I have some issues with grass rendering. I generate each grass bush as small grid and save with random rotation. Probably couse this rotation:

How can i fix this? I tried same with small boxes, same result.

My guess is that you are doing one-bit alpha on the grass, and that the grass texture is mipmapped. The mipmap downsampling is producing results that make your 1-bit alphas disappear in the higher mip levels.

In the past I have fixed this with distance field alpha instead of a 1-bit interpreted alpha channel. As long as you are using a 1 bit alpha you can adjust your threshold to make the further mips 'thinner' or 'thicker'. Both versions tend to look bad! A thinner threshold will make grass disappear like you are seeing.

Here's the paper. http://www.valvesoftware.com/publications/2007/SIGGRAPH2007_AlphaTestedMagnification.pdf

You use that technique but for grass instead of text. A distance field is much more tolerant of the mip downsampling.