Much of the world's agricultural productivity growth over the past fifty years has
been attributed to the international spillover of benefits from research and develop-
ment (Alston, 2002). Because the impact of these spillovers often varies with distance,
geography, and climate, attention has increasingly focused on measuring their spa-
tial dimensions Evenson (1989). In this paper, spatial spillovers are examined in the
context of country borders. Using high-resolution worldwide grid cell data covering
yields for 11 major crops, we test whether spatial dependencies in agricultural yields
fall in the presence of country borders, controlling for geography and climate as well
as country-specific effects. Two different complementary analyses show that country
borders significantly and sizeably diminish the transmission of spatial spillovers be-
tween locations. The results thus point to a clear \border effect" on an important
determinant of agricultural productivity.
