Peah 5:3

One may not irrigate his field before the needy come to collect the leket (because the water ruins the leket that is still in the field); this is the opinion of Rabbi Meir. The Sages permit it because it is possible to do so without ruining the leket.

Peah 5:4

If a homeowner was traveling and he needed to use leket, shich’cha, peah and tithe for the poor, he may do so and repay it when he returns home; this is the opinion of Rabbi Eliezer. The Sages say that he need not repay because these gifts are intended for the needy and when he was out of town without means, he was needy.