Here is information from UGA Extension Pecan Specialist Dr. Lenny Wells and fertilizing young trees:
Most soils on which new pecan orchards are established here in Georgia are old row crop fields or cleared pine land. In the case of row crop fields, soil levels of P and K may be in fairly good shape, while Zn levels and pH are low. On cutover pine land, everything tends to be low. Desired soil levels for these nutrients should be 60 lbs P, 100 lbs K, and 15 lbs Zn by the time the trees begin production. It takes a few years for surface applications of these nutrients to reach the trees. The sooner growers can get up to these levels, the better. In general, once you get P, K, and Zn levels to this desired range, they tend to remain there for quite a while because so little is removed with the crop or lost to the environment in an orchard system.
Our general recommendation for fertilization of young trees is to apply 10-10-10 + Zinc Sulfate by hand to each tree. With regard to tree growth and leaf N status, this still appears to be an effective and efficient method of fertilization. As far as the tree is concerned, there is no difference between this method and fertigation. There are a number of growers who are applying fertilizers through the irrigation system on young trees. There is nothing necessarily wrong with this. It can be done safely as long as the irrigation system is in good working order. In fact, for larger orchards, fertigation may be an easier and more efficient method of fertilizing young trees from a labor stand-point. However, the best use of fertigation is for the application of N. Our trials have shown that 25 lbs N per acre applied via fertigation is excessive for first through third year trees. A more reasonable rate would be 10 lbs N per acre (and that may be high as well). The tree will only use the N it needs and excessive N will leach from the root zone, therefore N must be applied annually in a manner suitable for optimum uptake. However, earlier P, K, and Zn are more stable in orchard soils.
As young trees grow their roots are exploring the soil at a length twice that of the canopy width. Therefore the roots of a young pecan tree quickly outgrow the area wet by the irrigation system. In newly established orchards, this area may remain deficient of P, K, and Zn for a number of years unless dry broadcast applications are made to bring soil levels up to the desired range. With fertigation of these nutrients, the wetted zone may be sufficient but the larger area around it in which the roots are trying to explore is still low. This is especially critical for P, which plays a large role in root growth.
The tree will reach a point in which it needs sufficient P, along with K, and Zn in the entire root zone for optimal growth and production. Broadcast applications beginning with directed applications toward the herbicide strip in young trees will help get these soil levels up in a broad swath around the trees. As the trees grow and leaves are deposited in the middles, they redistribute and recycle these nutrients back into the orchard soil. A broadcast application of poultry litter is also a good way to elevate levels of these nutrients in the orchard. Begin building up soil levels early on young pecan trees in order to avoid problems down the road.