Any modern farmer worth their salt would know what the use of this stick and rope was. They were used to transplant the rice seedlings in an orderly manner!
Lin Yuelan said to Jiang Zhennan, "We'll start transplanting in these few days. The weather is sunny, so remember to water them every evening. If it rains," she said as she looked at the clear sky, "I doubt it'll rain but to be safe, we should build a greenhouse for each plot."
In modern times, a greenhouse was built using plastic. It was waterproof and transparent. Plastic would let the sun in, while shielding the plants from other more damaging elements.
However, there was no plastic here.
Thus, the greenhouse was only built to prevent the sudden heavy rain from washing away the seedlings that had not yet stabilized.