Changes in Soil Organic Carbon and Its Labile Fractions after Land Conversion from Paddy Fields to Woodlands or Corn Fields

Land use change could significantly affect soil organic carbon (SOC) and other soil chemical properties. However, the responses of soil labile C fractions at different soil depths to land-use change are not still clear. The aim of this study was to investigate the effect of paddy field conversion on woodlands or corn fields on total soil organic C (TOC) and its labile C fractions including particulate organic C (POC), microbial biomass C (MBC), and potassium permanganate-oxidizable C (KMnO4–C) along a 0–100 cm soil profile. Our results indicate that soil TOC concentrations increased by 3.88 g kg−1 and 3.47 g kg−1 in the 0–5 cm soil layer and 5.33 g kg−1 and 4.68 g kg−1 in the 5–20 cm soil layer during 13 years after the conversion from paddy fields to woodlands and corn fields, respectively. In the 20–40 cm soil layer, the woodlands had the highest TOC concentration (12.3 g kg−1), which was 5.13 g kg−1 and 3.5 g kg−1 higher than that of the paddy and corn fields, respectively. The increase in TOC was probably due to the absence of soil disturbance and greater root residue input into the woodland soil. In corn fields, pig manure addition contributed to the increase in soil organic C concentrations. In addition, the proportion of soil KMnO4–C increased after conversion from paddy fields to woodlands or corn fields in the 0–40 cm soil layer, ranging from 39.9–56.6% for the woodlands and 24.6–32.9% for the corn fields. The soil POC content was significantly higher in woodland and corn field soils than in paddy field soils at lower soil depths (5–40 cm). However, there were no differences in MBC contents in the whole soil profile between the woodlands and paddy fields. The KMnO4–C and MBC was the most important factor affecting the CMI values through the whole 0–100 cm soil profile. Overall, converting paddy fields to woodlands or corn fields increased the TOC and labile C fractions in the 0–40 cm soil layer. Future studies should focus on the response of the deeper soil C pool to land-use change.

L-Band SAR Co-Polarized Phase Difference Modeling for Corn Fields

This research aims at modeling the microwave backscatter of corn fields by coupling an incoherent, interaction-based scattering model with a semi-empirical bulk vegetation dielectric model. The scattering model is fitted to co-polarized phase difference measurements over several corn fields imaged with fully polarimetric synthetic aperture radar (SAR) images with incidence angles ranging from 20° to 60°. The dataset comprised two field campaigns, one over Canada with the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR, 1.258 GHz) and the other one over Argentina with Advanced Land Observing Satellite 2 (ALOS-2) Phased Array type L-band Synthetic Aperture Radar (PALSAR-2) (ALOS-2/PALSAR-2, 1.236 GHz), totaling 60 data measurements over 28 grown corn fields at peak biomass with stalk gravimetric moisture larger than 0.8 g/g. Co-polarized phase differences were computed using a maximum likelihood estimation technique from each field’s measured speckled sample histograms. After minimizing the difference between the model and data measurements for varying incidence angles by a nonlinear least-squares fitting, well agreement was found with a root mean squared error of 24.3° for co-polarized phase difference measurements in the range of −170.3° to −19.13°. Model parameterization by stalk gravimetric moisture instead of its complex dielectric constant is also addressed. Further validation was undertaken for the UAVSAR dataset on earlier corn stages, where overall sensitivity to stalk height, stalk gravimetric moisture, and stalk area density agreed with ground data, with the sensitivity to stalk diameter being the weakest. This study provides a new perspective on the use of co-polarized phase differences in retrieving corn stalk features through inverse modeling techniques from space.

A survey of plant-parasitic nematodes in Illinois corn fields, 2018 and 2020

One hundred and forty-seven soil samples were collected from corn fields located within 63 Illinois counties during the 2018 and 2020 corn growing seasons. The soil samples were analyzed for frequency and population density of plant-parasitic nematodes. A total of 10 plant-parasitic nematode taxa were identified. Spiral nematode (Helicotylenchus spp.) was the most frequently observed nematode (frequency: 98.6%), followed by lesion nematode (Pratylenchus spp., 85.7%). Other taxa identified included cyst (Heteroderidae, 66.7%), stunt (Tylenchorhynchus spp., 33.3%), lance (Hoplolaimus spp., 29.9%), dagger (Xiphinema spp., 12.9%), pin (Paratylenchus spp., 12.2%), needle (Longidorus spp., 1.4%), stubby-root (Trichodoridae, 1.4%), and ring nematodes (Criconematidae, 0.7%). Nematodes with the greatest population densities included spiral (89 nematodes per 100 cm3 of soil), pin (36), and cyst nematodes (26). Among the 10 nematode taxa, 4.1%, 7.1%, and 2.3% of spiral, lesion, and lance nematodes positive samples exceeded estimated damage thresholds for corn for Illinois, respectively. Results from this survey will help the agricultural community with understanding pathogenic corn nematode populations in the state and prioritize research in this understudied area.

Assessing the effects of Bt maize on the non-target pest Rhopalosiphum maidis by demographic and life-history measurement endpoints

The most commercialized Bt maize plants in Europe were transformed with genes which express a truncated form of the insecticidal delta-endotoxin (Cry1Ab) from the soil bacterium Bacillus thuringiensis (Bt) specifically against Lepidoptera. Studies on the effect of transgenic maize on non-target arthropods have mainly converged on beneficial insects. However, considering the worldwide extensive cultivation of Bt maize, an increased availability of information on their possible impact on non-target pests is also required. In this study, the impact of Bt-maize on the non-target corn leaf aphid, Rhopalosiphum maidis, was examined by comparing biological traits and demographic parameters of two generations of aphids reared on transgenic maize with those on untransformed near-isogenic plants. Furthermore, free and bound phenolics content on transgenic and near-isogenic plants were measured. Here we show an increased performance of the second generation of R. maidis on Bt-maize that could be attributable to indirect effects, such as the reduction of defense against pests due to unintended changes in plant characteristics caused by the insertion of the transgene. Indeed, the comparison of Bt-maize with its corresponding near-isogenic line strongly suggests that the transformation could have induced adverse effects on the biosynthesis and accumulation of free phenolic compounds. In conclusion, even though there is adequate evidence that aphids performed better on Bt-maize than on non-Bt plants, aphid economic damage has not been reported in commercial Bt corn fields in comparison to non-Bt corn fields. Nevertheless, Bt-maize plants can be more easily exploited by R. maidis, possibly due to a lower level of secondary metabolites present in their leaves. The recognition of this mechanism increases our knowledge concerning how insect-resistant genetically modified plants impact on non-target arthropods communities, including tritrophic web interactions, and can help support a sustainable use of genetically modified crops.

Siklus Hidup Spodoptera frugiperda Dengan Pemberian Pakan Kangkung dan Daun Bawang di Laboratorium

Spodoptera frugiperda was found to have entered Indonesia and damaged maize crops. There is a concern that climate change in Indonesia will cause these pests to migrate to other crops besides corn, such as kale and leeks. This research was conducted to observe the life cycle of S. frugiperda with feed treatment of kale leaves, leeks and corn leaves as a control. The larvae came from corn fields that were infested by S. frugiperda and were cultured in the laboratory. The variables observed were larva length, head diameter, pupa length, number of eggs, sex ratio, and time to complete one cycle. The life cycle of S. frugiperda varies between 37 and 47 days. Kale leaf feed is a good feed for the growth of S. frugiperda compared to the other two feeds, while corn leaf is good in fecundity. Keywords: corn, fecundity, growth, life cycle, sex ratio

Control of glyphosate-resistant horseweed (Conyza canadensis L.) with tiafenacil mixes in corn

Four field experiments were completed in commercial corn fields during 2019 and 2020 to determine glyphosate-resistant (GR) horseweed control in corn with tiafenacil alone or in combination with bromoxynil, dicamba, or tolpyralate applied preplant (PP). Corn planted 1 to 10 d after herbicide application was not injured with any of the herbicides tested. GR horseweed interference reduced corn grain yield 32% when left uncontrolled. Herbicides reduced GR horseweed interference and resulted in corn grain yield that was similar to the weed-free control. Glyphosate (900 g ae ha−1) + tiafenacil at 12.5, 25, and 37.5 g ha−1 controlled GR horseweed 63, 68, and 72% at 4 weeks after treatment (WAT) and decreased GR horseweed density 64, 43, and 83%, and dry biomass 69, 55, and 83%, respectively. Glyphosate + tiafenacil at 12.5, 25, and 37.5 g ha−1 plus bromoxynil (280 g ai ha−1) controlled GR horseweed 81, 88, and 87% at 4 WAT, and reduced GR horseweed density 82, 94, and 93% and dry biomass 93, 93, and 98%, respectively. Glyphosate + tiafenacil at 12.5, 25, and 37.5 g ha−1 plus dicamba (300 g ai ha−1) controlled GR horseweed 86, 88, and 88% at 4 WAT and decreased GR horseweed density 76, 89, and 86% and dry biomass 94, 98, and 98%, respectively. Glyphosate + tiafenacil at 12.5, 25, and 37.5 g ha−1 plus tolpyralate (30 g ai ha−1) controlled GR horseweed 90, 90, and 91% at 4 WAT and decreased GR horseweed density 93, 91, and 95% and dry biomass 98, 97, and 97%, respectively. The industry standards in Ontario, glyphosate + dicamba/atrazine and glyphosate + saflufenacil/dimethenamid-p controlled GR horseweed 95 and 100% at 4, 8 and 12 WAT and caused a 99 and 100% density or biomass reduction, respectively.

ON THE GROWTH OF SOLANUM NITIDIBACCATUM BITTER AND SOLANUM X PROCURRENS A.C. LESLIE IN THE UDMURT REPUBLIC

The article provides information about the growth of Solanum nitidibaccatum and Solanum x procurrens in the Udmurt Republic. The very first discovery of Solanum nitidibaccatum in the republic dates back to 1992. A list of its locations in the Udmurt Republic is given, and the history of its distribution in Russia is discussed. In Udmurtia, this species is known from two cities (Sarapul, Izhevsk), as well as from the Zavyalovsky district. The largest concentration of its localities is associated with the Zavyalovsky district. The most optimal conditions for the growth of Solanum nitidibaccatum in the Udmurt Republic are the conditions of field ecosystems (especially corn and potato fields), in which this species has become naturalized, shows high coenotic activity and a tendency to further spread. Solanum x procurrens is a hybrid found in co-growing areas of Solanum nitidibaccatum and Solanum nigrum in corn fields in 2020. It is indicated for the first time for the Udmurt Republic and Russia.

Phosphorus saturation index and water-extractable phosphorus in high-legacy phosphorus soils in southern British Columbia, Canada

Understanding of the risk of phosphorus (P) loss to the environment is crucial to monitor soil P and implement policies for P management. We assessed P sorption characteristics and adapted a P saturation index (PSI) for silage corn and blueberry fields in south coastal British Columbia (BC), Canada. We used 284 composite soil samples with contrasting P levels collected from eight silage corn and 23 blueberry fields across south coastal BC. The P sorption maximum (Smax) varied between 982 and 2532 mg P·kg−1 and was influenced by aluminum concentration and organic matter content. The degree of P saturation was related to water-extractable P (Pw) by a quadratic regression with R2 = 0.85. A critical Pw = 3.7 mg·kg−1 was established across the two cropping systems. The silage corn fields with pH > 5.5 had critical PSI value of 10.4%, and blueberry fields with pH < 4.7 had critical PSI value of 18.0%. These results showed that the risk of P loss from soil in the silage corn was high, but it was low for blueberry because the critical PSI for silage corn fields was lower than for blueberry fields, and therefore, saturation would be more easily reached, even though more P is applied to blueberry fields. The combination of a critical PSI and Pw as agri-environmental indicators will help farmers and professionals to identify fields with risk of P loss, to implement a nutrient management plan, and to monitor how this risk changes with time.

Types and quantities of weeds found in corn fields and the effect of herbicides on grain yield

Agrotechnical measures and crop rotation also do not ensure complete eradication of weeds. Therefore, it is necessary to use herbicides. Mapping by type and quantity of weeds grown among agricultural crops should be carried out in all crop rotation fields and herbicides should be applied on this basis, i.e. it is important to choose one or another herbicide based on the study of the composition and amount of weeds grown in fields. In the cultivation of corn in Uzbekistan, first of all, it should be aimed at obtaining high yields from its grain. To do this, it is necessary to use all available agro-technical measures. In modern intensive farming, weed control, which is common among agricultural crops, is a key measure.