A top lobbyist for food and beverage giant PepsiCo Inc. who was formerly a top aide to Senate Agriculture Chairman Pat Roberts is taking over as the Agriculture Committee's chief of staff as it prepares to rewrite federal child nutrition policy. Joel Leftwich, a native of Wellington, Kansas, worked for Roberts, R-Kan., as deputy staff director for the committee before becoming senior director for PepsiCo's public policy and government affairs team in March 2013.