I've been fortunate to be able to take a lot of walks outside this winter thanks to the mild weather that we've had so far. During my walks, I've looked at the taller grasses and other ground vegetation that have gone dead or dormant for the winter and wondered how I could recreate them on my layout.
During my research online, I've found that many modelers recommend using 6mm-8mm static grass or field grass made from natural hair fibers. The former will allow you to cover areas while the later is well suited for smaller areas or clumps. You can read more about static grass in my Static Grass post.
I also found another technique using faux fur. This is a synthetic fabric material that can be bought at most fabric stores. It resembles natural furs from animal hides. The fur requires some preparations including cutting to the desired height and dying to the desired color. It can be applied to your layout in strips or patches cut to any shape that you want.
The results look pretty good especially if you're going for sweeping fields of grains such as wheat. Bear in mind that the examples in the link below are for gauges much larger than n gauge. I'd like to try it out for n scale and see how it looks compared to other techniques.
Check out this link for more info: http://www.pacificcoastairlinerr.com/fur_grass/article/