Evaluation of two types of superabsorbent polymer on soil water and some soil microbial properties

Paddy and Water Environment - In this study, two types of superabsorbent polymers, Luquasorb (Luqua) and Stockosorb (Stock), at 180 kg ha−1 were applied by scattering and...     

Interpreting redox potential (Eh) and diffusive fluxes of phosphorus (P) and nitrate (NO3−) from commercial rice grown on histosols

Paddy and Water Environment - In South Florida, approximately 11,000 ha of rice is grown every summer on highly organic histosols. With no added fertilizer inputs of phosphorus (P) or...     

Analysis of the nitrogen pollution load potential from farmland in the Tedori River Alluvial Fan Areas in Japan

A nitrogen balance study was carried out by setting up a test paddy in order to estimate the nitrogen pollution load potential (NPLP) from farmland in the Tedori River Alluvial Fan Areas and the load from the entire area under consideration was estimated using the cropping record and fertilizer application rate (FAR). The total NPLP was estimated to be 261 tons/year and the load from the paddy 79 tons/year for 5,704 ha, which would translate to an intensity of 14 kg/ha, while the load from the vegetable field was estimated to be 118 tons/year for 215 ha, which would equate to an intensity of 549 kg/ha. The pollution loads for the vegetables were significantly greater than those for the rice. The load for the barley was 57 tons/year for 261 ha (216 kg/ha) and that for the orchards was 23 tons/year for 64 ha (359 kg/ha). The estimation of soybean load was a negative 15 tons/year for 717 ha (−21 kg/ha), which meant that the nitrogen in the yield was greater than the FAR. The results also confirmed the yield absorption ratio in relation to the FAR. The load from the paddy for the entire area was also estimated using the percolation rate and the water quality load underneath the farmland was estimated to be 89 tons/year.     

Establishment techniques affect productivity,nutritive value and atmospheric N2 fixation of two sunn hemp cultivars

Nitrogen fertilization is a common practice for sustaining forage production in forage systems in southeastern United States. Warm-season annual legumes may be an alternative forage to warm-season perennial grasses that do not require N fertilization. Sunn hemp (Crotalaria juncea L.) is a fast-growing, warm-season annual legume native to India and Pakistan. The objective of this 2-year study was to assess the herbage accumulation (HA), atmospheric N₂ fixation (ANF) and nutritive value of sunn hemp. Treatments were the factorial arrangement of two sunn hemp cultivars (“Crescent Sun” and “Blue Leaf”), three seeding rates (17, 28 and 39 kg seed/ha) and seed inoculation (inoculated or non-inoculated seeds), distributed in a randomized complete block design with four replicates. Crescent sun had greater HA (3,218 vs. 1764 kg DM/ha) and ANF (41 vs. 25 kg N/ha). Blue leaf had greater crude protein (CP) (188 vs. 176 g/kg) and in vitro digestible organic matter (IVDOM) concentrations (564 vs. 531 g/kg) than crescent sun. Non-inoculated seed had greater CP than inoculated seed, 188 and 177 g/kg, respectively, and inoculation did not affect HA. Intermediate seeding rate (28 kg/ha) decreased HA (2002 kg DM/ha), while HA from high and low seeding rates (17 and 39 kg/ha, respectively) did not differ (2,863 and 2,615 kg DM/ha respectively). Planting non-inoculated crescent sun at 17 kg/ha seeding rate is a feasible management practice to produce sunn hemp in subtropical regions; however, inoculation should always be recommended for proper establishment.     

Evaluation of N and P mass balance in paddy rice culture along Kahokugata Lake, Japan, to assess potential lake pollution

Kahokugata Lake, a closed lake, has been subject to eutrophication. This research was conducted to clarify the actual phenomena and evaluation of the discharges of N and P from paddy test fields in the lowlands into Kahokugata Lake. A comprehensive mass balance of N and P was obtained from 4 years of study. About N, the mean value of harvested unhulled rice (79.9 kg/ha) was greater than mean controlled release fertilizer inputs (56.7 kg/ha). Other inputs and outputs include N in atmospheric acid deposition (21.4 kg/ha) and N fixation–denitrification (9.2 kg/ha). The rice straw recycled after harvest was balanced by straw produced in the succeeding year. The runoff and percolation losses discharged into the lake was 11.3 kg/ha, (8.6% of total inputs). Since the rice harvested was consumed domestically, which taking out from the farmland and, therefore, nitrogen pollutant into the lake was becoming small, paddy rice at this site is considered an “anti-polluting, purifying or cleansing” crop. The P content in harvested rice (39.4 kg/ha) was balanced by fertilizer inputs (36.4 kg/ha). Previous studies examining inflow–outflow relationships without considering a comprehensive mass balance may lead to erroneous conclusions. Our findings indicate paddy rice in lowlands could be an environmentally friendly crop and can play an important role in reducing pollution of lakes, and therefore should be considered in land use planning.     

Response of weeds and soil microorganisms to imazaquin and pendimethalin in cowpea and soybean

Herbicides applied to combat weeds and increase crop yields may also have undesired effects on beneficial soil microorganisms. Field studies were conducted in 2005 and 2006 in Zaria, Nigeria, to evaluate the response of weeds and soil microorganisms to imazaquin applied at 0.05, 0.10, 0.20 and 0.40 kg a.i./ha and pendimethalin applied at 1.0, 2.0, 4.0, and 8.0 kg a.i./ha in cowpea and soybean. Hoe-weeded and unweeded (no herbicide) plots were controls. Both herbicides significantly reduced weed biomass in both crops, when compared to the unweeded control, which had the highest weed biomass at all sampling dates. Treatments with 0.40 kg a.i./ha of imazaquin, 2.0 and 4.0 kg a.i./ha of pendimethalin, and the hoe-weeded control, had the highest cowpea grain yield. The unweeded control had the lowest grain yield which was comparable to that in all other herbicide treatments. All treatments except 4.0 and 8.0 kg a.i./ha of pendimethalin had higher soybean grain yield than the unweeded control. Soybean yield was lowest in the unweeded control, and treatments that received 4.0 and 8.0 kg a.i./ha of pendimethalin. All rates of imazaquin gave similar soybean grain yields that were 29–41% higher than that from pendimethalin. The hoe-weeded control had the highest yield, which was 79% more than that in the unweeded control. Higher rates of imazaquin and pendimethalin reduced nodulation, nitrogen fixation, and vesicular arbuscular mycorrhizal (VAM) fungi colonisation in both crops. VAM fungi species diversity and species richness in cowpea rhizosphere soil and species diversity in soybean rhizosphere soil were reduced relative to the controls due to application of both herbicides with the rates of 0.10, 0.20, and 0.40 kg a.i./ha of imazaquin and 8.0 kg a.i./ha of pendimethalin being significantly effective.     

Rice yield variability in Punjab: an overview of five decades

Rice is a major kharif cereal crop cultivated in Punjab. Over the past five decades the rice yield has increased from as low as 1800 kg/ha during 1970–4815 kg/ha during 2017, i.e., an overall increase of 167.5% or increase @ 3.5% per year. One of the major reasons for this increase has been the introduction of improved and high-yielding varieties (PR 106, PR 111, PR 116, PR 118, PR 121, PR 122, PR 126, PR 127, etc.). Other important factors are the improved crop production and protection practices coupled with mechanization of farm operations. However, weather factors have always been a major bottleneck shattering the steady plateau of high rice yield (3443 kg/ha during 1979, 3231 kg/ha during 1995, 3273 kg/ha during 1998, 4257 kg/ha during 2011 and recent low yield of 4387 kg/ha during 2018). The actual weather data of the recent two decades at Ludhiana (2000–2018) were correlated with the historical rice yield. The results revealed a combination of high temperature coupled with clear sunny (total seasonal sunshine?~?900–1000 h) and dry (low relative humidity) days is conducive for proper growth, development and yield of rice in Punjab. The rainfall and rainy days were found to be negatively correlated with yield since heavy rainfall events and more number of rainy days create a humid weather which is conducive for insect-pest and disease incidence in rice and also reduces sunshine duration. Hence, a combination of ample sunshine hours and well-distributed rainfall during the vegetative stage of rice leads to high productivity of cultivars grown under optimized crop management techniques.

     

Field evaluation of Lymantria obfuscata multiple nucleopolyhedrovirus for the management of Indian gypsy moth in Jammu & Kashmir,India

The Indian gypsy moth (Lymantria obfuscata) is a pest of national significance, which attacks a wide range of forest and fruit crops in India. The outbreaks of this pest over the past few years spurred interest towards sustainable biointensive approaches for quality fruit production of apple and walnut for agricultural export in Jammu & Kashmir (J & K). The exploratory survey's were conducted for the isolation of native strains of L. obfuscata multiple nucleopolyhedrovirus (LyobMNPV) and field evaluation was conducted to determine the most promising strain as a potential biological control agent of this pest. The virus was recovered from different locations of J&K with its natural incidence varying from 0.77 to 7.43 percent. This is the first report from the Indian sub-continent and worldwide of the occurrence of NPVs in natural larval populations of L. obfuscata. The in vivo mass production was optimised by inoculating per os late 3rd instar L. obfuscata larvae with an inoculum dose of 1.44 × 10⁵ OBs/larva and followed by a 10 day incubation period. To prevent the disintegration of larval cuticle and microbial contamination, moribund larvae were harvested with an average yield of 1.42 × 10⁸ OBs/larva. The field application of LyobMNPV against the host populations on apple and willow with the pre-standardised dosage of 2.5 × 10¹² OBs/ha reduced the larval population density by 25–63%. In the year following application, the larval population density in the treated blocks was 19–28% lower as compared to controls on both apple and willow. This suggests that the virus has considerable potential as a biocontrol agent and the timely application with LyobMNPV on non-fruit trees such as willow which are the preferred hosts for egg laying may help to initiate viral epizootics to keep population outbreaks under check.     

Application strategies for an anthraquinone-based repellent to protect oilseed sunflower crops from pest blackbirds

Non-lethal alternatives are needed to manage the damage caused by wild birds to oilseed sunflower crops (Helianthus annuus Linnaeus). We evaluated field residues and experimental applications of an anthraquinone-based repellent (active ingredient 50% 9,10-anthraquinone) to minimize red-winged blackbird (Agelaius phoeniceus Linnaeus) depredation of oilseed sunflower. Chemical residues from experimental applications of the anthraquinone-based repellent (4.7 l/ha and 9.4 l/ha; low, high) in a ripening oilseed sunflower field were 481 ppm and 978 ppm anthraquinone at the beginning of blackbird damage, and 385 ppm and 952 ppm anthraquinone at the end of blackbird damage, respectively. Prior to harvest, we observed 402 ppm and 462 ppm anthraquinone in the oil, and 27 ppm and 165 ppm anthraquinone in the pomace from crushed sunflower achenes previously sprayed with the low and high applications, respectively. For the purpose of developing application strategies useful for avian repellents, we subsequently investigated blackbird feeding response to oilseed sunflower treated with the anthraquinone-based repellent and either a registered insecticide or a registered fungicide popularly used for ripening sunflower. We observed a positive concentration–response relationship among blackbirds exposed to anthraquinone and the insecticide (a.i. 8.4% esfenvalerate), or anthraquinone and the fungicide (a.i. 23.6% pyraclostrobin). Blackbirds reliably discriminated between untreated sunflower and that treated with 1810 ppm anthraquinone and 0.1% of the insecticide or 1700 ppm anthraquinone and 0.14% of the fungicide during our preference experiments. Given that ripening achenes are inverted from conventional pesticide applications throughout much of the period associated with blackbird depredation, we also evaluated blackbird repellency of the anthraquinone-based repellent applied to involucral bracts (i.e., the back of sunflower heads) of oilseed sunflower. Blackbirds did not discriminate between untreated involucral bracts and those treated with foliar applications comparable to 4.7 l/ha or 9.4 l/ha; blackbirds consumed more achenes from untreated sunflower heads than from those treated with 18.7 l/ha of the anthraquinone-based repellent. Supplemental repellent efficacy studies should investigate blackbird response to anthraquinone-based repellents (e.g., ≥4.7 l/ha) within 10–100 ha sunflower fields and include independent field replicates with predicted bird damage, repellent application strategies developed for protection of ripening crops, pre- and at-harvest repellent residues, and bird damage and crop yield measurements.     

Improved guayule lines outperform old lines in south-east Queensland

Guayule (Parthenium argentatum Gray) is a source of high quality rubber and low-allergenic latex as well as resin for use as a wood preservative. Demand for high value latex products has increased with the advent of deadly diseases such as AIDS. The objective of this study was to evaluate the performance of six improved guayule lines (AZ-1 to AZ-6) in south-east Queensland: released jointly by the Agricultural Research Service (ARS) of the United States Department of Agriculture (USDA) and The University of Arizona. Trials were conducted at two sites, Chinchilla and Gatton. Overall performance of improved lines for plant growth and yield of dry matter, rubber and resin was better at both Gatton and Chinchilla than the standard check lines (N 565 and 11591). AZ-1 and AZ-2 maintained the best combinations of desirable traits, including plant uniformity, early vigorous growth, increased dry matter, and increased rubber and resin yields. Of these two, AZ-2 had more uniform plant growth and has commercial potential for Queensland production areas. In the summer harvest at Gatton, 32-month-old AZ-1 and AZ-2 produced rubber yields of 789 kg/ha and 771 kg/ha, respectively, while controls, N 565 and 11591 produced 675 kg/ha and 618 kg/ha, respectively. At Chinchilla, at 33 months, spring harvested AZ-1 and AZ-2 produced rubber yields of 717 kg/ha and 787 kg/ha; these yields were significantly higher than N 565 and 11591 which produced 385 kg/ha and 380 kg/ha, respectively. Thus, rubber yields of AZ-1 and AZ-2 were consistently high across sites. AZ-1 and AZ-2 produced resin yields of 1158 kg/ha and 1115 kg/ha at Gatton and 1318 kg/ha and 1476 kg/ha at Chinchilla. This compared with a mean of 612 kg/ha and 352 kg/ha for the standard check lines at Gatton and Chinchilla. Thus resin yields of AZ-1 and AZ-2 were consistently high across sites. Rubber content appeared to be influenced by time of harvest although this effect is compounded with plant age. At Gatton, in spring, 17-month-old plants produced a mean rubber content of 7.7% (all lines), while, in summer, when the plants were 32-month-olds, rubber content dropped to 6.4%. At Chinchilla, 33-month-old plants harvested in spring produced a mean rubber content of 7.4%, similar to the spring value at Gatton. By contrast, resin content appeared to be little affected by season.     

Efficacy of a new glyphosate formulation for weed control in maize in southwest Nigeria

A field trial in 2003 and 2004 assessed the efficacy of a new formulation of glyphosate, Touchdown Forte HiTech (glyphosate-TF) and two older versions, Roundup (glyphosate-RP) and Touchdown (glyphosate-TD) for weed control in Nigeria. Treatments were glyphosate-TF at 0.25–1.25 kg a.i./ha, glyphosate-RP at 1.8 kg a.i./ha, and glyphosate-TD at 1.0 kg a.i./ha. Weeded and unweeded treatments were controls. Visual evaluations of weed control at 4 and 8 weeks after treatment (WAT) in both years indicated that glyphosate-TF at all doses gave moderate to complete control of all major weeds (50–100%). At 4 WAT, control of Ageratum conyzoides L., Commelina benghalensis L., Ipomoea involucrata P. Beauv., Brachiaria comota [Hochst ex A. Rich] stapf, and Acalypha ciliata Forssk was at a level similar to that in the weeded control. In 2003, all herbicide formulations and the weeded control reduced Imperata cylindrica (L.) Beauv. shoot dry biomass to the same level at 8 WAT (91–100%) and at maize harvest (83–88%). In 2004, 0.50–1.25 kg a.i./ha of glyphosate-TF and 1.8 kg a.i./ha of glyphosate-RP gave 95% reduction at 8 WAT and 97% at harvest, similar to the weeded control. Maize grain yield in the weeded control and herbicide treatments was 2.8 times higher than that in the unweeded control in both years. These results indicate that glyphosate-TF is effective for weed control in maize at herbicide doses lower than the older formulations.     

Integrating the effects of climate and plant available soil water holding capacity on wheat yield

In the Mediterranean farming systems of the Western Australian wheatbelt, crop yields are influenced primarily by the amount and distribution of rainfall and the soil's capacity to hold moisture. The wheatbelt's growing season rainfall varies in the range of 200–400 mm (average) and the plant available water holding capacity (PAWC) of soils is generally in the 40–140 mm range. The grain yield of wheat is sensitive to this combination of small rainfall and small storage capacity.In this study, we explore the relationship between yield and PAWC using a combination of simulation modelling and analysis of field data. Crop yields and soil properties were monitored in detail at 17 locations (PAWCs 43–131 mm) across six seasons (1997–2005). Crop yields were also simulated using the APSIM crop simulator (RMSE = 311 kg/ha) to evaluate the long-term relationship between crop yield and plant available water capacity using 106 years of historical climate data.The relationship between crop yield and PAWC varied with season, and two important factors emerged: (1) for PAWC < 65 mm, there was a linear relationship with crop yields that ranged from 17 kg/ha/mm to 58 kg/ha/mm of PAWC across seasons; (2) for PAWC 65–131 mm the crop yield response to PAWC ranged from 11.5 kg/ha/mm in 45% of seasons to no response.The impact of PAWC on crop yield was reduced in seasons with late rainfall, and magnified in seasons with reduced rainfall late in the growing season. Six distinct season types with different yield–PAWC relationships are identified and season-specific management strategies that exploit within-field variation in PAWC are developed to manage the spatial variation of PAWC in a field.     

Forage quality of species-rich mountain grasslands subjected to zero,PK and NPK mineral fertilization for decades

To maintain species-rich swards from which forage of a high nutritional quality can be produced, it is essential to adapt grassland fertilization strategies. In this study, we investigated how different long-term mineral fertilization treatments affect dry-matter (DM) yield, plant species composition, and nutrient and mineral concentrations of forage from mountain grasslands. During 2 years, forage was sampled from three different long-term fertilization experiments located at 930 (L), 1,190 (M) and 1,340 (H) m a.s.l. at different sites in Switzerland. At each site, three mineral fertilization treatments (0, PK and NPK) had been maintained for three to six decades, with two (L and M) or three harvests (H) per year. Yield, the botanical composition and concentrations of net energy, utilizable crude protein and different phenolic fractions were determined. Nutrient and mineral concentrations were also determined. For all three sites (L, M and H), unfertilized swards had lower annual DM yields (3.39, 5.17 and 2.73 t/ha) compared to PK (6.33, 7.17 and 4.44 t/ha) and NPK fertilized swards (7.69, 7.22 and 7.44 t/ha), respectively. Long-term fertilization had little effect on the gross nutrient and phenolic composition, but forage P and K concentration increased. The decades-long fertilization of either PK or NPK of up to 85 kg N, 80 kg P₂O₅ and 240 kg K₂O/ha reduced plant species richness only at site H. Fertilization of PK may allow to simultaneously increase forage productivity and maintain forage quality in mountain grasslands.     

Effects of harvesting perennial ryegrass at different levels of herbage mass on voluntary intake and in vivo digestibility in sheep

The production performance of herbage‐fed animals is affected by herbage voluntary dry‐matter intake (VDMI) and organic matter digestibility. The objective of this study was to determine the effect of herbage mass (HM) on in vivo herbage voluntary intake and digestibility in sheep. The three HM treatments were as follows: 1,100 kg dry matter (DM)/ha (low, L), 2,300 kg DM/ha (medium, M) and 3,700 kg DM/ha (high, H). The study was a Latin square design, repeated on two occasions in 2012: 24 May to 20 July (summer) and 21 July to 5 October (autumn). Twelve Texel wether sheep (individually housed) were offered fresh cut perennial ryegrass herbage for ad libitum consumption. Using the total faecal collection method, the digestibility of dry matter, organic matter, neutral detergent fibre and acid detergent fibre was determined. In summer, L had a similar VDMI to M and both had a higher VDMI than H. In autumn, L had a higher VDMI than both M and H. For dry‐matter digestibility and organic matter digestibility, there was no significant difference between L and M, which were both higher than H. For every 1% increase in neutral detergent fibre digestibility, VDMI increased by 0.03 kg. In the zero‐grazing scenario examined, offering low (1,100 kg DM/ha) HM swards enabled animals to achieve high intakes of highly digestible herbage, which should ensure high animal production performance.     

Reduction of nitrogen,phosphorus, and suspended solids effluent loads from paddy fields by transplanting into retained ponding water using a GNSS-controlled rice transplanter

Paddy and Water Environment - We measured nutrient inflows and outflows on reclaimed land (157&nbsp;km2, including 100&nbsp;km2 of paddy fields) in Lake Hachiro. The net effluent loads...     

Methane production and nitrogen mineralization in paddy soil treated with sludge from anaerobic digestion enhanced by hyperthermophilic pretreatment

Paddy and Water Environment - Hyperthermophilic pretreatment (80&nbsp;°C, 24&nbsp;h) is a technology that promotes methane yield in the anaerobic digestion of sewage sludge. However,...     

Assessment of rice hydraulic loading impacts on groundwater and salinity levels

This paper describes the impact of rice hydraulic loading (percentage area under rice crop) on groundwater levels and salinity in the Murrumbidgee irrigation area (MIA), Australia using a MODFLOW-based modelling approach. The model simulations show that the groundwater levels will be in equilibrium after a fall of approximately 1 m under most of the areas, however, the groundwater salinity levels will rise by more than 1,000 μs/cm in most parts of irrigation area. If the rice growing area is reduced by 50 and 75%, there can be a net decline in groundwater levels during the first 2 years and then a new quasi-equilibrium will be established. To downscale these results at the farm level, SWAGMAN Farm model in conjunction with groundwater outflow rates obtained from a three-dimensional MODFLOW model was applied for determining net recharge rates under rice for different areas within the MIA. The highest net recharge during 2005–2006 season was 0.84 ML/ha (84 mm) in parts of the irrigation system, whereas the average net recharge due to rice hydraulic loading for the whole MIA during 2005–2006 season was estimated as 0.34 ML/ha (34 mm).     

Animal and forage responses on lucerne (Medicago sativa L.) pastures under contrasting grazing managements in a temperate climate

This study determined the impact of a change in grazing system on beef production from lucerne pastures in Argentina. One system (T500) used the traditional recommendation to commence grazing in spring when lucerne was near to 10% flowering. The grazing interval was ~ 500 growing degree-days (GDD; above a base temperature for growth of 5°C) from mid-spring to mid-autumn. In contrast, the T350 system commenced grazing 11–15 days earlier at ~ 1,000 kg DM/ha and the grazing interval was ~ 350 GDD from mid-spring to mid-summer, and from mid-summer to mid-autumn, it was ~ 500 GDD. Total live-weight production was ~ 30% or 185 and 115 kg/ha higher in T350 than T500 in Years 1 and 2 respectively. This was due to a higher live-weight production per head and a higher stocking rate, because T350 produced 1,600 kg DM ha⁻¹ year⁻¹ more forage. Plant population (~70 plants/m²) and perennial biomass (root plus crown) at the end of the second year did not differ between treatments. This suggests that lucerne persistence was not affected by the more intensive spring grazing of T350, because an adequate period of autumn recovery was allowed. This work quantified the live-weight gain (+30%, +150 kg/ha) when the grazing management of lucerne during the spring–summer period was based on crop growth status (i.e. standing biomass, canopy height) rather than on crop phenology.     

Impact of increasing shade levels on the dry-matter yield and botanical composition of multispecies forage stands

Botanical diversity has been linked to increased biomass production of grasslands, but these relationships have not been explored as extensively in silvopasture systems where shade impacts on forage mass are variable due to the unique structure and environment of each system. The objective of this study was to evaluate the impact of multiple artificial shade levels on the DM yield and botanical composition of three cool-season forage mixtures near Blackstone, Virginia, USA. Mixtures were as follows: simple = tall fescue [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.] and white clover (Trifulium repens L.); intermediate = simple + orchardgrass (Dactylis glomerate L.) and red clover (Trifolium pretense L.); and complex = intermediate + Kentucky bluegrass (Poa pratensis L.), birdsfoot trefoil (Lotus corniculatus L.) and alfalfa (Medicago sativa L.). Slatted structures created conditions of 30%, 50% and 70% shade relative to a full sun control. Forages were harvested mechanically (no grazers present). Annual yield (DM kg/ha) did not differ among mixtures. As compared to full sun, annual yield was no different at 30% shade, but was reduced by 22 and 36% at 50 and 70% shade respectively. In contrast to other species in the mixtures, orchardgrass increased in proportion when grown beneath all shade levels and is recommended for silvopasture use. Orchardgrass is not particularly well-adapted to the transition zone between the northern temperate and southern subtropical United States; therefore, these results indicate that silvopastures may be an effective way to integrate marginally adapted, shade-tolerant cool-season forages into transition zone grazing systems.     

Tolerance of selected weed species to broadcast flaming at different growth stages

Organic producers rank weeds as the most important pests that limit their crop production. In order to optimize the use of propane flaming as a weed control tool, the objective of this study was to test tolerance of selected weed species to broadcast flaming performed at different growth stages. Six annual species, including one grass [barnyardgrass (Echinochloa crus-galli)] and five broadleaves [field bindweed (Convolvulus arvensis), kochia (Kochia scoparia), ivyleaf morning glory (Ipomoea hederacea), velvetleaf (Abutilon theophrasti) and Venice mallow (Hibiscus trionum)] were flamed at three growth stages with six doses of propane. The propane doses applied were 0, 12, 31, 50, 68 and 87 kg/ha. Flaming treatments were applied utilizing a custom built flamer mounted on a four-wheeler moving at a constant speed of 6.4 km/h. Species response to propane were described by log-logistic models based on visual injury ratings and dry matter (DM) for each weed species. Overall response to flaming varied among species, growth stage and propane dose. Broadleaf weeds were more susceptible to flaming than the grass regardless of the growth stage. A dose of 76 kg/ha of propane was needed to obtain 90% DM reduction for 7-leaf (L) barnyardgrass compared to much lower doses of 40, 49, 55, 56 and 51 kg/ha propane for 8-L bindweed, 6-L kochia, 10-L morning glory, 7-L velvetleaf and 5-L Venice mallow, respectively. Moreover, the tolerance of both grassy and broadleaf weed species to broadcast flaming increased with increase in plant size. A 90% DM reduction in velvetleaf was obtained with 42, 56 and 102 kg/ha of propane for 5-L, 7-L and 16-L stages, respectively. The tested broadleaf weed species were effectively controlled (90% DM reduction) with propane dose of 30–60 kg/ha when flamed at early growth stages (3-L to 14-L), while the same dose of propane provided only 80% DM reduction in barnyardgrass when flamed at vegetative stages (4-L to 7-L). It was not possible to obtain 90% DM reduction in barnyardgrass when flamed at flowering stage with the propane doses tested in this experiment.