The main problem is that, not ploughing increases the need for pesticides, currently around 8% of energy used and reduces yield. While not ploughing increasing requiring 3x the pesticides might not be the case, a 20% reduction in yield seems plausible.
The main energy consumption in farming is fertilizer at around 50%, but more importantly half the emissions are related to animal agriculture. Cutting back on that would actually make a difference.
I had the same question a few hours ago, but I found some science.
Tldr: 30% of energy use is in diesel, and about half of that is for tilling fields.
Rant:
Note that this is energy use, so only CO2 emissions are counted, while methan is ignored. If we stopped farming animals, the effective emissions of the sector would be cut in half. Even if we are unwilling to change out diet, maybe we should look at reducing the amount of fertilizer instead.