How to farm.
Buy a Basic sickle at Ssal's Market, in the Kugnae wheat field (110, 138). There are two places to farm, either this field, or the Nagnang woodlands field (center is at about 118, 56).
Hold the sickle in your hand and walk around in the field. You will get pop ups with some text that explains a little about the crop you have discovered, and 4 options. You must pick the option that fits the text, or you don't even have a chance of getting anything.
For Rice and Wheat pop ups:
Very tall = Swing high
Rained down to the right = Swing right
Blown to the left = Swing left
Barely tall = Swing low
For pea pop ups, always pick the option that says Pick peas.