As far as my best knowledge is concerned, you are not eligible to pursue a Master's in Landscape Architecture after completion of a Bachelor's degree in Agriculture. 

The minimum basic educational qualification required for M.Arch from RIT Bangalore is given below,

• Admission to the Master of Architecture Program is open to all the candidates who have passed B.Arch. (as per the eligibility criteria specified from time to time) of COA, VTU, or any other recognized University / Institution. 
• For foreign degrees, an Equivalence certificate from the Association Of Indian Universities is required.
• The candidates who have completed their degree through the distance mode education from any University are not eligible for admission to M.Arch. Programs under any quota.
• Candidates holding the degree awarded by Associate of the Indian Institute of Architects (AIIA) are also eligible for M.Arch., programs.
• Candidates who have passed the prescribed qualifying examination with not less than 50% of the marks in the aggregate of all the years are also eligible for M.Arch. (5% relaxation for reserved categories.

You have completed a Bachelor's Degree in Agriculture which is not a relevant subject to Architecture that's why you are not eligible to pursue this course.