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Soil Nitrate Profile And Response Of Potatoes To Fertilizer N In Relation To Time Of Incorporation Of Lupin (Lupinus Albus)

J. B. Sanderson, J. A. MacLeod

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Lupin (Lupinus albus L. ’Ultra’) was evaluated as a green manure crop the year preceding potato production on Prince Edward Island for 3 yr. One pass of tandem disc was used to incorporate lupin green manure on 1 September (early) or 1 October (late). Barley residue following combine harvest was also incorporated in the same way in early September. One treatment of lupin was left unharvested with no fall incorporation (none), and in another treatment of lupin the seed was fall harvested with no fall incorporation. All treatments were moldboard plowed the following spring. Potato (Solanum tuberosum L. ’Russet Burbank’) was planted with three rates of nitrogen (0, 50, and 200 kg ha−1) band applied. Tuber yield and tuber N content increased with increasing rates of N applications in all incorporation treatments. Following late incorporated lupin, potato had higher tuber yield at 0 N than following the early incorporated lupin, while both treatments were higher than barley. Potato petiole nitrate-N levels and the mean spring nitrate-N concentrations in the soil were lower following barley than following lupin, and generally lower following early compared to late incorporation of lupin green manure. These data indicate the time of fall incorporation of a legume can have a significant effect on the N response of a succeeding crop. Early fall incorporation can result in significant fall N mineralization and winter leaching. Research on N response after legumes in rotation should consider the impact of time and method of residue incorporation. Key words: Petiole nitrate-N, nitrate leaching, green manure