Hello

Your question is not clear. Assuming that you  mean that a student has got 400 rank more than what is needed (according to common merit rank) and he wants to get admission in PUSA. Since you are from ST category the chances of you getting  an agriculture seat in pusa is high since you have got only 400 higher than needed. If you were from obc then the scenario would have been tricky but for ST a rank below 2000 is good enough to ftech you a seat in pusa. All the best!