I have not been able to put my hands on Washington's own copies, but in the library of the Department of Agriculture I have examined the works of Tull, Duhamel and Young.
Tull's _Horse-Hoeing Husbandry_ was an epoch-making book in the history of English agriculture.

It was first published in 1731 and the third edition, the one I have seen and probably the one that Washington possessed, appeared in 1751.

Possibly it was the small piece in octavo, "a new system of Agriculture, or a speedy way to grow rich" concerning which he wrote to his agent.

It deals with a great variety of subjects, such as of roots and leaves, of food of plants, of pasture, of plants, of weeds, of turnips, of wheat, of smut, of blight, of St.Foin, of lucerne, of ridges, of plows, of drill boxes, but its one great thesis was the careful cultivation by plowing of such annuals as potatoes, turnips, and wheat, crops which hitherto had been tended by hand or left to fight their battle unaided after having once been planted.
Duhamel's book was the work of a Frenchman whose last name was Monceau.
It was based in part upon Tull's book, but contained many reflections suggested by French experience as well as some additions made by the English translator.

The English translation appeared in 1759, the year of Washington's marriage.