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It is not yet clear whether the carbon released from biochar in the soil solution stimulates biological activities. Soluble fractions (AQU) from wheat and maize biochars, whose molecular content was thoroughly characterized by FTIR, 13 C and 1 H NMR, and high-resolution ESI-IT-TOF-MS, were separated in dilute acidic solution to simulate soil rhizospheric conditions and their effects evaluated on maize seeds germination activity. Elongation of maize-seeds coleoptile was significantly promoted by maize biochar AQU, whereas it was inhibited by wheat biochar AQU. Both AQU fractions contained relatively small heterocyclic nitrogen compounds, whose structures were accounted by their spectroscopic properties. Point-of-Zero-Charge (PZC) values and van Krevelen plots of identified masses of soluble components suggested that the dissolved carbon from maize biochar behaved as humic-like supramolecular material capable to adhere to seedlings and deliver bioactive molecules. These findings contribute to understand the biostimulation potential of biochars from crop biomasses when applied in agricultural production. [ABSTRACT FROM AUTHOR]

Development of semi-dwarf wheat (Triticum aestivum) and rice (Oryza sativa) led to increased yields and agronomic efficiencies with less lodging. While these short-stature cereals have become common in global crop production, commercial maize (Zea mays L.) hybrids remain tall. There is no information currently available on plant N uptake or yield responses to N timing for short stature maize hybrids. We tested three hypotheses on short-stature and tall maize hybrids 1) short-stature maize hybrids would have similar yield response to in-season N application compared to tall hybrids, 2) short-stature maize hybrids would have similar dry matter and N uptake patterns to tall hybrids, and 3) there would be significant partitioning differences between short-stature and tall hybrids in dry matter and N within the plants at multiple growth stages. In ten side-by-side field trials across eight site-years in the Midwestern USA, we tested the yield response and underlying nitrogen physiology of short-stature maize hybrids and tall comparators to split-rate N application. We show that split-rate application of 50% of the total N at mid-vegetative stages (V6) averaged 0.24 t ha−1 more grain yield across 10 field trials (positive yield response in 6 out of 10 trials) compared to a single 100% up-front N application, with the same pattern for short-stature and tall hybrids. In both hybrid statures, V6 N applications showed more frequent improvement in grain yield than V12 N applications. Total N uptake at maturity was not different between short-stature hybrids and their tall counterparts (p = 0.62). N partitioning differed between short-stature and tall hybrids; leaves in short-stature hybrids had 5% higher N concentration and 13% more N content in early vegetative development, stalks had 18–27% less dry matter and 5–25% less N content, depending on growth stage, while R1 ears averaged 18% more dry matter and N accumulation (p < 0.10 in all cases). At maturity short-stature hybrids had 4% higher harvest index and 3% higher N harvest index (p < 0.10). Based on these results, we expect that N management recommendations in short-stature maize hybrids would be similar to their tall counterparts, but that short stature mitigates logistical risk by providing more flexibility for in-season N applications. This study provides a unique, robust dataset on yield and physiological response to split-rate N treatments in commercially relevant maize hybrids. • Short stature in maize simplifies in-season N application and later crop management. • Split-rate N applications at V6 increased hybrid yields 60% of the time, with similar patterns for short-stature and tall hybrids. • Overall, short-stature maize yielded similarly to tall comparators. • Short stature led to greater partitioning of N and dry matter to the grain than tall hybrids. • Greater flexibility for in-season N fertilization in short-stature maize reduces in-season application risks. [ABSTRACT FROM AUTHOR]

Abstract: On sites where C4-plants have replaced C3-plants, changes in soil δ13C allow the turnover of C3- and C4-derived C to be separated. Studies of decadal scale turnover of soil C following conversion to C4-plants generally lack δ13C values for previous C4-residue inputs and assume that estimates of C4-derived soil C to be based on a fixed δ13C value. Further assumptions are that changes in the initial (time-zero) soil δ13C values are insignificant following conversion to C4-plants. We tested these assumptions by measuring: 1) the δ13C of annual samples of silage maize biomass (C4-plant) and winter wheat grains (C3-plant) grown during 1988 to 2006, and 2) the δ13C of soil kept under bare fallow during 1956 to 1983. The δ13C of plants was related to climate variables, and the impact of maize δ13C was based on estimates of maize-derived soil C using different approaches to establish the δ13C in maize inputs. The δ13C of both maize and wheat decreased with time, but the rate of change and annual variations were considerably larger for wheat than for maize. Maize as well as wheat δ13C was best related to year (probably reflecting a decrease in atmospheric δ13C) and the water balance during the active growth period. Using the smallest (−12.44‰) and the largest (−11.26‰) δ13C measured during 1988 and 2006, estimates of maize-derived C in soil after 18 years ranged from 13.2% to 14.2% of the soil total C. Despite a loss of 31% of the soil C pool under bare fallow, the increase in soil δ13C was significant only at P < 0.10. We conclude that annual variations in maize δ13C values and changes in the δ13C of the soil C fraction derived from the pre-conversion C3-vegetation have only little impact on estimates of maize-derived soil C that cover a few decades. For estimates covering several decades to centuries, the subtle but consistent changes in plant and soil δ13C need to be accounted for. The variability in δ13C in wheat grains suggest that the use of any fixed δ13C value for C3-residues in estimates of C turnover in soils on which C4-plants have been replaced by C3-plants can be associated with considerable uncertainty. [Copyright &y& Elsevier]

Abstract: Contamination of cereals with Fusarium species is one of the major sources of mycotoxins in food and feed. Quantification of biomass of Fusarium species is essential to understand the interactions of individual species in disease development. In this study quantitative real-time PCR assays based on the elongation factor 1 α (EF1α) gene for the 11 Fusarium species F. graminearum, F. culmorum, F. poae, F. langsethiae, F. sporotrichioides, F. equiseti, F. tricinctum, F. avenaceum, F. verticillioides, F. subglutinans and F. proliferatum were developed and tested on 24 wheat and 24 maize field samples. The assays were found to be specific and sensitive. Generally, the results from the quantitative real-time PCR assays corresponded well with mycotoxin data of the field samples. [Copyright &y& Elsevier]

Abstract: In northwest Mexico wheat is planted as a winter crop in rotation with maize in summer. Permanent beds as a form of conservation tillage is an alternative planting system for grain production in this area. The planting system on permanent beds reduces the operational costs up to 40% and enhances physical and biological soil quality parameters. Research plots were established in the 1992 crop season to study the effect of conventional tilled-bed (CTB) with all plant residues incorporated versus permanent beds (PB) with four plant residue alternatives (all burned, removed, as stubble, and partially removed, maize stover removed and wheat straw retained). The objective of this work was to compare, after 10 and 12 years of plot establishment, the effect of CTB with PB management on biological and physical soil attributes during the wheat phase of the rotation. Results indicate that degree of soil aggregation, estimated by means of fractal dimension (D) from dry sieving, was comparable for CTB-all residues incorporated and PB-all residues retained as stubble. But the soil dispersion index, as shown by the numerical difference of D from wet and dry sieving (ΔD), was less for PB-all residues retained as stubble, indicating that soil aggregates are greater in size and more stable for this treatment. By contrast, soil aggregates from dry and wet sieving for PB-all residues burned were highly fractionated. The largest degree of dispersion between the wet and dry aggregate size distribution in all PB treatments was for the 1–2mm soil fraction, while for the CTB-all residues incorporated, a constant and high degree of dispersion occurred to each of the soil fractions from 0.053 to 8mm. The amount of C and N from microbial biomass for PB treatments was bigger, as the amount of crop residues left on the soil surface increased. Kernel weight from PB treatments was negatively related to the N mineralized from microbial biomass (r =−0.57 in 2002 and r =−0.39 in 2004). [Copyright &y& Elsevier]

Site-specific management of fields based on spatial variability should reduce the total input of chemicals and reduce their negative effects on the environment. The objective of this study was to determine whether spatial variability of crop biomass in a small field (0.25 ha) is stable over several years, and whether site-specific management can be applied to the field.We examined the pattern of spatial variability of above-ground biomass of wheat and maize for 3 years. The field was divided into two plots. One plot was minimum-tilled (MT) with a rotary tiller and the other was conventionally tilled (CT) with a moldboard plow and disc-harrows. Above-ground biomass was measured at harvest at 100 locations on a 2.5 m×5 m spacing in each plot. For the analysis of spatial variability patterns, the raw data were divided into trends (large-scale structure) and residuals (small-scale structure) by median polishing. Comparison among trends showed that the spatial variability pattern was stable only in conventionally tilled (CT) maize over the 3 years. This result suggests the possibility of site-specific management based on prior knowledge. Wheat and maize tended to show inverse spatial variability patterns in trends. The trends in wheat were considered to reflect the variability among rows, suggesting the opportunity for post-emergence, site-specific management along the direction of field management. The residual data, on the other hand, showed no significant correlation among sampling locations. Semivariograms based on the residual data showed that the range of spatial correlation of biomass was not clearly larger than 2.5 m, which was the distance between rows. Therefore, site-specific management based on the residual data is difficult because of the weak spatial dependence and the lack of temporal stability. [Copyright &y& Elsevier]