31 P NMR Analysis of African Tropical Savanna Herbivore Manure.

In Africa tropical savanna large herbivores are a major ecosystem driver. Plant primary productivity is dependent on nutrient availability.  Phosphorus (P) is one the major limiting nutrients in this ecosystem, which limits plant productivity and influences the availability and quality of forage for herbivores.  Herbivore grazing accelerates P cycling through the deposition of primarily organic P in manure and promotes soil fertility and plant productivity. However, little is known about the forms and stability of the organic P in manure which likely regulates plant available P.  The objective of this study was to determine the forms and stability of organic P in manure deposited by herbivores. In addition, we aimed to determine the effects of feeding habits and digestive system efficiency on P stability. Fresh manure was sampled from large herbivores at Mpala Research Centre, Laikipia, Kenya during the dry season. Herbivores included; grazers (cattle, Bos indicus; zebra, Equus burchellii), mixed feeders (elephant, Loxodonta africana; impala, Aepyceros melampus) and browsers (giraffe, Giraffa camelopardalis; camel, Camelus dromedaries). Manure samples were extracted with 0.5 M NaOH and 100 mM EDTA solution and analyzed for specific organic P functional groups using ³¹P NMR.  Total P varied amongst animals ranging from 6.8 – 1.8 g P/kg.  All herbivore manure ³¹P NMR spectra showed the presence of orthophosphate, phosphomonoesters (comprised of breakdown products of RNA and phospholipids), and pyrophosphate.  Due to the presence of these compounds and the absence of more recalcitrant phytic acid, the manure composition deposited by all of the herbivores consists of similar labile P forms but with different intensity.  Therefore, while P limits plant productivity in African savannas, P availability through herbivore manure would be readily available for plant growth.