The last few days of Daf Yomi have dealt with the "beit hashalchin" or irrigated field and when you are allowed or not allowed to irrigate it. Unfortunately, most of us today have no idea what a "beit hashalchin" is or how you might water it. This it makes it hard to understand some of the Gemara's considerations, for example what is considered excessive labor and what is not.
Fortunately, I have been privileged to visit a real live "beit hashalchin" in Israel, and had its operation explained by an expert in these kinds of matters, and can thus explain how it works. This was in the Palestinian village of Battir (picture of fields here), on a well-armed field trip organized by Gush.
Basically, you start with a source of water (river, aqueduct or spring), and a field. Then you dig shallow, closely spaced channels in the field, all connected to the source of water. In between the channels you plant rows of vegetables. Each vegetable has to be close enough to a channel that the earth it is growing from stays moist, even though the vegetable is above water level. The field has to be extremely flat, or else all the water will flow down to the bottom and the highest channels or parts of channels will dry up. Here is a good example of a modern "beit hashalchin" in California:
This Californian "beit hashalchin" distributes water using plastic siphons which draw water from the main channel. In the olden days they used a less high-tech method: they would kick out the dirt wall blocking one channel from another, thus allowing the channels to meet. This is the method of "irrigation with your feet" which the Torah describes:
"For the land which you are coming to in order to possess, is not like the land of Egypt which you left, where one plants seed and irrigate with his feet like in a vegetable garden. Rather, the land which you are going to in order to possess is a land of hills and valleys; where one drinks water from the rain of the sky." (Devarim 11:10-11)
The Torah here is contrasting the typical agricultural practices in Egypt and Israel. In Egypt, the entire country was covered by "batei shalchin", fed by canals from the Nile. In Israel this would not be possible. The only constant water sources in Israel are springs. These are relatively rare and mostly found in mountainous areas which do not have much flat area. Thus "batei shalchin" were (and still are) uncommon in Israel. But in some areas they do exist, and are therefore discussed in the Mishnah. Of course, the Torah knows that for most of our agriculture we would have to rely on rain.
Back to the Gemara: I'm pretty sure that the "irrigation" discussed in Moed Kattan meant not carrying buckets of water to wherever your plants were, but rather "irrigation with your feet" - opening and closing the "gates" of dirt so as to distribute water into the different channels as necessary. This explanation is especially helpful on page 4a. There you find a prohibition to water your field on Chol Hamoed from a pool of water, because it might become "interrupted" and cause you to do extra work. The "interruption" apparently occurs when so much water flows into the channels that the pool's water level drops until it reaches the level of the channels. Then no water can flow, and the only ways to irrigate are to dig the channels deeper, or use buckets. Both options require huge amounts of work, and are thus prohibited on Chol Hamoed even though the crops need them.
Near the bottom of 4a, the Gemara prohibits drawing a bucketful of water from a low channel to an adjacent high channel. This is clear evidence that the normal irrigation which is allowed is done not by carrying water, but by a less strenuous activity: opening and closing the "gates" of the various channels. The Gemara is telling us that sometimes, depending on the circumstances, even this can be prohibited on Chol Hamoed.
Let's hope for the day when we all live in circumstances that will not require us to do annoying labor, agricultural or otherwise, on Chol Hamoed so make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah make aliyah!!!!!