Farming and Fertility

Michael Halila 5 minute read

We talked about farming in last month’s Devlog, and I thought I’d return to the subject from a design perspective. So I’m going to talk briefly about how farming and soil fertility work, and how we’ve implemented them in Goblin Camp.

Farming is going to be one of the most important ways of feeding your goblins, especially as settlements get bigger. So even though our goal is not to make a farming game, farming still matters, and players are going to have to think about how they go about growing crops.

Plants need several things to grow: sunlight, carbon dioxide, water and nutrients in the soil. As we know all too well in our day, carbon dioxide is abundant in the atmosphere, and in climates like the one we have in Finland, there’s plenty of water. Sunlight is also quite freely available, although it’s worth noting that we do take shade into account in Goblin Camp. Farm tiles next to trees and on the north slopes of hills receive a small fertility penalty to account for them receiving less light when the crops are growing.

The sticking point for farming, then, tends to be the nutrients in the soil. The most important ones are nitrogen, phosphorus and potassium, but there are also lots more substances in small amounts. Plants need them to grow, and if you grow enough plants on the same ground, these nutrients start to run out. When we talk about soil fertility, it covers a lot of things that affect how good the soil is for growing plants, but this supply of nutrients is one of the most important factors in it.

In Goblin Camp, there are two kinds of soil: sand and clay. Of these two kinds of soil, clay is more fertile, but because it’s heavier, more advanced tools are needed to work it. Later on, our goblins will develop them, but at first, with only light tools available, farming is confined to the sandy soils.

We model fertility by giving each tile a certain base amount of fertility points. To keep things simple, one point of fertility means the soil holds enough nutrients to produce one food point’s worth of crops. In turn, one food point is the amount of food a goblin needs to live for one season. When a player builds a farm plot, the game calculates the amount of fertility points available. A maximum is set by the technology used to till the field: more advanced tools turn over the soil more effectively, and provide a better growth environment for plants.

As a side note, the field sizes in Goblin Camp are about 10% of what they would really need to be, at the kind of crop yields that were possible with the technology we’re modeling. If we assume that one tile is approximately a square meter, then a hectare would be a square with sides 100 tiles long. The fields required to support even a small settlement would be several hectares, and on our map they would be simply gigantic. So we’ve taken the decision to model farming in equivalent hectares that are 10% of the size of an actual hectare of land.

In every growth cycle, a maximum of half of the available fertility points are extracted by plants on the farm plot. This drains the fertility of each tile in the farm plot equally. The staple crop of Goblin Camp is the turnip, and you’ll find that if your goblins plant turnips on sandy soil, and keep the farm plot going for several years, the number of turnips it produces will start to fall. Eventually, the fertility of the plot will be totally exhausted, and it will be impossible to farm at all. You’ll need a new field - until the fertility runs out there as well.

So how do you get fertility back into soil? This is quite a crucial question in farming, and for a long, long time after farming was invented in what we call the Neolithic Revolution, no-one really understood the role of nutrients in soil. As late as in the 18th century, British agricultural innovator Jethro Tull believed that simply plowing the soil would restore its fertility. For centuries, people believed that soil needed to “rest” and it would recover, and you sometimes still see this claim being made. It’s not true: the fertility of soil can only be restored by adding nutrients to it. There are natural processes that do this, but they are very, very slow.

There are several ways to do this faster. In the ancient Near East, systems of hydraulic farming were developed, where the soil carried by rivers was used in farming. The Egyptian version of this system was, for a long time, some of the most productive farming in the world. The system most commonly used in Europe was fertilizing fields with manure from animals, and this is something we’ll be looking into in the future in Goblin Camp. The most exciting version, and certainly the one that we’re most keen to see our players try, is the one that we looked at in July’s devlog: setting the forest on fire.

Slash-and-burn agriculture is a way of farming that involves burning down a patch of forest, and using the ashes as soil to farm on. This is probably one of the oldest forms of agriculture in the world, and it’s still practiced in several places. The ashes contain most of the organic matter of the forest that once grew on the plot, and the crops sown there will use them as nutrients. This can produce much larger crop yields than the land would normally be capable of, for several years in a row.

Once the fertility in the slash-and-burn plot, also called a swidden, begins to drop, the farmers move on and burn another plot in the woods. Surprisingly for a system of farming that literally involves setting things on fire, this is actually sustainable, if you have enough forest: there are systems of slash-and-burn cultivation that operate on a 20-year cycle, which is enough for the first plot on the cycle to have grown back into woodland again. In the mean time, the swidden can even be used as pasture for cattle.

It’s believed that slash-and-burn cultivation was the first kind of farming practiced in what is now Finland, and it was still being done in Savo in the 20th century. So both for reasons of history and fire, it’s a kind of farming we were keen to portray in Goblin Camp.