Decomposition, nitrogen and carbon mineralization from food and cover crop residues in the central plateau of Haiti

Abstract

Cover crops are a major focus of conservation agriculture efforts because they can provide soil cover and increase nutrient availability after their mineralization in cropping systems. To evaluate the effect of residue type and placement on rate of decomposition and carbon (C) and nitrogen (N) mineralization, residues from two food crops, maize (Zea mays L.) and common bean (Phaseolus vulgaris L.), and two promising cover crops, sunn hemp (Crotalaria juncea L.) and sorghum sudangrass (Sorghum bicolor [L.] Moench x S. bicolor var. Sudanese [Piper] Stapf) were used in a litterbag study in the Central Plateau region of Haiti from May to September, 2013. Residues were placed in litterbags at a rate equivalent to 3.25 Mg residue ha−1 either on the soil surface or buried at 15 cm to represent a tilled and no-tillage system, respectively. Initial C:N ratios were: maize > common bean > sorghum sudangrass > sunn hemp. Highest residue mass loss rates and C and N mineralization generally occurred in the reverse order. Overall, surface-placed residues decomposed more slowly with 40 and 17 % of initial residue mass of surface and buried residues, respectively, remaining at 112 days. Carbon and N mineralization was higher when residues were buried. Net N mineralization of buried residues was 0.12, 0.07, 0.06, and 0.03 g N g residue−1 for sunn hemp, sorghum sudangrass, maize, and common bean, respectively over 112 days. To achieve the goal of increasing nutrient supply while maintaining year-round cover, a combination of grass and legume cover crops may be required with benefits increasing over multiple seasons.

A comparative analysis of whole genome sequencing of esophageal adenocarcinoma pre- and post-chemotherapy

“…We erred on the side of oversegmentation as there is little to no penalty for this in the analyses that follow. The cellularity and baseline copy number for each sample was identified using the Crambled tool (Lynch 2015), and depth and allele-fraction values for clonal copy-number states were predicted. Segments were assigned to these copy-number states, or subclonal combinations of those states, based on the mean values for the segments.…”

“…SNVs with the same copy-number combination pre-and post-chemotherapy were partitioned into early (coming before a copy-number change) and late mutations where copy-number states and power allowed. Vectors of trinucleotide mutation counts were deconstructed into the 30 COSMIC signatures (http://cancer.sanger.ac.uk/cosmic/signatures) using a quadratic programming approach (Lynch et al 2016).…”

Peanut Residue Carbon and Nitrogen Mineralization under Simulated Conventional and Conservation Tillage

“…Surface residues mineralized more N (on a kg ha -1 basis) over a subsequent cropping season compared to buried residues because there was more total N remaining in surface compared to buried residues, resulting in more total potentially mineralizable N over subsequent cropping seasons (Doran, 1987). It is important that Cooperative Extension recommendations regarding N credits to subsequent crops specify if those credits are applied to a subsequent winter crop or a subsequent spring crop-something that current recommendations typically do not clarify (Caddel et al, 2006;Buntin et al, 2007;Mitchell and Phillips, 2010;Maguire and Heckendorn, 2011;Wright et al, 2011;VDCR, 2014).…”

“…Th roughout the U.S. peanut-growing region, University Extension recommends a N credit ranging from 22 to 67 kg N ha -1 to a subsequent crop following peanut (Caddel et al, 2006;Buntin et al, 2007;Mitchell and Phillips, 2010;Jones et al, 2011;Maguire and Heckendorn, 2011;Wright et al, 2011;VDCR, 2014;Crozier et al, 2016), but the synchronicity of N from peanut residues to subsequent crops is unknown. Furthermore, N credit recommendations following peanut typically do not specify if those credits should be applied to a subsequent winter or spring crop.…”

Dynamiques de décomposition des résidus de cultures sur des exploitations pratiquant l'agriculture de conservation en région Grand Est, France

“…La dynamique de décomposition des résidus, dans ces conditions, est beaucoup moins étudiée que dans des conditions de mélange au sol lors d'un labour profond. En général, les études existantes s'appuient sur des cinétiques de décomposition avec des sacs à litières (technique du litter-bag) ou la mise en place de microparcelles (Lynch et al, 2016 ;Pascault et al, 2010), qui s'éloignent des conditions réelles de décomposition sur des parcelles d'agriculteurs (taille des brins, contact avec le sol, accès de la macrofaune, etc.). La dynamique de décomposition a une incidence directe sur la libération des nutriments que ces résidus contiennent.…”