Impact of fertilisation practices on soil respiration, as measured by the metabolic index of short-term nitrogen input behaviour

The main objective of this study was the evaluation of the impact of different sources of organic waste (used as an N source) on soil quality (as measured by CO2 release) and N transformation processes (available inorganic N forms) in a short-term field study of an almond tree plantation. Three compost types were used as organic fertilisers: EC compost constituted from organic agriculture farm (vegetables and manure), SC compost formed from sewage sludge and pruning waste composted, and XC compost comprised a mixture of composted sewage sludge plus slurry and manure from an intensive pig farm. The two compost doses were compared according to N content, and a high dose (H), corresponding to 210 kg N ha−1, and a low dose (L), equivalent to 105 kg N ha−1, were used. In addition, an N rate corresponding to 130 kg N ha−1, which resulted from the supplementation of NPK mineral fertiliser with compost application at a low dose (mixed fertilisation), was compared in a parallel study. Generally, almost all organically treated soils demonstrated an improvement in the levels of C, N and P, compared to controls (unfertilised soils). In addition, the nitrate content increased, predominating over ammonium content, with the highest values in the soils with the low dose application of SC. Furthermore, soil respiration improved in organically treated soils, which showed different responses according to the organic-exogenous source of the incorporated matter. In contrast, a mineral supplement promoted a decrease in biological activity and resulted in lower CO2 production in soils with XC and mineral fertiliser. Contrary to the organically treated soil, in soils with mix fertilisation the NH4+–N was the primary available form of nitrogen. However, the application of SC plus mineral fertiliser to soil caused a positive effect on CO2 emissions compared to the control soil. Soil respiration behaviour was closely related to the form of inorganic N available in the soils due to the fertilisation practice type (organic or mixed), where both parameters seemed to depend on the mobilisations of cations (Na+ and Ca2+) to the soil solution.

► Effect of fertilisation type in soil chemical characteristics and its respiration.
► The mixed fertilisation decreases the soil electrical conductivity, (E.C.).
► Composted sewage sludge plus inorganic fertilises mobilizes Ca in calcareous soils.
► The changes in E.C. by fertilization practices affects the soil N transformation.
► Induced soil respiration is used as a biological index in fertilization studies.