Organic Cropping Systems do not Increase Weed Seed Numbers but do Increase Weed Diversity

The influence of different cropping systems on the soil weed seed bank after the first crop rotation within a five-field crop rotation (barley undersown with red clover, red clover, winter wheat, pea, potato) in three organic (Org) and in two conventional (Conv) cropping systems was investigated. In organic systems Org I and Org II cover crops were incorporated as a source of nutrient inputs to the soil and in Org II composted cattle manure was also applied. The Org 0 acted as the organic control system without cover crops and manure. The two conventional cropping systems were treated with herbicides and fungicides and differed in fertilizer application (i.e. Conv I no fertilizer use (as control) and Conv II mineral fertilizer use). In general, the lowest number of annual weed seeds was found in system Conv I, the highest in Conv II. In organic systems with cover crops (Org I, II) there was a strong tendency for decreased weed seed numbers and increased biodiversity. The highest values of the Shannon-Wiener diversity index and Margalef richness index were in Org II system. In all systems the most abundant species in weed seed banks were Chenopodium album L. and Viola arvensis Murr.

How the productivity of crops in organic arable farming may be sustainably increased remains a key issue. We combined measurements of crop yield, total aboveground biomass (AGB) and light interception over a 4-year crop rotation cycle from 2015 to 2018 in a long-term experiment in Denmark with arable organic and conventional cropping systems. These cropping systems comprise one conventional (CGL) and two organic (OGL and OGC) crop rotations, where CGL and OGL had three spring cereal and one grain legume crop (faba bean) in the rotation, and the faba bean was in OGC replaced with grass-clover. All crop rotations were grown with and without the use of cover crops, and the organic systems were grown with and without the manure application. The light interception was calculated from measurements of spectral reflectance, and this allowed the AGB to be decomposed into accumulated intercepted PAR (AIPAR) and radiation use efficiency (RUE).The conventional cropping system (CGL) had significantly greater AGB, AIPAR and RUE compared with the corresponding organic, grain legume-based system (OGL). AIPAR of the organic grass-clover-based cropping system (OGC) was greater than CGL, although the contrary conclusion was found in AGB and RUE. Across crops, RUE was greatest for cereals and smallest for faba bean and grass-clover. AIPAR was consistently greatest for grass-clover, and both grass-clover and faba bean had smaller variability in AIPAR between years and treatments than the cereal crops. Cover crops significantly increased AGB and AIPAR in the organic cropping systems but not in CGL. RUE was not significantly affected by the inclusion of cover crops. The use of manure in the organic systems increased AGB, AIPAR and RUE. The results show that AIPAR can be higher in organic cropping systems compared with conventional cropping systems, but this is not translated into a greater yield of cereal crops. There is, therefore, a need for novel approaches to management and the use of biomass in organic cropping systems for increasing yields for feed and food, and which sustains soil fertility.

Weed Abundance and Community Composition following a Long-Term Organic Vegetable Cropping Systems Experiment

Negative impacts of pesticides on the environment and human health, the risk of pesticide residues in the food chain, and the problems with herbicide‐resistant weed biotypes support the need for alternative cropping systems. The objective of this study was to investigate weed populations, weed management and crop yield in a pesticide‐free cropping system with the use of mineral fertilisers. Conventional‐, organic‐ and mineral‐ecological cropping systems (MECS) with 6‐year crop rotations including winter wheat, maize, winter triticale or winter rye, soyabean or spring pea, and spring barley were established in a randomised complete strip plot design with four repetitions. Experiments were conducted at four locations in Germany. Preventive and sensor‐guided mechanical weed management strategies were applied in all crops in the organic system and in MECS. Herbicide were applied in the conventional farming system. Weed densities, weed species composition, weed control efficacy (WCE) and crop yield were analysed over 2 years in 2020 and 2021. Conventional farming had the highest WCE and 1–7 weeds m−2 (2.7% weed coverage) after herbicide application. In the organic cropping system and MECS, up to 27 weeds m−2 were counted after camera‐guided weed hoeing. Weed coverage in MECS (9.7%) was higher than in the organic cropping system with 7.7%. Crop yield in MECS was equal to the conventional farming system and 20% higher yield than in the organic farming system. MECS represents a promising new and productive cropping practice if an effective integrated weed management strategy is applied.

Introduction: According to the importance of corn in supplying the human food directly and indirectly, it is one of the most important plants among crops. One of the major problems in corn production systems, is competition with weeds that reduce corn yield significantly. Weeds not only reduce crop yields but also decrease the commercial quality and the feeding palatability of main crops. They enhance the soil seed bank of weeds, which may cause continuous weed infestation of field crops as well. Herbicide application is a reliable and highly effective method for weed control. However, demand for safe food products that have been produced with a minimum application of chemical inputs is increasing. Therefore, farmers interested in weed management have to rely on other control approaches. An alternative weed control method is the use of cover crops, which can suppress the growth of weeds by preventing them from light and by producing allelopathic compounds. Cover crops successfully have been integrated into conservational agriculture systems in many areas of the world. Legumes are used as cover crop because of their rapid growth, in addition their potential to provide further nitrogen,along with high ability to compete with weeds. Materials and Methods: In order to study the effect of cover crops (soybean and wheat) and different fertilizers sources on yield of corn and weed control, a filed experiment was conducted in randomized complete block design with three replications in 2012. Treatments included two cover crop (wheat and soybean) and three fertilizer (no fertilizer, chemical fertilizer and compost)..Fertilizer treatments was used according to soil analysis and requirement of corn (as a main plant). Weed-infestation and weed-free plots were used as controls. Study cultivars of corn, wheat and soybean were NS-640, Milan and Sari, respectively. Planting of corn was in June and cover crop was planted with corn simultaneously and between corn rows. The dominant weed species were velvetleaf (Abutilon theophrasti Medic.), johnson grass (Sorghum halepense (L.) Pers.), wild melon (Cucumis melo var. agrestis) and giant foxtail (Setaria glauca L.) in the field. In order to determine the dry weight and density of weeds, three-stage sampling was performed from the middle rows of corn. Corn yield was also measured by mechanical harvesting in middle rows and adjusting to 14% moisture. A week before the final harvest, ten plants of corn were selected randomly from the three middle rows of each plot and yield components including the number of rows in corn, number of kernels per row, weight of 1000 grains was measured. Results and Discussion: The results showed that soybean cover crop reduced weed density compared to control in weed infestated plots, but wheat was not successful in suppressing weeds and reducing their density due to poor biomass and dying at the end of growing season . So, the lowest dry matter of velvetleaf, wild melon and other weeds were related to planted corn with soybean and compost and the maximum was related to monoculture of corn with weed infestation. Results of analysis of variance indicated treatments had significant effect on grain yield. The lowest yield of corn (2733.3 Kg ha-1) was in weed-infestation control while the highest one (12124.0 and 8351.3 Kg ha-1 respectively) was in weed-free control and soybean’ cover crop plus compost. For both cover crops between fertilizer treatments, compost and chemical fertilizer had more corn biological yield than no fertilizer and differences between this two fertilizer treatments wasn’t significant. Reduction of yield under no fertilizer treatments was due to competition for nutrients, light between weed and corn. The maximum and minimum number of rows in corn and number of kernels per row respectively was obtained with monoculture of corn in weed free and weed infestation, while the maximum weight of 1000 grains was observed in soybean with applying compost. Generally, the living mulch as cover crops can reduce competition between weeds and the main crop. Conclusion: As cover crops reduce weeds growth, and there was no significant difference between chemical and organic fertilizer in corn yield, so we can use these two options for producing optimum yield in sustainable agriculture. Results showed application of soybean as cover crop, especially integrated with organic fertilizers, can be an alternative approach for herbicides and are more effective than the others.

<p>Within the ERA-net CORE Organic Plus transnational programmes supported project PRODIVA producing of the information required for a better utilization of crop diversification for weed management in North European organic arable cropping systems was started. To fulfill the goal of this project- not to eradicate weed problems, which is unlikely to happen in any arable farming system, but to maintain a diversified and manageable weed flora that can support beneficial organisms- there were data from ongoing long-termed cropping system experiments from Latvia analyzed.</p><p>It is hypothesised that: a) perennial weeds can be suppressed in the post-harvest period by improved cover crop establishment and pertinent selection of cover crop species; b) on-farm practices of crop diversification are related to weed pressure and species composition.</p><p class="R-MainText">On the bases on data from organic farm and ongoing long-termed cropping system experiment on weed dynamics in six-field crop rotations with cover crop was concluded that red clover as cover crop after the harvest period is effective to manage perennial weeds. In crop rotation with higher proportions of cereals weed infection growth in six-field rotation with 50% share of cereals up to 3.4, but with 33.3 % share-up to 2.1 times.</p>

Soil microbes play a key role in the nutrient cycling by decomposing the organic material into plant-available elements and also by maintaining the soil health. The study of soil microbial hydrolytic activity (SMA) was carried out in a long-term crop rotation (barley undersown (us) with red clover, red clover, winter wheat, pea and potato) experiment in five different farming systems during 2014–2018. There were two conventional systems, with chemical plant protection and mineral fertilizers, and three organic systems, which included winter cover crops and composted manure. The aim of the present study was to evaluate the effect of the (i) cropping system and (ii) precrops in rotation on the soil SMA. The soil microbial hydrolytic activity was significantly affected by yearly weather conditions, farming system, and crops. In all farming systems, the SMA was the lowest after dry and cold conditions during early spring in 2018. In unfertilized conventional systems, the considerably lower SMA is explained by the side effects of pesticides and low organic residuals, and we can conclude that the conventional system with no added fertilizer or organic matter is not sustainable, considering soil health. In each year, the SMA of organic systems with cover crops and composted manure was 7.3–14.0% higher compared to all farming systems. On average, for both farming systems, the SMA of all the rotation crops was positively correlated with the SMA values of precrops. However, in conventional farming systems, the effect of undersowing on the SMA of the precrop was smaller compared to organic systems.

Corn grain yield in a six-year rotation (Org6), which includes summer annual (corn, soybean), winter annual (winter wheat), and herbaceous perennial (alfalfa for three years) cash crops was, on average, 10% greater than in a three-year rotation (Org3) that includes only summer and winter annual cash crops, and 30% greater than in a two-year rotation (Org2) that includes only summer annual cash crops (Table 1). These differences, which represent results for the first 10 years of the project, were the result of both increases in N availability and decreases in weed competition as crop rotation length and complexity increased (4,9,10). As a point of reference, mean corn yield for the two conventional systems during this same time period, which included substantial drought years, was 126 bu/acre, which is 29% greater than for Org6. In Org2, opportunities to kill weeds occur at the same time each year since the two cash crops, corn and soybean, are planted at similar times. Thus, summer annual weeds (primarily Amaranthus spp., Chenopodium album, Daturum stramonium, Setaria spp., and Abutilon theophrasti) that escape weed management practices in these summer crops increase populations in this system. When wheat is added to the rotation (Org3), the summer annual weeds either do not germinate under the wheat canopy or do not reach reproductive maturity as they are cut prior to setting seed when the wheat is harvested, and killed when soil is prepared for planting cover crops after wheat harvest. In Org6, a perennial forage crop, alfalfa, provides an additional level of phenological complexity that provides further weed control opportunities. Alfalfa is cut three to five times per year, a disturbance regime that tends to favor perennial and annual grasses with a prostrate growth habit rather than annual broadleaf weeds. Tillage prior to corn planting provides control of the grasses favored during the alfalfa phase of the rotation. Corn yield loss to weeds, as measured in adjacent weed-free and weedy plots, was reduced from 35% in Org2 to 14% in Org6 (9). When organic price premiums for corn, soybean, and wheat were included in an economic analysis for the years 2000 to 2002, net returns for the three organic systems were similar (mean, $286/acre) and substantially higher than for the conventional systems (mean, $78/acre). Economic risk, however, was 7.5 and 3.9 times greater for Org2 and Org3, respectively, than for Org6 (2), indicating a substantial economic benefit to more phenologically diverse crop rotations, as risk is spread over crops growing and harvested during different parts of the year. Mean risk for the two conventional systems was similar to that for Org2. Soil organic C (SOC) to a depth of 40 inches was 10% greater in the organic systems (mean, 27.0 T C/acre) than in no-till (NT) (24.5 T C/acre) and 17% greater than in chisel-till (CT) (23.1 T C/acre) after 11 years [(1), and unpublished]. While SOC in surface soils (0 to 2-inch depth) was 18% greater in NT than in the organic systems, SOC at 2-4 and 10 to 20 inch depths was 13-16% greater in the organic systems than in NT. At the 4 to 10 inch depth increment, SOC was 27% greater in the organic systems than in NT. Burying C inputs thus protected SOC from losses that likely occur near the soil surface with repeated tillage in the organic systems. By contrast, SOC in the surface of NT systems is susceptible to loss if or when tillage is resumed (5). Since the majority of farmers using NT do not use continuous NT (7), results from continuous NT research sites such as FSP represent an upper limit to C sequestration levels likely achieved on-farm in the absence of manure inputs. Greater soil organic C was associated with greater soil organic N. In addition, N mineralization potential in the organic systems was, on average, 34% greater than in NT after 14 years. In 2009, this increase in soil fertility resulted in up to 54% higher corn grain yields in the organic than the NT systems in weed-free microplots to which no exogenous N was added that year (8). These results illustrate the positive residual impact of organic management on soil fertility. Increasing crop phenological diversity can benefit soil nutrient management. While N mineralization potential, particulate organic matter N, and SOC were similar among the three organic systems and all were greater than in CT and NT (8), these benefits were attained in Org6 with substantially fewer inputs of poultry litter than in the two shorter organic rotations (Org2 and Org3). During a six-year time period, typical poultry litter application rates were 6.0, 8.0, and 4.0 T/acre in Org2, Org3, and Org6, respectively. In addition, phosphorus (P) removal in harvested crops was greater in Org6 than Org2 and Org3 such that soil test P was 21% lower in Org6 (55 mg/kg Mehlich 3 extractable P) than in Org2 and Org3 (70 mg/kg Mehlich 3 extractable P) after 16 years (3). Thus, the possibility of overloading soils with phosphorus, an important concern in many watersheds, especially when animal manures are applied, was reduced considerably with Org6 compared to the shorter organic rotations. Increasing crop phenological diversity also substantially decreased predicted soil erosion among organic systems. Predicted soil loss by erosion was reduced by 40% and 62% in Org3 and Org6, respectively, compared to Org2 when the Revised Universal Soil Loss Equation, Version 2 (RUSLE2) was applied to these systems (3). When compared using the Water Erosion Prediction Model (WEPP), predicted soil erosion was lower in Org3 than CT by 33% but NT reduced soil erosion an additional 54% (6). In summary, increasing crop rotation length and complexity among organic systems-especially when perennial forages are included-increased corn grain yield and economic stability while reducing weed pressure, predicted soil erosion, animal manure inputs, and soil P loading. While crop yields were lower and predicted soil erosion was greater in organic than conventional systems, net returns, SOC, and soil fertility were all greater in organic than conventional systems.

The paper presents the research conducted at the Joniškėlis Experimental Station of the Lithuanian Research Centre for Agriculture and Forestry on a clay loam Gleyic Cambisol during the period of 2006–2010. The research investigated the changes of mineral nitrogen in soil growing catch crops during the winter wheat post-harvest period and incorporating their biomass into the soil for green manure. Green manure implications for environmental sustainability were assessed. The studies were carried out in the soil with a low (1.90–2.00%) and moderate (2.10–2.40%) humus content in organic and sustainable cropping systems. The crop rotation, expanded in time and space, consisted of red clover (Trifolium pretense L.) → winter wheat (Triticum aestivum L.) → field pea (Pisum sativum L.) → spring barley (Hordeum vulgare L.) with undersown red clover. Investigations of mineral nitrogen migration were assessed in the crop rotation sequence: winter wheat + catch crops → field pea. Higher organic matter and nitrogen content in the biomass of catch crops were accumulated when Brassisaceae (white mustard, Sinapis alba L.) was grown in a mixture with buckwheat (Fagopyrum esculentum Moench.) or as a sole crop, compared with oilseed radish (Raphanus sativus var. Oleiferus Metzg.) grown with the long-day legume plants blue lupine (Lupinus angustifolius L.). Mineral nitrogen concentration in soil depended on soil humus status, cropping system and catch crop characteristics. In late autumn there was significantly higher mineral nitrogen concentration in the soil with moderate humus content, compared with soil with low humus content. The lowest mineral nitrogen concentration in late autumn in the 0–40 cm soil layer and lower risk of leaching into deeper layers was measured using organic cropping systems with catch crops. The highest mineral nitrogen concentration was recorded in the sustainable cropping system when mineral nitrogen fertilizer (N30) was applied for winter wheat straw decomposition. In the organic cropping system, the incorporation of catch crop biomass into soil resulted in higher mineral nitrogen reserves in soil in spring than in the sustainable cropping system, (mineral nitrogen fertilizer (N30) applied for straw decomposition in autumn and no catch crop grown). Applying organic cropping systems with catch crops is an efficient tool to promote environmental sustainability.

Nitrogen (N) deficiency is a major problem in organic and low-input farming systems. Growing spring cereals with undersown legumes has a positive effect on soil fertility, enriching it with nitrogen, through symbiosis of legumes with nodule bacteria. Two hypotheses were tested: 1) undersowing of red clover increases the protein content of barley grains and 2) mineral N has negative aftereffect on growth of legume plants. The aim of this study was to investigate the effect of organic (cattle manure, off-season cover crop) and mineral N in organic and conventional farming systems on (i) barley (Hordeum vulgare L.) grain yield and quality, (ii) biomass yield formation of undersown red clover (Trifolium pratense L.) and (iii) the aftereffect of mineral and organic N fertilisers on the red clover crop biomass yield in the following year. The experiment was established in 2008 at the Estonian University of Life Sciences (58°22ʹ N, 26°40ʹ E) on the soil described as Stagnic Albic Luvisol (LV ab-st) (WRB, 2014) with sandy loam surface texture, 1.38% C, 0.13% N, 133 mg kg-1 P, 210 mg kg-1 K and pHKCl 6.0. The crops were treated using different farming systems: three organic (Org0, OrgI and OrgII) and four conventional (N0, N40, N80 and N120); nitrogen sources during crop cycle period: N0 and Org0 = symbiotically fixed atmospheric N2, N40 = N2 + mineral N 40 kg ha-1 N, N80 = N2 + mineral N 80 kg ha-1 N, N120 = N2 + mineral N 120 kg ha-1 N, OrgI = N2 + N taken up by cover crops (NCC) and OrgII = N2 + NCC + N applied with manure (Nm). Our study revealed that grain yield of barley was strongly affected by undersown red clover; because of competition for nutrients in cereallegume mixture the grain yield of barley in organic system was 11‒61% lower than that in conventional system. The seed rate of undersown red clover (2.84 million viable seed per ha) was too high. The content of proteiin depended on the availability of mineralised nitrogen. The mean protein content of barley grains over the trial years and treatments was 99 ± 1.6 g kg-1 in the conventional system, which was 17% higher than that in the organic system. Undersowing of red clover had no significantly positive effect on the grain yield and protein content of barley. Mineral N fertiliser had no negative aftereffect on growth of the red clover crop the following year. Mean above ground biomass yield over the trial years for the red clover crop 2nd cut was 17% higher in the conventional system than in the organic system.

Organic crop systems rely on tillage as the primary means to control weeds, but negative impacts of tillage may prevent farmers from achieving the potential soil health benefits of organic management. Cover crops have been suggested as a solution for overcoming this tillage trade-off directly by enhancing soil health and indirectly by providing weed control, thus reducing the need for tillage. In order to characterize the state of published research on the effects of cover crops on weed control and soil health in organic crop systems, we conducted a formal literature search on this topic and identified 116 relevant studies which were subsequently categorized by research focus, management strategy, and variables measured. We found 83 studies examined effects of cover crops on weed control and 33 studies examined effects of cover crops on soil health, but only 10 of the studies reported on both weed control and soil health effects. The lack of integrated studies examining both weed control and soil health responses to management highlights a research gap not sufficiently addressed by researchers, even though it is a topic of great interest to many organic farmers. A majority of studies (79) included reduced or no-till treatments, and annual grasses, clover, and vetch species were the most common cover crops. Assessments of aboveground biomass were the most common weed control measurements, while soil organic matter was the most common soil health measurement. Recommendations for future research needs include the following: more integrated assessments of the effects of cover crops on both soil health and weed control under varying tillage regimes; greater effort to characterize the soil health impacts of cover crop systems utilizing newly developed soil health indicators including soil physical parameters; long-term studies to assess dynamic soil health responses as well as perennial weed pressure (particularly in reduced and no-till organic systems); and greater allocation of research funding to regions outside of North America and Europe.

Nitrogen (N) and carbon (C) cycles are closely linked in organic farming systems. Use of residues for biogas digestion may reduce N-losses and lead to higher farmland productivity. However, digestion is connected to large losses of organic C. It is the purpose of this paper (1) to compare farming systems based on liquid slurry and solid farmyard manure regarding the N, C and organic dry matter (ODM) inputs and flows, (2) to analyse the effect of digestion on soil N, C and ODM inputs and flows within the cropping system, (3) to assess the effects of organic manure management on biological N2 fixation (BNF), and (4) to assess the effect of biogas digestion on the sustainability of the cropping systems in terms of N and C budgets. The BNF by clover/grass-leys was the most important single N input, followed by the BNF supplied by legume cover cropping. Growth of crops in organic farming systems is very often N limited, and not limited by the soil C inputs. However, balances of N inputs showed that the implemented organic farming systems have the potential to supply high amounts of N to meet crop N demand. The level of plant available N to non-legume main crops was much lower, in comparison to the total N inputs. Reasons were the non-synchronized timing of N mineralization and crop N demand, the high unproductive gaseous N losses and an unfocussed allocation in space and time of the circulating N within the crop rotation (e.g. allocation of immobile manures to legumes or of mobile manures to cover crops). Simultaneously, organic cropping systems very often showed large C surpluses, which may be potentially increased the N shortage due to the immobilization of N. Soil organic matter supply and soil humus balance (a balance sheet calculated from factors describing the cultivation effects on humus increasing and humus depleting crops, and organic manure application) were higher in cropping systems based on liquid slurry than in those based on solid farmyard manure (+19%). Simultaneously, soil N surplus was higher due to lower gaseous N losses (+14%). Biogas digestion of slurry had only a very slight effect on both the soil N and the soil C budget. The effect on the N budget was also slight if the liquid slurry was stored in closed repositories. Digestion of residues like slurry, crop residues and cover crops reduced in a mixed farming system the soil C supply unilaterally (approximately −33%), and increased the amounts of readily available N (approximately +70–75%). The long-term challenge for organic farming systems is to find instruments that reduce N losses to a minimum, to keep the most limiting fraction of N (ammonia-N) within the system, and to enhance the direct manuring effect of the available manures to non-legume main crops.

The experiments were carried out during 2012–2017. There were 5 crops in rotation: Red clover, winter wheat, pea, potato and barley undersown (us) with red clover. There were 5 cropping systems in the experimental setup: 2 conventional systems with chemical plant protection and mineral fertilizers; 3 organic systems which included winter cover crops and farm manure. The aim of the present research was to study the effect of cultivating barley undersown with red clover and the preceding winter cover crop on the soil microbial hydrolytic activity, the change in the content of soil organic carbon (SOC) and total nitrogen (Ntot) compared to the same parameters from the field that was previously under potato cultivation (forecrop of barley in the rotation). The cultivation of barley with red clover (barley (us)) had a positive impact on the soil micro-organisms activity. In organic systems the soil microbial hydrolytic activity increased on average by 19.0%, compared to the conventional systems. By cultivating barley (us) the soil microbial hydrolytic activity had a significant effect on the SOC content only in organic systems where winter cover crops were used. Organic cultivation systems had positive impact on the soil nitrogen content; Ntot in samples taken before sowing the barley (us) was higher by 17.4% and after the cultivation of barley (us) by 14.4% compared to conventional systems, as an average of experimental years. After cultivation of barley (us) with red clover the soil microbial hydrolytic activity had no effect on the soil Ntot content in either cultivation systems.

Nitrogen balances in organic and conventional arable crop rotations and their relations to nitrogen yield and nitrate leaching losses

Peanut pod, seed, and oil yield for biofuel following conventional and organic production systems