Chemical-Structural Changes of Organic Matter in a Semi-Arid Soil After Organic Amendment

A 9-month incubation experiment using composted and non-composted amendments derived from vine pruning waste and sewage sludge was carried out to study the effects of the nature and stability of organic amendments on the structural composition of organic matter (OM) in a semi-arid soil.The changes of soil OM,both in the whole soil and in the extractable carbon with pyrophosphate,were evaluated by pyrolysis-gas chromatography and chemical analyses.By the end of the experiment,the soils amended with pruning waste exhibited less organic carbon loss than those receiving sewage sludge.The non-composted residues increased the aliphatic-pyrolytic products of the OM,both in the whole soil and also in the pyrophosphate extract,with the products derived from peptides and proteins being significantly higher.After 9 months,in the soils amended with pruning waste the relative abundance of phenolic-pyrolytic products derived from phenolic compounds,lignin and proteins in the whole soil tended to increase more than those in the soils amended with sewage sludge.However,the extractable OM with pyrophosphate in the soils amended with composted residues tended to have higher contents of these phenolic-pyrolytic products than that in non-composted ones.Thus,despite the stability of pruning waste,the composting of this material promoted the incorporation of phenolic compounds to the soil OM.The pyrolytic indices (furfural/pyrrole and aliphatic/aromatic ratios) showed the diminution of aliphatic compounds and the increase of aromatic compounds,indicating the stabilization of the OM in the amended soils after 9 months.In conclusion,the changes of soil OM depend on the nature and stability of the organic amendments,with composted vine pruning waste favouring humification.

Fertigation with Wastewater and Vermicompost: Soil Biochemical and Agronomic Implications

To study how wastewater(WW) and different organic sources(humic substances or vermicompost) affected soil chemical and biochemical fertility and agronomic productivity in field-grown melon, an experiment arranged in a randomized complete block design with three replications was conducted with the following treatments: three different mixtures of irrigation water(100% WW, 50% WW with 50% groundwater, and 100% groundwater) and, for each WW treatment, four different organic fertilization treatments of control without organic matter application(CK), vermicompost used as surface mulch(SM), vermicompost incorporated into the soil(VC),and humic substances extracted by vermicompost(HS). Chemical and biochemical results indicated an improvement in soil fertility,suggested by the increase in soil organic carbon and nutrient(nitrate and macro- and microelements) contents and in soil microbial activities(hydrolytic and oxidative enzymes), in particular in the VC treatments. In addition, even soil potential metabolism was stimulated by WW combined with organic treatments, as highlighted by the increase in the metabolic(dehydrogenase activity/watersoluble carbon) and nitrification indices(NO-3and NH+4). Melon productivity confirmed these results, with the highest yield and melon quality in the VC treatments irrigated with 100% WW. In conclusion, the combined use of WW and organic amendment,recovering both mineral and organic nutrients from these kinds of recycled materials, was effective in the improvement of soil quality and crop productivity.