Pure high grade Ag-lime with a neutralizing index zone "NIZ" of 80-89 is very important to apply to your hay fields "BEFORE" your plant your hay, or turn the field into a pasture.  The amount and quality of hay greatly depends of the PH of the soil.  4 tons of Ag-lime will last about 6 years depending on the original PH and the texture of the soil.  you should alwasy apply Ag-lime before you plant even if yor PH is ok now, because it will not be ok in a couple of years. youe can top dress your hay fields or pasture with 2 to of Ag-lime, but you get your best bang for the buck by mixing it in the soil "BEFORE" you plant.  Please don't confuse our high grade "80-89 Ag-lime" with our "Happy Horse Arena Lime".  has clay and silica particles in it, which gives it a different texture and a more stable base, for training your horse.  Whenever you clean out your stalls or arenas, try and spread the material as uniformity as possible on your field or pasture to keep the PH level as consistent as possible.  Happy Horse Arena Lime has "NIZ" of about 60-69 so it still makes a good liming material, an dpays for itself on both ends, which is a lot better than sand.