Phosphorus deficiency symptoms in Idaho sugarbeet.

Abstract

Phosphorus (P) is second only to nitrogen in importance for optimizing growth, crop yields, and quality. Despite its importance deficiency in sugarbeets can be common, particularly during early spring when soils are cold and sugarbeet roots are small.  Diagnosis is not always easy as phosphorus deficiency is widely regarded as the most difficult nutrient disorder to diagnose in sugarbeets. It is not uncommon for P-deficiency to be misdiagnosed as nitrogen (N) deficiency, resulting in potential for over-supply of N and reduced beet quality. A wide range of symptoms are attributed to P-deficiency, many of which, such as purpling of leaves, are often listed in one diagnostic key only to be omitted altogether by another. This has led to disagreement amongst sugarbeet agronomist as to what visual symptoms best describe P-deficiency in sugarbeet grown on Idaho soils. In response to this, a glasshouse study was established in 2020 to document the visual symptoms of P-deficiency across 4 levels of soil P supply (3, 10, 15, and 27 ppm-P).  A follow up study, with the same treatment levels, was established in 2021 to investigate symptom expression across 10 commercial sugarbeet varieties.  These studies found that many commonly described P deficiency symptoms, such as delayed emergence, yellow cotyledons, purpling of leaves, brown veining of older leaves, crinkling of leaf margins, and leaf cupping, were not reliable indicators of P-deficiency. Rather, the most reliable and consistent indicators of P-deficiency were slow leaf production and reduced plant size, smaller and somewhat darker green first true leaves, and some degree of upright leaf habit in young leaves. All ten varieties showed remarkably similar symptom expression. This work has helped Amalgamated crop advisors better recognize the symptoms of sugarbeet P deficiency in Idaho soils.