the reference crop evapotranspiration (T25, T50, T75, T100, T125, and T150, respectively). A seasonal pattern was observed in the number of metabolites of sesquiterpenes and phenolics in the essential oil extracted from the biomass, this outcome was correlated with irrigation regimes and air temperature. Principal component and hierarchical cluster analyses were used to discriminate the influence of abiotic conditions on secondary metabolite profiles. Spathulenol was the most abundant compound in the essential oils (95.43%) collected during the summer (December&ndash, March) season during the third harvest (H3) at T150. The essential oil content was 8.84% &plusmn, 0.05% and 10.52% &plusmn, 0.10% in summer and winter (June&ndash, September), respectively, with T100 at 45 and 46 days after planting.

Uma população mundial estimada em 10 bilhões em 2100 e a incerteza sobre o clima futuro acentuam os debates sobre fome, abastecimento de água e energia. Especialmente no tocante à segurança alimentar, o Brasil é colocado em destaque. Por isso, pesquisas direcionadas ao pleno entendimento das relações solo-planta-atmosfera tornam- se cada vez mais fundamentais. Neste trabalho, expomos uma revisão bibliográfica a respeito das bases biofísicas fundamentais à concepção da Agrometeorologia Digital. Sistemas de suporte à tomada de decisão, baseados em modelos, podem introduzir o fator clima no gerenciamento da produção agropecuária, agregando uma gama de serviços agrometeorológicos que auxiliam nas decisões de gerenciamento, tornando-as mais eficazes a curto e longo prazo.Palavras-chave: Biofísica. Ecofisiologia. Agrometeorologia Operacional. Modelagem. Tecnologia da Informação.

The expansion of sugarcane crop to regions with lower water supply in Brazil has increased the importance of correct estimation of crop water requirements. Currently, the irrigation management is generally done using the crop coefficient (Kc) based on the FAO 56 bulletin. Kc is used to determine the potential water demand of the crop for a given period of time and is considered constant for each crop stage. However, some recent studies have shown that Kc can be significantly variable under different evapotranspiration (ETo) rates. This paper aimed to analyse sugarcane water consumption at different scales: plant (sap flow measurements by energy balance method); canopy (Bowen ratio energy balance method); and plant–atmosphere coupling (infrared gas analyser) to reduce the uncertainties on the irrigation practices. Measurements were taken at two experimental sites, where a modern Brazilian cultivar CTC 12 was grown under drip irrigation and an old main Brazilian cultivar (RB867515) was grown under sprinkler irrigation by a central pivot. The mean crop evapotranspiration (ETc) values by the Bowen ratio energy balance method were 2.92 and 3.68 mm d−1 for RB867515 and CTC 12, respectively, resulting in a mean Kc of 0.99 at the full vegetative growth stage. Kc values were dependent on ETo and varied between 0.2 and 1.7 for both cultivars. This occurred in a crop coupled to the atmosphere (Ω = 0.37) and was the same found in other coupled crops such as coffee and citrus. In conclusion, the sugarcane Kc for southeast Brazil presented temporal variability due to coupling conditions according to reference evapotranspiration, and this should be considered in irrigation management.

The solar radiation is one of the most important weather variables for determining the potential yield of agricultural crops. Soybean is the main Brazilian agricultural commodity, with great social and economical importance for the country. It is well recognized that cloudiness is a limiting factor for crop growth rate. Few studies have been conducted to systematically evaluate how much cloud affect soybean yield and none, to our knowledge, is available for tropical soybean. The objective of this paper was to quantify the implications of cloudiness on soybean growth and development in tropical Brazil. To do so, experimental data associated with the simulations of the DSSAT/CROPGRO (DC) model was used, and two treatments were simulated: a) the first used measured solar radiation and b) the second used estimated solar radiation for non-cloud days. Thus, based on the model output variables (growth rate of aerial dry matter, grain yield, specific leaf weight, and light saturation point) and comparing the data with the literature review. We found that simulations exhibited an increase in the dry matter production rate of up to 23%, during days of clear sky, resulting in a yield increase between 26 and 37%. Also, the DC could simulate some adaptation in the plant when the solar radiation changes, like the specific foliar weight and the light-saturated photosynthesis rate.

Diante da importância econômica e social da produção de fibras no Brasil e no mundo, é relevante antever os possíveis impactos do clima futuro na produtividade de algodão em uma região onde a cultura é representativa. O presente estudo teve como objetivo simular cenários agrícolas futuros para a cultura do algodão, com base em projeções de mudanças climáticas, para o município de Barreiras, BA. Para isso, o modelo DSSAT/CROPGRO-COTTON foi calibrado com as características genéticas da cultivar CNPA ITA 90. A produtividade foi simulada para os últimos 30 anos (1980 - 2010), representando a produtividade no clima atual e, a fim de representar a produtividade em 2050, foram realizadas simulações para o período de 2040 - 2069 para seis cenários climáticos futuros gerados a partir da metodologia descrita pelo Agricultural Model Intercomparison and Improvement Project (AgMIP). A produtividade média nos cenários futuros variou de 4.652 kg ha-1 a 5.389 kg ha-1, apresentando um expressivo aumento nos seis cenários estudados, porém indicando maior risco climático para o cultivo do algodoeiro nesta região.

SUMMARYDue to the lack of basic information on water required by maize (Zea mays L.) in Brazil, the large amount of water applied usually exceeds crop requirements, wasting water and energy. In this study, we measured crop evapotranspiration (ETc) as evaporative heat flux from a centre pivot-irrigated maize plantation in Southern Brazil during winter and summer seasons, using the Bowen ratio method to evaluate how the degree of canopy-atmosphere coupling affects crop water needs and irrigation management. Irrigation requirements were determined by comparing ETc with reference evapotranspiration (ETo), derived from the Penman–Monteith equation and expressed as the ETc/ETo (Kc) ratio. In this study, the average Kc values obtained were 1.31 and 0.90 for the winter and summer, respectively. Using aerodynamic and canopy resistance measurements, the decoupling factor (Ω) was computed. Ω values tending to zero (0.09 and 0.20 for winter and summer, respectively) showed that strong coupling of maize plants to the atmosphere and sensitivity to high air temperatures, vapour pressure deficits and wind speed caused variations in Kc in relation to ETo ranges. During the experimental period, the Kc value ranged from 0.92 when the ETo exceeded 4 mm d−1 to 1.64 when the ETo was less than 2 mm d−1.

The deterministic approach in crop modeling simplifies uncertainty present in the environment using a unique parameter set. In practice, this uncertainty is seen in the variability of data collected in a field experiment. One way to exploit this uncertainty is to use the stochastic approach, by inserting the range of plausible variability into the simulation’s parameters and inputs. This study aims to evaluate the ability of a process-based crop model to simulate the uncertainty of a sugarcane field. We employed the recently updated version of SAMUCA model to simulate the sugarcane growth and development in a 4-year field experiment, where the crop was grown under the effect of green cane trash blanket (GCTB) and bare soil (Bare). To analyze the effect of genotype and soil variability on output variables, a stochastic approach was applied to the corresponding parameters of the SAMUCA model. A global sensitivity analysis was utilized to prioritize and identify the most important parameters to explain the model uncertainty. Then, the uncertainty was analyzed in three different ways: uncertainty analysis only for genotype parameters (UG), uncertainty analysis only for soil parameters (US) and the analysis of both soil and genotype parameters (UGS). We quantified the variability of the stochastic simulation by the ratio between the average of the standard deviation of the simulations and the average of the standard deviation of the observed data. The variability observed in the field is not fully explained by the hydraulic parameters of the soil, possibly due to irrigation and good rainfall distribution in the area. Furthermore, the variability in US simulations were higher for GCTB than in Bare treatment, suggesting that the GCTB has a larger influence in SAMUCA’s variability than for the hydraulic parameters in the conditions of this study. The UG and UGS had the same capacity to quantify the variability present in the environment for the treatments Bare and GCTB. In this case, sensitivity to soil parameters can simply be ignored and genotype parameters can be chosen as the only source of variability for practical applications. Our suggestion for future work is to explore environments without irrigation, different amounts of GCTB and other soil parameters present in the model.

In the next decades, the population is expected to rise by more than two billion people, and the projections of climate change have been considered as one of the greatest future challenges for world food security. Soybean represents more than 60 % of all plant protein produced in the world, and Brazil is the largest world exporter and the second-largest producer. In this paper, we simulated soybean yields for 16 strategically selected agroclimatic zones (CZs) to represent Brazilian production. Experiments conducted throughout the country were used to calibrate the CROPGRO-Soybean model for Brazilian conditions, for the main maturity groups used in Brazil, to simulate current and 40 future climate scenarios, provided by Coupled Model Intercomparison Project 5 (CMIP5) for 2050 in the both 4.5 and 8.5 representative concentration pathways (RCP). We found soybean yield varying by +1 to +32 % across 16 CZs in the average scenario of future climate when compared to the current yields. Yet, we found an increase of about 5% in the yield production risk for RCP 8.5. The main reason for such results was associated with the positive effect of increasing CO2 on crop water productivity, which overcomes the negative effects of temperature and water stress increases on rainfed Brazilian soybeans.

O milho é considerado uma das culturas mais cultivadas mundialmente porem, rendimento da cultura depende da relação intrínseca estabelecida entre a planta e o ambiente em que se encontra, sendo o acoplamento responsável pela intensidade do fluxo de massa e energia entre a interação planta-atmosfera. Objetivou-se analisar a variação do acoplamento (Ω) de milho cultivado no verão e outono a fim de compreender a interação existente entre vegetação-atmosfera. Foram conduzidos dois experimentos, o primeiro na época do outono e os segundos no verão, ambos instalados no município de Piracicaba-SP. O fator de acoplamento (Ω) foi calculado pela equação proposta por McNaughton e Jarvis (1983) e os dados de transpiração para o período do outono foram estimados por meio do modelo CERES-MAIZE. Verificou-se acoplamento da vegetação com a atmosfera na safra de outono devido à ação conjunta entre os componentes aerodinâmicos e radiativos no controle da troca de vapor de água com a atmosfera; na safra de verão houve desacoplamento devido à ocorrência de temperaturas elevadas, o que favoreceu as atividades metabólicas da planta. Concluiu-se que na safra de outono, o acoplamento das plantas de milho com a atmosfera ocorreu com o aumento da velocidade do vento, redução da resistência aerodinâmica e da camada limite foliar, com queda na transpiração; temperaturas entre 25 a 30 °C favoreceram o desacoplamento das plantas de milho com a atmosfera, na safra de verão. A B S T R A C TMaize is considered to be one of the most cultivated crops worldwide, crop yield depends on the intrinsic relationship established between the plant and the environment in which it is found, and coupling is responsible for the intensity of mass and energy flux between the plant-atmosphere interaction. The objective of this study was to analyze the coupling variation (Ω) of maize grown in summer and autumn in order to understand the interaction between vegetation and atmosphere. Two experiments were conducted, the first in the fall season and the second in the summer, both installed in the municipality of Piracicaba-SP. The coupling factor (Ω) was calculated by the equation proposed by McNaughton and Jarvis (1983) and the transpiration data for the autumn period were estimated using the CERES-MAIZE model. It was verified the coupling of the vegetation with the atmosphere in the fall harvest due to the joint action between aerodynamic and radiative components in the control of the exchange of water vapor with the atmosphere; In the summer crop there was decoupling due to the occurrence of high temperatures, which favored the metabolic activities of the plant. It was concluded that in the autumn harvest the coupling of corn plants with the atmosphere occurred with the increase of wind speed, reduction of aerodynamic resistance and leaf boundary layer, with decrease in transpiration; Temperatures between 25 and 30 ° C favored the decoupling of corn plants with the atmosphere in the summer season.

Timely crop yield forecasts at regional and national level are crucial to manage trade and industry planning and to mitigate price speculations. Sugarcane is responsible for 70% of global sugar supplies, thus making yield forecasts essential to regulate the global commodity market. In this study, a sugarcane forecasting system was developed and successfully applied to Sao Paulo State, the largest cane producer in Brazil. The system is based on multiple linear regressions relating agro-climatic indicators and outputs of the sugarcane model Canegro to historical yield records. The resulting equations are then used to forecast the yield of the current season using 10-day period updated values of indicators and model outputs as the season progresses. We quantified the reliability of the forecasting system in different stages of the sugarcane cycle by performing cross-validations using the 2000–2013 time series of official stalk yields. Agro-climatic indicators alone explained from 38% of inter-annual yield variability (at State level) during the boom growth phase (i.e., January–April) to 73% during the second half of the harvesting period (i.e., September–October). When Canegro outputs were added to the regressor set, the variability explained increased to 63% for the boom growth phase and 90% after mid harvesting, with the best performances achieved while approaching the end of the harvesting window (i.e. at the beginning of October, SDEP = 0.8 t ha − 1 , R 2 cv = 0.93). It is concluded that the overall performances of the system are satisfactory, considering that it was the first attempt based on information exclusively retrieved from the literature. Further improvements to operationalize the system could be possibly achieved by the use of more accurate inputs possibly supplied by the collaboration with local authorities.

CONTEXT Brazil is one of the main producers of common beans (Phaseolus vulgaris L.), which have high nutritional value as human food. The climate changes predicted in the 21st century might be a possible threat to the planet’s food security, given the expected population increase, and hence, increased demand for food. OBJECTIVE This study aimed to project the impact of climate change on common bean cropping systems using an upscaling climate approach and crop modeling to represent the Brazilian production regions. METHODS We considered the representative CO2 concentration pathway scenarios (RCPs) 4.5 and 8.5 presented by the 5th IPCC Assessment Report from 20 atmospheric global circulation models covering the main bean-producing region in Brazil. The well-calibrated CROPGRO-Drybean crop model simulated two representative cultivars of the “black” and “colors” types and three cropping seasons applied by Brazilian farmers. RESULTS AND CONCLUSIONS On average, we found that yield increased by 5.56% and 9.12% for the RCP 4.5 and 8.5 scenarios, respectively. Increased photosynthetic efficiency due to the increased atmospheric CO2 concentration was identified as the main cause of this yield increase. Crop respiration rates increased due to the raised air temperature, and were responsible for increasing the probability (production risk) of not meeting the future domestic demands for grains to 10.13% and 8.34% for the RCP 4.5 and 8.5 scenarios, respectively. For the national supply of grains, estimates pointed to a future in which crop production will probably rely more on area expansion than yield gains by crop intensification. SIGNIFICANCE Our findings emphasize the need for new policies for land utilization and investments in scientific research programs aimed towards genetic adaptation in all main Brazilian crops in the face of potential climate change.

This article assesses sugarcane yield gaps (YG) in Brazil to determine the degree to which production can be increased without land expansion. In our scenario assessments, we evaluated how much of the projected sugarcane demand to 2024 (for both sugar and bioethanol) can be satisfied through YG closure. The current national average yield is 62% of yield potential estimated for rainfed conditions (i.e., a YG of 38%). Continuing the historical rate of yield gain is not sufficient to meet the projected demand without an area expansion by 5% and 45% for low- and high-demand scenarios, respectively. Closing the exploitable YG to 80% of potential yield would meet future sugarcane demand, with an 18% reduction in sugarcane area for the low-demand scenario or a 13% expansion for the high-demand scenario. A focus on accelerating yield gains to close current exploitable YG is a high priority for meeting future demand while minimizing pressure on additional land requirements.