Nutrient Management Research Database

Cumulative yield over five years was increased by phosphorus (P) primarily as a result of an increase in annual apple number rather than average fruit size. In two of three measurement years, water core was decreased by P fertigation and in two years fruit browning was inhibited by P, implying a role for this nutrient in postharvest, apple membrane stability. Research on sweet cherry is still in the early stages but increasing irrigation frequency to four times daily, relative to applying the same quantity of water every two days, increased tree (canopy) size by the end of the second growing season and improved tree response to mulch and P fertigation.

This paper details two studies:
1) The effect of an annual application of ammonium polyphosphate near bloom on leaf P concentrations, yield, and fruit quality of apples.
2) The effect of high frequency irrigation (4 time daily) and application of a surface mulch on early tree growth, yield, tree water relations, and leaf P and K concetration of cherries.

Each of these studies was conducted for five full seasons.

Apples
When ammonium polyphosphate was applied via fertigation once per year near bloom:
1) Midsummer leaf P and harvested fruit P nearly always increased, with the exception of fruit P levels for 'Gala' apples.
2) Total field and per-tree yield increased, with no effect on fruit size.
3) Incidence of water core was reduced in 2 of 3 years when it was measured.

Cherry
When high frequency irrigation (4 times daily versus every other day) was practiced
1) Early growth trunk thickness increased, when a surface mulch was applied.
2) Tree-water relations were improved during the mid-summer period, a time of heightened water stress.
3) Regardless of whether a surface mulch was applied, leaf K concentration increased and P concentration was not effected. However, leaf K concentrations were higher when trees were mulched.