Pastures and Hayfields are like Hay Forks and Pitch Forks. They are similar and can actually be interchanged, but the differences are significant.
Pastures are used primarily as places where animals directly graze (consume) the herbage in-situ. The plants in them tend to be low-growing and tolerant of hoof traffic and highly competitive vs. other plants.
Hayfields are used primarily as places where herbage is harvested and preserved in some fashion for consumption at a later time. Usually it is preserved as hay, which is drying the herbage using sunlight/wind. It can also be preserved as silage/haylage, which uses fermentation of the herbage inside air-tight bags by anaerobic bacteria for preservation. The plants in hayfields tend to be taller-growing and less tolerant of hoof traffic. Height helps it mow nicely and increases the yield.
But of course, you can cut the herbage in a pasture and dry it–making hay. In fact, this is almost necessary in Spring and early Summer. Cool season pastures grow so vigorously at this time the animals will not be able to keep up with it if you have a stocking density that will work out for the rest of the year. For example, Bluegrass makes 70% of its annual growth before the month of June and doesn’t really start growing in earnest until mid-April. So 70% of its growth occurs in just 2.5 months! So what I do is mow all my pastures once or twice in the Spring and early Summer for hay. This sets back weeds and solves the over-production problem by conserving all that growth for the winter. In fact, you can usually grow enough hay for the winter this way off your pastures if your pastures are so large as to be the primary source of nutrition for your animals and you live in a moderate winter climate.
And you can also allow animals to graze a hayfield. In fact, there is a technique for winter feeding in-situ called “stockpiling” that is essentially allowing a hayfield (usually of Tall Fescue grass) to grow tall towards the end of the season (October) and allowing animals to graze it in the winter rather than cut it for a final cutting of hay. This is a very economical technique, but one I think is best suited for meat animals (not dairy). Keeping dairy animals clean (not muddy) is important, not so much with animals going to slaughter.
Stockpiling works particularly well with Tall Fescue because it is among the few pasture/hayfield plants that seem to actually improve when they are frosted. It is also cold hardy and one of the most tolerant of being trampled. Tall Fescue, though, is only OK in terms of palatability, and it tends to dominate in a mixed pasture, though you could stockpile with a Tall Fescue rich pasture. Perennial Ryegrass, Tall Fescue’s better tasting but less rugged cousin, doesn’t do as well. But Timothy and Perennial Ryegrass do pretty well in more moderate winter areas like mine.
I’ve tried a few times now to get a formal hayfield going–something I only harvest hay from–in the manner of most farmers. I am officially giving up. To begin with, almost all my attempts fail. White Clover is so aggressive in my soil type that it overwhelms almost any attempt to grow something other than another clover. Grasses and less aggressive legume species (Birdsfoot trefoil, Sainfoin) are hard to get started on my place. I’ve decided to just roll with it instead of fighting it. After all, White Clover is a wonderful plant, and is the clear favorite of our cow.
I have been able to get Red Clover to grow up into a nice hayfield, as you can see. That was the Rye field I posted about earlier, but I no longer use these hayfields for making hay. To begin with, I think pure Red Clover is too rich as hay. Our cow’s urine smelled like straight amonia after a few days on Red Clover hay. Put her back on Timothy-Red clover hay (that I bought) and things went back to normal. I now use my Red Clover almost entirely for soil-improvement purposes (cover croppping) or as a source of mulch. I rotate them through with my garden. I’ve found that Red Clover is quite good at shading out many weed species, too, so it “cleans the soil” for gardens and since all clovers fix their own nitrogen plus a significant surplus, they fertilize the soil for gardens at the same time, something that Buckwheat and Brassicas, two popular “cleaning” crops, don’t do.
So for hay, I entirely rely on the Springtime overproduction of my pastures. It also means that I make hay that is shorter, which is harder to mow, and that I make hay out of very moist Ryegrass and White Clover, which are both slow to dry. I read recently of the practice of adding a significant portion of very late maturing Timothy to pastures (Timothy is usually thought of as a hayfield plant, not a pasture plant) to help the pasture “stand” and dry down a little better. An added benefit is that is seems to improve the overall palatability of a White Clover/Ryegrass pasture. I know that for equids at least, the Timothy adds long-chain fibers which help keep the animals teeth in good shape. I am not so sure this matters much to cattle, but hey, I doubt it will hurt. I’m going to put 50 pounds of Timothy out there this August. We’ll see what happens next year!