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

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

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—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

Contents (percent of dry matter) of acid detergent fiber (ADF), acid detergent lignin (ADL), and neutral detergent fiber (NDF) in glanded (Gd) and glandless (Gl) cottonseed meals and their water insoluble (WIF) and soluble (WSF) fractions.

<p>Data are presented in average with standard error (n = 2 or 3).</p><p>^a Less than detected limit.</p><p>Contents (percent of dry matter) of acid detergent fiber (ADF), acid detergent lignin (ADL), and neutral detergent fiber (NDF) in glanded (Gd) and glandless (Gl) cottonseed meals and their water insoluble (WIF) and soluble (WSF) fractions.</p

Contents of Fe, Zn, Cu, Mn, Al, and B in glanded (Gd) and glandless (Gl) cottonseed and soy 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

Selected carbohydrates in glanded (Gd) and glandless (Gl) cottonseed and soy 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

Content (% of dry matter) of crude protein in cottonseed and soy meal and their products.

<p>Data are presented in average with standard error (n = 2 or 3) per total nitrogen (TN) and amino acid (AA) contents.</p><p>^a Not determined.</p><p>^b No PIw and PIa were prepared from glandless cottonseed and soy.</p><p>Content (% of dry matter) of crude protein in cottonseed and soy meal and their products.</p