Surveying the Impact of Phosphorus and Salts From Dairy Waste On Potato Yield and Quality.

Idaho faces the challenge of disposing of over 12 million tons of dairy manure per year.  Overlap is occurring between lands where manure is spread and potato production fields, causing potato growers to question the impact of the phosphorus and salts contained in the manure on potato yield and quality.  The objective of this two season study is to survey the impact of phosphorus and salts from dairy wastes on potato yield and quality in the Magic Valley of Idaho.  In the 2009 growing season, soil from 50 potato fields, receiving dairy waste in the form of manure, lagoon water, compost, or only conventional fertilizer were collected, along with corresponding non-agricultural soils and irrigation water.   Soils were tested for field moisture, pH, electrical conductivity (EC), soluble sodium, potassium, calcium and magnesium, and Olsen phosphorus.  Water was tested for electrical conductivity, pH, and dissolved metals if EC was greater than 1 dS/m.  The difference between field soil and non-agricultural soil EC, Olsen phosphorus, soluble calcium, magnesium and sodium was greater in fields receiving dairy waste than those just receiving conventional fertilizer.  These results suggest dairy waste applications do increase soil content of salts and phosphorus.   Sodium adsorption ratio was greatest in fields receiving compost.  Only fields receiving manure or both manure and lagoon water had potassium levels greater than non agricultural soils.  The effects of these nutrients on potato yield and quality must be further analyzed with data from completed grower surveys.