For long grass, the seed tassles of pompass grass works good for rice. Or you could cut cisal rope or twine up and use it. Paint it and you have the rice stalks.
If the paddies are wet you can simulate rotar wash by taking a small paint spatula or piece of styrene and use it to "pick" up the hardening resin or whatever you are going to use for water. As it sets it will be tacky and still form a ridge if you stipple it or use an old stiff brush. (PRACTICE THIS FIRST BEFORE DOING IT ON YOUR DIORAMA) you want to get a feel for when its the right consistency or a hand or method that gives you the best result. But it looks awsome once done. Since paddy water is really an open sewer, you can use just about anything that will make water. gesso, acrylic modeling paste, wall board compound, what ever. Its all brown stinky water.
The causeways surrounding the paddys can be made with a strip of foam glued to your base and then covered with a thin layer of celuclay. (If you use the resin, be sure that the foam is covered with the celuclay, it may react with the particular resin you use)
Mike
"Imagination is the dye that colors our lives"
Marcus Aurellius
A good friend will come and bail you out of jail...but, a true friend will be sitting next to you saying, "Damn...that was fun!"