Phosphorus application strategies in potato: constraints and potential improvements

Phosphorus (P) is an essential element that plays an important role in carbohydrate metabolism and energy transfer systems in all plants. Sufficient P supply is therefore essential for providing adequate food, fibre and fuel for society. In potato, P deficiency reduces yield and tuber number due to reduced radiation interception by the canopy. Phosphorus is a limited, non-renewable resource. When lost to water bodies, P causes environmental problems such as eutrophication. Potato fields may be a significant contributor to P loads to water due to high P recommendations and a tendency for P leaching in soils where the P sorption/binding capacity is saturated. Efficient use of P in potato cultivation is therefore crucial in order to reduce P consumption and environmental impacts. The thesis improves the current understanding of potato P requirements as regards optimising P application strategies, use efficiency and potato tuber yield. The results show that split P applications can improve P recovery by 25%, particularly on soils with low P content and low buffering capacity, and can improve physiological P use efficiency (PPUE) where P availability is limiting yield. Irrigation and subsoiling can both significantly improve P recovery, PPUE and yield. Foliar application does not improve PPUE, but can increase P concentration and yield if the plant is supplied with sufficient water. However, foliar P application should not be used as a general strategy, but can be recommended where the soil buffering capacity is extremely high. It is shown in this thesis that many Swedish soils contain sufficient amounts of P to support optimal growth and are no longer responsive to P fertilization. To determine the responsiveness of potato yields to P, data on soil organic material, pH, soil buffering capacity and varietal characteristics are needed, in addition to the amount of P-extractable with ammonium lactate (P-AL value) used in Sweden today. More sophisticated P recommendation models which take these parameters into account are urgently needed. As long as yield effects from P fertilization cannot be predicted, excessive P fertilization will probably continue, resulting in waste of a non-renewable resource, eutrophication of the aquatic environment and reduced farm profits. The findings in this thesis contribute to understanding the complex picture of P acquisition in potato and, hopefully, to more efficient use of the non-renewable P resource.