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Cropping Systems and Climate Change in Humid Subtropical Environments

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Cropping Systems and Climate Change in Humid Subtropical Environments agronomy Review Cropping Systems and Climate Change in Humid Subtropical Environments Ixchel M. Hernandez-Ochoa and Senthold Asseng * Agricultural & Biological Engineering Department, University of Florida, Frazier Rogers Hall, Gainesville, FL 32611, USA; ixchel@ufl.edu * Correspondence: sasseng@ufl.edu; Tel.: +1-352-392-1864 Received: 15 December 2017; Accepted: 10 February 2018; Published: 14 February 2018 Abstract: In the future, climate change will challenge food security by threatening crop production. Humid subtropical regions play an important role in global food security, with crop rotations often including wheat (winter crop) and soybean and maize (summer crops). Over the last 30 years, the humid subtropics in the Northern Hemisphere have experienced a stronger warming trend than in the Southern Hemisphere, and the trend is projected to continue throughout the mid- and end of century. Past rainfall trends range, from increases up to 4% per decade in Southeast China to −3% decadal decline in East Australia; a similar trend is projected in the future. Climate change impact studies suggest that by the middle and end of the century, wheat yields may not change, or they will increase up to 17%. Soybean yields will increase between 3% and 41%, while maize yields will increase by 30% or decline by −40%. These wide-ranging climate change impacts are partly due to the region-specific projections, but also due to different global climate models, climate change scenarios, single-model uncertainties, and cropping system assumptions, making it difficult to make conclusions from these impact studies and develop adaptation strategies. Additionally, most of the crop models used in these studies do not include major common stresses in this environment, such as heat, frost, excess water, pests, and diseases. Standard protocols and impact assessments across the humid subtropical regions are needed to understand climate change impacts and prepare for adaptation strategies. Keywords: climate; climate variability; climate adaptation; wheat-soybean rotation; wheat-maize rotation 1. Introduction Global food security faces many challenges in the future, including a growing population expected to reach more than 9 billion by mid-century, and to cause an increased demand for grain-fed, meat-based food [1,2]. Global crop production has increased over the last decades with advances in technology, land use intensification, and improvement in cultural practices [3]. Yet, increasing environmental degradation, such as soil erosion, loss of biodiversity, and pollution of water bodies, has raised concerns about improving sustainability in crop production systems, while maintaining and increasing crop production levels [4,5]. In addition, global food security faces the challenge of climate change, which can potentially cause significant reductions in global food production in the future [6–8]. Currently, anthropogenic greenhouse gas emissions, especially CO2, are the largest contributors to climate change [9]. Global atmospheric CO2 concentrations have reached 400 ppm by the end of 2015, which is approximately 40% higher than preindustrial levels [10]. As a direct effect of this process, combined global land and ocean mean temperature have increased approximately 0.85 ◦C from 1880 to 2012, with the last three decades being the warmest since 1850 [9]. Precipitation has increased, mostly in the Northern Hemisphere, while other regions show no general trend [11,12]. Climate change will also affect the occurrence of extreme events, such as increased heat waves, heavy rainfall, and drought periods [13]. Agronomy 2018, 8, 19; doi:10.3390/agronomy8020019 www.mdpi.com/journal/agronomy Agronomy 2018, 8, 19 2 of 17 ClimateAgronomy 2018 change, 8, x FOR and PEER variability REVIEW pose risks to food production from many perspectives. Heat2 of 18 stress during anthesis may reduce pollen viability, resulting in fewer grain sets [14–17]. Likewise, generalized negativeClimate effects change are observedwill also affect when the crops occurrence are subjected of extreme to events water, stress,such as resultingincreased inheat reduced waves, dryheavy matter rainfall, and drought periods [13]. accumulation and grain yield [18–20]. In future conditions, potential atmospheric CO2 enrichment Climate change and variability pose risks to food production from many perspectives. Heat could be advantageous for plant growth, as long as temperature and water are not limiting factors [21]. stress during anthesis may reduce pollen viability, resulting in fewer grain sets [14–17]. Likewise, This reviewgeneralized aims negative to synthesize effects andare compareobserved thewhen past crops trends are andsubjected future to climate water stress, projections, resulting as wellin as impactsreduced on main dry matter agricultural accumulation crops in and the grain humid yield subtropical [18–20]. In future regions conditions, of the world, potential and atmospheric also to identify researchCO2 gaps.enrichment could be advantageous for plant growth, as long as temperature and water are not limiting factors [21]. This review aims to synthesize and compare the past trends and future climate 2. Humidprojections Subtropical, as well Environmentsas impacts on main agricultural crops in the humid subtropical regions of the world, and also to identify research gaps. 2.1. Importance of Agriculture Humid2. Humid subtropical Subtropical regions Environments are located within the mid-latitudes, between 20◦ and 35◦ N and S, with the2.1. Importance major regions of Agriculture being the southeast U.S., southeast China, South America, and east Australia (Figure1 and Table1). Agriculture in these regions plays an important role in food security and the regional economies.Humid subtropical Winter regions wheat are constitutes located within the majorthe mid cereal-latitudes crop, between during 20 the° and winter 35° N season and S, in all with the major regions being the southeast U.S., southeast China, South America, and east Australia humid subtropical regions (Table1). Summer crops vary among these regions, with maize and soybean (Figure 1 and Table 1). Agriculture in these regions plays an important role in food security and the beingregional the most econom important.ies. Winter In the wheat southeast constitutes U.S., the major humid cereal subtropical crop during region the includeswinter season the states in all from Missourihumid to Virginiasubtropical in theregions north, (Table and Louisiana1). Summer to crops Florida vary in among the south these (Figure regions,1). Approximatelywith maize and 10% of thesoybean U.S. national being the maize most production important. occursIn the s inoutheast this region, U.S., the followed humid bysubtropical soybean regio at 3%n andincludes wheat the at 1% of thestates U.S. nationalfrom Missouri production to Virginia [22]. in In the China, north the, and humid Louisiana subtropical to Florida region in the is asouth diverse (Figure agricultural 1). area locatedApproximately in the southeast,10% of the U extending.S. national from maize the production south of occurs Shaanxi in this to theregion, south followed of Jiangsu by soybean provinces, and toat the3% and southern wheat at border 1% of ofthe China U.S. national (Figure pr1oduction). Approximately [22]. In China, 25% the of humid the Chinese subtropical national region wheat is and soybeana diverse productionagricultural area occurs located in this in the region, southeast, whereas extending maize from accounts the south for of approximately Shaanxi to the south 6% of the Chineseof Jiangsu national provinces production, and to [23 the]. Insouthern South border America, of China the humid (Figure subtropical 1). Approximately region 25% comprises of the the Chinese national wheat and soybean production occurs in this region, whereas maize accounts for Pampas in northeast Argentina, Uruguay, and South Brazil, including the states of Rio Grande do approximately 6% of the Chinese national production [23]. In South America, the humid subtropical Sul, Santaregion Catarina, comprises and the Pampas Paraná. in Northeast northeast Argentina, Argentina Uruguay, produces an mored South than Brazil, 75% including of Argentina’s the states wheat, soybean,of Rio and Grande maize. do Sul, In Uruguay, Santa Catarina, soybean and isParaná. the major Northeast production Argentina crop, produces contributing more than to 75% 65% of of the agriculturalArgentina’s area wheat, for those soybean, three cropsand maize. [24]. More In Uruguay, than 90% soybean of the totalis the national major wheatproduction is produced crop, in the southerncontributing states to of65% Brazil of the [25 agricul]. In easttural Australia, area for those the humidthree crops subtropical [24]. More region than extends90% of the to thetotal Great Dividingnational Range wheat in the is statesproduced of Queensland, in the southern New states South of Wales, Brazil and[25] Victoria. In east (FigureAustralia,1). Approximatelythe humid 46% ofsubtropical national wheatregion productionextends to the occurs Great in Dividing the eastern Range region, in the but states little of soybean Queensland, and maize New South are grown thereW [26ales,,27 ].and Victoria (Figure 1). Approximately 46% of national wheat production occurs in the eastern Mostregion, wheat, but little soybean, soybean and maize maize are are grown grown there under [26,27] rain-fed. conditions in humid subtropical Most wheat, soybean, and maize are grown under rain-fed conditions
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