Fate of Legume and Fertilizer Nitrogen‐15 in a Long‐Term Cropping Systems Experiment

Abstract

iRelying more on biological N~ fixation has been suggested as a way to meet one of the major challenges of agricultural sustainability. A study was conducted to compare the fate of applied legume and fertilizer N in a long-term cropping systems experiment. Nitrogen-15-1abeled red clover (Trifolium pratense L.) and (NH4)2SO4 were applied microplots within the low-input and conventional cropping systems of the Farming Systems Trial at the Rodale Institute Research Center in Pennsylvania. The ~SN was applied to soil and traced into corn (Zea mays L.) in 1987 and 1988. Residual ~SN was also traced into second-year spring barley (Hordeum vulgare L.). Legume and fertilizer ~SN remaining in soil was measured and loss of N was calculated by difference. More fertilizer than legume N was recovered by crops (40 vs. 17% of input), more legume than fertilizer N was retained in soil (47 vs. 17% of input), and similar amounts of N from both sources were lost from the cropping systems (39% of input) over the 2-yr period. More fertilizer than legume N was lost during the year of application (38 vs. 18% of input), but more legume than fertilizer N was lost the year after application (17 vs. 4% of input). Residual fertilizer and legume ~SN was distributed similarly among soil fractions. Soil microbial biomass was larger in the legume-based system. A larger, but not necessarily more active, soil microbial biomass was probably responsible for the greater soil N supplying capacity in the legume-based compared with fertilizerbased system. M ANAGING NITROGEN INPUTS in crop production systems to achieve economic and environmental sustainability is a major challenge facing agriculture. Relying: less on commercial fertilizer N and more on biological N2 fixation by legumes has been suggested as a way to meet this challenge (Keeney, 1982; National Academy of Sciences, 1989). Nitrogen-15 methodology is recognized as a valuable tool for determining the fate and behavior of N applied in the environment (Hauck, 1971(Hauck, , 1982 L'Annunziata and Legg, 1984). Field experiments using SN have studied the recovery of fertilizer N by crops and have documented that use efficiency varies due to a number of factors, including timing and method of N application, tillage method, and climate. A well-managed, firstyear, single-harvested crop recovers between 50 and 70% of applied fertilizer N (Allison, 1966; Stanford, 1973). In addition, 10 to 40% of applied fertilizer N may remain in soil, 5 to 10% may be lost by leaching, and 10 to 30% may be lost to the atmosphere in gaseous forms (Kundler, 1970; Westerman et al., 1972).Studies evaluating the fate of ~SN from legume residues decomposing under field conditions concluded that: (i) <30% of legume N was recovered by a subsequent nonlegume crop; (ii) large amounts of legume N were retained in soil, mostly in organic forms; (iii) total recovery of le- 910gume N in crops and soils after 1 yr averaged 70 to 90%; and (iv) <5% of legume N from the original application was recovered by a second nonle...

Utilização do nitrogênio (15N) residual de coberturas de solo e da uréia pela cultura do milho

“…Deste modo, possivelmente, a maior porção do N remanescente, principalmente das culturas de cobertura, deve ter permanecido no solo dentro da zona explorada pelas raízes do milho, a exemplo do verificado por Azam et al (1985), para N de culturas de cobertura, e de Coelho et al (1991), para o N da uréia. A maior recuperação no solo do N oriundo de fontes orgânicas é bastante citada na literatura, encontrando-se entre 44 e 89 % do N para adubos verdes, e entre 12 e 53 % para fertilizantes minerais (Azam et al, 1985;Harris & Hesterman, 1990;Harris et al, 1994;Scivittaro et al, 2003), o que se deve, em parte, à maior absorção do N de fontes minerais pela planta em curto prazo (Ladd & Amato, 1986).…”

“…Ladd et al (1983) encontraram, também, valores menores do que 5 % de recuperação do N de leguminosas pelo trigo no segundo cultivo. O baixo aproveitamento do N pelo milho no ano agrícola subseqüente deve-se, provavelmente, ao fato de o N remanescente das culturas de cobertura e do fertilizante mineral ser encontrado, predominantemente, sob a forma de compostos orgânicos e sua disponibilidade seguir o padrão de mineralização da MOS (Harris et al, 1994). Por esta razão, o aproveitamento por cultivos subseqüentes é, em geral, bastante pequeno, da ordem de 1 a 6 % do montante aplicado (Harris & Hesterman, 1990;Scivittaro et al, 2000).…”

“…O conhecimento dos processos envolvidos na incorporação e transformação do N no sistema solo-planta-atmosfera é imprescindível ao desenvolvimento de estratégias de manejo que aumentem o seu aproveitamento pelas culturas. No caso do milho, no cultivo que recebeu a aplicação, o aproveitamento raramente ultrapassa 50 % do aplicado como fertilizante mineral (Lara Cabezas et al, 2004) e 20 % do aplicado como adubos verdes (Scivittaro et al, 2000), permanecendo N residual no solo que poderia ser aproveitado por cultivos subseqüentes (Harris et al, 1994;Amado et al, 1999).…”

Use efficiency and residual effect of 15N-labelled ryegrass green manure over a 9-year field micro-plot experiment

“…These results indicated that the use efficiency of ryegrass green manure N was lower. Some studies suggested that organic N from crop residue or manure showed lower N use efficiency than mineral N fertilizers (Harris et al, 1994;Glendining et al, 1997Glendining et al, , 2001Kramer et al, 2002).…”

Underseeded clover as a nitrogen source for spring wheat on a Gleysol

“…The value obtained is the legume fertiliser N replacement value. These N credits were found to be overestimated (Lory et al 1995) because legumes in rotation not only supply N (Ladd and Amato 1986;Janzen et al 1990;Harris et al 1994;Hossain et al 1996), but can also result in non-nutritional effects on the main crop (Janzen and Schaalje 1992;Stevenson and van Kessel 1996). Evidence suggests that underseeded legume can also affect cereal yields other than by simple contribution through improved N nutrition; competition for light, water and nutrients, reduction of weeds and diseases etc.…”