If one stone is marked with lime the area beneath it is Tamei. If two stones are marked with lime and there is no lime between them the area between them is Tahor. (1)
If up to three borders of a field have been marked, only the marked borders are Tamei and the rest of the fields is Tahor. If all four borders are marked the field is Tamei but the borders are Tahor.
The agents of Beis Din go out to the fields on the fifteenth day of Adar and on Chol ha'Mo'ed to dispose of Kilayim. (2)
The agents of Beis Din that dispose of the Kilayim are paid from the Terumas ha'Lishkah. (3)
At first the agents of Beis Din disposed of the Kilayim by feeding it to the animals and when this proved to be an ineffective deterrent they threw it into the street. Subsequently they decreed that the entire field that contains Kilayim would be ceded.
Rebbi Elazar ben Yakov maintains that crops that were watered prior to the Mo'ed may be watered on the Mo'ed and the Chachamim maintains that even if they were not watered prior to the Mo'ed they may be watered on the Mo'ed.
It is permitted to water a field on Shevi'is so that the vegetables will grow on Shevi'is and it is also permitted to water the field on Shevi'is so that the vegetables will grow on Motzei Shevi'is.
It is permitted to destroy ant holes on Chol ha'Mo'ed by taking earth from one ant hole and putting it into another. When the ants smell unfamiliar dirt they will choke each other.
A BIT MORE
1. If two stones are marked with lime and the lime spilled over to the sides of the stones, the area between them is Tamei unless the area between the stones was plowed.
2. Beis Din must go out twice to the fields for the Kilayim, once for the early crops and again for the later crops. According to another opinion the first time they go out is for the grain and the second time is for the vegetables.
3. Since the agents of Beis Din are paid from the Terumas ha'Lishkah they are sent out on Chol ha'Mo'ed in order to minimize the costs.
The Rambam decides the Halachah according to the opinion of Rebbi Elazar ben Yakov that it is forbidden to water a field on Chol ha'Mo'ed if it does not need constant watering. Yet with regards to Shemitah the Rambam follows the lenient opinion of the Chachamim that it is permitted to water a field on Shemitah even if it does not need constant watering. The discrepancy between Shemitah and Chol ha'Mo'ed is because only agricultural work is forbidden on Shemitah while on Chol ha'Mo'ed other forms of work are forbidden. Therefore we are more stringent with regard to Chol ha'Mo'ed. Additionally Shemitah is an entire year and it is more difficult to be stringent. (Tosfos Yom Tov from the Yerushalmi)
Water may be drawn from one tree to the next as long as one does not water the entire field. If the field was moist it is permitted to water the entire field. (Shulchan Aruch OC 537:7)
Small water filled depressions are made next to the trees; therefore it is not difficult to make a gully and draw the water from one tree to the next. (Mishnah Berurah)