Optimizing Peach Fertilization: Nutrient Guidelines and Sampling Procedures

1. Welcome to the North San Joaquin Valley Cling Peach Day Sponsored by UC Cooperative Extension & the California Cling Peach Board

2. Fertilization Guidelines for Peaches Roger Duncan Pomology & Viticulture Advisor University of California Cooperative Extension Stanislaus County

3. Today we will discuss: • Nitrogen • Phosphorus • Potassium • Zinc

4. A good fertility program is based on: • Replacing what is removed with the crop • shouldn’t be based on “what I always do” • Monitoring long term trends with annual tissue samples • Occasional soil samples for gradual changes in soil chemistry. • Yield is already affected by the time you see symptoms

5. Nitrogen Deficiency • Mild deficiency: lack of growth, smaller, pale green leaves with red tinge • N is mobile, shows in old and new leaves

6. Nitrogen Deficiency • As deficiency worsens, leaves get yellower and smaller • May develop red spots

7. Nitrogen Deficiency • Lower N favors good color in fresh market fruit

8. Crop load drives demand for N: • Between 2 – 3 pounds of N removed with every ton of peaches • Perennial structure requires additional ~ 20 lb. per acre • More in high density orchards • Leaves & prunings ~ 60 lb. (80-90% recycled)

9. Approximate N fertilizer requirements for mature peach and nectarine orchards. • Assumes that prunings are not removed from the orchard • 2.69 lbs. N are removed per ton yield • 19 lb for perennial part of tree • 90% recycle of leaves & prunings (~ 9 pounds) • N use efficiency is 70%

10. Excessive N Fertilization Leads to: • Excessive shoot growth • Increased (summer) pruning costs • Excessive shading of lower wood • Shorter orchard lifespan • More brown rot • Poor coloration and delayed harvest (fresh market) • Potential ground water contamination • Regulations

11. Leaf sampling procedure: • June – July • Sample each variety / block separately • Weaker or “different” areas of a block should be sampled separately

12. Leaf sampling procedure: • 60 – 100 mid shoot leaves from current season shoots. • Leaves treated with foliar zinc are not useful to determine zinc status • Trees sprayed with N should not be sampled for at least one week • Analyze promptly or refrigerate

13. Dormant Shoot Sampling: • July sampled leaves too late for current season adjustment and for zinc contamination • Sample 30 – 40 moderately vigorous shoots 10-20 inches long from lower canopy. • Guidelines are for January but fall may give similar results

14. UC Guidelines for Nitrogen in July-Sampled Leaves and Dormant Shoots

15. Nitrogen Fertilizers: • Trees don’t care – N is taken up as nitrate whether organic or inorganic • Nitrate very mobile in soil, leachable • Ammonium less mobile but converted to NO3 within days at warm temps • Nitrification; acidifies soil • Urea converted to ammonium, will volatilize quickly on soil surface

16. Time of Nitrogen Fertilizer Application: • Trees take up almost no nitrogen when leaves are absent. • Nitrogen for spring growth comes from N stored in roots, trunk, shoots. • Nitrogen applied before leaf out is susceptible to loss by leaching and volatilization.

17. Time of Nitrogen Fertilizer Application: • Peaches relatively low users of nitrogen compared to almonds so don’t need to “front load” so much. • Extra earlies (especially May – June fresh market peaches) • Too much N early leads to excessive growth after harvest, poor quality • Late summer applications might be good strategy • Provides N for next year’s crop without excessive post-harvest growth • Foliar urea in fall

18. Foliar Nitrogen Application: • Studies show that 20 – 50% of N can be supplied through the leaves • Urea is cheapest and mostly easily absorbed into the leaf • Up to 50 lbs. of N / acre (100 lbs. urea) can be sprayed per application • Multiple applications OK two weeks apart

19. Foliar Nitrogen Application: • When to spray • October • Before natural leaf senescence • September too soon due to earlier defoliation • If combined with zinc, more N (and Zn) mobilized into storage than if applied alone

20. Phosphorus • P deficiency is very rare in California • Most soils contain a lot of P, most is in unavailable form

21. Phosphorus Deficiency • Lack of spring growth

22. Phosphorus Deficiency • Reddening of new growth in spring • More mature leaves can be darker green than normal

23. Phosphorus Deficiency • Phosphorus deficient leaves turn purple in fall

24. Phosphorus Deficiency • Branches can defoliate and collapse under severe deficiency

25. Phosphorus Deficiency • Some varieties may crack under severe P deficiency

26. UC Guidelines for Phosphorus in July-Sampled Leaves and Dormant Shoots *Previous literature cited 0.10% P as adequate for leaves

27. Phosphorus Fertilization: • Very rarely needed in California peaches • 0.5 – 1.0 lb. P2O5 removed per ton of fruit • 10 – 20 lb. P205 in a 20 ton crop • P is very immobile in soil. Cannot be leached with irrigation or rain. Therefore timing is not important. • Usually drilled 6 -8 inches deep • If fertigated by drip, be careful not plug with calcium phosphate precipitate

28. Phosphorus Fertilization: • Side note – phosphorous acid materials (phosphites) do not supply tree with P • Good for Phytophthora management, not as a P fertilizer

29. Potassium (a.k.a. Potash) • More potassium removed than N • Can influence fruit size • Might be neglected more than it should be

30. Potassium (a.k.a. Potash) • Deficiency usually first seen in early summer • Potassium deficient leaves tend to roll at the edges • Midshoot leaves affected most

31. Potassium Deficiency • Leaves may also be a little pale. Margins may scorch

32. Potassium Deficiency • Fruit set, shoot growth and leaf size is reduced • Fruit size and color are reduced • *Fruit size can be reduced before other signs are obvious

33. Potassium Deficiency • Severe potassium deficiency can lead to defoliation and limb death

34. UC Guidelines for Potassium in July-Sampled Leaves *Probably should be > 1.5% K to ensure that the majority of trees are over 1.2%

35. Potassium Fertilization: • Average of 4 – 5 lb. K2O (3.3 – 4.2 lb. K) removed per ton of fruit • = 80 – 100 lb. K2O in 20 ton yield

36. Potassium Fertilizers: • Potassium can be tightly bound to clay particles so generally we apply high quantities in concentrated applications to overcome problem • Less of an issue in sandy soil or where active roots are very shallow • Drip or microsprinklers • Adding gypsum (CaSO4) can help K move deeper in soil

37. Potassium Fertilizers: • Potassium chloride (KCl) • Probably cheapest form per pound of K2O but risky due to Cl component • Should be applied after leaf drop in fall • Sulfate of potash (K2SO4) • More expensive than KCl but safer • Not soluble but can be applied through solutionizer • May be able to broadcast in sandy soil under microsprinkler

38. Potassium Fertilizers: • If banding sulfate of potash (K2SO4) in drip-irrigated orchard, drip hose must be placed over band

39. Potassium Fertilizers: • Potassium nitrate (KNO3) • Also supplies N which should be accounted for • Can be applied as foliar spray • Foliar KNO3 applied during stage III may be effective – high demand period • May require multiple sprays at 40 lb to correct deficiency • Potassium thiosulfate (KTS 0-0-25) • Efficiently applied with fertigation but more expensive

40. Zinc - Influences on Deficiency: • Soil pH – Zn availability decreases over pH 6.0 • Lime (calcium carbonate) ties up zinc. Magnesium carbonate is worse • Land leveling - zinc content decreases with soil depth. • High amounts of phosphorus (ties up zinc)

41. Zinc - Influences on Deficiency: • Organic matter and manure • Zinc is less available in soils with a high OM content. • Heavy manure - chicken manure is particularly bad • High levels of other metallic elements (copper, iron, manganese) can induce zinc deficiency • Cool, wet soils • Rootstock (nemaguard is bad)

42. Zinc Deficiency • Interveinal yellowing with mild zinc deficiency

43. Zinc Deficiency Very small, pale, pointy leaves in a rosette (very short space between leaves) with more severe zinc deficiency

44. Zinc Deficiency Extreme deficiency looks like glyphosate damage

45. UC Guidelines for Zinc in July-Sampled Leaves and Dormant Shoots 1Leaf samples are not reliable if orchard has been previously sprayed with zinc 2Recent experiments indicate that a threshold of 10 ppm zinc is more appropriate for July-sampled leaves

46. Foliar Applications of Zinc

47. Basic Chemicals Zn sulfate Zn oxide Zn carbonate Zn chloride Zn oxysulfate Zn nitrate Chelates & Complexes EDTA Lignosulfonate Amino acid Sugar Citric acid Fulvic acid, humic acid Zinc Materials

48. Zinc Materials Zinc Sulfate (35% Zn) • Inexpensive • Very soluble • Widely used • Considered to be effective • Can be phytotoxic

49. Zinc Materials Basic or Neutral Zinc • Cost = 2x Zn sulfate • Mostly insoluble • Widely used • Considered to be effective • Not phytotoxic • Can be mixed with oil

50. Zinc Materials Amino Acid Complexes • Expensive • Considered to be effective • Can be phytotoxic • 6 to 7% zinc