Influence of Soil Amendment History on Decomposition of Recently Applied Organic Amendments

Abstract

Predicting N mineralization from organic amendments is necessary to match crop N demand with N availability, especially in organic farming systems, which mainly rely on organic fertilization. Because decomposition is a multilevel process infl uenced by numerous factors, however, the prediction of N availability to plants is oft en inaccurate. Soil microorganisms play a key role in the turnover of organic matter, which they decompose to obtain mineral nutrients and energy. Apart from abiotic factors such as soil temperature, soil water content, and soil aeration, the properties of the organic amendment itself aff ect the decomposition process, partly via their eff ect on the soil microfl ora. Relationships between the chemical composition of organic amendments and their C and N Long-term use of organic soil amendments, compared with unamended or mineral fertilized soils, can change soil organic matter content, microbial biomass content, the microbial community structure, and the activity of enzymes involved in organic matter decomposition. It is not clear, however, whether long-term use of organic amendments, by means of these changes, leads to modifi ed decomposition rates of newly added organic amendments. Therefore, this study was used to test the hypothesis that amendment history has an infl uence only on the decomposition of recalcitrant organic amendments and not on less recalcitrant organic amendments. Soils used for experimentation were taken from a fi eld experiment where contrasting organic amendment regimes of farmyard manure, pine (Pinus sylvestris L.) bark, vegetable crop residues, and an unamended control had been applied for 35 yr. In a full factorial, laboratory-based incubation experiment, each soil was treated with each of these amendments and net C and N mineralization and microbial biomass C contents were monitored during a 147-d period. Collected data were then used to estimate gross turnover rates of newly added amendments with a modeling approach based on the soil organic matter module of the Daisy model. The modeling results suggested that the turnover of farmyard manure and pine bark, not however of crop residues, should be simulated in consideration of an amendment history effect. In contrast, the results of the ANOVA indicated that amendment history had an insignifi cant effect on net C and N mineralization from recently applied amendment. We concluded that the effects of amendment history on gross turnover rates of recently added organic amendments may depend on the type of amendment but that these effects on net C and N mineralization are minor in magnitude and hence irrelevant to N fertilization practice. Leif

Nitrogen mineralization from organic amendments is variable but predictable

“…Our results are in line with many studies that observed that soil management history has only a transitory effect on net N mineralization from recently added amendments (Hadas et al., 1996; Nett, Ruppel, Ruehlmann, George, & Fink, 2012; Stark, Condron, O'Callaghan, Stewart, & Di, 2008). However, the difference in the first week of the spring incubation has implications for the shape of the mineralization curve.…”

The effects on soil aggregation and carbon fixation of different organic amendments for restoring degraded soil in semiarid areas

“…Although this cover was quite similar in all plots (ranging from 77 to 85%), differences in microbial abundance and soil C org concentrations were observed among treatments even 5 years after the amendments were added, suggesting that the microbial population is still dependent on the ongoing decomposition of the added OM. It is also possible that the OM and microbial populations provided with the amendments produced initial changes in the degraded soil that affected its physical, chemical and microbiological properties, which has resulted in lasting modifications to the soil in terms of aggregation and exogenous OM breakdown (Nett et al ., ).…”

“…Respiration reflects stability of the carbon compounds in the different aggregate size classes. The respiration patterns observed in the restored soils were the reverse of those in the control, which confirms that the amendments have produced changes in the breakdown of C org inputs in the different aggregate size classes (Nett et al ., ). The larger respiration values in the soil treated with fresh sludge than that treated with composted sludge in all soil fractions suggest that the quality of organic substrates in the soil fractions is affected by the stability of the added amendment.…”

Influence of Long-term Application of Feedlot Amendments to Cropland on Ground Elevation, Ah Horizon Depth, and Soil Color

“…Decomposition of organic C in the soil may have been greater for SM than CM because of more labile C in the SM amendment. Decomposition of soil organic matter in long-term amended soils is dependent on the soil amendment type and history (Nett et al 2012). In addition, masking of the manure type effect by dilution when amendments were incorporated and mixed into the soil may have also occurred.…”