A farmer has 120 kilograms of fertilizer and want to distribute it among his 3 fields in the ratio of 4:5:3, how much fertilizer will each field receive

The ratio for the 3 fields is $4:5:3$.
Total parts $= 4 + 5 + 3 = 12$

Total fertilizer $= 120 \text{ kg}$
Amount per part $= \frac{\text{Total fertilizer}}{\text{Total parts}} = \frac{120 \text{ kg}}{12} = 10 \text{ kg/part}$

Field 1 (ratio 4) $= 4 \times 10 \text{ kg} = 40 \text{ kg}$
Field 2 (ratio 5) $= 5 \times 10 \text{ kg} = 50 \text{ kg}$
Field 3 (ratio 3) $= 3 \times 10 \text{ kg} = 30 \text{ kg}$

Field 1 will receive $\boxed{40 \text{ kg}}$.
Field 2 will receive $\boxed{50 \text{ kg}}$.
Field 3 will receive $\boxed{30 \text{ kg}}$.