So I wondered to myself: “What happens if an upland hill dry rice field is never harvested?”.
I asked a few people, but the only answer they gave was “The rice would re-seed itself”.
That is nice to hear, but it is a very simplistic and not-so-satisfying answer. There are a lot more factors at play in the re-seeding of rice in a dry field.
So instead I asked the rice experts at PhilRice and here is my conversation with them (If there are any other rice experts out there who wish to comment please do so):
JIHATSU: What would happen to an upland hill (rain-fed only) rice field if it is never harvested?
Has any research ever been done into this?
I am wondering how the rice field would develop if the rice is never harvested and the field is left to its own.
PHILRICE: So far there is no project conducted relating to dropped seeds from the previous crop.
JIHATSU: Based on your personal knowledge and experience what do you suppose would happen?
PHILRICE: If the panicles are not harvested then you let them germinate for the next season, the result is there are overcrowded seedlings resulting in poor growth. Considering that the common seedling density per m2 if direct seeding is 100 to 150 seeds; then for a rough estimate if the previous crop for example is transplanted where there are an average of 25 seedlings per m2 with 10 productive tillers (with panicles) and each panicle have 100 grains. Then all of these are dropped and germinated you would have a population density of more or less 25 000 seeds per m2. This is would not be possible to have a good crop even if you manage the fertilizer and weeds.
JIHATSU: Do you have any estimates on how many seeds would be eaten by ants, mice, and birds, and other creatures, and how many seeds would perish from fungi rot?
If insects, animals, and microorganisms can remove around 99% of the seeds and leave 1% of seeds for germinating. If say another 0.06% of rice plants are thinned by rice leafhoppers or is outcompeted by weeds left growing then one would end up with around 150 seeds per m2.
Do you think this would be possible in real life? or would the natural thinning effect from animals, insects, and microorganisms still not be enough to reduce the rice plants to a number for a good harvest?
PHILRICE: With regards to the assumptions for the pests, this situation might become worse since there are available foods, the pests will be multiplied and they will not leave vigorous plants since the pest like rats attacks in every stage of the crop from seeds stored to the seeds to be harvested.
JIHATSU: What if the rats would be eaten by snakes, hawks, and eagles so the population of rats decreases where the rice seeds fallen to the ground will be reduced so there is enough thinning for the rice crop to grow a good harvest?
Do you think that could be possible or not?
PHILRICE: In this current situation natural predators of pests are limited since they are also hunted by farmers, for us this may not be possible.
JIHATSU: Thank you for the answers. My final question is what would be the best time to sow upland rice on a dry field?
PHILRICE: Dry seeding always depends on the available moisture of the soil, it may vary depending on the location and situation, always consider the seed sowing during the onset of the rainy season., we recommend also that if there are other farms planting upland rice, you should always plant asynchronous to avoid pests.