Recovery of Fertilizer Nitrogen Under Field Conditions Using Nitrogen‐15

Abstract

An experiment was conducted under field conditions to study the movement and recovery of N15‐enriched nitrogen fertilizer added to soil in the forms of NaNO3 and (NH4)2SO4. The plots consisted of the soil mass inside cylinders 30 or 60 cm in diameter, which were pressed into the soil to a depth of 45–60 cm. These plots were either seeded to sudangrass (sorghum sudanense) or left uncropped. The plant tops, roots, and the soil, by 15‐cm layers, were analyzed for total N and excess N15 content. Recovery of added N15 from the 32 plots ranged between 96.3 and 101.8%, and averaged 99.0%. There was no significant difference in recovery of the fertilizer N due to the percent of excess N15 in the fertilizer, size of plot, exposure to natural rainfall, cropping, N source, or the time of application of the fertilizer. Wide variation in recovery of excess N15 occurred with core sampling and it was found necessary to remove, weigh, mix and subsample the entire soil mass from within the rims. The small amounts of unrecovered N were probably due to procedural errors in the field and laboratory, and leaching and root growth beyond the sampling zone. There was no indication of any N loss in the gaseous form. The fate of applied fertilizer N was followed under field conditions using N15‐enriched nitrogen fertilizer applied to the soil in situ enclosed by large steel cylinders. Total recovery of the fertilizer N from these experiments after 8 weeks ranged from 88 to 96%, but dropped as low as 77% after 10 months. Recovery of the fertilizer N was greater from an ammonium source than from nitrate. Retter recovery of fertilizer was obtained when the plots were cropped to sudangrass rather than left fallow. Doubling the rate of application of the fertilizer N from 336 to 672 kg/ha did not affect percent of total recovery. The 4 to 12% of fertilizer N unrecovered after 8 weeks appears to be due to a loss in the gaseous form, since special precautions were taken to restrict leaching and to eliminate errors in sampling and analysis.

Short-term cycling of15N-urea in a ryegrass—white clover pasture

“…Plants on the urea treatment utilised nearly twice as much cf the 10N as those on the ammonium sulpllale t,"eatment, and by the end of the experiment, nearly 89% of the urea-15 N could still be accounted for compared with 61 % for the ammonium sulphate plots. Lower recovery of I5N from ammonium sulphate than (rom urea applied to a pasture was reported by Vallis et al (1973) and I5N recoveries in buried pot, lysimeter, and microplot txperiments have ranged from 37 to 100% (Dih: & Woldendorp 1960;Carter et al 1967;Simpson 1968;Henze1l1971;Vallis et al 1973;}tchpovb 1975). The reason for the low 15N recovery with &mmonium sulphate at 22 days is not clear Sampling or analytical errors cannot be ruled out; chemical denitrification is also a possibility because of the low pH of these plots (Table 3).…”

Utilização de nitrogênio e produtividade da cana-de-açúcar (cana-planta) em solo arenoso com incorporação de resíduos da cultura

“…Em campo, as raízes poderiam explorar um volume maior de solo, o que reduziria a absorção do Nfertilizante em relação ao N-mineral do solo. Carter et al (1967), Chan & Weng (1983) e Sampaio et al (1984) verificaram a redução na percentagem de recuperação do N-fertilizante com o aumento das doses de N, mesmo com o aumento nos valores absolutos de recuperação (kg ha -1 ou mg vaso -1 de N). Muitas vezes, a redução na recuperação percentual do N-adubo com o aumento das doses é justificada pelas perdas do N aplicado, por lixiviação ou volatilização de amônia.…”

INNOVATIVE15N MICROPLOT RESEARCH TECHNIQUES TO STUDY NITROGEN USE EFFICIENCY UNDER DIFFERENT ECOSYSTEMS

“…An early study that was unique in helping establish some of the parameters that needed to be considered for an 15 N study that used physical barriers was that conducted by Carter, et al (1967). They established that a single cylinder, approximately 30 cm in diameter and pressed into the soil 45 to 60 cm, could serve as a satisfactory microplot.…”