Perennial Replanting Rice and Challenges of Climate Change
One Science Magazine breakthrough of 2022 was the establishment of Perennial Rice (PR23), a cross of a Chinese rice with a perennial African wild rice. This rice will effectively replant itself for four years before significantly declining. This saves 77 person-days of planting per hectare per year, or 31 person-days per acre. In 2021, it was used in 15,000 hectares in China, or 37,000 acres.
Rice provides 20% of world calories, mostly in Asia. It is eaten by half of humanity, and for 3 billion it is their staple grain. There are hundreds of millions of rice farmers, covering 165 million hectares, or 400 million acres, using the conversion factor of about 2.5 acres per hectare. (For us US city dwellers, a US football field is 1.32 acres, a UK soccer pitch is 1.86 acres, and there are 640 acres per square mile, so global rice covers 0.64 million square miles). California produces 20% of the US rice harvest, including all of Sushi rice, with 550,000 acres, or 860 square miles.
The current and future challenges to rice are brought about by climate change, as reported in the New York Times by Somini Sengupta. This includes damaging by extreme heat, erratic rains, and rising sea levels which cause salt intrusions. The flooded fields where rice decomposes is also said to contribute nitrous oxide and 8% of world methane, but a US made graph puts it at about 20% of methane, while another source puts it at 5% with cows generating 20%. US methane emission by rice is only 2% of the US total methane emissions.
Seeds are being developed by crossing popular rice with hardier heirloom varieties that can take higher temperatures and salty soil. The rice planting calendars are also being shifted. China has already lost 8% of its production to extreme heat, and by the year 2100 China expects to lose another 8% from extreme rainfall.
World rice production in 2022 was 515 million tons, led by China and India which total 53%, with leading countries given below.
