Nutrient Management Research Database

Nutrient uptake by trees is determined by root interception, soil availability, and  tree  demand.  Fruit  trees  have  low  rooting  density,  especially  in  the  case  of   dwarfing rootstocks. Mobility in the soil is a key factor in determining nutrient  availability,  and  good  management  of  nutrients  requires  that  supply  is  matched   to  demand,  in  terms  of  amount,  timing  and  retention  in  the  root-zone,  and  that   nutrients  are  placed  where  they  can  be   accessed  by  roots.  Fertigation  allows   such flexibility in the timing and precision of nutrient supply. The efficiency of  N  fertigation  is  closely  related  to  irrigation  management.  Scheduling  irrigation   to  meet  tree  evaporative  demand  mini mizes  the  drainage  of  excess  water   through  the  root  zone  and  the  conseque nt  N  leaching.  Timi ng  the  N  supply  to   coincide   with   the   period   of   rapid   canopy   development   avoids   excess   N    application  when  tree  growth  is  supported  by  remobilization  of  stored  N.   Fertigation  gives  greater  P  and  K  mobility  than  broadcasting,  increasing  the   potential for timely application of these nutrients in the root zone. P fertigation  is beneficial at planting and as a single application at bloom. Fertigation with K  can  prevent  the  development  of  K-defici ency  in  drip-irrig ated  trees  on  sandy   soil.  Fertigation  with  acidic  fertilizers  th rough  drip  systems  can  be  detrimental   in  coarse-textured  soils,  where  it  can  result  in  soil  acidification  and  nutrient   deficiencies, which can develop in as short a period as three years.

This source summarizes the findings on a handful of studies investigating fertigation practices in apple and cherry trees.

Fertigation refers to the application of fertilizer through irrigation systems, particularly drip irrigation or micro-sprinklers.

In all of the studies, water was applied based on measurements of soil water evaporation.

Irrigation Amount

Utilizing soil water evaporation rates to adjust irrigation patterns saved as much as 170 gallons of water per tree.

Nitrogen

As irrigation water moves down through the soil, it carries the highly mobile N with it. This can remove N from the root zone, and make it unavailable to trees.

Apple trees should be fertilized with N during the 6 weeks following bloom, as this is the period of maximum N demand.

Cherry trees fertilized at 56 lbs per acre via a micro-sprinkler system were able to access more N than those fertilized by broadcasting fertilizer on the soil surface at the same rate. Yields did not increase when fertilized at higher rates.

Potassium

The use of acidfiying fertilizers can deplete soil K after 3 years. Daily K fertigation can help remedy this problem.

Potassium Chloride, Potassium Magnesium Sulfate, Potassium Sulfate, and Potassium Thiosulfate did not show any differences in tree K levels.

Phosphorus

Fertigation improves P mobility, especially in sandy soils.

Spreading P fertilization over 8 weekly applications immediately after tree planting was more effective than a single application following planting.