Agriculture directly accounts for about 11% of CO2 emissions worldwide. 14% other emissions includes massive burning of biomass, deforestation to obtain agricultural land, etc.
The agricultural related emissions not accounted for include fuel for tractors, harvesters, production of fertilizers, herbicides, and pesticides, which are necessary components of contemporary high-input agriculture.
Plowing and tilling releases large amounts of CO2 from the soil, ultimately turning the soil into simple dirt incapable of growing anything other than weeds. Fertilizers and herbicides are then necessary for crop growth.
There are ways to produce without adding fertilizers or using herbicides and pesticides. Moreover, these ways of growing food sequester carbon by constantly improving and increasing soil. See http://unctad.org/en/publicationslibrary/ditcted2012d3_en.pdf for a relevant report from the United Nations Conference on Trade and Development:
“Developing and developed countries alike need a paradigm shift in agricultural development: from a ‘green revolution’ to a ‘truly ecological intensification’ approach.”