Nutrient Management Research Database

The effect of potassium fertigation through subsurface irrigation lines on processing tomato fruit yield and quality was evaluated in four field trials in California from 2002-2004. Fields had exchangeable soil potassium between 0.48 to 0.85 cmol per kg, with high exchangeable magnesium, and a history of yellow shoulder occurrence. Potassium treatments evaluated included seasonal amount applied (o to 800 kg per hectare), fertigation method (continuous versus weekly), and timing (early, mid, or late season); foliar potassium treatments were also included in the 2002 trial. In two fields total and marketable fruit yield were significantly increased by potassium fertigation, and fruit color improvements were observed in all trials. Among color parameters improved by potassium fertigation were yellow shoulder incidence, blended color, and the hue of the shoulder region of the fruit. Potassium fertigation did not affect fruit soluble solids concentration. Yield increased only with fertigation treatments initiated during early fruit set. The effects of fertigation method and rate were inconsistent. Foliar potassium application was ineffective in increasing either fruit yield or quality.

• This study evaluated the effect of potassium fertigation on processing tomatoes for yield and quality from 2002-2004.
• Treatments included:
  • amount of potassium applied (from 0 to 800 kg per hectare)
  • fertigation method (continuous or weekly)
  • timing of applications (early, mid, or late season).

• Fertigation increased yield as compared to the traditional methods of applying potassium (preplant, sidedress soil applications, or injection into furrow irrigation water).
• Yield increases were attributed to increased fruit set; the fertigation treatments that increased yields were initiated during early fruit set.
• This study found a positive correlation between plant potassium status and fruit color.
• Fertigation may not be economically justifiable. Growers would need the increased yield or receive a price premium for quality fruit to cover the extra cost of liquid potassium fertilizer.
• 225 to 250 kg per hectare of potassium was needed in the 2002 and 2004 trials to obtain yield responses, this would cost at least $140- $160 at current fertilizer prices, meaning that growers would need a 1.4mg per hectare increase in yields to recover this cost at the average 2005 fertilizer and processing tomato contract prices.
• Results suggest that fertigation of potassium during early fruit set will increase yields, whereas fertigation after fruit set may improve fruit quality.