In the light of the latest scientific achievements the great role played by the geomagnetic processes in a variety of phenomena in the world (in the atmosphere, the biosphere and the social sphere) becomes more and more apparent. It is known that the temporal variation of the geomagnetic field is determined by interplanetary processes, the Earth's rotation, as well as fluctuations in solar activity. In this connection, the data on the phenomena on the Sun and changes in the Earth's magnetic field have been widely used in various fields of science and technology and in solving many applied problems. The impact of artificial magnetic fields on the crop growth was demonstrated in the vast number of scientific publications. However, the effect of fluctuations of the natural Earth's magnetic field caused by the influence of the Sun on the crop yield is still practically unknown. The evaluation of the level of correlation was conducted between solar-caused fluctuations in Earth's magnetic field and statistical wheat yield for countries where the crop is grown. This crop is cultivated in many countries of the world, which allows to include in the analysis regions with different natural and agronomic conditions. Actual information about the wheat yield was obtained from FAO's statistical database FAOSTAT (http://faostat.fao.org/site/339/default.aspx). As an indicator of the global geomagnetic activity Kp index was used. Kp index values were averaged for individual days, months, and years. The average value of the index is rounded to the closest standard value of it. Monthly average Kp values were used to calculate the average values of the index for the period of wheat growth. As a result, a statistically significant correlation between the annual change in the yield of wheat and solar-caused changes of Earth's magnetic field was found. The coefficient of correlation in some countries reaches a sufficiently high value. The highest rates of positive correlation set for Belgium (r = 0.7), Kenya, Mali and North Korea (at r = 0.6 for each country). The negative relationship is most pronounced in Russia (r = -0.8), Ukraine, Moldova, Uzbekistan and Bolivia (r = -0.7 for each). Specificity of the manifestations of the correlation around the world suggests the presence of both direct and indirect (through a change in the meteorological conditions) impact of fluctuations of the geomagnetic field on crop yield. In the case of direct impact, the observed correlation of crop yield with the Kp, index averaged for the growing season, should be expressed more clearly than with Kp index, averaged for the year. Our analysis revealed more countries with a statistically significant correlation in the case of usage of seasonal Kp index. It is often observed the following situation: in the case of a negative correlation of crop yield with the annual value of the Kp value of r increases when using the seasonal Kp index, and for a positive relationship between crop yield and the annual value of the Kp index r in the case of the seasonal index decreases (sometimes up to statistically insignificant values). The latter can be explained by the inertia of the reaction of atmospheric processes on the impact of fluctuations of geomagnetic activity, which is similar to that in relation to the impact of El Niño and La Niña on changes in air temperature and precipitation (R. Stefanski, 1994). A more confident conclusion about the importance of the direct and indirect effects can be apparently obtained by carrying out a similar analysis for other crops, as well as through a more precise allocation of time during the growing season in each year and growing region.