I'll tell you what intensive gardening is to me.

Early, I plant sugar podded pea (english peas-snap pea), I will have 
another crop planted and coming up when I am taking down the used up 
vines of the pea crop. I leave the pea vine roots in the ground to 
give up its free nitrogen, and snip its body into tiny pieces and let 
it fall back on top of the bed where it grew to give of its deeply 
retreived nutrients to the top of my growing bed.

Perhaps I'll follow the peas with squash or canteloupe: both of these 
veggies will benefit from what the peas left in the ground. Both of 
these plants sprawl hither and yon, but still allow a bit of sunlight 
to the soil.nbsp; Along toward time the fruits of these begin to wain, 
I'll have sown late fall greens under their leaves.

When I have squash enough, or the leaves begin to tire and brown, 
I'll snip the leaves off even with the plant body, and snip it into 
pieces to fall near where it grew. Same with the 'lopes. 
Occasionally, I'll do vine pruning on the 'lopes to make bigger 
fruits, and create less stress on the plant. 

The greens coming up under these sprawlers will then be the 3rd crop 
raised on the same bits of soil--hence--INTENSIVE gardening.
Jon 
************
And again:
intensive gardening is:

Basically put it is using every inch of available space. Traditional 
gardening had neat rows of veggies, evenly spaced with rows between, 
and lots of bare earth showing. Intensive gardening plants crops 
together, sharing the same spaces, with little to no dirt showing at 
all. Carrots and onions and nasturtiums surrounding tomatoes and 
peppers, bean teepees covering thickly sown beds of leafy greens, 
radishes in between cabbages and broccoli, Corn planted with beans 
and cucurbits...herbs and self seeding plants growing here and there 
also help to improve things. Mints help to improve the flavor of 
tomato and pepper and eggplants, they also attract beneficial 
insects. Borage attracts pollinators, as does dill and fennel.

When one crop is ready to fade out, you cut it off at soil level, and 
put in another crop right in the bare spot. If you plant a few 
seeds a week, rather than using the whole packet at once, then you 
can harvest enough produce each week, without having too much at 
once. The same holds with most veggies. Even potatoes can be 
planted early, mid and late season. Planting pole beans and vining 
tomatoes and cucurbits will extend your harvesting season, too. 

All in all, intensive gardening is just using every square inch of 
soil to plant in, by growing vertically, sucession planting, 
companion planting, etc... It can take some trial and error to get a 
really good system, especially if you want to rotate your crops as 
well. Once you have hit on a good system, however, you will find 
that your fertilization, watering, and pest control problems nearly 
vanish.
Jon Wood