Contradiction with John 4:35
Mark 4:29 talks about harvest being immediate once fruit is ripe, but John 4:35 suggests waiting for the right time for harvest.
John 4:35: Say not ye, There are yet four months, and [then] cometh harvest? behold, I say unto you, Lift up your eyes, and look on the fields; for they are white already to harvest.
Contradiction with Matthew 13:30
In Mark 4:29, the harvest is described as prompt, while Matthew 13:30 indicates that there is a time of waiting before the harvest.
Matthew 13:30: Let both grow together until the harvest: and in the time of harvest I will say to the reapers, Gather ye together first the tares, and bind them in bundles to burn them: but gather the wheat into my barn.
Contradiction with James 5:7
Mark 4:29 implies a swift harvest, but James 5:7 talks about waiting patiently for the harvest.
James 5:7: Be patient therefore, brethren, unto the coming of the Lord. Behold, the husbandman waiteth for the precious fruit of the earth, and hath long patience for it, until he receive the early and latter rain. [Be...: or, Be long patient, or, Suffer with long patience]
Contradiction with Jeremiah 8:20
Mark 4:29 describes the immediacy of harvest, contrary to Jeremiah 8:20, which speaks of missing the harvest time.
Jeremiah 8:20: The harvest is past, the summer is ended, and we are not saved.