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The distribution of macronutrients in a broad leaf woody savanna

1983; Elsevier BV; Volume: 2; Issue: 3 Linguagem: Africâner

10.1016/s0022-4618(16)30113-9

1727-9321

Derek R. du Preez, Charlotte Gunton, G. C. Bate,

Soil and Water Nutrient Dynamics

Early work at Nylsvley, the study site of the South African Savanna Ecosystem Project, showed a low soil nutrient status. On the basis of this and in view of the low vegetation biomass compared to other similar ecosystems, it was suggested that nutrients may be limiting productivity in this Burkea africana dominated savanna. This study examined concentrations of total, ammonium and nitrate nitrogen in Burkea savanna (Hutton form, Chester series) soils with respect to depth and time of year. It further examined the concentrations of total Mg, K and P in the soil with respect to depth. The three major tree species, B. africana, Ochna pulchra and Terminalia sericea and the two dominant grasses, Digitaria eriantha and Eragrostis pallens were examined and N, Mg, K, P and S concentrations were determined in various components of each of these species. Results obtained for the three nitrogen forms in the soil showed spatial and a considerable temporal variation. The spatial variation can partly be ascribed to tree canopies and faunal disturbance. The considerable temporal variation can not be accounted for. From the low amount of Mg and K in vegetation relative to that in the soil, it was concluded that these nutrients are unlikely to be limiting. The data for P and S are insufficient to assess their possible limitation to productivity. The possibility that nitrogen may be a factor limiting productivity is discussed. Vroeë werk op die Nylsvley studieterrein van die Suid-Afrikaanse Savanne Ekosisteemprojek, het ’n lae grondvoedingstofkonsentrasie ge-toon. Met die oog hierop en die lae plantbiomassa van die gebied relatief tot ander soortgelyke ekosisteme, is voorgestel dat die produktiwiteit van hierdie savanne wat deur Burkea africana oorheers word, deur die voedingstofstatus van die grond beperk word. In hierdie studie is die totale-, ammoniak- en nitraatstikstofkonsen-trasie van Burkea savanne grond (Hutton Chester) ten opsigte van diepte sowel as die tyd van jaar ondersoek. Die totale Mg-, K- en P- konsentrasies in die grond ten opsigte van diepte is ook bepaal. N-, Mg-, K-, P- en S-konsentrasies is ook in die verskillende onderdele van die drie hoof boomsoorte, naamlik B. africana, Ochna pulchra en Terminalia sericea sowel as die twee hoof grassoorte, Digitaria eriantha en Eragrostis pallens ondersoek. Resultate vir die drie stikstofvorms in die grond het ’n ruimtelike variasie sowel as ’n aansienlike variasie met tyd getoon. Die ruimtelike variasie kan gedeeltelik deur kroonbedekking sowel as deur dierversteuring verklaar word. Die tydsgebonde variasie is onverklaarbaar. Die verhouding van die Mg- en K-inhoud van die plante tot dié van die grond is laag. Hieruit word afgelei dat dit onwaarskynlik is dat hierdie voedingstowwe beperkend is. Die gegewens vir P en S is onvoldoende om hulle moontlike beperkende invloed op produktiwiteit vas te stel. Die moontlikheid dat stikstof produktiwiteit beperk, word bespreek.