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What is your opinion regarding exponential nutrient loading of conifer seedlings, primary species being Picea glauca and Picea mariana? In order to accomplish this process we load our crops over a 15 week period and monitor nutrient levels with destructive tissue smpling bi-monthly. During the process we have very high EC's upwards of 2000PPM. I have found that if we increase the amount of N later in the season we severely restrict the plants ability to utilize potassium. -- Douglas H.

A.A very interesting subject! Exponential nutrient loading is a cultural practice developed to build nutrient reserves in seedling plants by reaching a steady-state nutrient level in the plant. The technique is most often used to promote survival of container-grown seedlings for reforestation. Research has shown the following benefits of exponetial nutrient loading in conifers:

- increased nutrient reserves without increasing biomass

- improved performance of seedlings after planting out

- stimulated mycorrhizal formation

- increased nutrient uptake efficiency

In the situation you have described, I would be concerned about the EC value but not too alarmed. EC's around 1000ppm are considered acceptable for containerized plants; your value of 2000ppm is on the edge of acceptable levels but could be potentially harmful if it goes higher.

Unfortunately, I have not seen a study that reports corresponding EC values with exponential nutrient loading for comparison. I would be most concerned about how the plants are over-wintered; as the media dries out, EC will continue to rise.

N will certainly compete with K and P for uptake. The key here is to recognize the form of N applied. NH4+ will compete with K+ and can induce deficiencies if it is the predominant form of N applied. However, if NO3-is applied or NH4+ is being rapidly converted to NO3-, this is not a problem. NO3- can compete with P because NO3- uptake is more regulated by the plant and P will often be taken up in luxury consumption. Some authors have recognized this problem and included various P levels as treatments in their nutrient loading studies. Timmers (1991) found that black spruce seedlings provided half doses of N and full doses of P were the best treatment when grown out. Xu-XinJian (1998) conducted an experiment with Cunninghamia lanceolata in which extra P was added at the high N level to test for induced deficiency of P by high N. Results showed that the extra P stimulated P uptake without altering growth or N uptake.

In my opinion, exponential nutrient loading, if managed properly, can be a great tool for improving fertilizer efficiency in container-grown seedlings and improving survival of seedlings after being planted out. I have listed several references below that pertain to exponetial nutrient loading of coniferous seedlings. These should provide a more complete overview of the subject. Thanks for the great question!

-- David Sanrock

TI: Growth, nutrient dynamics, and ectomycorrhizal development of container-grown Picea mariana seedlings in response to exponential nutrient loading.
- AU: Quoreshi-M; Timmer-VR
- SO: Canadian-Journal-of-Forest-Research. 2000, 30: 2, 191-201; 45 ref.

TI: Steady-state nutrient preconditioning and early outplanting performance of containerized black spruce seedlings.
- AU: Timmer-VR; Armstrong-G; Miller-BD
- SO: Canadian-Journal-of-Forest-Research. 1991, 21: 5, 585-594; 23 ref.

TI: Manual for exponential nutrient loading of seedlings to improve outplanting performance on competitive forest sites.
- AU: Timmer-VR; Aidelbaum-AS
- SO: NODA-NFP-Technical-Report. 1996, No. TR-25, vi + 24 pp.; 38 ref.

TI: Nutrient dynamics and carbon partitioning in nutrient loaded Picea mariana [Mill.] B.S.P. seedlings during hardening.
- AU: Miller-BD; Timmer-VR
- SO: Scandinavian-Journal-of-Forest-Research. 1997, 12: 2, 122-129; 25 ref.

TI: Exponential nutrient loading: a new fertilization technique to improve seedling performance on competitive sites.
- AU: Timmer-VR; Colombo-SJ (ed.); Noland-TL
- SO: Special issue. Making the grade: proceedings of an international symposium on planting stock performance and quality assessment, held in Sault Ste Marie, Ontario, Canada on September 11-15, 1994. New-Forests. 1997, 13: 1-3, 279-299; 31 ref.

TI: Growth and nitrogen nutrition of Chinese fir seedlings exposed to nutrient loading and fertilization.
- AU: Xu-XinJian; Timmer-VR; Xu-XJ
- SO: Plant-and-Soil. 1999, 216: 1-2, 83-91; 33 ref.

TI: Biomass and nutrient dynamics of Chinese fir seedlings under conventional and exponential fertilization regimes.
- AU: Xu-XinJian; Timmer-VR; Xu-XJ
- SO: Plant-and-Soil. 1998, 203: 2, 313-322; 41 ref.

TI: Exponential fertilization increases nutrient uptake and ectomycorrhizal development of black spruce seedlings.
- AU: Quoreshi-AM; Timmer-VR
- SO: Canadian-Journal-of-Forest-Research. 1998, 28: 5, 674-682; 63 ref.

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