Boosting zinc in wheat, Guatemala’s food security problem, maize and climate change

Foliar vs. soil zinc fertilization in wheat​

Zinc deficiency is the fifth most important risk factor associated with illness and death in the developing world, and affects about one-third of the world's population. The two main contributing factors to zinc deficiency in the diet are zinc-deficient soil and limited bioavailability of zinc due to phytic acid.

Thus, researchers used field and greenhouse experiments to compare the efficacy of soil and foliar zinc fertilization in improving grain zinc concentration and bioavailability of wheat grain grown on potentially zinc-deficient calcareous soil. They found that foliar application of zinc increased grain zinc concentration more than soil application did. Zinc fertilization had no significant effect on grain yield.

Results from the two-year field experiment on triticum aestivum L. determined that soil zinc application increased soil DTPA-Zn (zinc) by an average of 174%, but had no significant effect on grain zinc concentration. In contrast, foliar zinc application increased grain zinc concentration by an average of 61%, and Zn bioavailability by an average of 36%. Soil DTPA-Zn concentrations varied depending on wheat cultivars. There were also significant differences in grain phytic acid concentration among the cultivars. 

Source: Science of Food and Agriculture​
DOI: 10.1002/jsfa.6518​
“Comparison of soil and foliar zinc application for enhancing grain zinc content of wheat when grown on potentially zinc-deficient calcareous soils”​
Authors: Ai-qing Zhao, Xiao-hong Tian, Yu-xian Cao, Xin-chun Lu and Ting Liu

Liberalized trade in Guatemala compromising food security​

The neoliberal restructuring of the Guatemalan economy has undermined the country's long-standing self-sufficiency in maize, its staple crop, and likely contributed to the loss of crop genetic resources in a megacenter of agricultural biodiversity, according to a paper by University of Toronto assistant professor S. Ryan Isakson.

The author argues that the liberalization of trade and agricultural policies in Guatemala has undermined a range of objectives, such as access to food, the environmental sustainability of production practices, the nutritional composition of diets and the rights of food producers -thereby compromising domestic food sovereignty and global food security. Small-scale farmers have been encouraged to conform to the country's supposed comparative advantage in non-traditional export crops, resulting in widening inequality, a growing dependence upon imported grain and agrochemicals, environmental degradation and decreased food security.

“The displacement of maize agriculture in favor of non-traditional agricultural exports has benefited powerful actors in Guatemala and abroad, but it has also compromised the ecological base for agriculture and undermined the foundation for a reliable, nutritious and culturally meaningful diet for a significant portion of the country's rural poor,”​ he wrote. “Rather than expanding choice, neoliberal restructuring has constrained the economic autonomy of the Guatemalan peasantry, conscripting it into an economically and environmentally vulnerable food system that is rendered even more so by the peasantry's very conscription.”​

Source: Agrarian Change​
DOI: 10.1111/joac.12023​
“Maize Diversity and the Political Economy of Agrarian Restructuring in Guatemala”​
Author: S. Ryan Isakson

Charting temperature changes’ effects on maize yields​

The largest maize crop model intercomparison to date found that temperature changes resulting from global climate change will likely have the largest impact on maize yields by the end of this century. With the goal of analyzing the sensitivity of simulated yields to changes in temperature and atmospheric carbon dioxide concentrations (CO2), researchers created the largest maize crop model intercomparison of its kind, comparing 23 different models. The models were evaluated for four locations representing a wide range of conditions: Lusignan (France), Ames (USA), Rio Verde (Brazil) and Morogoro (Tanzania).

Temperature increase had strong negative influence on modeled yield response of roughly −0.5 Mg ha⁻¹​ per degree Celcius. Doubling CO₂​ from 360 to 720 μmol mol⁻¹​ increased grain yield by 7.5% on average across models and the sites, thus making temperature the main factor altering maize yields at the end of this century. Furthermore, the researchers found a large uncertainty in the yield response to CO₂​ among models. Model responses to temperature and CO₂​ did not differ whether models were simulated with low calibration information or a high level of calibration information.

While individual models differed considerably in absolute yield simulation at the four sites, a minimum number of models was able to simulate absolute yields accurately at the four sites even with low data for calibration, thus suggesting that grouping the models has merit. 

Source: Global Change Biology​
DOI: 10.1111/gcb.12520​
“How do various maize crop models vary in their responses to climate change factors?”​
Authors: Bassu, S., Brisson, N., Durand, J.-L., Boote, K., Lizaso, J., Jones, J. W., Rosenzweig, C., Ruane, A. C., Adam, M., Baron, C., Basso, B., Biernath, C., Boogaard, H., Conijn, S., Corbeels, M., Deryng, D., De Sanctis, G., Gayler, S., Grassini, P., Hatfield, J., Hoek, S., Izaurralde, C., Jongschaap, R., Kemanian, A. R., Kersebaum, K. C., Kim, S.-H., Kumar, N. S., Makowski, D., Müller, C., Nendel, C., Priesack, E., Pravia, M. V., Sau, F., Shcherbak, I., Tao, F., Teixeira, E., Timlin, D. and Waha, K.