Plant litter quality affects the accumulation rate, composition, and stability of mineral-associated soil organic matter

Mineral-associated organic matter (MAOM) is a relatively large and stable fraction of soil organic matter (SOM). Plant litters with high rates of mineralization (high quality litters) are hypothesized to promote the accumulation of MAOM with greater efficiency than plant litters with low rates of mineralization (low-quality litters) because litters with high rates of mineralization maximize the synthesis of microbial products and most MAOM is microbial-derived. However, the effect of litter quality on MAOM is inconsistent. We conducted four repeated short-term incubations (46-d each) of four plant litters (alfalfa, oats, maize and soybean) in two low-carbon subsoils (sandy loam and silty loam) with and without nutrient addition. Our short-term incubations focused on the initial stage of litter decompositionduring the time when litter quality has a measureable effect on mineralization rates. Plant litter quality had a much greater effect on litter-C mineralization rate and MAOM-C accumulation than did soil type or nutrient addition. Soils amended with high-quality oat and alfalfa litters had greater MAOM-C accumulation than soils amended with low-quality maize and soybean litters. However, soils amended with high-quality litters also had greater litter-C mineralization than soils amended with low-quality litters. As a result, the accumulation of MAOM-C per unit of litter-C mineralization was lower in soils amended with high-vs. low-quality litters (0.65 vs. 1.39 g MAOM-C accumulated g−1 C mineralized). Cellulose and hemicelluose indices of accumulated MAOM were greater for maize and soybean than oats and alfalfa, however, most carbohydrates in MAOM were plant-derived regardless of litter quality. At the end of the incubations, more of the accumulated MAOM-N was potentially mineralizable in soils amended with high quality litters. Nevertheless, most of the litter-C remained as residual litter; just 12% was mineralized to CO2 and 13% was transferred to MAOM. Our results demonstrate several unexpected effects of litter quality on MAOM stabilization including the direct stabilization of plant-derived carbohydrates

Plant Litter Quality Affects the Accumulation Rate, Composition, and Stability of Mineral-associated Soil Organic Matter

Mineral-associated organic matter (MAOM) is a relatively large and stable fraction of soil organic matter (SOM). Plant litters with high rates of mineralization (high quality litters) are hypothesized to promote the accumulation of MAOM with greater efficiency than plant litters with low rates of mineralization (low-quality litters) because litters with high rates of mineralization maximize the synthesis of microbial products and most MAOM is microbial-derived. However, the effect of litter quality on MAOM is inconsistent. We conducted four repeated short-term incubations (46-d each) of four plant litters (alfalfa, oats, maize and soybean) in two low-carbon subsoils (sandy loam and silty loam) with and without nutrient addition. Our short-term incubations focused on the initial stage of litter decomposition during the time when litter quality has a measureable effect on mineralization rates. Plant litter quality had a much greater effect on litter-C mineralization rate and MAOM-C accumulation than did soil type or nutrient addition. Soils amended with high-quality oat and alfalfa litters had greater MAOM-C accumulation than soils amended with low-quality maize and soybean litters. However, soils amended with high-quality litters also had greater litter-C mineralization than soils amended with low-quality litters. As a result, the accumulation of MAOM-C per unit of litter-C mineralization was lower in soils amended with high-vs. low-quality litters (0.65 vs. 1.39 g MAOM-C accumulated g−1 C mineralized). Cellulose and hemicelluose indices of accumulated MAOM were greater for maize and soybean than oats and alfalfa, however, most carbohydrates in MAOM were plant-derived regardless of litter quality. At the end of the incubations, more of the accumulated MAOM-N was potentially mineralizable in soils amended with high quality litters. Nevertheless, most of the litter-C remained as residual litter; just 12% was mineralized to CO2 and 13% was transferred to MAOM. Our results demonstrate several unexpected effects of litter quality on MAOM stabilization including the direct stabilization of plant-derived carbohydrates

The effect of rotation, tillage, and fertility on rice grain yields and nutrient flows

ABSTRACT Rice is one of the most intensively cultivated row crops in America. In order to move away from current tillage practices it will be necessary to maintain current yield levels. A key to successful no-till rice production will be to maintain plant fertilizer efficiency in a system that is flooded much of the growing season and not increase nutrient runoff. A study was established in 2000 that compares fertility, variety, and conventional-and no-till rice rotations. Rice grain yields, across all treatments, were between 140 and 195 bu a -1 . Yields were most affected by rotation and tillage. Continuous rice grain yields averaged 34 bu a -1 lower than a rice-soybean rotation. Plant P and K uptake varied significantly between rotation treatments but not between tillage, fertility, or variety treatments. Phosphorus concentrations in run off liquid were significantly higher in the no-till plots. Total P in runoff was lower in the no-till plots because of reduced P being carried in solids. Total nitrogen uptake was lower in the continuous rice rotation compared to the rice-soybean rotation with soil N uptake higher for the no-till compared to conventional-till in both rotations. MATERIALS AND METHODS Field #8 at the University of Arkansas Rice Research and Extension Center was selected for this study and cut to a 0.15% slope in February, 1999. This site had not been previously used for rice research because irrigation water was not available. Soil at the site is referred to as a Stuttgart silt loam and classified as a fine, smectitic, thermic Albaqultic Hapludolf. Initial soil samples showed a pH range of 5.6 to 6.2 with carbon content averaging 0.84% and nitrogen 0.08%. Plots measuring 250' x 40' were laid out in a north-south direction. These plots were then divided in half east-west with each side randomized as conventional or no-till treatments. Each tillage treatment was then split into a standard and high fertility treatment. For rice, 'standard' fertility consisted of a single preflood N application of 100 lbs urea a -1 plus 40 lbs a -1 P 2 O 5 , and 60 lbs a -1 K 2 O applied prior to planting. Rates increased to 150 lbs a -1 N, 60 lbs a -1 P 2 O 5 , and 90 lbs a -1 K 2 O for the 'enhanced' treatment with application times remaining the same. Two varieties of each crop species were planted in a continuous strip across the conventional-and no-till treatments. In March, soil samples were collected for fertility evaluations. Soil samples were ground and dried. Phosphorus and potassium determinations were made using a Melich III extraction at a 1:10 extraction ratio. Plant samples were collected following physiological maturity but before leaf senescence for nutrient determinations in 1999, 2000, and 2001. Plants were divided into grain, leaf, and stem portions for analysis. Plant analysis was completed using a HNO 3 digest and read with a ICP (Spectro Model D). The following rotations were started in 1999: 1) continuous rice, 2) ricesoybean, 3) soybean-rice, 4) rice-corn, 5) corn-rice, 6) rice (wheat) rice (wheat), 7) rice (wheat)-soybeans (wheat), 8) soybeans (wheat)-rice (wheat), 9) rice-corn-soybeans, 10) rice-corn (wheat)-soybeans. Yield data and nutrient uptake will be presented for the continuous rice and rice-soybean rotations. 2

Corn and Soybean Response to Humic Product Applications on the Clarion-Nicollet-Webster Soil Association

Humic products have been used as an amendment for crop yield enhancement for nearly a century. However, very little field research has been conducted with these products on university research farm settings in the U.S. Midwest. One of the issues that has hampered scientific progress of humic products has been their inconsistent crop responses. There are a myriad of possible reasons for crop response variability, some being environmental, some could involve variability in the humic product’s integrity. The objective of this study was to examine corn and soybean growth and production responses to a humic product across enough growing seasons, to generate a database to include a range of growing conditions (i.e., drought, average and wet precipitation amounts).</p

On-Farm Evaluation of a Humic Product in Iowa (US) Maize Production

The benefit to corn (Zea mays L.) production of a humic product derived from lignite was evaluated for 3 years under otherwise conventional crop management in Iowa farmers’ fields. A liquid extract, it was applied at a rate of 3.57 L ha‒1, generally as a foliar spray mixed into routine pesticide applications during early stages of crop growth. In each of 3 years, hand-sampled corn plants collected at physiological maturity in 30–35 farmers’ fields across Iowa showed a significant increase in grain weight with product application in 70–80% of the cases, covering a range of soil types and grain yield levels. Mean increases were 630–940 kg ha 1, and these were inflated, as expected, compared to a limited number of yield increases estimated by mechanical combine, typically 310–630 kg ha‒1, or about 5% of normal yield levels. Grain weight increases were associated with longer, thicker, and heavier cobs and slightly larger stover biomass. Plant nutrient concentrations were not affected at harvest. In-season measurements in a few intensively monitored farmers’ fields associated product application with slightly taller plants, increased leaf area, earlier onset of pollination, extended grain filling, and delayed senescence, i.e., extended duration of photosynthesis and decayed rotting of stems. Limited visual observations indicated great proliferation of roots, especially lateral roots. Ongoing data assessment will identify any environmental factors of product efficacy, an issue that to date remains unexplored in the humic product literature. Initial studies of alfalfa (Medicago sativa L.) found biomass increases with product application of 7–29%. A newly begun corn trial on nitrogen fertilizer response will estimate the amount of N fertilizer input that can be replaced by humic product application to save input costs and mitigate environmental degradation. The humic product increased economic yield in a large majority of cases by amounts that were agronomically modest but economically significant. Future work will expand to soybean (Glycine max (L.) Merr.) production

Degree of woody encroachment into grasslands controls soil carbohydrate and amino compound changes during long term laboratory incubation

Up to 50% of organic C and 80% of organic N within soil can exist as amino acids, amino sugars and carbohydrates. To determine how potential microbial accessibility and turnover of these compounds is impacted by encroachment of woody plants into grasslands, we investigated changes in evolved CO2 during thermal analysis and in carbohydrate and amino compound chemistry after long term laboratory incubation of sandy loam grassland woodland soils from southern Texas, USA. Thermal analysis showed that incubation increased the amount of soil organic matter (SOM) released at higher temperatures and that evolved CO2 profiles correlated with increases in amino C. During incubation, total carbohydrate C decreased slightly faster than bulk soil C, with preferential loss of plant-derived carbohydrates and/or production of microbial carbohydrates most strongly expressed in grassland and younger woodland soils. Total N content did not change during incubation, so the reduction in extractable amino N in older woodland soils suggested that N became more resistant to extraction during incubation. These data, along with previous measurements of respired CO2, indicate that changes in carbohydrate C and amino C did not predict mineralized CO2 yields and that amino compounds and microbial carbohydrate C were not selectively lost during incubation. The differing response in SOM loss (or enrichment) during incubation of the older woodland soils revealed a system with altered SOM dynamics due to woody encroachment, confirming that the short term ‘lability’ or ‘recalcitrance’ of SOM components is dependent on a number of interacting variables

Carbohydrate and Amino Acid Profiles of Cotton Plant Biomass Products

To achieve the optimal and diverse utilization of cotton (Gossypium hirsutum) plant residues in various agricultural, industrial, and environmental applications, the chemical composition of cotton biomass tissues across different plant parts (e.g., seed, boll, bur, leaves, stalk, stem, and root) is of essential information. Thus, in this work, we collected field-grown whole mature cotton plants and separated them into distinct biomass fractions including main stems, leaf blades, branches, petioles, roots, and reproductive parts (mid-season growth stage) or bur, peduncles/bract, and seed cotton (pre-defoliation stage). The contents of selected carbohydrates and amino acids in these cotton biomass materials were determined. Both essential and nonessential amino acids were enriched in cotton leaf blades and reproductive parts. The distribution pattern of the selected carbohydrates differed from that of amino acids&mdash;higher contents of carbohydrate were found in roots, main stems, and branches. Although glucose was the most abundant non-structural carbohydrate in cotton plant parts at mid-season, xylose was the most abundant in most plant parts at the pre-defoliation stage. Nutritional carbohydrates and amino acids were further accumulated in seeds at pre-defoliation. The information reported in this work would be helpful in exploring and optimizing management practices and processing strategies for utilizing cotton crop biomass materials as valuable and renewable natural resources

Content of gossypol enantiomers in glanded cottonseed meal products.

<p>Data are presented in average with standard error (n = 2 or 3).</p><p>Content of gossypol enantiomers in glanded cottonseed meal products.</p

Contents (percent of protein) of essential amino acids (EAAs), non-essential and non proteinous amino acids (NAAs), amino acids with polar side chains (AAsP), and amino acids with nonpolar side chains (AAsN) in glanded (Gd) and glandless (Gl) cottonseed and soy meals and their water insoluble (WIF) and soluble (WSF) fractions, total protein isolate (PI) and water(PIw)- and alkali (PIa)-extracted protein isolates.

<p>Data are presented in average (n = 2 or 3). Different letter after values in a column of the same type of meals indicate significantly difference at <i>P</i> ≤ 0.05.</p><p>Contents (percent of protein) of essential amino acids (EAAs), non-essential and non proteinous amino acids (NAAs), amino acids with polar side chains (AAsP), and amino acids with nonpolar side chains (AAsN) in glanded (Gd) and glandless (Gl) cottonseed and soy meals and their water insoluble (WIF) and soluble (WSF) fractions, total protein isolate (PI) and water(PIw)- and alkali (PIa)-extracted protein isolates.</p

Contents of amino acids in glanded (Gd) cottonseed meal and their water soluble (WSF) and insoluble (WIF) fractions, total protein isolate (PI) and water (PIw)- and alkali (PIa)-extracted protein isolates.

<p>Data are presented in average with standard error (n = 2 or 3).</p