Dinitrogen-fixation by three neotropical agroforestry tree species under semi-controlled field conditions

Abstract

Cultivating dinitrogen-fixing legume trees with crops in agroforestry is a relatively common N management practice in the Neotropics. The objective of this study was to assess the N 2 fixation potential of three important Neotropical agroforestry tree species, Erythrina poeppigiana, Erythrina fusca, and Inga edulis, under semi-controlled field conditions. The study was conducted in the humid tropical climate of the Caribbean coastal plain of Costa Rica. In 2002, seedlings of I. edulis and Vochysia guatemalensis were planted in one-meter-deep open-ended plastic cylinders buried in soil within hedgerows of the same species. Overall tree spacing was 1 · 4 m to simulate a typical alley-cropping design. The 15 N was applied as (NH 4 ) 2 SO 4 at 10% 15 N atom excess 15 days after planting at the rate of 20 kg [N] ha -1 . In 2003, seedlings of E. poeppigiana, E. fusca, and V. guatemalensis were planted in the same field using the existing cylinders. The 15 N application was repeated at the rate of 20 kg [N] ha -1 15 days after planting and 10 kg [N] ha -1 was added three months after planting. Trees were harvested 9 months after planting in both years. The 15 N content of leaves, branches, stems, and roots was determined by mass spectrometry. The percentage of atmospheric N fixed out of total N (%N f ) was calculated based on 15 N atom excess in leaves or total biomass. The difference between the two calculation methods was insignificant for all species. Sixty percent of I. edulis trees fixed N 2 ; %N f was 57% for the N 2 -fixing trees. Biomass production and N yield were similar in N 2 -fixing and non-N 2 -fixing I. edulis. No obvious cause was found for why not all I. edulis trees fixed N 2 . All E. poeppigiana and E. fusca trees fixed N 2 ; %N f was ca. 59% and 64%, respectively. These data were extrapolated to typical agroforestry systems using published data on N recycling by the studied species. Inga edulis may recycle ca. 100 kg ha -1 a -1 of N fixed from atmosphere to soil if only 60% of trees fix N 2 , E. poeppigiana 60-160 kg ha -1 a -1 , and E. fusca ca. 80 kg ha -1 a -1 .

Detection of nitrogen transfer from N2-fixing shade trees to cacao saplings in 15N labelled soil: ecological and experimental considerations

“…The soil was enriched with 15 N following the procedure by Leblanc et al (2007) was diluted with water and applied at a rate of 200 ml m -2 to each barrel. Fifteen and 10 l of water were added after the first and second enrichment, respectively, to assure a uniform distribution of the 15 N in the soil.…”

Coffee agroforestry systems in Central America: I. A review of quantitative information on physiological and ecological processes

“…For example, some of the spread in reported N-fixation rates (Table 2) may be due to the use of the acetylene reduction assay in older studies, which tends to give lower values than isotopic methods (Leblanc et al 2007). However, for many parameters, reported differences may reflect true spatial variation.…”

Cooperative management and its effects on shade tree diversity, soil properties and ecosystem services of coffee plantations in western El Salvador

“…Yet other studies have examined the relationship in shade coffee between specific management practices and soil characteristics, such as organic matter content, soil aggregation and nutrient content from shade tree residues (Beer 1988;Mendoca and Stott 2003;Hoyos and Comerford 2005;Payan et al 2007;Teklay 2007), weed and mulch management (Afrifa et al 2003;Sarno et al 2004;Watanabe et al 2007). Although we know from other systems that plant species composition can have significant impacts on availability and recycling of key nutrients in agroecosystems (Leblanc et al 2007;Redel et al 2007), and greater plant species diversity can increase nutrient use efficiency and reduce nutrient leaching (Tilman et al 1996;Schroth et al 2001), there has been little work on interactions between the agroecosystem properties of shade coffee systems and their collective impact on soil characteristics. A notable exception analyzed the effects of plant functional types (PFTs) and species assemblages on soil properties and other factors of coffee agroecosystems in Indonesia (Gillison et al 2004).…”