Farmers in developing countries cannot afford inorganic fertilizers. Multipurpose tree leaves or livestock manure are major sources of nutrients for soil fertility replenishment. Nutrient release from these organic inputs depends on their chemical composition and on soil properties. This study determined the chemical composition of leaves of four African browse species and manure from goats fed leaves as protein supplements, and their mineralization of C, N and P. Cumulative evolved CO2 was significantly correlated with the initial N content of the organic inputs (r 0.83, P<0.05) and the C:N ratio (r 0.80, P<0.05), and was negatively correlated with the lignin:N ratio (r–0.71, P<0.05). Cumulative P released was negatively correlated with the C:P ratio (r 0.76, P<0.05) and positively correlated with initial P content of the organic amendments (r 0.76, P<0.05). Cumulative N mineralized was not significantly correlated with initial N, lignin or P concentrations of the organic inputs. Leaves from Acacia karro and Acacia nilotica had high concentrations of polyphenols, which may have caused immobilization of N in both leaves and manure. Gliricidia sepium leaves had low amounts of soluble polyphenols, a high N content and a high rate of N mineralization, but the manure from goats fed Gliricidia leaves immobilized N. The leaves of all browse species immobilized P, but the manure released P. The results suggested that some browse leaves cannot meet the N and P requirements of crops due to their low P content and prolonged N and P immobilization. However, the manures had higher P contents and rates of P mineralization, which suggested that manure is a good source of P for crops. The implications of these results for nutrient cycling in mixed farming systems is discussed.
Tag: manures
Suppression of amino acid and oligopeptide mineralization by organic manure addition in a semiarid environment
The rapid mineralization of organic nitrogen (ON) in semiarid soils frequently results in large N losses, reduced crop yields, and environmental pollution. The addition of manures to soil has the potential to promote microbial growth, increase N immobilization, reverse the decline in soil organic matter, and enhance soil quality. In this study, three contrasting organic manures were used to determine their influences on amino acid and oligopeptide dynamics in soil (as key component of the soil ON‐cycle) as well their effects on the size of the microbial biomass and N immobilization. Laboratory incubation experiments were set up with soil obtained from experimental field trial sites for growing maize. Treatments included soil amended with either poultry manure (PM), farmyard manure, pressmud, or unamended (control). Radio‐ and stable‐isotope (14C–15N) techniques were used to assess ON mineralization, immobilization, and leaching using the amino acids alanine and valine as well as the oligopeptides trialanine and valine–proline–proline as model substrates. Quantitative polymerase chain reaction was used to determine soil bacterial biomass. The results showed that all manures increased microbial growth and total soil amino acids as well as protein content. Greater immobilization and subsequently lower mineralization and leaching were also observed in the manure‐amended soils, with this being most pronounced in the PM treatment. The application of PM also enhanced the half‐lives of the ON compounds in soil and increased the size of the bacterial biomass. Overall, our findings indicate that manure amendments, particularly PM, can help promote more efficient ON cycling in semi‐arid ecosystem by controlling N mineralization, reducing amino acid leaching, and elevating oligopeptide immobilization.