Abstract
Broadcast fertilization with an array of amendments was investigated for its capacity to stimulate growth and enhance nutrition of a three-year-old Jeffrey pine (Pinus jeffreyiGrev. & Balf.) plantation growing on an acidic Sierra Nevada surface mine. Four formulations that differed in N source, duration of release, and the suite of nutrients provided were evaluated, with each applied using four rates. Free Flow 29-3-4, a conventional amendment featuring urea as its near exclusive N source, and High N 22-4-6, a controlled release formulation containing ammoniacal, nitrate, and urea N, were the most stimulatory while an organic formulation relying exclusively on a municipal biosolid N source, Milorganite 6-2-0, was the least so. The lowest application rates employed were inadequate while the most advantageous was not the highest rate for any formulation. Foliar analysis revealed that improved N nutrition was probably critical in the favorable growth responses to fertilization, that of P was a likely contributor, and amelioration of potential Mn toxicity may have assumed an accessory role.
Highlights
Reforestation of infertile sites presents a conundrum for natural resource managers
Above-ground volume was greater initially in seedlings fertilized with the Viking formulation applied at the 25 g rate than in those receiving 100 g of the Free Flow amendment, with all other treatments assuming intermediate values that did not differ statistically according to the least significant difference (LSD) test from the former or the latter
The four formulations incorporated into this study exemplify the marked differences in chemical composition that exist among readily available commercial fertilizers, especially concerning the forms of N they contain and the duration of nutrient release, with the latter factor dependent in part upon the former with respect to critical N nutrition
Summary
Reforestation of infertile sites presents a conundrum for natural resource managers. If the stunting of planted seedlings that frequently results from shortages of critical nutrients is to be averted, it is necessary to devise a nutritional augmentation approach that can rectify the soil deficiencies. Delaying fertilization until seedlings are well established on the outplanting site may prove to be more stimulatory, if less convenient, but questions remain about how long to delay, the application approach, the type and formulation of amendment, and the amount to apply. As for the timing, a delay of sufficient duration to be reasonably assured that fertilization will not impinge on survival would appear prudent, but not so long that malnourishment produces irreversible stunting, and, as for the application approach, it is reasonable to assume that some form of topdressing should be employed, but questions arise concerning the necessity of subsequent tillage of the amendment beneath the soil surface. Choices extend beyond conventional and controlled release fertilizers to include organic forms, and, for each, the appropriate formulation will likely depend on seedling species as well as soil characteristics. The most advantageous application rate will reflect amendment type and formulation as well as seedling and soil characteristics and may depend in part on such climatic factors as precipitation regime and ambient temperatures during the growing season
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