Complex sentence: Conservation tillage systems leave a minimum of 30% of crop residue on the soil surface in order to slow water movement which will reduce the amount of soil erosion and to warm the soil for the next year's crop to be planted earlier in the spring.
Split into simpler sentences: Conservation tillage systems are methods of soil tillage which leave a minimum of 30% of crop residue on the soil surface. This slows water movement, which reduces the amount of soil erosion; it also warms the soil, enabling the next year's crop to be planted earlier in the spring.