Days After Crop Emergence Research Articles

Classification of Soybean Genotypes as to Calcium, Magnesium, and Sulfur Content Using Machine Learning Models and UAV–Multispectral Sensor

Making plant breeding programs less expensive, fast, practical, and accurate, especially for soybeans, promotes the selection of new soybean genotypes and contributes to the emergence of new varieties that are more efficient in absorbing and metabolizing nutrients. Using spectral information from soybean genotypes combined with nutritional information on secondary macronutrients can help genetic improvement programs select populations that are efficient in absorbing and metabolizing these nutrients. In addition, using machine learning algorithms to process this information makes the acquisition of superior genotypes more accurate. Therefore, the objective of the work was to verify the classification performance of soybean genotypes regarding secondary macronutrients by ML algorithms and different inputs. The experiment was conducted in the experimental area of the Federal University of Mato Grosso do Sul, municipality of Chapadão do Sul, Brazil. Soybean was sown in the 2019/20 crop season, with the planting of 103 F2 soybean populations. The experimental design used was randomized blocks, with two replications. At 60 days after crop emergence (DAE), spectral images were collected with a Sensifly eBee RTK fixed-wing remotely piloted aircraft (RPA), with autonomous takeoff control, flight plan, and landing. At the reproductive stage (R1), three leaves were collected per plant to determine the macronutrients calcium (Ca), magnesium (Mg), and sulfur (S) levels. The data obtained from the spectral information and the nutritional values of the genotypes in relation to Ca, Mg, and S were subjected to a Pearson correlation analysis; a PC analysis was carried out with a k-means algorithm to divide the genotypes into clusters. The clusters were taken as output variables, while the spectral data were used as input variables for the classification models in the machine learning analyses. The configurations tested in the models were spectral bands (SBs), vegetation indices (VIs), and a combination of both. The combination of machine learning algorithms with spectral data can provide important biological information about soybean plants. The classification of soybean genotypes according to calcium, magnesium, and sulfur content can maximize time, effort, and labor in field evaluations in genetic improvement programs. Therefore, the use of spectral bands as input data in random forest algorithms makes the process of classifying soybean genotypes in terms of secondary macronutrients efficient and important for researchers in the field.

Effect of weed control methods on weed biomass and grain yield of maize (Zea mays L.) under rainfed condition in Basketo Special District, Southern Ethiopia

Maize (Zea mays L.) is a major crop grown in Basketo Special district by smallholder farmers. However, its production and productivity is challenged by many factors of which weeds are the key factor that reduce the productivity of maize in the district. Therefore, field experiment was conducted at Basketo Special district during 2017 main cropping season under rainfed condition to evaluate weed control methods on weed biomass and grain yield of maize. The experiment consisted of six treatments namely; once hand hoeing at 20 days after crop emergence (DACE), twice hand hoeing at 20 and 40 DACE, Primagram Gold 660SC + once hand hoeing at 40 DACE, Primagram Gold 660SC + twice hand hoeing at 40 and 60 DACE, farmer practice and weedy check. It was laid-out in Randomized Complete Block Design with four replications. Weed and crop parameters were collected. The highest maize grain yield and the lowest weed biomass were obtained from Primagram Gold 660SC + twice hand hoeing without significant difference with Primagram Gold 660SC + once hand hoeing whereas the lowest grain yield and highest weed biomass were found in weedy check. Moreover, the results revealed that integration of Primagram Gold 660SC with once (at 40 DACE) and twice (at 40 and 60 DACE) hand hoeing significantly reduced weed density and biomass and gave better maize grain yield and maximize net benefit. Therefore, these two treatments could be recommended to improve maize productivity and net income of the farmers in the study area.

Soybean yield loss from delayed postemergence herbicide application based on weed height, days after emergence, accumulated crop heat units, and soybean growth stage

AbstractLimited information exists on the critical time of weed removal (CTWR) with the currently used soybean cultivars in Ontario. A study consisting of eight field experiments was conducted from 2017 to 2019 in Ontario, Canada, to determine the impact of delayed postemergence (POST) herbicide application on soybean yield based on average weed height at application, days after crop emergence (DAE), accumulated crop heat units (CHU) from the date of planting, and soybean growth stage. The regression model estimated the weed size at herbicide application that led to 1%, 2.5%, and 5% yield loss in soybean was 9, 14, and 20 cm under low weed density (averaging 73 to 134 plants m−2) and 3, 4, and 6 cm under high weed density (143 to 153 plants m−2) conditions, respectively. The estimated DAE at herbicide application time that led to 2.5%, 5%, 10%, and 25% yield loss in soybean was 24, 30, 37, and 53 DAE under low weed density and 8, 10, 14, and 23 DAE under high weed density, respectively. The predicted crop stage at herbicide application that resulted in 2.5%, 5%, 10%, and 25% yield loss in soybean was V4, V5, R2, and R5 under low weed density and VE, VC, V1, and V4 under high weed density, respectively. This study concludes that soybean yield loss is influenced by the weed density (low vs/high) and the time of the first POST herbicide application. When the first POST herbicide application was delayed until soybean was at the V2 stage the monetary loss was Can$20.46 and Can$221.20 ha−1 in low and high weed-density environments, respectively.

Determination of Critical Weed Competition Period in Chamomile (Matricaria chamomilla L.) Production at Wondo Genet, Southern Ethiopia

The study was carried out at Wondo Genet to determine the critical weed competition period for growth, yield, and yield components of the chamomile plant. The weed competition duration had a significant influence on plant height, the number of primary branches/plants, fresh stem yield/plant, fresh leaves yield/plant, fresh and dry flower/plant, fresh and dry flower yield/ha, essential oil content (v/w) and yield kg/ha. The highest fresh and dried flower yield (3780.10 kg/ha) and (798.32 kg/ha) was recorded from weed-free check followed by weed-free for 60 DACE (Days After Crop Emergence) (3652.10 kg/ha) and (789.43 kg/ha), respectively. The maximum essential oil content and yield were recorded from the weed-free check (0.79v/w) and (6.25 kg/ha) whereas the minimum was in the weedy-check (0.10 v/w) and (0.15kg/ha), respectively. The yield losses of chamomile were estimated based on the fresh and dry flower and essential oil yield per hectare. Thus, the highest fresh and dry flower yield losses were recorded from the weedy-check (83.58%) and (81.05%) while the lowest was from weed-free check (0.00%), respectively. The highest essential oil yield loss was also recorded from the weedy for 60DACE (97.92%) followed by weedy-check (97.60%). To determine the beginning and the end of the critical period of crop-weed competition 5 and 0% acceptable yield loss levels were used. Therefore, to reduce the yield losses of chamomile by more than 10% and higher economic return, plants must be kept weed-free within 40 to 60DACE to reduce the risk of economic yield losses as it is the critical period of weed-crop competition in chamomile plants.

Crop Establishment and Weed Control Options for Sustaining Dry Direct Seeded Rice Production in Eastern India

Dry direct seeded rice (DSR) has emerged as an economically viable alternative to puddled transplanted rice to address emerging constraints of labor and water scarcity and the rising cost of cultivation. However, wide adoption of DSR is seriously constrained by weed management trade-off. Therefore, the availability of effective weed control options is critical for the success and wide-scale adoption of DSR. A field study was conducted at ICAR-National Rice Research Institute, Cuttack, India, in the dry seasons of 2015 and 2016 to evaluate the performance of three crop establishment methods and five weed control practices on weed management, productivity, profitability and energetics of dry DSR. The results demonstrated that weed density and weed dry weight was lower in drill seeding than broadcast seeding by 26–36% and manual line-seeding by 16–24%, respectively, at 30 and 60 days after crop emergence (DAE). Among herbicides, post-emergence application (17 DAE) of azimsulfuron was most effective in controlling weeds compared to early post application of bispyribac-sodium and bensulfuron-methyl+pretilachlor. Weed competition in the weedy check treatment resulted 58% reduction in rice yield. Among establishment methods, drill-seeding was most profitable with US $ 685 ha−1 higher net income than broadcast seeding primarily due to higher yield. Among weed control treatments, azimsulfuron was most profitable resulting in US $ 160 and 736 ha−1 higher net income than weed free and weedy check, respectively. The specific energy was lowest for drill seeding among establishment method and azimsulfuron among weed control practices, suggesting lowest energy consumed in producing per unit of grain yield.

Response of chickpea to foliar supply of Hoagland’s solution under rain-fed condition

Under rain-fed conditions, foliar application of nutrients is an efficient tool to eliminate the adverse effects of nutrients shortage and helpful to catch the maximum yield of any crop. Field experiments were executed to evaluate the effect of foliar spray of different strengths and application times of Hoagland’s solution on growth and yield characteristics of chickpea (Cicer arietinum L.) under rain-fed conditions. The treatments consisted of distilled water (control), 25, 50, and 75% strength of Hoagland’s solution sprayed at 7, 14, and 21 days after crop emergence (DACE) on two chickpea cultivars C-44 and CM-72. In terms of growth and yield, CM-72 showed superiority over C-44. The 75% strength of Hoagland’s solution showed an improvement of 32.9, 37.9, 35.3, 13.5, and 35% in dry weight, plant height, 100- seed weight, seed yield, and biological yield, respectively when sprayed at 21 DACE than distilled water. However, the lower strength (25%) of Hoagland’s solution produced similar results to distilled water. It is recommended that under rain-fed conditions chickpea cultivar CM-72 should be cultivated with a foliar supply of 75% strength of Hoagland’s solution at 21 DACE to obtain the maximum growth and yield.

Evaluation of the potential of jack bean [Canavalia ensiformis (L.) DC.] and velvet bean [Mucuna pruriens (L.) DC.] aqueous extracts as post-emergence bio-herbicides for weed control in maize (Zea mays L.)

The objective of the study was to evaluate the effect of jack bean and velvet bean aqueous extracts when applied post-emergence alone or in combination with half dosage rates of atrazine on goosegrass, beggarticks, and maize. Three potted experiments with fifteen treatments were laid out in a completely randomized design replicated four times and repeated once. The bio-herbicidal treatments were applied to maize at two weeks after crop emergence and on the weeds at the 3-4 leaf stage. Results showed that maize height increased significantly (p<0.05) across all treatments from 24 to 34 days after crop emergence (DACE). Maize chlorophyll content significantly (p<0.05) increased from 24 to 34 DACE in all the treatments. In contrast, dry weight, height, and chlorophyll content of goosegrass were significantly (p<0.05) reduced by all treatments. The height of beggarticks was not significantly (p>0.05) affected while chlorophyll content and dry weight were significantly (p<0.05) reduced by all treatments. All the treatments caused complete weed control at 6 and 10 DAS in beggarticks and goosegrass, respectively. It was concluded that velvet bean and jack bean aqueous extracts are phytotoxic to weeds of divergent morphology.

Critical period for weed control in sesame production

Planning effective weed control in cropping systems requires exact appraisal of the weed intensity and duration of their competition with the crops. This 2‐year study was carried out in order to determine the critical weed control period in sesame fields. Related and relative crop yields were monitored and analyzed using a four‐parametric log‐logistic model. We recorded data from weed‐free plots and compared these with data from different periods of weed interference. In both the study years, the longer period of weed interference decreased the relative yield of sesame, whereas the yield was increased with increasing duration of the weed‐free period. A 51–78.7% decline in sesame yield was noted if the weeds were allowed to compete with the crop from planting to harvest. In the first year, the duration of the critical period for weed control (CPWC) was 177–820 growing degree days (GDD), which corresponded to 14–64 days after crop emergence (DAE), and between 170 and 837 GDD (13–64 DAE) in the second year; this was based on a 5% acceptable yield loss. The results of this study clearly elaborated that maintaining weed‐free conditions is compulsory from as early as the second week after the emergence of sesame plants, and this should be maintained at least until the ninth week to avoid sesame yield losses by more than 5%. These findings show that growers can benefit from CPWC to improve weed control in sesame production, including the efficacy of a weed control program and its cost.

Effects of weed management and plant arrangements on yield index of sweet sorghum

Sweet sorghum is currently an important alternative for ethanol production in sugar cane off-season. In this study was to evaluate the effects of plant arrangements and the application of atrazine and S-metolachlor on growth and productivity of sweet sorghum. An experiment was conducted in randomized block design and, arranged in split plots with four repetitions. Plots consisted of spacing (0.25 m, 0.45 m 0.45-0.45-0.90 m) and sub-plots of weed control methods - atrazine (2000 g ha-1), atrazine + S-metolachlor (2000 + 720 g ha-1), atrazine + S-metolachlor (2000 + 960 g ha-1), atrazine + S-metolachlor (2000 + 1200 g ha-1), atrazine + S-metolachlor (2000 + 1440 g ha-1). Besides that, manual hoeing control was added. The intoxication of sorghum plants and weed control was evaluated at 7, 14 e 28 days after herbicides application (DAA). Plant height, stem diameter, total fresh matter, juice mass and total soluble solids (°Brix) were evaluated at 120 days after crop emergence (DAE). There was no interaction between the factors spacings and control method for variables total matter fresh (TMF), height (H), stem diameter (D), juice mass (JM), and Brix. Application of the mixture (atrazine + S-metolachlor) in the highest doses reduced total fresh matter and °Brix. The spacing of 0.25 m provided the highest productivity of fresh matter, juice mass and increased the °Brix. The application of mixture (atrazine + S-metolachlor) controlled 90% of the weeds at 28 days after application. The increasing in doses of S-metolachlor elevates the intoxication in sorghum plants. The mixture (atrazine + S-metolachlor) has a potential for use in weed control in sweet sorghum, but at doses below 960 g ha-1 of S-metolachlor.&#x0D; metolachlor.

Interference Periods in Soybean Crop as Affected by Emergence Times of Weeds

ABSTRACT: Weeds emergence times modify competition with crops. Thus, the hypothesis was that the increase in weed emergence flow decreases the period prior to interference (PPI) in soybeans and increases the critical period of interference prevention (CPIP). The objective was to determine the PPI and the CPIP of weeds in soybean crops as affected by the preferred time of weeds emergence flow. Three experiments were conducted in the field in a randomized block design with four replications. The treatments were arranged in a factorial design with factor A consisting of coexistence or weed control in soybeans and factor B for eight periods (0, 7, 14, 21, 28, 35, 42 and 135 days after crop emergence (DAE)). The numbers of emerged plants and weed dry mass by genus and crop productivity were evaluated. The weed interference in culture during all the crop cycle reduces the soybean average yield 73, 94 and 89% in the first, second and third sowing times, respectively. Chemical control may be adopted at the end of PPI, which must be done at 14, 15 and 5 DAE crop, for the first, second, third times, respectively. The sowing in advance and intermediate time of recommendation increase the PPI in about 10 days, favoring the weed management in soybean crops.

Assessment of Weed Competition Critical Period in Sugar Beet

Weed control constitutes the most essential issue in cropping systems. The critical periods should especially be determined for each crop. Field experiments were conducted during the seasonal growing periods of sugar beet in 2012 and 2013 in Kayseri, Turkey to assess the critical weed control period (CPWC). A log-logistic model having four parameters was used to assist in monitoring and analyzing two sets of related, relative crop yield. Data was obtained during the periods of increased weed interference and as to compare, during the weed-free periods. In both years, the relative root yield of sugar beet decreased with a longer period of weed-interference and increased where there was a longer weed-free period. In 2012, the CPWC varied between 122-595 GDD (growing degree days) corresponding to 12 to 46 days after crop emergence (DAE). The following year, CPWC were found to be between 82-735 GDD, (8-54 DAE) based on 5% acceptable yield loss. Weed-free conditions are needed to be arranged as early as the first week after crop emergence and maintained up to and including nine weeks thereafter to avoid more than a 5% loss in sugar beet root yield. Those results could assist sugar beet producers through reducing the expenses significantly, as well as improving the efficacy of their weed management programs.

English

A research was carried out to study phytosociology and to determine the periods of weed interference in the okra crop in organic cropping system. The experiment was laid out in a randomized complete block design with 20 treatments and four replications. The treatments were 10 periods of weed coexistence with the crop during 0-7, 0-14, 0-21, 0-28, 0-35, 0-42, 0-49, 0-56, 0-63 and 0-74 days after crop emergence (DAE) and 10 periods weed free during 0-7, 0-14, 0-21, 0-28, 0-35, 0-42, 0-49, 0-56, 0-63 and 0-74 DAE. The weeds were evaluated by the number of individuals and accumulated dry biomass of each population in the treatments. The relative frequency, relative density, relative dominance and importance value index of each species were used to determine the effect the weeds. The most important weeds based on the Importance value index were Commelina benghalensis L., Cynodon dactylon (L.) Pers., Eleusine indica L., Phyllanthus niruri L. and Alternanthera tenella Colla. The period prior to interference and the total period of interference prevention were respectively of 12 and 36 days after emergence. The weed community caused yield losses of around 51%. In okra organic cropping system, weed control should be done early to boost okra plant growth in order to provide shade on the weeds to reduce the need for long control period. &nbsp; Key words: Abelmoschus esculentus (L.) Moench, competition, weed community.

Weed Interference Periods in Early Wheat in the Midwest of Paraná

ABSTRACT Several factors can influence wheat crop yield, they include the interference imposed by weeds is one of the most important. The objective of this study was to evaluate the critical periods of weed interference in early wheat in the midwest of the state of Paraná, Brazil. The experiment was conducted in an experimental area located in Campo Mourão - PR, during the year 2013, using the BRS Pardela cultivar. The treatments consisted of periods of coexistence and weed control in wheat. Periods of coexistence and control were 0, 7, 14, 28, 35 and the whole cycle at days after crop emergence (DAE). Number of reproductive tillers per plant, spike length, number of spikelets per spike, plant height and wheat crop yield, were significantly affected by coexistence with prevailing infestation of Raphanus raphanistrum, therefore, a critical period of interference was determined at 16 to 24 DAE.

The Critical Period for Weed Control (CPWC) in Potato (&lt;i&gt;Solanum tuberosum&lt;/i&gt; L.)

Accurate assessment of crop-weed control period is an essential part for planning an effective weed management for cropping systems. Field experiments were conducted during the seasonal growing periods of potato in 2012 and 2013 in Kayseri, Turkey to assess critical period for weed control (CPWC) in potato. A four parameter log-logistic model was used to assist in monitoring and analysing two sets of related, relative crop yield. Data was obtained during the periods of increased weed interference and as a comparison, during weed-free periods. In both years, the relative yield of potato decreased with a longer period of weed-interference whereas increased with increasing length of weed free period. In 2012, the CPWC ranged from 112 to 1014 GDD (Growing Degree Days) which corresponded to 8 to 66 days after crop emergence (DAE) and between 135-958 GDD (10 to 63 DAE) in the following year based on a 5% acceptable yield loss. Weed-free conditions needed to be established as early as the first week after crop emergence and maintained as late as ten weeks after crop emergence to avoid more than 5% yield loss in the potato. The results suggest that CPWC could well assist potato producers to significantly reduce the expense of their weed management programs as well as improving its efficacy.

Critical competition period of parthenium weed (Parthenium hysterophorus L.) in maize

For minimizing yield losses due to infestation of a weed, it is essential to know about its critical period of competition in a specific crop. The yield response of maize (Zea mays L.) to different competition periods (0, 35, 42, 49 and 56 days after crop emergence (DAE), and competition throughout growing season) of the invasive weed Parthenium hysterophorus L. was tested during autumn seasons of two consecutive years 2012 and 2013. Increasing parthenium competition period increased its dry weight up to 448% and relative competition index up to 52%. The corresponding increases in the uptake of N (up to 581%), P (up to 700%) and K (up to 669%) were also recorded. Parthenium weed competition period of 35 DAE decreased grain yield and harvest index of maize. However, number of grains and grain weight per cob, and 100-grain weight of maize were reduced at parthenium weed competition period beyond 42 and 56 DAE, respectively. Maize grain yield losses varied between 21 and 53% with parthenium competition period ranging from 35 DAE to full growing season. Maximum N, P, and K uptake by parthenium was 18.4, 2.4 and 17.7 kg ha−1, respectively. A three parameter logistic model was fitted to yield data in response to increasing durations of weed infestation. The critical timing of parthenium weed removal to avoid 5% and 10% maize grain yield loss was 8 and 17, and 13 and 23 DAE during year 2012 and 2013, respectively. Relatively shorter critical period of parthenium weed competition in maize crop suggested this weed to be highly allelopathic in addition to its competitive behavior.

Row spacing impacts the critical period for weed control in cotton (Gossypium hirsutum)

The knowledge on the critical crop-weed competition period is important for designing an efficient weed management program. Field studies were conducted in 2012 and 2013 at the Agricultural Research Institute, Kahramanmaras, Turkey to determine the effects of three row spacing (50, 70 and 90 cm) on the critical period for weed control (CPWC) in cotton. A four parameter logistic equation was fit to data relating relative crop yield to both increasing duration of weed interference and length of weed-free period. The relative yield of cotton was influenced by the duration of weed-infested or weed-free period, regardless of row spacing. In cotton grown at 50 cm row spacing, the CPWC ranged from 117–526 growing degree days (GDD) (V2–V11 growth stages) in 2012 and 124–508 GDD (V2–V10) in 2013 based on the 5% acceptable yield loss level. At 70 cm row spacing, the CPWC ranged from 98–661 GDD in 2012 (V2–V13) and 144–616 GDD (V2–V12) in 2013. At 90 cm row spacing, the CPWC ranged from 80–771 GDD in 2012 (V1–V14) and 83–755 GDD (V1–V14) in 2013. In order to obtain a 95% weed-free yield, the weed management should start at 16 days after crop emergence (DAE) and continued until 52 DAE (V2–V11) for crops grown in 50 cm row spacing, 15 and 60 DAE (V2–V13) for 70 cm row spacing and 11 and 67 DAE (V1–V14) for crops grown in 90 cm row spacing. This suggests that cotton grown in narrow row spacing (50 cm) had greater competiveness against weeds compared with wider row spacing (70 and 90 cm). Cotton growers can benefit from these results by improving cost of weed control through better timing of weed management.

Períodos de interferência de plantas daninhas na cultura do quiabo

Poucas pesquisas têm sido realizadas sobre interferência de plantas daninhas na cultura do quiabo. Objetivou-se com este trabalho estimar os períodos de interferência da comunidade infestante no quiabeiro. Um experimento de campo foi conduzido sob dois grupos de tratamentos, mantendo períodos crescentes de 0 (testemunha), 7, 21, 28, 35, 42, 49, 63, 77, 91 e 105 dias após a emergência da cultura (DAE), com e sem controle das plantas daninhas. As plantas daninhas com maior importância relativa foram Portulaca oleracea, Nicandra physaloides e Eleusine indica. A convivência do quiabeiro com as plantas daninhas por todo o ciclo de cultivo reduziu a produtividade da cultura em 95%. O período anterior à interferência foi de 57 DAE, enquanto o período total de prevenção à interferência foi de 14 DAE. Não houve período crítico de prevenção à interferência, sendo um único controle das plantas daninhas entre 14 e 57 DAE suficiente para prevenir a interferência na cultura do quiabo.

Eficácia do glufosinato de amônio associado com outros herbicidas na cultura do algodão Liberty Link®

The objective of this study was to evaluate the efficiency of ammonium-glufosinate in management programs for weeds in cotton crop FiberMax 966 Liberty Link ® genotype. The experiment was installed in experimental area of Paiaguas Farm, located in municipality of Diamantino, Mato Grosso State. The experiment was conducted in a randomized block design with eight treatments and four replications. For weeds efficient management in FiberMax 966 LL genotype, the application of herbicide treatment in pre-emergence may reduce up to two post-emergence applications with no significant losses in production, but the pre-emergence treatment needs to be effective. If the application of a herbicide treatment in pre-emergence is not possible, the use of three sequential applications of ammonium-glufosinate (0.5, 0.4, 0.6 kg ha -1 ) at 10, 25 and 40 days after crop emergence (DAE) result in similar information. In the conditions that the experiment was conducted, all herbicide treatments were selective to the crop, without significant differences in bolls number and yield.

Potencial de utilização do clomazone em cultivares de feijoeiro comum

Weed interference can cause severe damages to common bean grain yield. Although the use of herbicides is considered as an efficient means to control weeds, there are just a few alternatives to use in pre-emergence applications. The objective of this work was to evaluate the potential use of pre-emergence applications of clomazone for five cultivars of common bean. Experiments were carried out under greenhouse conditions in a completely randomized design, and the treatments were increasing rates of clomazone (0, 300, 600 and 900 g ha -1 ) applied to five cultivars of common bean: Diamante Negro, Jalo Precoce, Perola, BRS Pontal and BRS Radiante. Increased rates of clomazone caused more visual injuries for all varieties. Increased rates of clomazone also inhibited plant growth, chlorophyll content and shoot dry mass for all cultivars except BRS Pontal. Cultivar Jalo Precoce was the most sensitive in relation to all parameters of crop injury. Chlorophyll contents in cv. BRS Radiante at 28 days after crop emergence (DAE) were not changed with increases in clomazone rate. For cv. BRS Pontal, increases in herbicide rate up to 900 g ha -1 did not cause any reduction of crop growth, chlorophyll content and shoot dry mass at 28 DAE.

Effects of Weed Interference and Starter Fertilizer on Subsequent Seed Germination and Vigour of Soybean (Glycine max [L.] Merr.)

The study was conducted to investigate the effect of weed interference and starter fertilizer on subsequent soybean seed quality at the Agricultural Research Farm and Laboratory of Razi University, Kermanshah, Iran. Two factorial experiment was laid-outon a randomized complete block design with four replications. First factor was starter fertilizer levels (0 and 25 kg <TEX>$ha^{-1}$</TEX>) applied in the forms of monoammonium phosphate, the second factor was different weed interference periods consisted of five initial weed-free periods (in which, plots were kept free of weeds for 0, 15, 30, 45 and 60 days after crop emergence (DAE) and then weeds were allowed to grow until harvest) and five initial weed-infested periods (in which, weeds were allowed to grow for 0, 15, 30, 45 and 60DAE, after which the plots were kept free of weeds until harvest). Full season weedy condition reduced 100-seed weight, seed germination percentage and seedling dry weight by 25.9, 13.3 and 22.5%, respectively and increased mean germination time and seed electrical conductivity by 55.8 and 24.3%, respectively as compared with full season weed-free control. However, the traits under study were not significantly influenced when field was kept free of weeds for at least 45 DAE (R1) or weedy condition was continued for less than 30 DAE (V8). There was a significant and negative correlation between weed biomass and seed weight (r = -0.93), so that when weed free condition was less than 45 DAE or weed infested period was continued for at least 30 DAE, soybean plants produced wrinkled and underdeveloped seeds with lower weights and qualities. Moreover, soybean seed quality reduction due to weed interference was more evident when starter fertilizer was applied and weeds interfered with soybean from the beginning of the growing season. Information from the present study is beneficial in soybean seed production systems and where farmers use the harvested seeds for the following planting.