Nitrogen (N) captured by cover crops can be recycled for use by the following crop via decomposition and net mineralization. This study assessed the magnitude of inorganic‐N released from radish ...(Raphanus sativus L.) and cereal rye (Secale cereale L.) residue. The experiment was designed using a five by two factorial treatment structure with five cover crop residue treatments (radish shoots, radish roots, whole radish, cereal rye shoots, and no cover crop) and two levels of residue incorporation (incorporated and surface applied). Cover crop residues were applied to a silt loam soil on an equivalent N basis, incubated for 25 weeks and sampled periodically. Generally, NH4‐N concentration increased for 7–11 days after residue application, after which, NH4‐N concentration declined and NO3‐N concentration increased due to nitrification. Mineralization during the later days (42–179 days after residue application) was negligible from radish residue, but cereal rye shoots and radish roots released significant amounts of NH4‐N, which decreased over the last 137 d. Radish roots generated significantly more NO3‐N from day 42 through 141 than any other residue, while cereal rye shoots mineralized the least amount of NO3‐N from day 42 through 86. Incorporating cereal rye residue increases the occurrence of immobilization within the first 35 days after residue application; however, incorporation increases the rate at which NO3‐N is released from residues between 42 and 179 days after residue addition, regardless of cover crop species. Incorporation of residue can increase N mineralization rate, but the effect varies across cover crop species.
Core Ideas
Cover crop species influences rate of residue decomposition and mineralization of N.
Immobilization of N was lower for radish residue than cereal rye regardless of incorporation.
Nitrate concentrations were similar for all cover crop residues following 154 days of incubation.
The evolution of secondary sex-specific traits of dioecious species under abiotic stress conditions has received limited research, especially in the case of Amaranthus palmeri, a fast adapting and ...highly competing plant. Here, we have examined the interactive effects of abiotic stress on mineral accumulation, chlorophyll a and b content, and the operating capacity of Photosystem II (PSII) in both male and female A. palmeri plants grown under three different intensities of white light, and under N, K or P deficiency. Mineral profiling of the leaves and stems (with inflorescence) highlighted intra- and intersexual differences in their accumulation pattern and mineral associations. Chlorophyll a and chlorophyll b were different between the male and the female plants, being slightly lower in the latter, at high light intensity towards maturity, or under K or P deficiency. Further, slight, although statistically significant differences were recorded in the chlorophyll a/b ratio, which was lower at the higher light intensity in the female, over that in the male, plants towards maturity. Chlorophyll fluorescence parameters, i.e., steady state and maximum fluorescence increased under high light intensity, whereas the PSII operating efficiency decreased in the female plants, indicating reduced PSII capacity. Sex-specific differences in A. palmeri showed a differential response to stressful conditions because of differences in their ontogeny and physiology, and possibly due to the cost of reproduction. We suggest that the breeding system of dioecious species has weaknesses that can be used for the ecological management of dioecious weeds without relying on the use of herbicides.
Dicamba was labeled in dicamba-resistant cotton (Gossypium hirsutum L.) and soybean Glycine max (L.) Merr. in 2017, resulting in a record number of off-target complaints. To address off-target ...movement via volatilization, experiments were conducted to evaluate the effectiveness of potassium tetraborate tetrahydrate (KBo) as a volatility-reducing agent (VRA) with dicamba. Low-tunnel experiments examined: (1) whether KBo functions as a dicamba VRA, (2) the relationship between KBo concentration and dicamba volatilization, (3) the effectiveness of KBo compared with potassium acetate as a VRA, and (4) the impact of KBo on dicamba volatilization with and without glufosinate. In a large-scale trial (0.4-ha plots), the effectiveness of KBo in reducing dicamba volatilization was quantified relative to a commercial dicamba application labeled for use in 2020. The addition of KBo to dicamba reduced volatility over dicamba alone and a dicamba plus potassium acetate premix. As KBo concentration increased in the dicamba spray solution, volatilization was exponentially reduced. Dicamba volatilization with the addition of KBo at 0.01 M was comparable to dicamba plus potassium acetate at 0.05 M. Potassium tetraborate tetrahydrate was more effective than potassium acetate at reducing volatility of a dicamba plus glufosinate mixture. In large-scale experiments over a 30-h period, the addition of KBo to a diglycolamine plus glyphosate mixture lowered dicamba volatilization 82% to 89% over the herbicide mixture alone. Overall, the addition of KBo to dicamba appears promising as a VRA compared with what is commercially available.
Rice (Oryza sativa L.) production in the Mid‐Southern United States has traditionally been under conventional flood (CF) production, namely, direct‐seeded and delayed‐flood production. However, ...furrow‐irrigated rice (FIR) has grown to comprise over 15% of Arkansas’ and 30% of Missouri's rice hectarage. The uptake of several nutrients, including phosphorus (P), potassium (K), and zinc (Zn), has been shown to differ between aerobic and flooded rice production. Hence, a nutrient uptake survey was conducted from 2018 to 2020 in FIR fields to determine the difference in nutrient uptake (macro‐ and micronutrients) between the upper generally aerobic environment at the top of the field and the bottom of the field, where a generally anaerobic or flooded environment existed from R1 to maturity. Aboveground biomass samples were taken at R3 from four nitrogen (N) treatments at the top and bottom of five sites on a clayey soil texture and four sites on a loamy soil texture. Results suggest that there is significantly lower P, K, sodium (Na), and manganese (Mn) uptake at the top of the field compared to the bottom of the field on both soil textures. Additionally, the N treatments that yielded the highest biomass generally led to the greatest uptake of all nutrients examined. The decrease in P and K uptake in the aerobic portion of an FIR field suggests that they may require altered fertilizer recommendations compared to the traditional CF rice system.
Core Ideas
P and K uptake are inhibited in the upper, aerobic portion of a furrow‐irrigated rice production field.
Increased biomass leads to increased uptake of P, K, Ca, Mg, S, Na, Fe, Mn, Zn, Cu, and B.
Decreased P and K uptake under upland conditions may require fertility program adjustments.
Potassium (K) fertilizer has important yield and cost ramifications in soybean Glycine max (L.) Merr. production. Rate recommendations are often based on expected yield response as predicted by a ...soil test. To that end, soybean response to K application rate studies were analyzed using 86 site‐years from 2004 to 2019. We estimated a generic yield response curve across soybean cultivar and soil texture to allow calculation of profit‐maximizing K rates for producers in the mid‐southern United States that also consider crop value and fertilizer cost. Further, we compared profit‐maximizing fertilizer‐K rates with those currently recommended. Using a spreadsheet‐based decision aid, soybean prices and yields, fertilizer‐K cost, and a range of initial soil‐test K (STK) values, as observed over the last 10 yr, we find that current uniform fertilizer‐K rate recommendations were greater than the predicted profit‐maximizing rates. Profit‐maximizing rates added profit ranging from US$2.32 ha−1 at initial Mehlich‐3 K availability values of 110 mg K kg−1 to US$29.35 ha−1 at 60 mg K kg−1 on average. The corresponding fertilizer‐K rate reductions were 11 and 48 kg K ha−1, respectively, resulting in attendant yield penalties of only 28 and 52 kg ha−1. Furthermore, K fertilization was not economically justifiable beyond STK of 128 mg K kg−1 on average. Hence, performing soil tests and calculating profit‐maximizing fertilizer‐K rates showed promising returns to producers at lesser fertilizer‐K use by sacrificing a minimal amount of yield. Also, variable‐rate applied K fertilizer in comparison to uniform rate application was rarely cost effective within the tested assumptions.
•Field waterlogging at late tillering reduced soft red winter wheat yield by 34%.•Tolerant lines that showed limited grain yield reduction were identified.•NDVI was highly predictive of wheat grain ...yield under waterlogging stress.•NDVI has potential for selection of productive genotypes under waterlogging stress.
Soil waterlogging impacts 25% of the global area planted to wheat and the development of waterlogging tolerant cultivars lags behind progress that has been made for other abiotic stresses. This study was conducted to identify sources of waterlogging tolerance in soft red winter wheat (SRWW) adapted to the southeastern United States, a region prone to yearly waterlogging. A set of 28 SRWW genotypes were evaluated over two growing seasons in field waterlogging experiments at the Rice Research and Extension Center in Stuttgart, Arkansas. Waterlogging at the late tillering stage resulted in a mean grain yield (GY) reduction of 34%, ranging from 16 to 49% within the tested lines. Total GY was impacted by lower kernel weight spike−1 resulting from reductions in kernels spike−1 and 1000 kernel weight, total biomass and to a lesser extent spike density. An interaction between genotype and the waterlogging treatment (GxT) was observed for days to heading, plant height, kernel weight spike−1, kernels spike−1 and 1000 kernel weight with significant GxT detected for total GY during the first season only. Spectral reflectance measurements of normalized difference vegetative index were highly predictive of both GY (R2=0.77) and total biomass (R2=0.64) under waterlogging but not in the control, indicating potential for indirect high-throughput screening and selection. Overall, the genotypes 26R22, AR01167-3-1, Magnolia and USG 3555 had significantly higher GY than other genotypes under waterlogging, with USG 3555 also showing a non-significant GY reduction, indicating its potential as a genetic source of waterlogging tolerance.
Expansion of dicamba-resistant crops increased the frequency of off-target movement issues, especially in the midsouthern United States. Six field trials were conducted over two growing seasons with ...the purpose to determine the contribution of volatilization and physical suspension of particles to the off-target movement of dicamba when applied with glyphosate and imazethapyr - a non-volatile herbicide used as a tracer for physical off-target movement. Applications included dicamba at 560 g ha−1, glyphosate at 1260 g ha−1, and imazethapyr at 105 g ha−1. Applicators include glyphosate with dicamba to increase the spectrum of weed control from these applications; however, this addition increases potential for dicamba volatilization. Following application of the mixture, air samplers were placed in the field to collect dicamba and imazethapyr. Results showed there was at least 50 times more dicamba than imazethapyr detected even though the dicamba:imazethapyr ratio applied was 5.3:1. Dicamba was detected in the treated area and the off-site locations and all intervals of air sampling, ranging from 126 to 5990 ng. No more than 37.5 ng of imazethapyr was detected during the first 24-h after application (HAA) inside the treated area. Imazethapyr was only detected in 9 of the 20 sampling combinations during these experiments, and most of these detections (6) occurred during the first 24 HAA and inside the treated area. While some movement from the suspension of particles occurred based on the detection of imazethapyr in air samples, results show that most dicamba detection was due to the volatilization of the herbicide.
Display omitted
•Imazethapyr was used as a tracer to determine the sources of off-target movement of dicamba.•Low imazethapyr detections during trials indicated the presence of suspended spray particles.•Suspension of spray particles in air had a minor impact on the overall dicamba detection.•The detection of dicamba was at least 50 times greater than imazethapyr in air samples.•Volatility was the main source for the detection of dicamba in air samples.
Abstract
Growing degree days (GDD) is a tool to predict plant growth and can be adapted for use in any plant species, including cover crops. A limitation of the GDD calculation is accurate ...temperature parameters used to predict plant development. For most cover crop species, the cardinal temperatures are not well defined in the literature, leading to a less accurate calculation of GDD. The objective of this study was to determine the cardinal temperatures of eight cover crop species, including Austrian winter pea (
Pisum sativum
), balansa clover (
Trifolium michelianum)
, barley (
Hordeum vulgare
), black‐seeded oats (
Avena sativa
), common vetch (
Vicia sativa
), cereal rye (
Secale cereale
), crimson clover (
Trifolium incarnatum
), and hairy vetch (
Vicia villosa
), using a growth chamber experiment. Seven different temperature regimes from 4 to 34°C were implemented, and the number of leaves was counted from day 0 to 21. As a result, the data were regressed to estimate the cardinal temperatures for each species. The results of this research identified base (2), optimum (3), and maximum (8) temperatures for cover crops that were not previously reported. Five cardinal temperatures determined in this study were different from what was previously recorded; base and optimum temperatures were −4.5 and 24.8°C for cereal rye, 3.9 and 26.6°C for crimson clover, and the base temperature was 3.4°C for balansa clover. The successful identification of these cardinal temperatures for cover crops will allow the development of plant growth and biomass prediction models to aid in cover crop termination decision support tools.
Core Ideas
Cardinal temperatures are required to model plant growth and development.
Cardinal temperatures are not readily available, and reported values were often not empirically determined.
Fourteen newly identified cardinal temperatures were determined for eight cover crop species.
Five cardinal temperatures empirically determined here were different from those previously reported.
Core Ideas
The most common soil‐test‐based fertilization recommendation error is a false positive.
Surface soil sample P and K concentrations are qualitative indicators of subsoil P and K ...concentrations.
The R2‐stage, leaflet‐K concentration of irrigated soybean is an accurate indicator of yield responsiveness to K fertilization.
Soil testing is the best available technology for making crop fertilizer recommendations, and precision agriculture has increased the demand for soil‐testing. Our primary research objectives were to validate the accuracy of soil‐test P (STP) and K (STK) availability (Mehlich‐3) and trifoliolate leaflet‐P and leaflet‐K concentration interpretations for predicting irrigated‐soybean Glycine max (L.) Merr. yield response to P and K fertilization at 22 site‐years. Each trial contained six treatments involving two P rates and four K rates including a no fertilizer‐P or ‐K control and the soil‐test recommendation. Yield and tissue nutrient concentration responses were assessed at three significance levels (p ≤ 0.05, p ≤ 0.10, or p ≤ 0.25) and identified as correct or incorrect according to the response predicted by soil‐test recommendations. The accuracy of soil and tissue analyses to predict the correct plant response to fertilization increased as the significance level moved from conservative (p ≤ 0.05) to liberal (p ≤ 0.25). Mehlich‐3 STP accurately identified soils that did not respond to fertilizer P and had an overall accuracy of 40 (p ≤ 0.05) to 48% (p ≤ 0.25) in predicting yield response to fertilization. Existing STK interpretations were 72 (p ≤ 0.05) to 82% (p ≤ 0.25) accurate. Critical leaflet‐K concentrations accurately identified soybean response to K fertilization at 46 (p ≤ 0.05) to 60% (p ≤ 0.25) of the sites. Interpretation errors were most common in the very low and low STP levels, low and medium STK levels, and the low tissue‐K level. The accuracy of the soil and tissue testing and their interpretation process were reasonably accurate for K but substantial improvements are needed for P.
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