Role of organic amendment application on greenhouse gas emission from soil.

The combined application of organic resources (ORs) and mineral fertilizers is increasingly gaining recognition as a viable approach to address soil fertility decline in sub-Saharan Africa (SSA) We conducted a meta-analysis to provide a comprehensive and quantitative synthesis of conditions under which ORs, N fertilizers, and combined ORs with N fertilizers positively or negatively influence Zea mays (maize) yields, agronomic N use efficiency and soil organic C (SOC) in SSA Four OR quality classes were assessed; classes I (high quality) and II (intermediate quality) had >25% N while classes III (intermediate quality) and IV (low quality) had <25% N and classes I and III had <4% polyphenol and <15% lignin On the average, yield responses over the control were 60%, 84% and 114% following the addition of ORs, N fertilizers and ORs + N fertilizers, respectively There was a general increase in yield responses with increasing OR quality and OR-N quantity, both when ORs were added alone or with N fertilizers Surprisingly, greater OR residual effects were observed with high quality ORs and declined with decreasing OR quality The greater yield responses with ORs + N fertilizers than either resource alone were mostly due to extra N added and not improved N utilization efficiency because negative interactive effects were, most often, observed when combining ORs with N fertilizers Additionally, their agronomic N use efficiency was not different from sole added ORs but lower than N fertilizers added alone Nevertheless, positive interactive effects were observed in sandy soils with low quality ORs whereas agronomic use efficiency was greater when smaller quantities of N were added in all soils Compared to sole added ORs, yield responses for the combined treatment increased with decreasing OR quality and greater yield increases were observed in sandy (68%) than clayey soils (25%) While ORs and ORs + N fertilizer additions increased SOC by at least 12% compared to the control, N fertilizer additions were not different from control suggesting that ORs are needed to increase SOC Thus, the addition of ORs will likely improve nutrient storage while crop yields are increased and more so for high quality ORs Furthermore, interactive effects are seldom occurring, but agronomic N use efficiency of ORs + N fertilizers were greater with low quantities of N added, offering potential for increasing crop productivity

/pdf/does-the-combined-application-of-organic-and-mineral-3p639mwrkg.pdf

Does the combined application of organic and mineral nutrient sources influence maize productivity? a meta analysis

Protective shade, tree diversity and soil properties in coffee agroforestry systems in the Atlantic Rainforest biome

Straw decomposition plays an important role in soil carbon sequestration. Litter quality and climate condition are considered to be key factors that regulate straw decomposition. This study investigated the decomposition characteristics of wheat and maize straw under cold temperate, warm temperate, and midsubtropic climate conditions, and examined whether the chemical structures of straw residues became similar during decomposition under different climate conditions. Straws were put in 0.074-mm-mesh size litter bags to exclude soil fauna and buried in black soil plots at three experimental stations located in the aforementioned climate regions to rule out the impact of soil type. The decomposition rate constants of wheat straw and maize straw increased linearly with temperature, and the former was more sensitive to temperature. Climate conditions and straw quality had marked effects on the residual material structure in the first half year of decomposition, but then decreased. Wheat and maize straw showed common decomposition characteristics with a decrease of O/N-alkyl carbons and di-O-alkyls, and a simultaneous increase of alkyl carbons, aromatic carbons, aromatic C-O groups, and COO/N-C ═ O groups. Overall, the results indicated that the chemical compositions of the two types of straw became similar after 2-year decomposition under different climate conditions.

Structural convergence of maize and wheat straw during two-year decomposition under different climate conditions.

Many field experiments have indicated that litter decomposition in semi-arid areas may be partly or fully controlled by photodegradation. We devised a study to test our hypothesis that light exposure makes plant litter more degradable. Dry, senescent, aboveground plant litter from Miscanthus x giganteus was exposed to light including ultraviolet (UV) radiation for various lengths of time from 0 to 289 days. Weight loss was measured after exposure and appeared to be modest and did not increase with time of exposure. The litter of the longest and shortest exposure time as well as controls were then incubated with soil and moisture for 35 days and CO2 and N2O production were measured. The longest exposed litter degraded much faster than any other treatment during incubation with moisture, about twice as fast as the unexposed control. The shortest exposed however, degraded only slightly faster than the unexposed control. This suggests that increasing litter degradability is a more important mechanism for photodegradation than direct light-induced mass loss. N2O production from decomposition of the exposed litter was high in the beginning, suggesting that nitrogen may be released quickly. The mechanism is probably that light exposure leaves the nitrogen in plant litter easily available to microbial utilisation upon wetting. Such a mechanism might play an important role for nutrient cycling in semi-arid areas.

Does light exposure make plant litter more degradable

Field litterbag studies were conducted in the 2000 rainy season and the 2000/2001 dry season along the transect of West African major agroecological zones (agroeco-zones) to measure the decomposition of, and N and P release from 5 plant residues (leaves of woody species) with increasing quality: Dactyladenia barteri, Pterocarpus santalinoides, Alchornea cordifolia, Senna siamea and Gliricidia sepium. The decomposition rate constant (wk−1) ranged from 0.034 (Dactyladenia, subhumid zone) to 0.49 (Gliricidia, humid zone) in the rainy season, and from 0.01 (Dactyladenia, subhumid zone) to 0.235 (Pterocarpus, arid zone) in the dry season. The direct correlation between the decomposition rate of plant residues and their quality was only valid in agroeco-zones where there is not moisture stress. Similarly, the direct correlation between the decomposition rate of plant residues and moisture availability was only valid for plant residues with high quality. The decomposition rate of the low quality plant residue could increase from humid to arid zone in West Africa. In the arid zone, the low quality plant residue could also decompose faster than high quality plant residue. The climate-residue quality interactive effects on plant residue decomposition in West Africa were attributed to the feedback of low quality plant residue’s mulching effect, soil fauna and appreciable photodegradation in dry regions. A decomposition equation that could be used to predict the decomposition rate of plant residues with various qualities across agroeco-zones in West Africa was obtained from this study. The equation was expressed as follow: k = 0.122 − 0.000747*PRQI2− 0.0233*PRQI*CI + 0.00337*CI* PRQI2, in which k is the decomposition rate constant (wk−1), PRQI the plant residue quality index, and CI the climate index (ratio of rainfall to sunshine hours cumulative during the entire decomposition). The response of N and P release from plant residues to residue quality and climate was similar to that of residue decomposition. At the late stage of the dry season decomposition, the high C/N and C/P ratio plant residue (Dactyladenia leaves) that immobilized N and P in wet zones showed a release of N and P in the dry zone.

Effects of residue quality and climate on plant residue decomposition and nutrient release along the transect from humid forest to Sahel of West Africa

F. Ishida

Papers

Effects of residue quality and climate on plant residue decomposition and nutrient release along the transect from humid forest to Sahel of West Africa