15N‐Labelled Single‐treatment Fertility Experiments¹

Abstract

There is only one way of measuring directly the uptake of nutrient from applied fertilizer as affected by timing, placement, fertilizer source, and environmental interactions. This is by isotope labelling of the fertilizer. The purpose of the present study is not only to demonstrate the effectiveness of this technique in field experiments, but to extend the technique to the direct measurement of these fertilizer efficiencies without interactions. A further extension permits the direct quantitative measurement of interactions. The method has been referred to as “single‐treatment fertility experiments” because all treatments, as far as the plant soil or environment are concerned, are identical. The only difference is which of the fertilizer applications within a given treatment was isotopically labelled. Thus growth, nutrient uptake, amount, and pattern in all plots is identical within normal experimental variation. The presence of the label permits the quantitative measure of treatment effects without interaction. The method has been successfully used in field experiments in various areas of the world with rice (Oryza sativa L.), maize (Zea mays L.), and wheat (Triticum aestivum L.), Problems quantitatively evaluated were: the relative effectiveness of NH4+ and NO3− as a source of N to rice at different placements; the effect of NH4+‐N in the fertilizer band on the uptake of P and of P on the uptake of NH4‐N; and the uptake of fertilizer N by corn, rice, and wheat as related to growth stage at which it was applied. Interactions can be directly and quantitatively measured by adding additional treatments.

Utilization of nitrogen from green manure and mineral fertilizer by sugarcane

“…However, there were differences in Ca and K contents; the latter showed higher values in treatments involving fertilizer applica- Both N and K absorption are greatly influenced by moisture; this relation has been known for a long time (Humbert, 1968), and the fact that treatments involving green manure crops maintained environments with higher moisture due to soil mulching with plant mass could have favored better potassium nutrition. With regard to calcium, nitrogen seems to favor absorption (Silva & Casagrande, 1983).…”

“…The assessments of transformations undergone by nitrogen in the soil-plant system are often impaired by the difficulty to discriminate different sources of the element. By using mineral or organic compounds enriched with 15 N, the nitrogen stable isotope, its pathways in the environment can be traced with precision (Smith et al, 1963;Fried et al, 1975). This technique allows precise information to be obtained on the fate of nitrogen in the soil-plant system.…”

Fertilizer nitrogen budget of Na15NO3 and (15NH4)2SO4 split-applied to winter wheat in microplots on a loam soil

“…Owing to the rainy weather conditions in the spring of 1983, the second and third split applications were applied rather late. In order to follow the fate of each N split application, NalSNO3 and (15NH4)2504 containing 10 atom% excess 15N were used and split-applied as indicated in Table 1 ( Fried et al, 1975). The seven N treatments were replicated twelve times and distributed according to the randomized block layout.…”

Balanço da adubação nitrogenada sólida e fluida de cobertura na cultura de milho, em sistema plantio direto no Triângulo Mineiro (MG)

“…O método da diferença (eficiência aparente), utilizado na maioria dos estudos efetuados no País, fornece uma medida do impacto da aplicação do fertilizante na absorção total de N pela planta (N-nativo + Nfertilizante) e assume que a mineralização, imobilização e outras transformações do N são as mesmas em áreas fertilizadas ou não, o que sabidamente não ocorre (Westerman & Kurtz, 1974). A adição de N ao solo acelera a mineralização de Norgânico, aumentando a disponibilidade de N-nativo e, conseqüentemente, levando a uma superestimativa da quantidade de N-fertilizante absorvido pela planta (Fried et al, 1975;Calvache et al, 1982). Esta última afirmativa só é válida para solos com adição de resíduos orgânicos, como é o caso do sistema plantio direto (Jenkinson et al, 1985;Rao et al, 1992).…”