Rationale for growing .
Potatoes have been grown on our farm since Lionel Munns first grew them at Westmoor in 1960. They are traditionally a very important crop on the fertile soils of the Fens. They are usually not grown more frequently than once in every six years, this prevents a build up of certain soil borne pests and diseases. Potatoes require generous amounts of fertiliser in order to achieve an optimum yield of good quality tubers, the residues of which offer great benefits to the other crops in the rotation that follow the potato crop, such as Winter Wheat and Sugar Beet. For this reason potatoes are often considered a fertility builder in the rotation. They do have a potential downside though, for they are by far the most expensive of all the crops to grow and prices obtained for the crop can vary widely throughout the season, sometimes profits are large, sometimes they are non-existent. The crop is harvested in the Autumn and if soil conditions become wet then harvest can be delayed and structural damage can occur to the soil during harvest. This in turn will result in delayed establishment of the following wheat crop and subsequent yield loss. It can be seen from this that the potato crop is an important element in the rotation but it is critical to grow the crop correctly and get the management right.
Place in the Rotation.
Potatoes are only grown on the lightest and most fertile soils on the farm and rotation is far more important for the Potato crop than for any other crop we grow. We try to keep our rotation as simple as possible to make it easy to manage and plan forward. The main consideration in our rotation is to ensure that potatoes are not grown more often than once in six years. This prevents build up of soil borne pests and diseases, most notably Potato Eelworm. Residues from the applied fertiliser to the potato crop are available to other crops in the rotation. Generally on the land we grow our potatoes on, the Rotation is as follows:-
Year 1. Wheat
Year 2. Wheat
Year 3. Sugar Beet.
Year 4. Barley
Year 5. Wheat
Year 6. Potatoes
As with many things on farms this has to have a degree of flexibility to accommodate the weather and other variables.
Seed bed preparation for Potatoes starts in the autumn immediately after harvest of the proceeding crop. If there are any signs of bad drainage in the field it is immediately cultivated deeply to remedy the situation and improve the drainage thus preventing any issues with flooding during the coming year. Ploughing takes place during mid October before the land gets too wet. This prevents structural damage to the soil and allows the winter frosts to break down the soil to a friable well structured tilth ready for planting in the Spring.
Planting Potatoes is as close to a lottery as you might find on a Fenland farm. Too early in the Spring and you run the risk of getting the young plants cut back by frost. Too late and we reduce yield by shortening the growing season and make the crop late maturing. Generally at Westmoor we try to plant when soil conditions are good and we aim for early April if possible. It is important that we are not late as the varieties we grow are first earlies and early maincrop so we need them to have time to grow and yield to their full potential in the shortest time possible.
We grow our potatoes in rows 36 inches apart and the tubers are planted 15 inches apart in the rows. This allows plenty of room for the new tubers to develop ready for harvest. The rows are automatically ridged up by special ridging bodies (much like mini ploughs) attached to the rear of the planter, this facilitates future mechanical weed control and prevents greening of the new tubers as they develop in the row later during the summer. Fertiliser is applied to the soil at the same time as planting. See section below for more details.
Weed control is of paramount importance in our potato crops and starts in the autumn immediately after harvesting the previous crop. This time of year is an ideal time to deal with any perennial weeds, such as creeping thistle that may be present. A single well timed spray of roundup onto the stubble left from the previous cereal crop, will ensure these injurous weeds are controlled.
Very little weed growth occurs in the fields during the winter after ploughing, and any that do are killed during seed bed preparation, during the spring. After planting however, the spring sunshine warms the soil and annual weeds begin to develop quickly and threaten to compete with the young potato plants. As the potatoes are planted in ridged rows we cultivate along the rows to both remove and add soil to the ridges during the same operation this has the effect of both pulling weeds out and covering them with soil. In addition we often incorporate one spray of a selective weed killer to assist in the control of weeds just before the crop foliage meets across the rows. Immediately after this we will mould up the rows which means we push earth up to the sides of the rows to prevent tubers “greening” during the summer and to kill the last few late germinating weeds that might be present. From then on the crop will be strong enough to compete with the threats of further germinating weeds.
Pest & disease control
There are many pests & diseases that attack and damage the potato crop. We have to be vigilant at all times. Basically pests and diseases cause problems in two ways. They can significantly reduce yield and they can reduce the quality of the crop or both.
The first prerequisite to growing a good potato crop is to start off with good quality seed potatoes. For these we go to Scotland. The seed potatoes grown here have a reputation throughout the world, for being of the best quality available. Due to the Northern latitude aphids are less common here and the yield damaging viruses carried by them are less common too. If present in the seed potato, viruses will affect the growth and vigour of the resulting crop. The transmission of virus diseases and their effect on yield is a complicated subject. The other important pre-planting consideration, is to choose land that is free from Potato cyst nematode. (PCN).This pest builds up in soil that has had potatoes grown on it often in the past. The effects can be devastating. The best control is by making sure we do not grow potatoes on the same land more often than one in six years. If we find it is unavoidable and we have to grow potatoes on land which is infected with PCN we can apply granular nematacides to the soil at planting. This is very expensive and only gives partial control so is avoided where possible.
In the growing crop.
The main disease of potatoes is late potato blight (Phytophthora infestans) without control the loss in yield from this fungal pathogen can be as much as 80-90%. Ireland’s great famine of the mid 1840’s was caused through a sudden outbreak of late blight which devastated the crop throughout the country. The potato crop was hit three years on the run, by the end of which the resultant death tole from starvation and disease reached a massive 1 million and a further 2 million people emigrated, mainly to North America, England and Australia. Fortunately now we understand the disease and have developed disease monitoring/predicting methods which help greatly. We usually have to spray the crop every 2 weeks in order to reliably control blight. Aphids are another serious pest for potatoes. As mentioned above they transmit viruses in the crop and they also starve the crop of water/nutrients through their sap feeding habits. Usually we need to spray our potatoes with an insecticide twice during the growing season. There is a plethora of other potato diseases, which you can look at here.