Organic N and particulate organic matter fractions in organic and conventional farming systems with a history of manure application

Abstract

Indicators of soil fertility are needed for the eVective management of organic farming systems. Sustainable management hinges upon our gaining an improved understanding of C and N dynamics. The inXuence of cropping systems and amendments applied in the Lakeland Wisconsin Integrated Cropping Systems Trial on total hydrolyzable organic N (THN) fractions and particulate organic matter (POM) was investigated after a decade in a conventional cash grain system (Conv) of continuous maize amended with inorganic fertilizer, an organic cash-grain system (Org-CG) that relied on legume N, and an organic animal-based system (Org-AN) that included alfalfa and manure additions. Maize yields had consistently ranked Org-CG < Conv < Org-AN. The THN and amino acid-N (AA-N) contents were ranked Org-AN > Org-CG > Conv. Amino sugar-N (AS-N) contents, which reXect microbially derived N, did not diVer among systems and concentrations were quite high (346.5 mg AS-N/kg soil in the 0-50 cm depth). This, and soil variability were attributed to the sites' history of manure application. The amount (1.3 g POM-C/kg soil) and proportion (t7.5% of total SOC) of POM-C were quite low and did not diVer among systems. Failure to accumulate SOC or POM in these soils, even under organic management, is attributed to rapid C decay and/or limited root growth. An N rate study was added the fall before samples were taken and N addition did increase yield in the Conv and Org-CG systems despite evidence of soil N surplus. This suggests that either amino N is unavailable to plants or that root N acquisition is limited by other constraints. Low POM-C contents accompanied by high AS-N and AA-N levels reveal an imbalance in these soils which are likely to be C limited. Based on this, we conclude excess N has prevented use of organic practices from enhancing soil quality at this site.

Influence of tillage practices on soil biologically active organic matter content over a growing season under semiarid Mediterranean climate

“…The POM fraction is quite sensitive to crop residue inputs, fertiliser and soil disturbance, and may vary seasonally (Wander et al, 2007). In the present study, the POM fraction varied significantly over the growing season (Fig.…”

“…The generally higher C-MB content found under NT than under CT may be related to the higher SOC and POM contents associated with NT. Other authors also report tillage practice to have a significant influence on the MB content (Madejón et al, 2009;Melero et al, 2009), and it is well known that the POM is usually the first fraction to be colonised by microorganisms (Wander et al, 2007). In general, the NT treatment was associated with a gradient in C-MB over the soil profile; this was not seen with CT. Further, only under NT were significant differences seen in C-MB values between the two soil layers studied (Table 5).…”

Effects of Reduced Tillage on Crop Yield, Plant Available Nutrients and Soil Organic Matter in a 12-Year Long-Term Trial under Organic Management

“…Consequently this material may not have provided considerable contribution to the enrichment of C org under organic management [31]. In another field trial in Wisconsin/USA, where high amounts of fresh cattle manure were used and grass/clover leys were a part of the crop rotation for organic farming but not for the conventional system used for comparison, the lack of differences in C org content between the systems were attributed to a rapid C decay [46]. As composted sheep manure was used only in moderate amounts of approximately 5.5 t ha −1 yr −1 in the current study, the amount of organic matter from composted manure, which decomposes slowly, was probably not sufficient to lead to overall higher C org contents, as documented for fertilization with composted materials [47].…”

Alterações nas propriedades químicas e microbianas de solos cultivados com videiras sob manejo orgânico e convencional no sul do Brasil

“…Organic farming practices increased soil C and organic matter compared with conventional farming due to organic supplementation (Marriott & Wander, 2006;vanDiepeninge et al, 2006). The low amount of SOC in the soils with history of manure application, even under organic management, was ascribed to restricted root growth or fast C mineralization (Wander et al, 2007).…”