Green Cover Crops Research Articles

Prevalence of Verticillium spp. and Pratylenchus spp. in Commercial Potato Fields in Atlantic Canada

A survey of New Brunswick (NB) and Prince Edward Island (PEI) potato fields in crop rotation phase prior to potato production was conducted in fall (October and November) between 2017 and 2021. A total of 113 and 126 fields for NB and PEI, respectively, were surveyed with 20 to 35 fields each year tested in each province. Root lesion nematodes (RLN, Pratylenchus spp.) were detected in 99 and 98% of the fields for NB and PEI, respectively, and two root lesion nematode species, P. crenatus and P. penetrans, were identified in both provinces from 2017 to 2021. Based on 2019 and 2020 results, all surveyed fields in NB and PEI were detected with P. crenatus, while only 29 and 43% of the fields in NB and PEI were detected with P. penetrans, respectively. P. crenatus accounted for 96 and 89% of the populations for NB and PEI, respectively, while P. penetrans accounted for 4 and 11% in commercial fields, respectively. In a single in-depth sampled experimental field with a history of severe potato early dying complex in 2018 in NB, P. crenatus accounted for 88% and P. penetrans was 12%. Verticillium dahliae was detected in 94 and 92% of potato fields in NB and PEI, respectively. All isolates obtained from potato cv. “Russet Burbank” in a baiting trial were V. dahliae, belonging to two lineages. V. albo-atrum was detected in a few fields at very low level, except two fields in NB where V. albo-atrum was predominating over V. dahliae. Rotation crops did not affect V. dahliae population densities for NB and PEI, and did not affect RLN population in NB, but significantly affected RLN in PEI. Fall green cover crop did not affect the populations of RLN and V. dahliae in PEI. The present study revealed that the potato pathogenic root lesion nematode P. penetrans was present in less than 50% of surveyed fields and accounted for around 10% of root lesion nematode population in NB and PEI, and V. dahliae was the dominant species and was present in greater than 90% of surveyed fields in both provinces.

Integrating fall‐planted cereal rye cover crop with herbicides for reducing Palmer amaranth seed production in soybean under planting green conditions

AbstractCover crops are usually terminated prior to planting the cash crop; however, “planting green” is an alternative approach that allows growers to plant cash crop into an actively growing, green cover crop, which is then terminated after the establishment of the cash crop. The objectives of this study were (1) to determine whether planting soybean (Glycine max L. Merr.) into a standing cereal rye (Secale cereale L.) cover crop provides superior weed suppression compared to terminating cereal rye 2 weeks before soybean planting and (2) to evaluate an integrated effect of herbicide programs and cereal rye termination timing on Palmer amaranth (Amaranthus palmeri S. Watson) control, biomass, seed production, soybean grain yield, and benefit/cost ratio. Field experiments were conducted in southcentral Nebraska from 2020 to 2022. Preemergence (PRE) herbicide with 2 weeks after planting (WAP) termination of cereal rye provided >95% Palmer amaranth control in 2021 and varied from 88% to 98% in 2022 at 28 days after PRE. A PRE herbicide followed by (fb) late‐postemergence (LPOST) herbicide with 2 WAP termination of cereal rye controlled Palmer amaranth 85%–92% in 2021 compared with 97%–99% control 28 days after LPOST herbicide application in 2022. Palmer amaranth density was higher with 2 WBP cereal rye termination compared with 2 WAP termination regardless of the herbicide program. PRE fb LPOST herbicide programs integrated with 2 WAP termination of cereal rye reduced Palmer amaranth seed production to less than 9100 seeds plant−1 in 2021 and no seed production in 2022. In 2021, terminating cereal rye 2 WAP played an integral role in controlling and reducing the density of Palmer amaranth; however, it had noticeable impact on soybean yield compared to terminating 2 WBP. In 2022, hail and windstorm had a confounding effect on soybean stand and yield.

Application of herbicides in green cover crops to reduce Meloidogyne javanica inoculum in soybean plants

Nematodes are among the main plant parasites affecting Brazilian agriculture. Management practices involving the use of antagonistic or non-host plants are crucial for combating Meloidogyne javanica populations in the country. However, there is still limited information on the effects of herbicides on nematode populations. The aim of this research was to evaluate the impact of herbicides applied to crops on M. javanica populations in soybean and to examine the direct effect of herbicide products on the hatching of nematode juveniles. We conducted greenhouse and in vitro experiments. In the greenhouse experiment, soybean plants were grown in pots with sterile substrate, and a soybean seed was inoculated with 2000 nematodes per plant. The plants grew for 60 d, after which they were cut, and the following cover crops were planted: Crotalaria spectabilis, pigeon pea (Cajanus cajan), Stylosanthes, and buckwheat (Fagopyrum esculentum) for 60 d. These cover crops were desiccated with one of the following three herbicides: fomesafen, chlorimuron, or bentazone. Subsequently, soybeans were replanted and cultivated for additional 60 d. In vitro assays were used to determine the hatching percentage of M. javanica eggs exposed to herbicides. Both tests were repeated at different times of the year (Trials 1 and 2). Meloidogyne javanica reproduction was higher on soybean crops grown when buckwheat was a cover crop. Herbicide application reduced total nematode numbers in soybean grown in succession to buckwheat compared with the untreated control. The vegetative development of soybean crops was negatively influenced by herbicide treatment of cover crops, especially with the use of chlorimuron. Bentazone and fomesafen did not affect nematode hatching in vitro.

Back to the Future: Farming Systems in Transition

National policy levers play a central role in shaping agricultural systems. In his timely book Land Renewed: reworking the Countryside Peter Hetherington (2021) challenges British policy makers to form a far more coherent approach for land use supporting the transition towards improved national food security, seen through a lens of climate change and biodiversity loss. In the UK there are currently three separate government departments responsible for land, the environment, farming and climate change complicating policy alignment. He points out that without subsidies, in the form of area payments, over 60% of all British farms would be running at a loss. The challenge is to improve domestic crop production which currently provides just 60% of the nation's food (Lang, 2020) and hence make the food system more resilient to shocks in international food supply chains while addressing the climate emergency. Hetherington documents a number of cases where farmers, collaborating in organisations such as the Nature Friendly Farming Network, are successfully encouraging a resurgence of bird-life through reduced tillage, renewing and planting hedgerows and using lower doses of fertilisers, including on larger holdings with over 500 ha. This is perhaps the other side of the coin of the bleak future for biodiversity associated with major broad-acre crops outlined by Dewar (2021) in these pages. However, Hetherington (2021) points out that just under half of England's farms produce 2% of total agricultural output, while 8% of them account for over half of it. This implies room for landscape scale nature-friendly farming and even re-wilding, particularly in the uplands, with the caveat that local communities play a central role in plans and implementation. With heightened public interest in the climate emergency and biodiversity loss there is increasing desire for food which is local and particularly in food traceability. This is leading to increasingly sophisticated methods to track and publish farming and animal welfare standards with supermarket chains requiring producers to adhere to these (e.g., Waitrose and Partners, 2022 one of many examples). Underpinning such standards, methods of carbon accounting which may be applied to soil, whole farms or individual enterprises within the farm have been a focus of research for some time (e.g. Goglio et. al. 2015; Abram, 2020). At the most basic level regular soil organic matter tests and a soil management plan will allow British farmers signed up to the entry level of the recently announced Sustainable Farming Incentive (DEFRA, 2022) to be "paid with public funds for providing public goods". To receive payment, they will also be required to ensure 70% of the farm has a green cover through the winter from December to February and add organic matter, which can be via a green cover crop, on one third of the land each year. Currently there is no requirement to demonstrate that soil organic matter is increasing over time – this is assumed. As time goes on however it is possible to envisage more nuanced payments for increasing stored soil carbon, and even a "market" developing as is the case with woodland creation (Forestry Commission, 2022) as producers become the "carbon farmers" of tomorrow as suggested by Korres & Dayan (2020). External inputs including crop protection products will all be included in farm or enterprise carbon budgets. Policy levers are also a focus to regulate the quantity of agrochemicals used for crop protection. The European Union's "Farm to Fork" and Biodiversity strategies, aim reduce by 50% the use and potential risk of chemical pesticides by 2030 and reduce by 50% the use of the more hazardous pesticides also by 2030, although a recent assessment indicates slow and uneven progress towards targets and adoption of IPM measures (European Commission, 2020). Individual countries also take unilateral measures as seen with restrictions on use and in some cases phasing out of the use of glyphosate e.g. by 2024 in Germany (Sustainable Pulse, 2022). Glyphosate is a widely used tool for the destruction of green cover crops (e.g. Fogliato, 2020) so alternative approaches will be needed where these are used at scale as part of interventions to build soil health and store carbon.

Optimizing cover crop and fertilizer timing for high maize yield and nitrogen cycle control

Residues of cover crop grasses release nitrogen (N) to subsequent crops, which can contribute to sustainable agricultural management and prevent increases in N-loss-related microorganisms. Moreover, applying N fertilizer to cover crops can enhance the N-use efficiency and yields of subsequent cash crops and tighten the N cycle in the soil. However, the long-term effects of N fertilization of cover crops on soil microbiota and the N cycle in tropical grass-crop no-till systems are unknown. The aim of this study was to evaluate the long-term effects of the timing of N fertilization of cover crops or maize on crop yields, total microbial abundances and N-cycle gene abundances at the time of maize harvest. We carried out a field experiment with two cover crops (palisade grass (Urochloa brizantha) and ruzigrass (U. ruziziensis) fertilized with 120 kg N ha−1 (ammonium sulfate) at one of three times: (i) broadcast over the green cover crops at 35 days before maize seeding (35 DBS), (ii) broadcast over the cover crop straw residues at 1 day before maize seeding (1 DBS), and (iii) as side-dressing at the maize V4 growth stage according to the conventional method (band-applied 0.05 m from the maize row). A control treatment without N application was also carried out for both cover crop species. Except for the control, 40 kg N ha−1 as ammonium sulfate was subsurface band-applied in all treatments 0.05–0.10 m from the maize row at maize seeding, corresponding to 160 kg N ha−1. The total bacterial, archaeal and fungal abundances and abundances of microbial genes encoding enzymes of the N cycle in the soil were quantified by real-time PCR at the maize harvest stage. Overall, maize yield increased significantly in all N fertilizer applications (average 13 Mg ha−1) compared with the control (6 Mg ha−1) over three growing seasons, with maize following palisade grass having the highest yield. The abundances of archaea and fungi in soil were highest under palisade grass that received N at 35 DBS, with values of 4.6 × 106 and 1.7 × 107 gene copies/g of dry soil, respectively. Both cover crop straw production and N release to the soil were positively correlated with the total microbe densities. When ruzigrass was the cover crop, low N enhanced nifH abundance. Archaeal amoA abundance was positively correlated with cover crop biomass and N release regardless of the N treatment and was highest under palisade grass. Bacterial amoA, nirK, and nirS abundances were highest in soil under ruzigrass and were not linked to cover crop biomass mineralization. We conclude that N fertilizer should be applied using the currently recommended method (40 and 120 kg N ha−1 at seeding and side-dressed in maize, respectively) following palisade grass to achieve high maize yield while controlling the level of N loss from tropical soil via nitrification and denitrification.

Guilette Receives Inaugural CCA Conservationist of the Year Award

Guilette Receives Inaugural CCA Conservationist of the Year Award

Impact of water table levels and winter cover crops on greenhouse gas emissions from cultivated peat soils

Drainage and cultivation have turned peatlands from carbon (C) sinks into hotspots for greenhouse gas (GHG) emissions. Raising the water table and planting of winter cover crops are potential strategies to help reduce peat oxidation and re-initiate net C accumulation during the non-cropping period. However, the effects of these practices as well as their interactions on GHG emissions remain unclear. Here, we carried out an outdoor mesocosm experiment to elucidate the effect of water table levels (−30 cm and −50 cm) and winter cover crop cultivation (vetch, rye, no plant) on carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) fluxes during the winter period (November-April). Soil-atmosphere GHG exchange, GHG concentrations within the peat profile and soil water solute concentrations were monitored. Our results showed that high water table significantly reduced ecosystem respiration, while it had no net effect on N2O and CH4 fluxes. Uptake of available N by the cover crop significantly reduced nitrate in soil solution, thereby lowering the potential for leaching and both direct and indirect N2O emissions. No interactive effects between water table levels and cover crops were detected for any of the measured GHG fluxes. Seasonal variations of GHG fluxes were positively correlated with soil air concentrations at −15 cm and −40 cm depths, which were further regulated by dissolved organic C, nitrate concentration, and anaerobic conditions in the soil. This study suggests that there is great potential to raise water table levels and introduce green cover crops to reduce GHG emissions. Further studies are needed to achieve a complete evaluation of these strategies outside of the growing season, which may provide a significant mitigation benefit in C-rich cultivated peatlands.

Can Flowering Greencover Crops Promote Biological Control in German Vineyards?

Greencover crops are widely recommended to provide predators and parasitoids with floral resources for improved pest control. We studied parasitism and predation of European grapevine moth (Lobesia botrana) eggs and pupae as well as predatory mite abundances in an experimental vineyard with either one or two sowings of greencover crops compared to spontaneous vegetation. The co-occurrence between greencover flowering time and parasitoid activity differed greatly between the two study years. Parasitism was much higher when flowering and parasitoid activity coincided. While egg predation was enhanced by greencover crops, there were no significant benefits of greencover crops on parasitism of L. botrana eggs or pupae. Predatory mites did not show an as strong increase on grapevines in greencover crop plots as egg predation. Overall, our study demonstrates only limited pest control benefits of greencover crops. Given the strong within- and between year variation in natural enemy activity, studies across multiple years will be necessary to adequately describe the role of greencover crops for pest management and to identify the main predators of L. botrana eggs.

Mustard catch crop enhances denitrification in shallow groundwater beneath a spring barley field

Over-winter green cover crops have been reported to increase dissolved organic carbon (DOC) concentrations in groundwater, which can be used as an energy source for denitrifiers. This study investigates the impact of a mustard catch crop on in situ denitrification and nitrous oxide (N2O) emissions from an aquifer overlain by arable land. Denitrification rates and N2O-N/(N2O-N+N2-N) mole fractions were measured in situ with a push–pull method in shallow groundwater under a spring barley system in experimental plots with and without a mustard cover crop. The results suggest that a mustard cover crop could substantially enhance reduction of groundwater nitrate NO3--N via denitrification without significantly increasing N2O emissions. Mean total denitrification (TDN) rates below mustard cover crop and no cover crop were 7.61 and 0.002μgkg−1d−1, respectively. Estimated N2O-N/(N2O-N+N2-N) ratios, being 0.001 and 1.0 below mustard cover crop and no cover crop respectively, indicate that denitrification below mustard cover crop reduces N2O to N2, unlike the plot with no cover crop. The observed enhanced denitrification under the mustard cover crop may result from the higher groundwater DOC under mustard cover crop (1.53mgL−1) than no cover crop (0.90mgL−1) being added by the root exudates and root masses of mustard. This study gives insights into the missing piece in agricultural nitrogen (N) balance and groundwater derived N2O emissions under arable land and thus helps minimise the uncertainty in agricultural N and N2O-N balances.

Produtividade e composição de uva e de vinho de videiras consorciadas com plantas de cobertura

O objetivo deste trabalho foi avaliar a influência de plantas de cobertura verde sobre a produtividade das videiras e sobre a composição da uva e do vinho. Durante duas safras, foram feitas avaliações de três tipos de consórcio, dois manejos das coberturas e de um tratamento controle, com plantas espontâneas controladas por herbicidas e roçagem. Utilizou-se vinhedo de uvas 'Cabernet Sauvignon', localizado a 1.130 m de altitude, em um Cambissolo Húmico distrófico, em São Joaquim, SC. Os consórcios foram realizados com a sucessão de cultivos anuais de moha (Setaria italica) com azevém (Lolium multiflorum) e de trigo mourisco (Fagopyrum esculentum) com aveia‑branca (Avena sativa), bem como com a planta perene festuca (Fetusca sp.). Os manejos consistiram da transferência ou não do resíduo cultural da linha para a entrelinha. As videiras apresentaram maior produtividade de uva no consórcio com as plantas anuais, em comparação ao tratamento controle, ou com a planta perene festuca. O manejo da cobertura verde não teve influência sobre as variáveis avaliadas. Os consórcios não influenciaram de forma consistente os teores de N da uva nem a composição do mosto, embora, na última safra, o teor de sólidos solúveis totais do mosto tenha sido maior nos tratamentos com consórcio, em comparação ao controle. Além disso, as videiras consorciadas com festuca podem proporcionar vinho com maior teor de antocianinas e polifenóis totais.

Decomposição e liberação de nutrientes acumulados em leguminosas herbáceas perenes consorciadas com bananeira

A avaliação da decomposição dos resíduos vegetais adicionados ao solo pelas plantas de cobertura permite melhor compreensão do fornecimento de nutrientes para as culturas de interesse comercial. O presente estudo foi realizado no campo com o objetivo de avaliar a decomposição e a liberação de nutrientes pela parte aérea de leguminosas herbáceas perenes. Os tratamentos consistiram de diferentes plantas de cobertura do solo consorciadas com bananeira: amendoim forrageiro (Arachis pintoi Krapov. & W.C. Gregory), cudzu tropical (Pueraria phaseoloides (Roxb.) Benth.), siratro (Macroptilium atropurpureum (Sessé & Moc. ex DC.) Urb.) e vegetação espontânea com predomínio de capim-colonião (Panicum maximum Jacq.). Essas espécies foram cortadas na estação seca (abril de 1997) e na estação chuvosa (janeiro de 1998). Após cada corte, amostras da parte aérea foram acondicionadas em sacos de tela ("litterbags") distribuídos na superfície das parcelas. A decomposição da matéria seca e a liberação de nutrientes foram monitoradas por meio de coletas dos resíduos contidos nos sacos de tela, realizadas 5, 10, 15, 30, 60, 90, 120 e 150 dias após o corte das plantas de cobertura. Os resíduos de amendoim forrageiro apresentaram maior velocidade de decomposição, enquanto a vegetação espontânea mostrou um comportamento mais lento. As constantes de decomposição diminuíram e os tempos de meia-vida aumentaram na estação seca. Houve rápida liberação de N, Ca e Mg pelas leguminosas, enquanto a vegetação espontânea apresentou o mesmo comportamento para P. Com relação à composição química dos resíduos, os teores de celulose e hemicelulose mostraram-se correlacionados com as perdas de matéria seca. As liberações de N foram correlacionadas com os teores de C e hemicelulose. Os dados indicam o potencial das leguminosas herbáceas perenes na liberação de nutrientes, com destaque para cudzu tropical e siratro.

Influência da cobertura vegetal do solo na qualidade dos frutos de videira 'Niagara Rosada'

Devido ao aumento no custo de produção com a utilização de cobertura morta com capim nas ruas da videira 'Niagara Rosada' e à dificuldade para sua aquisição, objetivou-se a possibilidade de substituí-la por plantas de cobertura intercalares. Em experimentos realizados em Indaiatuba e Jundiaí-SP, de 1999-2000 a 2003-2004, instalaram-se seis tratamentos nas entrelinhas, em blocos ao acaso e quatro repetições, constando de área no limpo; vegetação espontânea roçada; cobertura com capim seco de Brachiaria decumbens; cobertura verde de aveia preta (Avena strigosa); cobertura verde de chícharo (Lathyrus sativus); cobertura verde de tremoço (Lupinus albus), de março a outubro, seguidas de cobertura verde de mucuna anã (Mucuna deeringiana) de outubro a março. Determinaram-se massa, comprimento e largura do cacho, engaço e bagas, número total de bagas por cacho e diâmetro do pedicelo de bagas, comparando-se os valores médios pelo teste de Duncan ao nível de 5%. Na média dos anos, os resultados com a cobertura verde foram similares ou mais favoráveis que os da cobertura com braquiária seca, podendo-se substituí-la por coberturas vegetais intercalares com gramínea e leguminosas, o ano todo, sem interferência negativa na qualidade comercial dos frutos.

Lixiviação de potássio da palha de plantas de cobertura em diferentes estádios de senescência após a dessecação química

O manejo químico de espécies de cobertura do solo é prática usual em sistemas de semeadura direta, e a mineralização de nutrientes dos restos vegetais deixados na superfície do solo pode ser intensificada pela ação da água da chuva ao longo da senescência das plantas submetidas ao herbicida. Avaliou-se a lixiviação de K da palha de seis espécies vegetais com potencial de uso como plantas de cobertura do solo, utilizando chuvas simulada em diferentes estádios após a dessecação química. Milheto (Pennisetum glaucum), sorgo de guiné (Sorghum vulgare), aveia preta (Avena strigosa), triticale (Triticum secale), crotalária juncea (Crotalaria juncea) e braquiária (Brachiaria decumbens) foram cultivados em vasos, em casa de vegetação, em Botucatu (SP). Aos 50 dias da emergência, as plantas foram manejadas com herbicida pós-emergente não-seletivo e submetidas à chuva simulada de 30 mm, aos 2, 4, 8 e 16 dias da dessecação, considerando uma quantidade de palha equivalente a 8,0 t ha-1 de matéria seca. As quantidades de K lixiviado das palhas aumentaram, à medida que o estado de senescência das plantas evoluiu após o manejo químico. No que diz respeito à nutrição potássica da cultura subseqüente, a palha do triticale apresentou-se como a melhor alternativa, uma vez que disponibilizou um montante de mais de 9 kg ha-1 de K até 16 dias após a dessecação química das plantas.

Farmers, fires, and forests: a green alternative to shifting cultivation for conservation of the Maya forest?

When fires blazed through Mexico's forests in 1998, the country experienced a new sense of urgency in its attempts to combat ecosystem degradation and loss of biodiversity. Secretaría de Medio Ambiente y Recursos Naturales (SEMARNAT, the federal environmental protection agency) identified the use of fire in agriculture as a major contributor to the conflagration. Traditional “slash-and-burn” systems are still widely practiced in the southeast of Mexico, and finding a substitute for burning, especially in and near protected areas, became imperative (SEMARNAT, 2001). Experience from different parts of Central America indicated that green manure/cover crop systems (g/cc) could increase soil fertility, reduce erosion, control weeds and raise the yield of maize; the hope was that this system could replace slash-and-burn practices with their attendant risk of forest fires. We present the case study of a project introducing a green cover crop to traditional, resource-poor, maize farmers in one community of the Yucatan peninsula and preliminary results from a similar project in the Calakmul Biosphere Reserve, discussing the data in the light of the on-going debates concerning both fire policy and soil erosion. We conclude that, in spite of demonstrating some advantages, adoption in the peninsula has been hindered by environmental, economic and socio-cultural factors. Mexican efforts to eliminate fire from the forests must also be assessed with reference to the scientific literature by fire experts and historical ecologists, indicating that prohibition of small fires may actually decrease total biodiversity, while increasing the probabilities of catastrophic forest fires.

Lixiviação de potássio da palha de espécies de cobertura de solo de acordo com a quantidade de chuva aplicada

Os restos vegetais deixados na superfície do solo em sistemas de semeadura direta, além de proteger o solo da erosão, constituem considerável reserva de nutrientes que podem ser disponibilizados para a cultura principal, subseqüente. Avaliou-se a lixiviação de K da palha de seis espécies vegetais com potencial de uso como plantas para cobertura do solo de acordo com a quantidade de chuva recebida após o manejo. Milheto (Pennisetum americanum, var. BN-2), sorgo de guiné (Sorghum vulgare), aveia preta (Avena strigosa), triticale (Triticum secale), crotalária juncea (Crotalaria juncea) e braquiária (Brachiaria decumbens) foram cultivados em vasos com terra, em casa de vegetação, em Botucatu (SP). Aos 45 dias da emergência, as plantas foram cortadas na altura do colo, secas em estufa e submetidas a chuvas simuladas de 4,4, 8,7, 17,4, 34,9 e 69,8 mm, considerando uma quantidade de palha equivalente a 8,0 t ha-1. A máxima retenção de água pela palha corresponde a uma lâmina de até 3,0 mm, independentemente da espécie, praticamente não ocorrendo lixiviação do potássio com chuvas da ordem de 5 mm. A máxima liberação de K por unidade de chuva ocorre com lâminas de até 20 mm, decrescendo a partir deste ponto. A quantidade de K liberado da palha logo após o manejo depende da espécie vegetal, não ultrapassando, no entanto, 24 kg ha-1 com chuvas da ordem de 70 mm, apresentando correlação positiva com a concentração do nutriente no tecido vegetal. O triticale e a aveia são mais eficientes na ciclagem do potássio.

Biocontrol of Amaranthus spp. in Europe: state of the art

Within European COST Action 816, a 5-year collaboration between scientists from 6 European countries has made an important contribution to the previously unstudied insect fauna associated with Amaranthus spp. in Europe. This provides a basis for future introductions of a non-native biocontrol agent into Europe. In addition, two promising microbial herbicides, based on the fungi Alternaria alternata and Trematophoma lignicola have been characterised. Further work on their use in integrated farming systems is required. The use of microbial herbicides in conjunction with new cropping systems, such as green cover crops or living mulch using Trifolium subterraneum is an approach which offers much potential.

Nitrate Sensitive Areas: a study of large scale control of nitrate loss in England

Abstract. The Pilot Nitrate Sensitive Areas Scheme was set up in England in 1990 to test measures aimed at reducing nitrate losses from agricultural land. Ten groundwater catchments were chosen to typify the geology and farming of areas where nitrate concentrations in abstracted water were high. Voluntary and compensated controls on farming, based on recent research, were introduced. Scheme membership was for 5 years from 1990 or 1991, and 86% of the agricultural land entered the Scheme. On all farms entering the Scheme, manure and fertilizer use were restricted and green cover crops were required over winter (Basic Scheme). Additional payments were available for conversion of arable land to zero or low‐input grassland (Premium Scheme). Intensive pig and poultry farmers were assisted with the costs of transporting manure for spreading over a wider area. The most effective changes were improved management of livestock manures, especially of the very large local quantities from housed pig or poultry units; conversion of arable land to low‐input grassland; and use of cover crops. There were no indications of reduced crop yields but some requirements increased costs and management complexities. Estimates based on both model calculations and measurements indicated that nitrate losses from agricultural land decreased by about 30%, with considerable variation between areas.

Interaction of planting times following the incorporation of a living, green cover crop and control measures on seedcorn maggot populations in soybean

The impact of delaying soybean [ Glycine max (L.) Merr.] planting following the incorporation of a living, green cover crop and using various insecticide management practices on seedcorn maggot [ Delia platura (Meigen)] populations was evaluated. Phorate soil insecticide in a 15.8 cm band and Agrox D-L Plus seed treatment [a mixture of diazinon (0.33% w/w), lindane (15.0% w/w), and captan (14.67% w/w) were applied at planting immediately after, and 1.5 or 3 weeks after, cover crop incorporation that occurred in early May. Seedcorn maggots were sampled with adult emergence traps, and subsequent soybean injury to plumules was estimated. The number of days following tillage that soybean was planted had little effect on maggot numbers collected, but injury was lowest on soybean planted 3.5 weeks after incorporation of the cover crop. Thermal unit accumulations indicated that seedcorn maggot oviposition occurred at the time of tillage, and that the majority of insects were nearing or entering the non-feeding pupal stage at the time of the last planting, resulting in less plant injury. Phorate treatments provided the largest reduction of maggot numbers. Plant injury was least, however, when soybean was protected by an Agrox seed treatment, especially when the seed and the Agrox were mixed in a bucket before use. These reductions were observed at all three planting times, although the percentage reduction from the control differed among the three planting dates. When spring tillage incorporates a green, living organic matter into the soil in the spring, plant injury can be reduced if a grower waits for 2.5–3 weeks after tillage until planting, when ∼250 thermal units (base of 3.9°C) are accumulated and the majority of insects are in the pupal stage. If planting is done immediately or shortly after tillage, it is recommended that soybean seed be protected with a seed treatment, preferably one that ensures complete coverage of the seed.

The influence of magnesium on different potato soil types

Observations made over a period of several years have disclosed well defined growth disturbances of potato plants in a number of important potato producing sections. The sections under observation have been chiefly along the Atlantic seaboard, including certain potato producing sections in Maine, New York, New Jersey and Virginia, although reports of similar plant disturbances have been reported elsewhere. Wherever the trouble prevailed the chief symptom has been a chlorotic condition of the foliage, the lowest leaves being most seriously affected. In severe cases these leaves finally turn brown, thicken, become hard and eventually die. The change of color from normal green to yellowish green to yellow starts at the margin of the leaf and gradually involves the entire leaf until in advanced stages brown necrotic areas develop. The plants were stunted in growth and while frequently the later growth possessed a more nearly normal color there would be enough of an upset in the life of the plants to cause marked reductions in yield. In practically every case examined, the main exceptions occurring in Virginia, the affected plants were found to be growing on very acid soil, pH 4.2 to 5.0, probably too acid for normal potato development. Coupled with this was the use of fertilizer containing a high proportion of ammonia nitrogen which tended to aggravate the acidity prevailing near the growing plants. With this high acidity factor prevailing it would be reasonable to assume that leaching of basic compounds would be active, particularly lime and magnesia. Where the pH reading went much above 5.2 very little, if any, trouble was in evidence, nor was it found where considerable quantities of manure were used or green cover crops turned under. As there were no recognizable pathological symptoms it was believed that the chief trouble was an improper nutrition of the plants, due to some deficiency of an essential element or possibly to the presence of some poisonous compound in the fertilizer. However, analytical work on samples of fertilizer which were applied for the potato crop showed no toxic material present and in every respect the fertilizer was normal so far as plant food content was concerned. About the only special feature brought out by the work was the large proportion of ammonia nitrogen in the fertilizer.