Two problems i noticed was that there was very less number of grass blades and for some grass blades have problem with their rotation.
*Increase the number of particles inorder to increase the density of particle population. (you might already know this)
*If you have mentioned regarding the rotation of the grass, the problem might have caused due to the following factors.
1) Origin, Scale and Rotation of grass blade set incorrectly.
To demonstrate quickly, below image shows where the origin has to be if you consider the triangle is a grass blade (origin have to be at the very bottom of the model). Set the origin of every grass blades like this.
Also, apply the transformation to the object (all the grass blades used as particles). To do this press Ctrl+A in "Object Mode" and apply "Rotation" and "Scale". [Scale will be set to "1" and Rotation will be set to "0" by doing so]
2) Rotation in Particle settings set incorrectly.
Check this settings under the "Rotation"
(i) "Initial orientation" to be set correctly.
(ii) Randomization values of orientation and rotation shouldn't to be too high values.
Also, "Recalculate Normals" for the plane you are using as ground. This will set all faces in correct directions if there are any flipped faces. (You can do this by going into edit mode and select all faces and by pressing "Ctrl+N")