The lack of crop rotation and the increase in rainfall make potato production even more difficult. A fertile soil has a good crop capacity, so the soil will produce a good harvest also in the future, as long as the growth conditions are maintained. The plants get all the nutrients they need from the fertile soil.

The potato crop produces a high yield, so it takes a large amount of nutrients in a short time. As the result of the potato monoculture the soil nutrient balance will be distorted. The growing of potatoes requires intensive soil treatment that leads to the collapse of the soil structure and it also decreases the soil organic matter content. The loosening of the soil structure and the low organic matter content increas the soil compaction. The loose soil has a low water retention and permeability, so water problems will increase during wet and dry seasons.

The purpose of this thesis is to find out what factors cause yield losses in the potato monoculture, how to observe the growth condition and how to raise the growth conditions to a good level. The thesis research material was collected from six different fields. In four of those fields potatoes have been grown several years and two of the fields have grown crops and grass. In the field quality test, we were looking for the differences between the fields. The results of the field quality test show how the farming history has been affected by the growth condition of the field and detect problems caused by the potato monoculture.

The field quality test shows that potato fields’ soil nutrient concentrations and the soil pH had fallen to a low level. The soil organic material content and soil respiration was low, because potatoes left very little organic matter in the ground. The potato fields’ soil structure was changed to a fine and loose one. Because of the loose soil structure the field was compacted and the root growth was limited to the plough layer.

The soil compaction can be prevented by reducing traffic in the field, by using dual wheels on tractors and by reducing the air pressure in the tires. The soil structure and the soil compaction will be repaired by rotational cropping and growing various deep-rooted plants. The soil organic material can be upheld by growing grass and the soil nutrient balance will be corrected by the soil improvement material. Field water management will be corrected by working water drainage, which is flushed on a regular basis. The soil biological activity can be increased by crop rotation and the use of organic fertilizers.

The problems of the monoculture caused yield and quality losses, and it also decreased the soil productivity. There are many yield variations in the bad soil structure of the fields between the growing seasons. The potato monoculture decreases the yield by over 25 % per year. The monoculture is a risk for total yield loss and in the end the field is no longer arable.