Weed seed bank as affected by crop rotation and disturbance

An experiment was conducted to determine the influence of crop rotations on soil seed bank to provide a comparison between crop fields and non-crop lands. Crop rotations were continuous dryland wheat (Wd), continuous irrigated wheat (Wi), wheat-sugarbeet (WS) and wheat-chickpea (WCh). Nearby pastures (P) and orchards (Or) were also studied for comparison purposes. Estimates of the density of seed banks ranged from 52779 seed m⁻² in P to 9906 seeds m⁻² in Wd. A total of 114 plant species from 24 families were identified from seeds collected from different farms. 33 weed species were at high frequency in weed communities. Crop rotations were dominated by annual weed species, while the weed species dominated in P were mostly not found in any crop rotation. The two weed species Roemeria refracta and Eragrostis cilianensis were frequently present in all the study sites. Amaranthus chlorostachys and Euphorbia esula were more abundant in the areas of moderate to high disturbance. In SW and WS rotations, due to use of grass herbicides and hand weeding, winter annual broadleaves such as Lactuca serriola and Anchusa italica were the prominent species in the seed bank. Results showed that a number of weed species are adapted to a specific crop sequences and disturbance levels. Weed species richness, seed bank abundance and diversity in soil depths are highly dependent on disturbance levels. The current study highlights the importance of agricultural practices including crop sequences or disturbance levels in determining the characteristics of weed populations. This provides useful information to improve methods for maintaining plant population balance.     

Stable high yields with zero tillage and permanent bed planting?

Subtropical highlands of the world have been densely populated and intensively cropped. Agricultural sustainability problems resulting from soil erosion and fertility decline have arisen throughout this agro-ecological zone. This article considers practices that would sustain higher and stable yields for wheat and maize in such region. A long-term field experiment under rainfed conditions was started at El Batán, Mexico (2240 m a.s.l.; 19.31°N, 98.50°W; fine, mixed, thermic, Cumulic Haplustoll) in 1991. It included treatments varying in: (1) rotation (continuous maize (Zea mays) or wheat (Triticum aestivum) and the rotation of both); (2) tillage (conventional, zero and permanent beds); (3) crop residue management (full, partial or no retention). Small-scale maize and wheat farmers may expect yield improvements through zero tillage, appropriate rotations and retention of sufficient residues (average maize and wheat yield of 5285 and 5591 kg ha⁻¹), compared to the common practices of heavy tillage before seeding, monocropping and crop residue removal (average maize and wheat yield of 3570 and 4414 kg ha⁻¹). Leaving residue on the field is critical for zero tillage practices. However, it can take some time—roughly 5 years—before the benefits are evident. After that, zero tillage with residue retention resulted in higher and more stable yields than alternative management. Conventional tillage with or without residue incorporation resulted in intermediate yields. Zero tillage without residue drastically reduced yields, except in the case of continuous wheat which, although not high yielding, still performed better than the other treatments with zero tillage and residue removal. Zero tillage treatments with partial residue removal gave yields equivalent to treatments with full residue retention (average maize and wheat yield of 5868 and 5250 kg ha⁻¹). There may be scope to remove part of the residues for fodder and still retain adequate amounts to provide the necessary ground cover. This could make the adoption of zero tillage more acceptable for the small-scale, subsistence farmer whose livelihood strategies include livestock as a key component. Raised-bed cultivation systems allow both dramatic reductions in tillage and opportunities to retain crop residues on the soil surface. Permanent bed treatments combined with rotation and residue retention yielded the same as the zero tillage treatments, with the advantage that more varied weeding and fertilizer application practices are possible. It is important small-scale farmers have access to, and are trained in the use of these technologies.     

Effect of emergence time,inter- and intra-specific competition on growth and fecundity of Echinochloa crus-galli in dry-seeded rice

Since 2005, the evolution and spread of herbicide-resistant Echinochloa crus-galli biotypes have posed a serious threat to crop production in the Philippines. A comprehensive knowledge of E. crus-galli ecology and fecundity is fundamental in managing different biotypes of this weed. It was hypothesized that (a) high weed plant density produces more biomass and fertile seeds per unit area, (b) rice interference reduces the biomass and fecundity of the weed, and (c) a delay in weed emergence reduces the soil seed bank. In 2013, experiments were conducted in the wet season (WS) and dry season (DS), to understand the effect of E. crus-galli densities (40 and 80 plants m⁻²) on its growth, survival, and fecundity, with varying emergence times of 2, 15, 30, and 45 d after rice emergence (DARE). Relative to the weed plants grown without rice interference, E. crus-galli growth and seed production was lower in the presence of rice. Percent survival and plant height of E. crus-galli declined in a linear manner in the DS, and declined in a quadratic manner in the WS. Tiller number, inflorescence number, inflorescence biomass, and shoot biomass per plant declined in an exponential manner, with a delay in emergence of each cohort relative to rice. Across rice seeding rate, weed density, and emergence time, there was a linear relationship (y = 110x − 272 in the DS and y = 100x − 220 in the WS) between E. crus-galli shoot biomass and the number of seeds plant⁻¹. Relative to the late-emerging weed cohorts, E. crus-galli seed production (1320–1579 seeds plant⁻¹), 1000-seed weight (2.2–2.9 g), and seed yield (2808–2334 kg ha⁻¹) were higher when seedlings emerged with the crop (2 DARE). None of the seedlings that emerged 45 DARE produced viable seeds. Seed germination of the first two cohorts (2 and 15 DARE) ranged from 84 to 91%. The delay in emergence of E. crus-galli beyond 30 DARE reduced the percentage of germinable and viable seeds, and increased the percentage of non-viable seeds produced plant⁻¹. The results suggest that cultural weed management approaches that delay the emergence of E. crus-galli can reduce weed biomass and seed production, and is thus valuable for preventing seed rain to the seed bank by noxious weed biotypes in the field.     

Effects of tillage,crop rotation and nitrogen fertilization on wheat-grain quality grown under rainfed Mediterranean conditions

The grain quality of wheat is influenced by the protein content, which in turn depends on environmental conditions and cropping practices. We carried out a 3-year field study in a rainfed Mediterranean region on the effects of tillage, crop rotation and nitrogen fertilization on the grain quality of hard red spring wheat (Triticum aestivum) in terms of protein content, test weight and alveogram indices. Tillage treatments were no tillage (NT) and conventional tillage (CT). Crop rotations were wheat–sunflower (Helianthus annus L.) (WS), wheat–chickpea (Cicer arietinum L.) (WCP), wheat–fababean (Vicia faba L.) (WFB), wheat–fallow (WF) and continuous wheat (CW). Fertilizer nitrogen was used at three different rates: 50, 100 and 150 kg N ha⁻¹. A split–split plot design with four replicates was used. Grain protein content was found to be inversely proportional to rainfall during the growing season. The tillage method was also found to affect grain protein content, test weight and some grain quality indices. Through its effect on moisture and nitrate in the soil. The crop rotations that included a legume (WCP and WFB) had marked effects on wheat quality. The increased grain protein content and resulted in improved rheological properties of the dough (viz. a higher alveogram index and a more balanced tenacity/extensibility ratio). However, no differences due to N dilution in the plant were observed in the wettest year studied, which was also the highest yielding. Increasing the fertilizer N rate increased the grain protein content; this variable had the most marked influence on grain quality indices, though in the year that gave the highest yield the N dilution effect was observed. The many significant interactions among experimental variables reveal a close relationship among grain yield, protein content, grain quality and the wheat growth conditions. Specifically, the amount of rainfall and its distribution in the growing season strongly influenced N availability and uptake by the crop, as well as wheat-grain quality indices.     

Management of herbicide-resistant Phalaris minor in wheat by sequential or tank-mix applications of pre- and post-emergence herbicides in north-western Indo-Gangetic Plains

Development of cross resistance or multiple cross resistance in Phalaris minor in wheat will continue to increase, as the weed develops mechanisms of resistance against new herbicides. This weed is a major threat to wheat productivity in north-western India, and as such needs to be addressed with integrated weed management approaches, including crop and herbicide rotations, herbicide combinations along with cultural and mechanical methods. Three field experiments were conducted during 2008–09 to 2012–13 along with large plot adaptive trials during 2012–13 with the objective to evaluate the efficacy of sequential applications of pendimethalin applied pre-emergent followed by clodinafop, sulfosulfuron, or pinoxaden applied post-emergent and tank-mix applications of metribuzin with these post-emergence herbicides for the management of herbicide-resistant P. minor in wheat. Clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 days after sowing (DAS) and pendimethalin 1000 g ha⁻¹ as pre-emergence did not provide consistently effective control of P. minor in wheat. An increase in the dose of clodinafop from 60 to 75 g ha⁻¹ and of sulfosulfuron from 25 to 30 g ha⁻¹ also did not improve their efficacy to a satisfactory level. However, pinoxaden 50 g ha⁻¹ provided effective control (97–100%) of P. minor but not of broadleaf weeds. The tank-mix application of metribuzin with clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 DAS and the sequential application of pendimethalin 1000 g ha⁻¹ or trifluralin 1000 g ha⁻¹ just after sowing followed by clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 DAS provided 90–100% control of P. minor along with broadleaf weeds in wheat, thus resulting in improved grain yields (4.72–5.75 t ha⁻¹) when compared to clodinafop 60 g ha⁻¹ (3.85–5.60 t ha⁻¹) or sulfosulfuron 25 g ha⁻¹ alone (3.95–5.10 t ha⁻¹). The efficacy of mesosulfuron + iodosulfuron (a commercial mixture) 14.4 g ha⁻¹ against P. minor was not consistent across the experiments and over the years. The ready-mix combination of fenoxaprop + metribuzin (100 + 175 g ha⁻¹) at 35 DAS provided effective control of weeds but its varietal sensitivity needs to be determined before its use in field conditions. The tank-mix or sequential application of herbicides would be a better option than their applications alone to manage the serious problem of herbicide-resistant P. minor in wheat.     

Model predictions of winter rainfall effects on N dynamics of winter wheat rotation following legume cover crop or fallow

Winter rainfall in a Mediterranean region varies from year to year. Both release of inorganic N from soil organic matter (SOM) or a legume cover crop (LCC) and subsequent nitrate movement in the soil profile are strongly affected by winter rainfall, through its effects on soil water status and on vertical flux. N accumulation of a LCC also varies over years due to weather effects on growth. Thus, these two factors need to be taken into account for efficient use of SOM-N and LCC-N in a wheat (Triticum aestivum L.) rotation. To determine how winter weather might affect the performance of wheat-fallow rotations that include an LCC grown and incorporated during the fallow year, we used the CERES-wheat model and a 46-season weather record to simulate N dynamics of 2-year unfertilized and irrigated winter-LCC wheat systems with high LCC (236 kg N ha⁻¹) or low LCC (118 kg N ha⁻¹) inputs. Unfertilized and fertilized fallow-wheat controls were also simulated. Within a given LCC input value, coefficients of variation for total seasonal N supply (the sum of predicted wheat N uptake, N leaching and inorganic soil N at wheat maturity) over years were <15%, despite the fluctuating winter rainfall (CV 48%). Average N leaching was predicted to be highest in the high LCC input system (108 kg N ha⁻¹), followed by the low LCC input system (86 kg N ha⁻¹) and midseason-intensive and planting-intensive fertilized wheat-fallow systems (82 and 72 kg N ha⁻¹, respectively), and least in the unfertilized wheat-fallow system (54 kg N ha⁻¹). N leaching exceeded 100 kg N ha⁻¹ in 4, 20, 16, 18, and 29 seasons out of 46 seasons, respectively, in the unfertilized and planting-intensive and midseason-intensive fertilized wheat-fallow rotations and in wheat rotations with low and high LCC inputs. There was no difference in predicted wheat yield among the four systems with N inputs from fertilizer or LCC, but yield was lower in the unfertilized wheat-fallow rotation. If the goal of use of LCC was to attain the same yield level as high LCC input or fertilized wheat system while diminishing the risk of N leaching, the low LCC input case met this goal in the short term. However, a simple balance sheet using the model showed that the N balance of the low LCC input system was −147 kg N ha⁻¹ season⁻¹, if we assumed 50% of LCC-N was derived from atmospheric fixation. The low-LCC-input system could therefore fail to maintain inherent soil N fertility in the long term unless nearly 100% LCC-N was derived from fixation.     

Effect of herbicides on weed management in dry-seeded rice sown under different tillage systems

In India, dry-seeded rice (DSR) production systems are rapidly replacing conventional rice production systems due to various advantages. DSR systems can be managed under zero-till (ZT) conditions or after a preparatory tillage, often referred to as conventional tillage systems (CONT). Although previous reports indicate the contribution of tillage to weed suppression, the effect of one-time preparatory tillage in a DSR system could vary depending on the dominant weeds in the system, vertical seed distribution and the weed seed dynamics. A study was conducted to test the efficacy of ZT and CONT and their interaction with herbicide treatments on the weed population dynamics and rice grain yield in 2010 and 2011. Tillage systems did not affect weed emergence, weed biomass, tiller production and crop yield. However, herbicide treatments varied in their efficacy on individual weeds. Hand-weeding treatments and pendimethalin combined with hand weeding did not effectively control Cyperus rotundus L. and Panicum maximum Jacq. (a perennial grass weed with underground parts). The herbicide combination of metsulfuron and chlorimuron was effective in controlling C. rotundus but not grass weeds. This indicates the need for sequential applications of herbicides for grass weed control or integration of hand weeding to achieve broad-spectrum weed control. Apart from hand weeding (three times), treatment with penoxsulam–cyhalofop and pendimethalin followed by (fb) hand weeding resulted in low weed density, high tiller production and grain yield. The study clearly indicates that tillage does not always lead to weed suppression compared with ZT, and herbicides must be chosen based on the dominant weeds in a system. The results of this study are pertinent as herbicide-resistant weeds are rapidly evolving under continuous herbicide selection pressure, which warrants studies on enhancing productivity through low-input, environmentally friendly and sustainable production technology.     

Effects of long-term tillage,crop rotation and nitrogen fertilization on bread-making quality of hard red spring wheat

The effect of tillage system, crop rotation and nitrogen (N) fertilization rates on the quality of hard red spring wheat (Triticum aestivum L.) was studied over a 6-year period under rainfed Mediterranean conditions. Grain yield, test weight, protein content and alveogram parameters (W: alveogram index; P: dough tenacity; L: dough extensibility; P/L: tenacity–extensibility ratio; G: swelling index) were analyzed. Tillage treatments included no tillage (NT) and conventional tillage (CT). Crop rotations were wheat–sunflower (Helianthus annuus L.) (WS), wheat–chickpea (Cicer arietinum L.) (WCP), wheat–faba bean (Vicia faba L.) (WFB), wheat–fallow (WF) and continuous wheat (CW). Nitrogen fertilizer rates were 50, 100 and 150 kg N ha⁻¹ on a Vertisol (Typic Haploxerert). A split–split plot design with four replications was used. Weather conditions over the study years strongly influenced wheat yield and quality. Test weights rose considerably with yield and increased rainfall during the filling period, and fell slightly as N rates increased. Grain protein content increased with rainfall in the month of May (when grain protein accumulation occurs) up to a maximum of 80 mm. Grain protein content peaked at average mean temperatures of around 26–27°C. Protein content and alveogram parameter also improved under CT, following a prior legume crop and with rising N fertilizer rates. Alveogram parameters rose with protein content, although the P/L ratio showed greater imbalance. N fertilizer proved to be a key factor in determining bread-making quality, and the best strategy available to the farmer for optimizing wheat quality. However, the influence of weather conditions and soil residual N should be borne in mind when deciding on the additional fertilizer N to be used as a top dressing with a view to increasing yield and, particularly, enhancing wheat protein content and bread-making quality.     

Relative abundance and damage of some insect pests of wheat under different tillage practices in rice–wheat cropping in India

Tillage changes the physical and chemical properties of soil and can also inhibit or enhance useful and harmful fauna. In agriculture, different tillage technologies are being tried to enhance crop productivity, but little concrete information seems to exist on their effects on pest abundance and damage. To address this lack of information, sowing of wheat was investigated under different tillage systems. In order to monitor pest abundance and damage in altered tillage systems, the present studies on the relative abundance and damage due to insect pests viz. pink stem borer (PSB, Sesamia inferens Walker), termites (Microtermes obesi Holmgren and Odontotermes obesus Rambur) and root aphid (Rhopalosiphum rufiabdominalis Sasaki) were undertaken in a rice–wheat cropping system during 2010–11 and 2011–12. Pest abundance and damage was monitored in four tillage systems i.e. conventional tillage (CT), zero tillage (ZT), ZT + mulch and rotary tillage (RT) under insecticide protected and unprotected conditions. The application of insecticide did not affect root aphid incidence or termite damage. However, significant differences in PSB damage in insecticide protected (0.9%) and unprotected (1.2%) conditions were observed. The investigations demonstrated that in CT, damage by PSB (0.6%) was minimum; however termite damage (2.2%) was maximum as compared to all other tillage conditions. In ZT, PSB damage (1.4%) was maximum and root aphid incidence (3.1 aphids/tiller) was minimum in comparison to other tillage conditions. ZT + mulch resulted in inter-mediate insect pest incidence/damage; however, RT was the least effective practice which showed relatively high incidence/damage of these three insects (1.2% PSB damage, 1.9% termite damage and 5.1 aphids/tiller). The insecticide × tillage interaction indicated that insecticide application is needed only in ZT and RT for PSB management.     

Winter cover crops influence Amaranthus palmeri establishment

Winter cover crops were evaluated for their effect on Amaranthus palmeri establishment and growth in cotton production. Cover crops examined included rye and four winter legumes: narrow-leaf lupine, crimson clover, Austrian winter pea, and cahaba vetch. Each legume was evaluated alone and in a mixture with rye. Cover crop biomass in monoculture was greatest for rye and lupine (>6750 kg ha⁻¹), while clover, pea, and vetch were less and ranged from 2810 to 4610 kg ha⁻¹. Cover crop biomass was more than doubled when rye was mixed with clover or vetch relative to the legume monoculture. In early-June, A. palmeri densities were 46 seedlings m⁻² in the non-disturbed areas between cotton rows in the fallow, while populations were <4 seedlings m⁻² with rolled vetch or pea and 18 and 29 seedlings m⁻² in rolled clover and lupine. Rye and legume mixtures reduced A. palmeri densities to <3 seedlings m⁻², while rye monocultures had 8 seedlings m⁻². There were no differences in A. palmeri densities (≥144 plants m⁻²) in the cotton row among cover crop treatments. By late-June, rye and winter pea controlled A. palmeri in the row middle >80% relative to the non-cover crop fallow treatment, while control from clover, vetch and lupine ranged from 64 to 70%. The relationship between A. palmeri control in between cotton rows and cover crop biomass was described by a log-logistic regression model with 4530 kg ha⁻¹ providing median weed control (Bio₅₀); predicted A. palmeri control was 25, 50, and 75% from 2950, 4900, and 8600 kg ha⁻¹ cover crop biomass, respectively. However, A. palmeri plants in the cotton rows prevented yield production in the absence of herbicides. Where A. palmeri was controlled with herbicides, the highest yields occurred following rye, with lower yields following lupin/rye mixture and treatments including pea. Management of herbicide resistant weed species requires diverse management tactics; this may include high-biomass cover crops to reduce weed establishment between crop rows. However, greater research effort is needed to devise weed management options for the crop row that do not rely exclusively on the diminishing array of herbicide tools.     

Impact of managing cover crop residues on the floristic composition and species diversity of the weed community of pepper crop (Capsicum annuum L.)

The decline of farmland biodiversity is mainly attributed to the intensive use of chemical inputs in agriculture. Cover crop residues may contribute to improve weed management while maintaining a high level of weed diversity. A 2-year field experiment was carried out in central Italy to study the effect of cover crop species and their residue management on weed community composition and weed species diversity in a winter cover crop – pepper sequence. Hairy vetch (Vicia villosa Roth.), oat (Avena sativa L.) and canola (Brassica napus L.) were sown in September 2009 and 2010 and grew undisturbed during the winter season until spring when they were suppressed one week before pepper transplanting. Cover crop residues were: (i) green manured at 30 cm depth (conventional tillage, CT), (ii) green manured at 10 cm depth (minimum tillage, MT), and (iii) left on the soil surface as mulch strips covering 50% of the ground area in no-tilled soil (NT). A winter weedy fallow and a bare soil without cover crop in NT, MT and CT were also included as controls. Weed plant density data in pepper were used for calculating weed species richness. Compared to weedy fallow, oat, hairy vetch and canola consistently reduced the weed density and weed aboveground biomass by the time of their suppression (on average 3.6, 21.5, and 41.3 plants m⁻² and 11.0, 49.2, and 161.8 g m⁻² of DM, respectively). In pepper, oat residues generally determined a higher reduction of weed density and species richness compared to hairy vetch and canola regardless the residue management treatments. Converting cover crop aboveground biomass into mulch strips greatly reduced weed species density but did not always imply a reduction of weed species diversity in pepper compared to MT and CT. The weed species richness was reduced inside the mulch strips, while a richer and more diverse weed community was found outside the mulch strips in NT. Weed community in pepper was mainly composed of annual dicot weeds such as Amaranthus retroflexus, Chenopodium album, Solanum nigrum, Polygonum aviculare which were mostly associated with MT and CT tillage systems, while in NT an increase of perennial species such as Rumex crispus was observed. These results suggest that it is possible to manage cover crop residues in NT in order to obtain a lower weed density and consequently a higher yield in pepper compared to MT and CT while maintaining a high level of weed diversity.     

Stubble retention and tillage in a semi-arid environment: 2. Soil mineral nitrogen accumulation during fallow

The accumulation of soil mineral nitrogen (SMN) was studied over 4 years at two sites in north-west Victoria, Australia in response to fallow treatments. The four combinations of stubble management (with and without) and tillage (with and without) in 18-month-long fallows of a fallow-wheat rotation were compared with a tilled summer fallow prior to field pea and wheat crops in rotation.Across both sites, root-zone SMN ranged from 66 to 222 kg N h⁻¹ during the fallows and at sowing time was generally less at Dooen than at Walpeup despite greater total soil N (Dooen 0.11%, Walpeup 0.05%). At Dooen, the long fallow with stubble retention and tillage accumulated 46 kg N h⁻¹ more SMN than the short fallow after field pea. In one year, stubble retention increased SMN by 20 kg N ha⁻¹ but reduced it by an average of 26 kg N h⁻¹ in two of the four years. At Walpeup, SMN increased in the pea-wheat rotation by an average of 46 kg N h⁻¹ above the tilled fallow without stubble in two of the four years. The inclusion of field pea in the rotation increased SMN at depth by the second cycle of the rotation at Walpeup only. Stubble retention and tillage had little effect on SMN accumulation at Walpeup. The distribution of SMN in the soil profile was different every year at each site despite some years having similar total SMN. There was a tendency for stubble retention to depress SMN in the surface layers possibly through immobilisation and denitrification.     

Rice straw mulching and nitrogen response of no-till wheat following rice in Bangladesh

Wheat (Triticum aestivum L.) cultivation in no-till soil of a postrice harvest field utilizes residual soil moisture and reduces the time period from rice harvest to wheat seeding in intensive rice-wheat cropping systems. Some of the major constraints in no-till wheat production are high weed infestation, poor stand establishment due to rapid drying of topsoil and low nitrogen use efficiency (NUE). A field experiment was conducted at the research farm of the Wheat Research Centre, Dinajpur, Bangladesh, for two consecutive years to overcome those constraints, to evaluate rice straw as mulch, and to determine the optimum application rate of nitrogen (N) for no-till wheat. The treatments included 12 factorial combinations of three levels of mulching: no mulch (M₀), surface application of rice straw mulch at 4.0 Mg ha⁻¹ that was withdrawn at 20 days after sowing (M₁), the same level of mulch as M₁ but allowed to be retained on the soil surface (M₂), and four nitrogen levels (control 80, 120 and 160 kg ha⁻¹). Rice straw mulching had a significant effect on conserving initial soil moisture and reducing weed growth. Root length density and root weight density of wheat were positively influenced both by straw mulching and N levels. N uptake and apparent nitrogen recovery of applied N fertilizer were higher in mulch treatments M₁ and M₂ as compared to M₀. Also mulch treatment of M₁ and M₂ were equally effective at conserving soil moisture, suppressing growth of weed flora, promoting root development and thereby improved grain yield of no-till wheat. N application of 120 kg ha⁻¹ with straw mulch was found to be suitable for no-till wheat in experimental field condition.     

Can winter cover crops influence weed density and diversity in a reduced tillage vegetable system?

Weeds are a major constraint for organic crop production. Previous research has found that cover crops in reduced tillage systems can provide weed interference, subsequently reducing inputs and improving crop yield. However, questions remain about effects of cover crop species identity and cover crop biomass on weed suppression and crop yield. This four-year study investigated how winter cover crops grown alone or in mixture influenced weed presence and crop yield in a reduced tillage organic vegetable system. Treatments were barley (Hordeum vulgare L.), crimson clover (Trifolium incarnatum L.), mixed barley + crimson clover, and a no-cover crop control. Plots were flail-mowed and strip-tilled prior to planting main crops (2011 and 2012: broccoli Brassica oleracea L.; 2013 and 2014: crookneck squash Cucurbita pepo L.). We measured density, diversity, and community composition of weeds and viable weed seeds, changes in weed percent cover within growing seasons, and crop yield. We found that the presence of barley, crimson clover, or barley + crimson clover reduced weed density by 50% relative to the control. Cover crop biomass negatively influenced weed density and weed seed diversity, and positively influenced squash yield. Weed percent cover within growing seasons did not respond differentially to cover crop treatment. Cover crop treatment and cover crop biomass had no influence on weed or weed seed community composition. These results suggest that reduced tillage winter cover crops in mixture or monoculture can similarly suppress weeds and improve yield, primarily due to biomass effects.     

Interactions between non-flooded mulching cultivation and varying nitrogen inputs in rice–wheat rotations

A 3-year field experiment examined the effects of non-flooded mulching cultivation and traditional flooding and four fertilizer N application rates (0, 75, 150 and 225 kg ha⁻¹ for rice and 0, 60,120, and 180 kg N ha⁻¹ for wheat) on grain yield, N uptake, residual soil N_min and the net N balance in a rice–wheat rotation on Chengdu flood plain, southwest China. There were significant grain yield responses to N fertilizer. Nitrogen applications of >150 kg ha⁻¹ for rice and >120 kg ha⁻¹ for wheat gave no increase in crop yield but increased crop N uptake and N balance surplus in both water regimes. Average rice grain yield increased by 14% with plastic film mulching and decreased by 16% with wheat straw mulching at lower N inputs compared with traditional flooding. Rice grain yields under SM were comparable to those under PM and TF at higher N inputs. Plastic film mulching of preceding rice did not affect the yield of succeeding wheat but straw mulching had a residual effect on succeeding wheat. As a result, there was 17–18% higher wheat yield under N0 in SM than those in PM and TF. Combined rice and wheat grain yields under plastic mulching was similar to that of flooding and higher than that of straw mulching across N treatments. Soil mineral N (top 60 cm) after the rice harvest ranged from 50 to 65 kg ha⁻¹ and was unaffected by non-flooded mulching cultivation and N rate. After the wheat harvest, soil N_min ranged from 66 to 88 kg N ha⁻¹ and increased with increasing fertilizer N rate. High N inputs led to a positive N balance (160–621 kg ha⁻¹), but low N inputs resulted in a negative balance (−85 to −360 kg ha⁻¹). Across N treatments, the net N balances of SM were highest among the three cultivations systems, resulting from additional applied wheat straw (79 kg ha⁻¹) as mulching materials. There was not clear trend found in net N balance between PM and TF. Results from this study indicate non-flooded mulching cultivation may be utilized as an alternative option for saving water, using efficiently straw and maintaining or improving crop yield in rice–wheat rotation systems. There is the need to evaluate the long-term environmental risks of non-flooded mulching cultivation and improve system productivity (especially with straw mulching) by integrated resource management.     

Weed control efficacy and winter wheat safety of a novel herbicide HW02

HW02, a pyruvate dehydrogenase inhibitor, is a newly developed herbicide for broadleaf weed control in wheat, maize and turf in China. Greenhouse and field experiments were conducted to evaluate its efficacy against weeds and safety to winter wheat. In the greenhouse experiment, this herbicide had higher activities than 2,4-D against Descurainia sophia (L.) Schur., Amaranthus retroflexus L., Capsella bursa-pastoris (L.) Medic., and Malachium aquaticum (L.) Fries.. When it was applied at late tillering stage of winter wheat in spring, the herbicide provided weed biomass reduction of 98%–100% at the rates 225–525 g a.i. ha⁻¹ and was safe to the crop at the rate of up to 900 g a.i. ha⁻¹. These results showed HW02 could be an alternative herbicide for resistant weed management because its mode of action is different from herbicides presently used.     

Long-term effect of tillage systems on soil microbiological,chemical and physical parameters and the incidence of charcoal rot by Macrophomina phaseolina (Tassi) Goid in soybean

A 20-year field experiment was employed with the aim of evaluating the effect of tillage systems on biological, chemical and physical aspects of the soil, and to establish whether there was a correlation of these parameters with the incidence of charcoal rot (Macrophomina phaseolina) of soybean and crop yield. The tillage systems evaluated were direct seeding (DS), DS + scarifier (DS + S), minimum tillage (MT) and conventional tillage (CT). DS presented higher values than CT in culturable total fungi (26.33 × 10⁵ vs. 2.33 × 10⁵ CFU g⁻¹ dry soil), total bacteria (182 × 10⁷ vs. 64 × 10⁷ CFU g⁻¹ dry soil), microbial respiration (0.77 mg CO₂ g⁻¹ week⁻¹ vs. 0.45 mg CO₂ g⁻¹ week⁻¹) and fluorescein diacetate (FDA) hydrolysis (4.17 ug fluorescein g⁻¹ h⁻¹ vs. 1.70 ug fluorescein g⁻¹ h⁻¹ in CT. Fungal and bacterial community fingerprints, by terminal restriction fragment length polymorphism (T-RFLP) analysis, of Intergenic spacer regions of rRNA and 16S rRNA genes, respectively, were influenced by the tillage system. Also FAME (fatty acid methyl ester) profiles showed that microbial community structure in DS and CT was clearly different. DS samples contained significantly higher total microbial biomass than the other tillage treatments, but there were no significant differences in fungal biomass or any consistent trend with respect to stress index. Our results showed that microbial communities were more abundant and active in DS than in CT in response to high nutrient content in soil. Indeed, DS systems presented higher soil OM, total N, K and Ca than CT. Electrical conductivity and aggregate stability (AS) were also improved by DS. Soybean grown in high-quality soil was not affected by charcoal rot, however, under CT, disease incidence in soybean was 54%. These differences were correlated to the higher microbial abundance and activity under DS, the biological component being a key factor determining soil capacity to suppress the soilborne pathogen.     

The implications of land preparation, crop establishment method and weed management on rice yield variation in the rice-wheat system in the Indo-Gangetic plains

The implications of adopting alternative seeding methods for rice and wheat establishment were examined at three geographically separate sites in the rice-wheat system of the Indo-Gangetic plains, across northern India. Rice yields in cultivated plots, established by either wet or dry seeding methods, were evaluated in comparison to yields from zero-tillage plots and under conventional transplanting methods. In the same trials, the effects of crop establishment methods in wheat were assessed both on wheat yields and rice yields. Rice crop establishment methods markedly influenced the emerging weed flora and attainable yields were measured in relation to intensity of weed management. Over four years, average rice grain yields in the absence of weed competition were greatest (6.56 t ha⁻¹) under wet seeding (sowing pre-germinated rice seed on puddled soil), and similar to those from transplanted rice (6.17 t ha⁻¹) into puddled soil, and dry seeded rice after dry soil tillage (6.15 t ha⁻¹). Lowest yields were observed from dry seeded rice sown without tillage (5.44 t ha⁻¹). Rice yield losses due to uncontrolled weed growth were least in transplanted rice (12%) but otherwise large (c. 85%) where rice had been sown to dry cultivated fields or to puddled soil, rising to 98% in dry seeded rice sown without soil tillage. Weed competition reduced multiple rice yield components, and weed biomass in wet seeded rice was six-fold greater that in rice transplanted into puddled soil and twice as much again in dry seeded rice sown either after dry tillage or without tillage. Wheat grain yields were significantly higher from crops sown into tilled soil (3.89 t ha⁻¹) than those sown without tillage (3.51 t ha⁻¹), and also were elevated (5% on average) where the soil had been dry cultivated in preparation for the previous rice crops rather than puddled. The method of wheat cultivation did not influence rice yield. Soil infiltration rates in the wheat season were least where the land had been puddled for rice (1.52 mm h⁻¹), and greater where the soil had been dry-tilled (2.63 mm h⁻¹) and greatest after zero-tillage (3.54 mm h⁻¹).These studies demonstrated at research managed sites across a wide geographic area, and on farmers’ fields, that yields of dry seeded rice sown after dry cultivation of soil were broadly comparable with those of transplanted rice, providing weed competition was absent. These results support the proposition that direct seeding of rice could provide an alternative to the conventional practice of transplanting, and help address rising costs and threats to sustainability in the rice-wheat rotation. Further, analysis of patterns of long-term rainfall data indicated that farmers reliant on monsoon rainfall could prepare fields for dry direct seeded rice some 30 days before they could prepare fields for either transplanting or seeding with pre-germinated seed. Dry, direct seeding of rice contributes a valuable component of an adaptive strategy to address monsoonal variability that also may advance the time of wheat establishment and yield. Whilst the results illustrate the robustness, feasibility and significant potential of direct seeded rice, they also highlight the critical nature of effective weed control in successful implementation of direct seeding systems for rice.     

Management of complex weed flora in dry-seeded rice

Dry-seeded rice has been introduced as an alternative to puddled hand-transplanted rice in the north Indian states of Punjab and Haryana. In dry-seeded rice, weed flora tends to be more diverse and weeds emerge in several flushes during the crop growth cycle and substantial yield reductions due to weed competition are quite common. The efficacy and compatibility of tank mixtures of different herbicides for the control of diverse weed flora in dry-seeded rice was evaluated in field experiments during the summer seasons of 2012 and 2013. The tank mixture of fenoxaprop with ethoxysulfuron improved the control of Echinochloa crus-galli and Echinochloa colona by 43–69% as compared to fenoxaprop alone while the tank-mix of azimsulfuron with fenoxaprop was antagonistic and reduced the control of Leptochloa chinensis by 86% as compared to fenoxaprop alone. Addition of azimsulfuron or ethoxysulfuron to bispyribac did not improve the control of grass weeds as compared to bispyribac alone. Weed control with the mixture of bispyribac and fenoxaprop varied over the two years. In 2012, bispyribac and fenoxaprop mixture was antagonistic for the control of Dactyloctenum aegyptium, Acrachne racemose, and L. chinensis but in 2013, there was no apparent antagonism and the addition of bispyribac to fenoxaprop reduced grass weed biomass as compared to fenoxaprop alone. In 2013, there was a strong negative correlation (r = −0.95, P < 0.001) between weed dry matter at 45 days after sowing and rice grain yield. According to the linear regression, rice crop is likely to produce no grain yield when weed dry matter exceeds 400 g m⁻². Over the two seasons, fenoxaprop-ethoxysulfuron tank-mix produced similar grain yields (5.6–6.2 t ha⁻¹) to the weed-free check (5.6–7.1 t ha⁻¹). At the farmer fields, rice grain yield in the plots treated with pendimethalin followed by post-emergence bispyribac or a tank-mix of fenoxaprop + ethoxysulfuron ranged from 6.2 to 7.7 t ha⁻¹ as compared to 5.3–5.6 t ha⁻¹ in the plots treated with pendimethalin alone. The tank mixture of fenoxaprop with bispyribac needs further evaluation as this mixture has the potential to effectively control aerobic and aquatic grasses in dry-seeded rice. Single hand weeding prevented crop yield loss from weeds that escaped herbicide treatments only when it was performed within six weeks of sowing.     

Rates of nitrogen application required to achieve maximum energy efficiency for various crops: results of a long-term experiment

A long-term experiment with four rates of mineral nitrogen (N) application (averaged across all the crops in a crop rotation: 0, 50, 100, 150 kg ha⁻¹ per year) was conducted on a fertile loess-derived soil in central Germany. The objectives of this study were to (i) determine the rates of mineral nitrogen N application required for maximum net energy output (energy output minus energy input), maximum energy output/input ratio, and minimum energy intensity (energy input per unit grain equivalent) for various crops in a realistic crop rotation (potatoes [Solanum tuberosum L.], winter wheat [Triticum aestivum L.], winter barley [Hordeum vulgare L.], sugar beets [Beta vulgaris L.], spring barley [Hordeum vulgare L.]): (ii) identify long-term trends (from 1968 to 2000) in the rates of mineral N application necessary to achieve the most efficient use of energy in the production of winter wheat and (iii) assess the effects of changing the system boundaries and the energy equivalents assigned to selected inputs on the energy balance by means of a sensitivity analysis. In the last two crop rotations (1989–1993 and 1994–1999), the amount of N fertilizer required to maximize net energy output of the main products (cereal grains, beet roots) increased in the order sugar beets–winter wheat–winter barley. At optimum N fertilization, the net energy output increased in the order winter barley–winter wheat–sugar beets. Averaged across the two rotations, the N fertilizer demand for a maximum output/input ratio and minimum energy intensity increased in the order sugar beets–winter wheat–winter barley. There was no clear-cut time trend in the rate of N application required to maximize grain yield and net energy output of wheat; maximum grain yield, maximum net energy output, and output/input ratio increased significantly with time, whereas the minimum energy intensity decreased over the experimental period. For all the crops, the rate of N application required for the maximum net energy output was much higher than that required for the maximum output/input ratio and minimum energy intensity.