Limits...
Neglecting rice milling yield and quality underestimates economic losses from high-temperature stress.

Lyman NB, Jagadish KS, Nalley LL, Dixon BL, Siebenmorgen T - PLoS ONE (2013)

Bottom Line: These dramatic losses result from reduced paddy yield and increased percentages of chalky and broken kernels, which together decrease the quantity and market value of milled rice.Recently published estimates show paddy yield reductions of up to 10% across the major rice-producing regions of South and Southeast Asia due to rising temperatures.The results of our study suggest that the often-cited 10% figure underestimates the economic implications of climate change for rice producers, thus potentially threatening future food security for global rice producers and consumers.

View Article: PubMed Central - PubMed

Affiliation: Department of Agricultural Economics and Agribusiness, University of Arkansas, Fayetteville, Arkansas, United States of America.

ABSTRACT
Future increases in global surface temperature threaten those worldwide who depend on rice production for their livelihoods and food security. Past analyses of high-temperature stress on rice production have focused on paddy yield and have failed to account for the detrimental impact of high temperatures on milling quality outcomes, which ultimately determine edible (marketable) rice yield and market value. Using genotype specific rice yield and milling quality data on six common rice varieties from Arkansas, USA, combined with on-site, half-hourly and daily temperature observations, we show a nonlinear effect of high-temperature stress exposure on yield and milling quality. A 1 °C increase in average growing season temperature reduces paddy yield by 6.2%, total milled rice yield by 7.1% to 8.0%, head rice yield by 9.0% to 13.8%, and total milling revenue by 8.1% to 11.0%, across genotypes. Our results indicate that failure to account for changes in milling quality leads to understatement of the impacts of high temperatures on rice production outcomes. These dramatic losses result from reduced paddy yield and increased percentages of chalky and broken kernels, which together decrease the quantity and market value of milled rice. Recently published estimates show paddy yield reductions of up to 10% across the major rice-producing regions of South and Southeast Asia due to rising temperatures. The results of our study suggest that the often-cited 10% figure underestimates the economic implications of climate change for rice producers, thus potentially threatening future food security for global rice producers and consumers.

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Rice (Oryza sativa L.) developmental stages.This figure describes the developmental stages relevant to this study. a, Vegetative, reproductive and ripening growth stages are defined relative to the observed 50% heading and emergence dates at each station. The vegetative, reproductive, and ripening stages are defined as the intervals [emergence, H –30 ), [H –30, H +5 ], (H +5, harvest ], respectively, where H denotes 50% heading. The ripening stage is divided into early and late grain filling denoted by W2 and W3 to account for the differential effects of temperature on the physiological processes occurring during these periods. b, Harvest dates are not available for the paddy yield data, so we approximate harvest as 40 days after 50% heading. Harvest dates are available for the milled rice yield and quality data, but some plots were not harvested at maturity to allow harvest moisture content (HMC) to decrease. To avoid inclusion of temperatures beyond maturity, H +40, harvest is used as the harvest date for milling yield and quality trials.
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pone-0072157-g001: Rice (Oryza sativa L.) developmental stages.This figure describes the developmental stages relevant to this study. a, Vegetative, reproductive and ripening growth stages are defined relative to the observed 50% heading and emergence dates at each station. The vegetative, reproductive, and ripening stages are defined as the intervals [emergence, H –30 ), [H –30, H +5 ], (H +5, harvest ], respectively, where H denotes 50% heading. The ripening stage is divided into early and late grain filling denoted by W2 and W3 to account for the differential effects of temperature on the physiological processes occurring during these periods. b, Harvest dates are not available for the paddy yield data, so we approximate harvest as 40 days after 50% heading. Harvest dates are available for the milled rice yield and quality data, but some plots were not harvested at maturity to allow harvest moisture content (HMC) to decrease. To avoid inclusion of temperatures beyond maturity, H +40, harvest is used as the harvest date for milling yield and quality trials.

Mentions: Recent research has shown that modest (1°C) increases in daily maximum and minimum temperatures can decrease paddy yields by as much as 10% [10], [11], dramatically alter the distribution of head and broken rice [16], [17], and greatly increase the proportion of chalky kernels [15], [16], [17], [19]. Despite the importance of milling outcomes to global food security and the economy, the research to date on paddy yield and milling quality does not intersect, leaving a significant gap in the literature on a crucial topic. We attempt to fill this gap by modeling paddy yield and milling quality as temporal functions of cumulative exposure to day temperatures above 33°C and night temperatures above 22°C during sensitive growth windows (Fig. 1). We estimate high temperature effects on paddy yield – the mass (kg ha−1) of unprocessed kernels; milled rice yield (MRY) – the mass percentage of milled kernels (milled rice) to an initial mass of paddy rice kernels; head rice yield (HRY) – the mass percentage of milled kernels ≥ three-quarters the length of an unbroken (whole) milled kernel (head rice) to an initial mass of paddy rice; broken rice yield (BKY) – the mass percentage of milled kernels<three-quarters the length of an unbroken (whole) milled kernel to an initial mass of paddy rice; and chalk content (CHK) – defined as the ratio of chalky to non-chalky area of 100 brown rice (kernels obtained immediately after removing the husk) kernels. Definitions of MRY, HRY, BKY, and CHK correspond to the experimental definitions stated in [16]. Estimating these components allows predictions of reductions in yield and milling quality attributable to growth-stage-specific, diurnal high-temperature events. We use these estimates to predict changes in paddy yield, chalk, HRY, and MRY given 1°C, 2°C, and 4°C increases in growing season air temperature. The predictions are used to calculate changes in the quantity and value of paddy and milled rice for producers and millers across temperature scenarios.


Neglecting rice milling yield and quality underestimates economic losses from high-temperature stress.

Lyman NB, Jagadish KS, Nalley LL, Dixon BL, Siebenmorgen T - PLoS ONE (2013)

Rice (Oryza sativa L.) developmental stages.This figure describes the developmental stages relevant to this study. a, Vegetative, reproductive and ripening growth stages are defined relative to the observed 50% heading and emergence dates at each station. The vegetative, reproductive, and ripening stages are defined as the intervals [emergence, H –30 ), [H –30, H +5 ], (H +5, harvest ], respectively, where H denotes 50% heading. The ripening stage is divided into early and late grain filling denoted by W2 and W3 to account for the differential effects of temperature on the physiological processes occurring during these periods. b, Harvest dates are not available for the paddy yield data, so we approximate harvest as 40 days after 50% heading. Harvest dates are available for the milled rice yield and quality data, but some plots were not harvested at maturity to allow harvest moisture content (HMC) to decrease. To avoid inclusion of temperatures beyond maturity, H +40, harvest is used as the harvest date for milling yield and quality trials.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3750041&req=5

pone-0072157-g001: Rice (Oryza sativa L.) developmental stages.This figure describes the developmental stages relevant to this study. a, Vegetative, reproductive and ripening growth stages are defined relative to the observed 50% heading and emergence dates at each station. The vegetative, reproductive, and ripening stages are defined as the intervals [emergence, H –30 ), [H –30, H +5 ], (H +5, harvest ], respectively, where H denotes 50% heading. The ripening stage is divided into early and late grain filling denoted by W2 and W3 to account for the differential effects of temperature on the physiological processes occurring during these periods. b, Harvest dates are not available for the paddy yield data, so we approximate harvest as 40 days after 50% heading. Harvest dates are available for the milled rice yield and quality data, but some plots were not harvested at maturity to allow harvest moisture content (HMC) to decrease. To avoid inclusion of temperatures beyond maturity, H +40, harvest is used as the harvest date for milling yield and quality trials.
Mentions: Recent research has shown that modest (1°C) increases in daily maximum and minimum temperatures can decrease paddy yields by as much as 10% [10], [11], dramatically alter the distribution of head and broken rice [16], [17], and greatly increase the proportion of chalky kernels [15], [16], [17], [19]. Despite the importance of milling outcomes to global food security and the economy, the research to date on paddy yield and milling quality does not intersect, leaving a significant gap in the literature on a crucial topic. We attempt to fill this gap by modeling paddy yield and milling quality as temporal functions of cumulative exposure to day temperatures above 33°C and night temperatures above 22°C during sensitive growth windows (Fig. 1). We estimate high temperature effects on paddy yield – the mass (kg ha−1) of unprocessed kernels; milled rice yield (MRY) – the mass percentage of milled kernels (milled rice) to an initial mass of paddy rice kernels; head rice yield (HRY) – the mass percentage of milled kernels ≥ three-quarters the length of an unbroken (whole) milled kernel (head rice) to an initial mass of paddy rice; broken rice yield (BKY) – the mass percentage of milled kernels<three-quarters the length of an unbroken (whole) milled kernel to an initial mass of paddy rice; and chalk content (CHK) – defined as the ratio of chalky to non-chalky area of 100 brown rice (kernels obtained immediately after removing the husk) kernels. Definitions of MRY, HRY, BKY, and CHK correspond to the experimental definitions stated in [16]. Estimating these components allows predictions of reductions in yield and milling quality attributable to growth-stage-specific, diurnal high-temperature events. We use these estimates to predict changes in paddy yield, chalk, HRY, and MRY given 1°C, 2°C, and 4°C increases in growing season air temperature. The predictions are used to calculate changes in the quantity and value of paddy and milled rice for producers and millers across temperature scenarios.

Bottom Line: These dramatic losses result from reduced paddy yield and increased percentages of chalky and broken kernels, which together decrease the quantity and market value of milled rice.Recently published estimates show paddy yield reductions of up to 10% across the major rice-producing regions of South and Southeast Asia due to rising temperatures.The results of our study suggest that the often-cited 10% figure underestimates the economic implications of climate change for rice producers, thus potentially threatening future food security for global rice producers and consumers.

View Article: PubMed Central - PubMed

Affiliation: Department of Agricultural Economics and Agribusiness, University of Arkansas, Fayetteville, Arkansas, United States of America.

ABSTRACT
Future increases in global surface temperature threaten those worldwide who depend on rice production for their livelihoods and food security. Past analyses of high-temperature stress on rice production have focused on paddy yield and have failed to account for the detrimental impact of high temperatures on milling quality outcomes, which ultimately determine edible (marketable) rice yield and market value. Using genotype specific rice yield and milling quality data on six common rice varieties from Arkansas, USA, combined with on-site, half-hourly and daily temperature observations, we show a nonlinear effect of high-temperature stress exposure on yield and milling quality. A 1 °C increase in average growing season temperature reduces paddy yield by 6.2%, total milled rice yield by 7.1% to 8.0%, head rice yield by 9.0% to 13.8%, and total milling revenue by 8.1% to 11.0%, across genotypes. Our results indicate that failure to account for changes in milling quality leads to understatement of the impacts of high temperatures on rice production outcomes. These dramatic losses result from reduced paddy yield and increased percentages of chalky and broken kernels, which together decrease the quantity and market value of milled rice. Recently published estimates show paddy yield reductions of up to 10% across the major rice-producing regions of South and Southeast Asia due to rising temperatures. The results of our study suggest that the often-cited 10% figure underestimates the economic implications of climate change for rice producers, thus potentially threatening future food security for global rice producers and consumers.

Show MeSH
Related in: MedlinePlus