The correct answer is Circular system. Contour system:It is followed in hilly areas where land is difficult for irrigation and soil erosion is a major problem. The main purpose of this system is to minimize the soil loss due to erosion and conserve sufficient soil moisture for crops. Square system:In this system, trees are planted on each corner of a square. Thus every four plants make one square. Examples: Banana, Manago, citrus. Quincunx system / diagonal / filler system:In this system, trees are planted on each corner of a square along with one plant in the middle of the square. Filler plant is planted in the centre of square. Examples: Papaya, Pineapple.