What is the test for establishing if a written agreement is binding on a land agreement?

Taking the written document by itself, and disregarding for the moment that portion of the evidence which could be read to suggest that the parties might still be "in treaty", using this term as it is used in such cases as Chinnock v. The Marchioness of Ely, (1865) 4 De G.J.& S. 638, 46 E.R. 1066, it becomes necessary to find whether there is sufficient certainty in the following respects: (a) When is the cash portion of the purchase to be paid; (b) Is the provision "the balance to be one-half the crop" unambiguous; (c) How is possession to be given and the production of crop to be worked out in respect of the one-quarter interest in Section 20?