MODELLING MANAGEMENT STRATEGIES TO MITIGATE THE EFFECTS OF ALTERATIONS OF TEMPERATURE AND OF CO2 CONCENTRATION ON MAIZE

DOI: https://doi.org/10.18512/rbms2021v20e1210 MODELLING MANAGEMENT STRATEGIES TO MITIGATE THE EFFECTS OF ALTERATIONS OF TEMPERATURE AND OF CO2 CONCENTRATION ON MAIZE Abstract – Ongoing climate change may affect rainfed maize yield in Brazil, which can be attenuated by some crop management strategies. This work aimed to evaluate, by using computational modeling, management practices with potential to mitigate the effects of changes in temperature and CO2 concentration on maize yield. The CSM-CERES-Maize model was applied to simulate the mitigating potential of using maize cultivars with 0.3 m, 0.5 m and 0.7 m deep root system, associated with 0 t ha-1, 2 t ha-1 and 4 t ha-1 of crop residue left on the soil surface. A set of 33 years of daily weather data, along with soil profile data, were used to evaluate the approach in 10 regions of the state of Minas Gerais, Brazil. For most of the regions, the use of mulching and of a maize cultivar with deeper root system was not capable of attenuating the temperature rise. In contrast, any factor limiting root growth of maize to a depth of 0.30 m, causes significant yield drop, even for a scenario of reducing temperature by 3 oC or rising CO2 concentration. In warmer and drier regions, the positive response of maize to the increase in CO2 concentration was more pronounced.

Maize crop is of great relevance for the Brazilian agribusiness since it is a part of the grain export agenda in addition to supplying the domestic market. In the 2018/2019 cropping season the state of Minas Gerais, Brazil was the second largest maize producer as regards the first harvest, and the fifth when considering the two cropping seasons commonly practiced in the Center-South region of the country (Acompanhamento da Safra Brasileira [de] Grãos, 2020). Most of the maize production system runs under rainfed conditions, that is, therefore subject to climate instabilities, which cause inter-annual fluctuations in yield as registered by the Brazilian Institute of Geography and Statistics (IBGE, 2020).
An aggravating factor to this problem is the ongoing climate changes (Intergovernmental Panel on Climate Change, 2014). The increase in the concentration of greenhouse gases GHGs in the earth's atmosphere, mainly CO 2 , besides the direct impact on some crop performance, causes changes especially in the air temperature (NASA, 2010).
Global agricultural yield is expected to reduce 17% by 2050 (Assad et al., 2019). In tropical and subtropical regions of Africa and South America a reduction of 3t ha -1 in crop yield is expected due to the increase in plant maintenance respiration and to the decrease in soil moisture, both in response to the rise in temperature (Levis et al., 2018). The increase in both CO 2 concentration and temperature can affect maize production, either by individual or by combined effect (Maldaner et al., 2014). These effects can influence traits as phenology, diseases incidence, evapotranspiration rate and soil water availability.
Changes in temperature directly affect the growth and development of maize, whose minimum, optimal and maximum limits are, respectively, 8-10 o C, 25-26 o C to 30-34 o C and 42-44 o C (Kiniry et al., 1991;Cruz et al., 2011). In regions with warmer climate, such as in the tropics, the temperature often exceeds the optimum range for maize, resulting in a shortening of the vegetative and reproductive phases and an increase in the evapotranspiration rate that depletes the soil water more quickly and can affect yield (Levis et al., 2018;Lizaso et al., 2018;Souza et al., 2019). On the other hand, nighttime temperatures above 24 o C increase the maintenance respiration, reduce photoassimilate accumulation, causing a drop in production (Sans and Santana, 2002).
Low temperatures, in turn, reduce the rate of crop development and in some cases can even paralyze the entire process (Bergamaschi and Matzenauer, 2014;Cruz et al., 2011).
A modeling study on climate change carried out for the Midwest region of Brazil pointed out that, by the end of the 21st century, there may be a 50 to 89% decrease in yield for the second (offseason) maize crop sowed late. The high temperatures shortened the crop cycle and reduced the water use efficiency (Andrea et al., 2019). In the United Sates, due to maize adaptation mechanisms, the increase in the air temperature has caused lower than expected yield drops, especially for irrigated crops (Butler and Huybers, 2013).
The increase in the atmospheric carbon dioxide (CO 2 ) concentration can be beneficial for the development of several plant species. It favors photosynthetic activity since this molecule is one of the substrates for the photosynthesis (Taiz and Zeiger, 2009). Due to the C4 mechanism of maize, the isolated effect of doubling the CO 2 concentration is relatively small on yield, less than 4% (Lin et al., 2017). Deryng et al. (2016) argue that the impact of temperature rise on maize yield can be 60%, compensated by concomitant increase of CO 2 concentration. However, 3 the increase in the concentration of GHGs, including CO 2 , favors temperature rise, which can compromise the crop development. Therefore, the combined effect of increasing CO 2 concentration and temperature is complex and still requires studies (Hatfield et al., 2011).
Some crop management strategies can be used to mitigate the effects of climate change on maize yield, such as the no-tillage system (NTS), cultivars tolerant to water and temperature stresses (Chapman et al., 2012;Lin et al., 2017), chemical and physical correction of the soil profile and the use of crop residues as mulching (Moraes et al., 2016). The combined effect of these strategies makes crops more resilient to climate change.
Crop residue left on the soil surface in the notillage system plays an important role to mitigate climate change. It reflects a larger fraction of the incident solar radiation, helps regulate the soil temperature, reduces water evaporation, increases infiltration and in the long term favors soil water retention (Moraes et al., 2016). In a literature review, Ranaivoson et al. (2017) encountered that 8 t ha -1 of mulching to reduce by 30% the soil water evaporation and at least 2 t ha -1 to have the maximum effect of increasing water infiltration and reducing runoff and soil loss are required.
The performance of the root system has a great impact on the economy of commercial maize production due to its effect on yield under drought conditions, on the nutrient absorption efficiency (Bänziger et al., 2000) and on the resilience to soil pests. Changes in the architecture of the root system and in the water absorption of cropping systems with high plant population are correlated with the historical yield of maize elite cultivars in the United States (Hammer et al., 2009). Therefore, the root system traits are important to mitigate the effects of climate change, which may or not impose conditions of water and thermal stresses to the crops. Considering that anatomical and molecular traits contribute to root performance (Meister et al., 2014), there is a need to shape maize root for increased stress tolerance and higher yield in a changing climate (Gong et al., 2015).
Conventional experimentation to evaluate the response of crops to strategies with potential to mitigate the effect of climate change is timeconsuming and has a high cost due to intensive use of equipment and labor. Process-based models, which allow the assessment of different crop management scenarios associated with long-term climate databases, are appropriate tools to address the problem. Models, such as those of the Decision Support System for Agrotechnology Transfer, DSSAT, (Hoogenboom et al., 2019), have been used for decades to obtain information on genotype-environment-management interaction and, more recently, to assess the effects of climate change on agricultural crops (Rosenzweig et al., 2014). In a study carried out in the Piracicaba region, Brazil, Soler et al. (2007)

Material and Methods
The CSM-CERES-Maize of the DSSAT The model was previously parameterized and evaluated by using data from field trials carried out for the single-cross hybrid DKB390PRO at different places, with and without water stress (Andrade et al., 2016;Magalhães et al., 2019). The DKB390PRO is a short cycle hybrid widely used in several producing regions of the Minas Gerais state and Brazil (Dekalb, 2016   (Cob4) -A well-managed no-till system that leaves 4 t ha -1 of crop residue or mulching on the soil surface.
The DSSAT was also programmed to alter the observed data of minimum and maximum air temperature and the atmospheric carbon dioxide     (Ferreira, 2011).

Crop Management Strategies versus Change in the Air Temperature
Statistical analyses indicated that no significant interaction, at 5% probability level, was found between depth of the root system, temperature and amount of residue left on the soil surface and also between depth of the root system and amount of residue in any of the study regions. However, the interactions between crop residue and temperature and between root depth and temperature were significant. Those were unfolded and the Tukey test at 5% probability was applied to evaluate the effects on maize yield (tables 5 and 6).
The only region that showed significant interaction between the amount of crop residue and changes in temperature was Araçuaí (table 5) and Viçosa showed significant interaction between changes in temperature and root system depth. In all Table 5. Comparison of maize yields (kg ha -1 ) for different levels of temperature and amounts of crop residue on the soil surface for Araçuaí, Brazil.

Amount of Crop Residue (t ha -1 ) 0 2 4
Araçuaí T-3  5080Aa  5893Ba  6112Ba  T0  4365Ab  4905Bb  5097Bb  T+3  2462Ac  2730ABc  2858Bc  T+6  748Ad  844Ad  887Ad  T+9  33Ae  36Ae  38Ae Values followed by the same upper-case letter, in the line, and lower-case letter, in the column, do not differ statistically from each other by the Tukey test at 5% probability. of these regions and for all scenarios of temperature change, the deepening of the maize root system from 0.5 m to 0.7 m did not provide significant differences in yield (  (table 6).
The over-response of maize crop to the 3 o C rise in the temperature as compared to the reduction of the same magnitude is evident. The effect of temperature rise on maize yield was stronger in warmer regions where temperature is already high (tables 2 and 4).
In the scenario with deeper root system and greater amount of crop residue on the soil surface (Rz70Cob4), Aimorés showed a yield reduction of 53%, while in Araçuaí the decrease was 42% (Figures 2A   and 2B). Lavras and Machado presented a yield drop of 24% and 25%, respectively ( Figures 2D and 2E). The reduction in maize yield was even more drastic for the scenarios of increasing 6 ºC (T+6) and 9 ºC (T+9) in temperature ( Figure 2). Yield breaks of 91% and 82% were simulated in Aimorés and Araçuaí, respectively, for the T+6 scenario, reaching a 100% drop in Aimorés for the T+9 scenario (Figures 2A and 2B). This sharp decrease in yield was obtained even for the scenario that represents a well-corrected soil profile, without restriction on root growth (Rz70) and with a well-established no-till system that leaves 4  of maize, the increase in air temperature has caused lower than expected yield losses in the United States, especially under irrigated conditions (Butler and Huybers, 2013). The increase in temperature, above 23 o C, causes a reduction in maize yield, which is even more accentuated when the daily values exceed 30 o C (Lobell et al., 2011). Several factors contribute to this yield reduction, among which, the increase of maintenance respiration, the reduction of soil moisture (Levis et al., 2018;Lizaso et al., 2018;Andrea et al., 2019) and the acceleration of vegetative development (Streck et al., 2012), which leads to the shortening of the maize cycle. In practice, fewer cardinal days are spent to achieve the thermal sums required in each phenological phase of maize, causing the shortening of the cycle, which by its turn, reduces the opportunity for the plant to accumulate and translocate photoassimilates to the grains (Bergamaschi and Matzenauer, 2014) and, evidently, affects yield (Cruz et al., 2011). In a modeling study conducted in Santa Maria, RS, Brazil, it was also found that the vegetative development of maize is accelerated due to the increase of temperature (Streck et al., 2012).
In all the studied regions, a practically linear reduction in the duration of the maize cycle was observed in response to temperature rise (Figure 1).
For all scenarios of temperature change, the maize days. The study also reported that the cycle is expected to reduce from two to eight days, in a scenario of climate change in the short term, and from six to 11 days, in the medium term (Minuzzi and Lopes, 2015).

Crop Management Strategies versus Change in the CO 2 Concentration
Statistical analyses indicated that the interactions of root depth with CO 2 concentration, crop residue on the soil surface versus CO 2 concentration, and crop residue with CO 2 concentration and with root depth were not significant at 5% probability. However, the individual effects on maize yield of the root depth and of the amount of residue were highly significant.
The same was verified for CO 2 concentration whose effect was highly significant at 5%. A comparison of these effects on maize yield, taking as a baseline the management strategy consisted of a cultivar with 0.5 m of root depth and a no-till system that leaves 2 t ha -1 of crop residue on the soil surface (Rz50Cob2), is presented in Figure 3.
In general, for all regions, regardless of the CO 2 concentration and the amount of residue on the soil surface, the root depth of 0.3 m resulted in lower yield compared to the baseline crop ( Figure 3). The deleterious effect on yield resulted from the shallow root system is even more drastic in the absence of mulching and in regions with higher temperature and less precipitation, such as Araçuaí and Janaúba (tables 2 and 4 and Figure 3). Even when 2 or 4 t ha -1 of residue was kept on the soil surface, for a root depth of 0.3 m, the yield drops in Janaúba and Araçuaí were greater than in the other regions. This is due to the combined effect of high temperature, with low rainfall, which causes faster depletion of the water available in the reduced volume of soil explored by the roots (Levis et al., 2018;Lizaso et al., 2018).
In regions with high temperature and less rainfall, such as Araçuaí and Janaúba, the positive response of maize crop to the increase in CO 2 concentration was more pronounced, regardless of the amount of residue and the deepening of the root system to 0.5 m and to 0.7 m ( Figures 3B and 3C).
Higher CO 2 concentration reduces the consumptive use of water due to the decrease in stomatal conductance of plants (Deryng et al., 2016). For this reason, the effect of CO 2 fertilization on C3 and C4 plants is greater in environments under water stress, compared to those without water limitation (Lobell et al., 2011;Hatfield et al., 2011).  (table 7). Crops grown in arid climate benefit the most from elevated CO 2 concentration, especially under rainfed conditions (Deryng et al., 2016).
Possibly the response of the maize crop to enrichment with CO 2 has been overestimated since the concomitant effect of changes in temperature and CO 2 concentration was not accounted for in the simulations. Increased concentration of GHGs, including CO 2 , favors the rise of temperature, which can compromise the crop development. Therefore, the combined effect of increasing CO 2 concentration and temperature is complex and still requires further studies (Hatfield et al., 2011).
Regardless of the root depth, the increase in CO 2 concentration, from 350 to 750 ppmv, and the amount of crop residue on the soil surface, from 0 to 4 t ha -1 , resulted in a continuous increase in yield ( Figure 3). It is worth mentioning that, even for CO 2 concentration of 750 ppmv and of 4 t ha -1 of mulching, a yield plateau was not reached, suggesting a potential for increase. In all the regions, the response of maize crop to variation in the CO 2 concentration was similar for the root depths of 0.5 m and 0.7m, irrespective of the amount of mulching. Therefore, for the study regions, a root depth of 0.5 m is still sufficient to guarantee the current levels of maize yield. Regions with milder climate and higher precipitation showed less increment in yield in response to increase in CO 2 concentration, as compared to the others. Vanaja et al. (2015) found that, in spite of having a C4 photosynthetic pathway, the maize crop was able to positively respond to a CO 2 concentration of 550 ppmv.

Conclusions
Considering a baseline scenario, which assumes a maize crop with a root depth of 0.5 m and a cropping system that leaves 2 t ha -1 of crop residue on the soil surface, a 3 ºC increase in the air temperature causes 26% to 54% yield reduction.
The warmer and drier the region, the higher the yield reduction in response to the rise in temperature. The use of mulching is not capable of mitigating the air temperature increase, except in Araçuaí where a 3 ºC rise can be attenuated by using 4 t ha -1 of crop residue on the soil surface. In general, for all study regions, regardless of the CO 2 concentration and the amount of mulching, the use of a maize cultivar with a root depth of 0.3 m resulted in lower yield, as compared to the baseline.
In warmer and drier regions, the positive response of maize to the increase in CO 2 concentration was more pronounced, regardless of the amount of crop residue and of the root depth. The increased maize yield can reach 13% in the warm and dry region of Janaúba.
Regardless of the root depth, the increase in CO 2 concentration, from 350 to 750 ppmv, and the amount of crop residue on the soil surface, from 0 to 4 t ha -1 , resulted in a continuous increase in yield.