Thinking about whether rice seedlings should be transplanted at 20 to 30 days for best yield

The window for successfully transplanting seedlings is usually thought of as a 20 to 30 days thing but this has been presented to us as a hard rule and no one really provides a clear understanding of the real differences between transplanting on day 18 and day 32. I'm not an experienced farmer but living in a place with a dozen farms both big and small you pick up a few nuggets of wisdom from the farmers

There is some difference, but smallholder farmers are most likely not counting the days since the nursery growing conditions vary so much that it's a bit complicated to count and know for sure.

I believe what really matters when it comes to potential transplanting success is the height of the seedlings and number of leaves they have developed. Generally speaking, three to four leaves is an optimal number of leaves for successful transplanting, but you may also see farmers who have transplanted seedlings with five leaves and their crops have been a success at harvest time. The reason that there is a stated 20 to 30 day range is based on studies conducted at agricultural research stations where conditions are controlled for temperature, water and also the fertilizer. When you look at the real world of farming, conditions can never be as controlled as those conditions at agricultural experiment stations. You can never tell what will happen that will cause your plans to be ruined.

The type of growing season can determine the timing of when to transplant seedlings. Wet growing seasons will give a much greater flexibility in terms of timing because there is a chance that additional rain will be available. But when you're in the dry growing season, if the timing is missed by just one week, you may be in a situation where you have a very high risk of irrigation costs that will take a huge amount of your profits before you have a chance to see the heads develop.

This perception that seedlings that are older than 30 days will not perform as well as younger seedlings is somewhat of an assumption and not always accurate and this is not me being subjective at all. I have seen farmers who have transplanted seedlings that had reached an age of 35 days because they did not have enough labor available. Their amount of yield lost was not catastrophic, the reduction was only around 10% to 15%. These numbers may be a big deal for large scale farms, but for farmers that work with two acres of farmland, the loss is not that impactful.