Residue quality and N fertilizer do not influence aggregate stabilization of C and N in two tropical soils with contrasting texture

Abstract

To address soil fertility decline, additions of organic resources and mineral fertilizers are often integrated in sub-Saharan African agroecosystems. Possible benefits to long-term C and N stabilization from this input management practice are, however, largely unknown. Our objectives were (1) to evaluate the effect of residue quality and mineral N on soil C and N stabilization, (2) to determine how input management and root growth interact to control this stabilization, and (3) to assess how these relationships vary with soil texture. We sampled two field trials in Kenya located at Embu, on a clayey soil, and at Machanga, on a loamy sand soil. The trials were initiated in 2002 with residue inputs of different quality (no input, high quality Tithonia diversifolia, medium quality Calliandra calothyrsus, and low quality Zea mays (maize) stover), incorporated at a rate of 4 Mg C ha -1 year -1 alone and in combination with 120 kg N ha -1 season -1 mineral fertilizer. Maize was grown in the plots each season, and a section of the plots was left uncropped. All aboveground maize residues were removed from the plots. Soil samples (0-15 cm) were collected in March 2005 to assess aggregation and C and N stabilization. The finetextured soil at Embu was more responsive to inputs than the coarse-textured soil at Machanga. Residue additions increased macroaggregation at Embu, and cropping increased aggregation at Machanga. At Embu adding organic residue, regardless of the quality, and cropping significantly increased total soil C and N. This increase was also observed in the macroaggregate and microaggregate-within-macroaggregate fractions. Input treatments had little effect on C and N contents of the whole soil or specific fractions at Machanga. Nitrogen fertilizer additions did not significantly alter C or N content of the whole soil or specific fractions at either site. We conclude that residue quality does not affect the stabilization of soil organic C and N. Inputs of C and soil stabilization capacity are more important controls on stabilization of soil organic matter.

Trade-offs between the short- and long-term effects of residue quality on soil C and N dynamics

“…5). Even within more sensitive soil aggregate fractions, residue quality did not alter C contents (Gentile et al 2008b). The addition of residues increased soil organic C over the control, but contrary to our hypothesis, it was by equivalent amounts regardless of quality.…”

“…Indeed, mineral N levels in the subsoil during the 2007 field season clearly show greater N losses from the top 60 cm from the fertilizer and ). Different letters indicate significant treatment differences at P< 0.05 (data adapted from Gentile et al 2008b) Fig. 4 Residue-derived C stabilized in the in the microcosm experiment after 3 months and 1.5 yr incubation following application of different quality residues (3.65 g C kg −1 soil).…”

“…Combining the results of mineral N dynamics from laboratory and field experiments (Gentile et al 2008a;Gentile et al 2009), long-term crop yields (Chivenge et al 2009) and field SOM stabilization (Gentile et al 2008b), establishes novel and integrated conclusions on the benefits of ISFM. These previous studies looked at a variety of organic residue qualities, but this paper focuses on the comparison of high versus low quality residues in order to elucidate general principles.…”

Relationship between residue quality, decomposition patterns, and soil organic matter accumulation in a tropical sandy soil after 13 years

“…These authors attributed the high SOC to higher lignin content of FYM relative to the other residues. However, residue quality was not found to influence C accumulation in aggregates and silt/clay particles in both clayey and loamy sand soils from Kenya treated for 3 years with organic residues (Gentile et al 2008) corresponding to three of the four classes proposed by Palm et al (2001). These authors suggested that soil disturbance, wetting and drying cycles and effects of crop root residues may have overridden the residue quality influence.…”

Contribution of Eucalyptus Harvest Residues and Nitrogen Fertilization to Carbon Stabilization in Ultisols of Southern Bahia

“…The losses recorded in this region were greater than those reported by Xiong et al (2008) and Gentile et al (2010). In central Kenya, with an average annual rainfall of 1,200 mm and in a soil with 650 g kg -1 of clay, removal of Eucalyptus harvest residues decreased the content of C-rich macroaggregates by 25 % compared to the content in the area where residues were maintained in the field (Epron et al, 2015).…”