Commercial organic fertiliser as supplementary fertilisers in potato crop production (OK-Net Arable Practice Abstract)

The nitrogen requirement varies depending on variety and usage. The conventional fertilisation amounts to 120 kg of N per ha in table potatoes and potatoes for processing. Early potatoes and seed potatoes require slightly less nitrogen at about 100 kg of N per ha. The nitrogen supply strongly depends on the conditions for N mineralisation (weather, humus content of the soil, preceding crop residues). Thus, optimising the N supply is complex. Nitrogen from the preceding crop: Grain legumes or cereals in combination with green manure are favourable preceding crops. Field peas may leave behind up to 50 kg net weight of available nitrogen, a mixture of grain legumes and barley up to 30 kg. Depending on the preceding crop and the soil, the nitrogen left behind may amount to zero. Using grass-clover ley as a preceding crop is not an option due to the high risk of wireworm infestation. Manure as basic fertiliser: A dosage of 15 to maximum 30 tonnes of manure per ha (1-2 kg of available N per t) in autumn during the preceding crop serves as basic nitrogen fertilisation. Mineralisation occurs slowly during the entire growth period. A dosage of manure also covers the high potassium demand of potatoes. Farms without livestock need to cover the K supply by using approved mineral fertilisers. Due to the risk of Rhizoctonia, only well-rotted or composted manure should be used. Manure compost has, like other composts, a low N effect. Undiluted cattle slurry: Depending on the slurry’s N content (1-3 kg of available N/m3), 30-90 m3 of slurry can be applied to the preceding crop or at a plant height of 10 -20 cm the latest (i.e. before creating the ridges) and worked into the soil. Later applications of slurry only promoted haulm growth and delay the maturation of the tubers. Commercial fertiliser: An additional dosage of fertiliser of about 30-60 kg of N per ha with a granulated, quickly mineralising commercial N fertiliser can complement the missing nitrogen supply. It should be applied during spring at planting or at the first round of hoeing the latest. In case of lacking farm manure, up to 90 kg of total N can be applied per ha. The coarser the grains, the earlier the commercial fertiliser needs to be applied. In Swiss trials, the yield of potatoes was increased by up to 30 % with the commercial fertiliser “Biorga Quick” (12 % of N). When using 50 kg of N fertiliser per ha, an additional yield of only 700 kg per ha is required to cover the fertiliser costs. Due to the high costs of commercial organic N fertiliser, its use is profitable in the case of lacking farm manure and low N mineralisation in the soil.