How to control weeds in transplanted paddy without too much chemical?

Transplanted paddy actually gives you a strong non-chemical tool that DSR does not: standing water. A shallow layer of water (about 5 cm) on a well-levelled field after transplanting suppresses many weeds, especially Echinochloa and other grasses, because they cannot establish under water, so good water management alone removes a large share of the weed problem. Build on that with: a well-puddled, level field so water stays even (high spots that dry out grow weeds), healthy vigorous seedlings transplanted at proper spacing and close planting for a competitive stand, and one or two hand weedings or a rotary cono-weeder run between rows at about 20 to 40 days, which also stirs the soil and helps the crop. If weed pressure is still high, a single early pre-emergence or post-emergence herbicide registered for rice, applied at the right stage, can be added rather than repeated sprays. This keeps chemical use low while holding weeds down. Use clean, certified seed so you do not bring in weed seed, keep bunds and channels clean, and for any herbicide use only products recommended for rice at the label dose, confirming with your KVK.