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University of KwaZulu-Natal (2022)

Effect of long-term application of nitrogen and liming on soil carbon dynamics in a semi-arid grassland.

Buthelezi, Kwenama.

Titre : Effect of long-term application of nitrogen and liming on soil carbon dynamics in a semi-arid grassland.

Auteur : Buthelezi, Kwenama.

Université de soutenance : University of KwaZulu-Natal

Grade : Master of Science in Soil Science 2022

Résumé partiel
Grassland ecosystems cover up a considerable portion of the earth surface (40 %) and provide a range of ecological services. These ecosystems are mostly limited by nitrogen and phosphorus and thus often supplemented with fertilizers and lime to maximize grassland productivity. Upon addition of mineral fertilizer, biomass production is improved and subsequently more return of carbon in a form of plant litter. This addition may result in a change in soil fertility subsequently affecting biomass production, stoichiometry and soil carbon (C) dynamics. The long-term addition of nitrogen and lime influences soil biogeochemical properties, and potentially hindering the sustainability of the ecosystem. The study was done at Ukulinga long-term (70 years) fertilized veld to examine the effect of long-term application of lime and nitrogen fertilizer on plant-soil interactions in relation to nutrient cycling and soil carbon storage dynamics. This study focused on nitrogen applied annually as ammonium nitrate and ammonium sulphate at 70 and 211 kg N/ha and lime applied as dolomite at 2250 kg/ha every five years. Ten treatments were selected : (1) control (0 lime or N fertiliser kg/ha), (2) L = lime (2250 kg/ha), (3) AS70 = ammonium sulphate at 70 kg/ha ; (4) AS211 = ammonium sulphate at 211 kg/ha ; (5) AN70 = ammonium nitrate at 70 kg/ha ; (6) AN211 = ammonium nitrate at 211 kg/ha ; (7) AS70L = ammonium sulphate at 70 kg/ha + lime ; (8) AS211L = ammonium sulphate at 211 kg/ha + lime ; (9) AN70L = ammonium nitrate at 70 kg/ha + lime and (10) AN211L = ammonium nitrate at 211 kg/ha + lime. Soil samples were taken in the autumn of 2020 using soil auger at 0-10 cm depth, sieved using (2mm sieve) and stored in plastic jars. Soil analysis was conducted at Cedara Soil Fertility Analytical Service for the analysis of extractable phosphorus (P), exchangeable bases, total cations, exchangeable acidity, acid saturation, trace elements (zinc (Zn), copper (Cu) and Manganese (Mn)) and particle size analysis. Aggregate stability was done using the wet sieving method and aggregate associated C was analysed using the Walkley-Black method. Plant samples were taken by cutting 0.25 x 0.25 m2 area in each of the chosen plots dried on an oven and measured. Roots samples were taken using soil core, washed the soil and dried the roots to a constant mass. Plant tissue was analysed for carbon (C), nitrogen (N) and phosphorus (P).

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