To solve this problem, we need to identify the agricultural practice described in the question.$\newline$The question describes a system of rotating crops with legume or grass pasture to improve soil structure and fertility.$\newline$Let's analyze each option:$\newline \bullet$Option 1: Ley farming.$\newline$ - Ley farming involves the rotation of crops with pasture, particularly legumes or grasses, to enhance soil fertility and structure.$\newline$ - This practice is specifically designed to improve soil health by incorporating nitrogen-fixing plants and organic matter.$\newline$ - Therefore, this matches the description given in the question.$\newline \bullet$Option 2: Contour farming.$\newline$ - Contour farming involves plowing along the contours of the land to reduce soil erosion.$\newline$ - It does not specifically involve rotating crops with legumes or grasses for soil improvement.$\newline \bullet$Option 3: Strip farming.$\newline$ - Strip farming involves growing crops in strips to prevent erosion and manage pests.$\newline$ - It does not focus on rotating crops with legumes or grasses for soil fertility.$\newline \bullet$Option 4: Shifting agriculture.$\newline$ - Shifting agriculture involves clearing a piece of land, cultivating it for a few years, and then moving to a new area.$\newline$ - It does not involve a systematic rotation with legumes or grasses.$\newline$Based on the analysis, the correct option is Option 1: Ley farming.