Papéis do arranjo de plantas e do cultivar de soja no resultado da interferência com plantas competidoras

O uso combinado de cultivar competitivo e de arranjo equidistante de plantas pode incrementar a habilidade competitiva das culturas com plantas daninhas. Conduziram-se dois experimentos em campo na Estação Experimental Agronômica da UFRGS, em Eldorado do Sul-RS, durante o ano agrícola 2001/02, com o objetivo de caracterizar a contribuição do cultivar e do espaçamento entre fileiras para a competitividade da soja com plantas concorrentes. No experimento 1, testaram-se condições de competição (ausência ou presença do cultivar de soja Fundacep 33, simulando planta daninha), espaçamentos entre fileiras (25 e 50 cm) e seis cultivares de soja reagentes. No experimento 2, compararam-se condições de competição (ausência ou presença de plantas daninhas dicotiledôneas), espaçamentos entre fileiras (25 e 50 cm) e cultivares de soja (IAS 5 e Fepagro RS 10). O cultivar Fepagro RS 10 apresenta características de planta que o destacam quanto à habilidade em competir com plantas daninhas, como plantas mais altas, com mais matéria seca, com maior razão de massa foliar e que proporcionam maior cobertura do solo, além de figurar entre os cultivares mais produtivos. O espaçamento reduzido entre fileiras proporciona cobertura precoce do solo pela soja, reduz a população e a matéria seca das plantas daninhas e mantém ou incrementa a produtividade de grãos de soja.

Photosynthetic characteristics of hybrid and conventional rice plants as a function of plant competition

The objective of this work was to evaluate the characteristics related to the photosynthetic ability of hybrid and inbred rice varieties, as a way to assess which of the two presented higher potential to stand out under conditions of competition. The trial was set in a greenhouse in completely randomized block design and 2 x 6 factorial scheme with four replications. Factor A consisted of rice varieties (hybrid or inbred) and factor B by competition levels. Treatments consisted in maintaining one plant of either BRS Pelota (inbred) or Inov (hybrid) variety at the center of the plot, under competition with 0, 1, 2, 3, 4 or 5 plants of the variety BRS Pelota at the periphery of the experimental unit, according to the treatment. Fifty days after emergence (DAE), sub-stomatal CO2 concentration (Ci - mmol mol-1), photosynthetic rate (A - mmol m-2 s-1) and CO2 consumed (DC - mmol mol-1) were quantified, as well as shoot dry mass(SDM).Hybrid plants present higher photosynthesis capacity than inbred plants, when competing with up to 3 times its own density. When under the same competitive intensity, hybrid plants surpass the inbred. However, it should be emphasized that, when in farm condition, the lower competitive capacity with weeds often attributed to the hybrid varieties, probably is due to their lower planting density, but if weed competition is kept at low levels, hybrid rice plants may perform in the same way or usually better than inbred plants.

The effects of pigweed redroot (Amaranthus retoflexus) weed competition and its economic thresholds in corn (Zea mays)

The aim of this study was to determine the economic damage threshold of Pigweed redroot for corn regarding its density. An experiment was conducted at the Agriculture Research station of Islamic Azad University branch of Gonabad during 2006. The experiment was carried out as a factorial in a randomized complete block design with three replications. In the experiments, the factors included corn (var. 704) densities of 7.5, 8.5 and 9.5 plants m-2 and pigweed redroot densities of 0, 2, 4, 6 and 8 plants m-2. The increase in Pigweed redroot density, decrease in crop grain and biomass yield components such as ear length, ear diameter, number of grains per row, row number, grain number in ear, grain yield and biological yield of corn, decreased. Also, with an increase in corn density, the number of grain per rows, row number, grain yield and biological yield of corn increased. The economic thresholds density of Pigweed redroot was 0.09 to 0.13 plants m-2 in corn different densities, and increased with corn density increases.

Competition between drought-tolerant upland rice cultivars and weeds under water stress condition

The objective of this study was to evaluate the competitiveness of two cultivars of upland rice drought-tolerant, cultured in coexistence with weed S. verticillata, under conditions of absence and presence of water stress. The experiment was conducted in a greenhouse at the Experimental Station of the Universidade Federal de Tocantins, Gurupi-TO Campus. The experimental design was completely randomized in a factorial 2 x 2 x 4 with four replications. The treatments consisted of two rice cultivars under two water conditions and four densities. At 57 days after emergence, were evaluated in rice cultivars and weed S. verticillata leaf area, dry weight of roots and shoots and total concentration and depth of roots. Was also evaluated in rice cultivars, plant height and number of tillers. Water stress caused a reduction in leaf area, the concentration of roots and vegetative components of dry matter (APDM, and MSR MST) of rice cultivars and Jatoba Catetão and weed S. verticillata. The competition established by the presence of the weed provided reduction of all vegetative components (MSPA, and MSR MST) of cultivars and Jatoba Catetão. It also decreased the number of tillers, the concentration of roots and leaf area. At the highest level of weed competition with rice cultivars, a greater decrease in vegetative components and leaf area of culture, regardless of water conditions.

Competitive ability of soybean cultivars with horseweed (Conyza bonariensis)

The existence of large areas infested with populations of Conyza spp. resistant to glyphosate in Brazil demands appropriate and integrated management strategies. This experiment aimed to identify soybean cultivars with greater competitive ability with horseweed plants and to determine plant characteristics associated with this ability. The experiment was arranged in a randomized complete block design with split plots. Seven soybean cultivars (CD 225 RR, BRS 232, CD 226 RR, NK 7054 RR, BMX Apollo RR, BRS 245 RR and BRS 255 RR) were allocated in the plots, and two interference situations (absence and 13.3 plants of Conyza m-2, transplanted seven days before soybean planting) in the subplots. The average yield loss due to competition with horseweed was 25%. Cultivar CD 226 RR showed no significant grain yield loss due to competition, compared to the control without infestation, but showed the lowest average grain yield. The BRS 232 genotype showed loss of grain yield of only 14%, and presented positive plant height and leaf mass at 20 DAE, as well as dry matter of stems+branches in all evaluations, features related to its higher performance and greater ability to withstand competition with horseweed plants.

Corn cultivar intercropping with arboreal legumes for weed control

Gliricidia (Gliricidia sepium) seedlings are usually beneficial to corn crops when planted between corn rows. The objective of this work was to assess the effects of corn intercropped with gliricidia and "sabiá" (Mimosa caesalpiniifolia), a species native to the Brazilian northeastern region, on weed control and corn green ear and grain yields. The experiment was carried out at Estação Experimental da Universidade Federal Rural do Semi-Árido - UFERSA (Mossoró, State of Rio Grande do Norte, Brazil). The experimental design consisted of randomized complete blocks (multifactorial design) with five replications, arranged in split-plots. The plots consisted of corn cultivars AG1051 and BM 2022; subplot treatments (six) were no-hoeing, twice-hoeing (at 20 and 40 days after sowing) and intercropping with gliricidia and "sabiá", either directly sown or transplanted, simultaneously with corn sowing. The intercropped leguminous plants were spaced 0.40 m from each other, and directly seeded or transplanted (30-day-old seedlings) in between two 1 m-spaced corn rows. Twenty three weed species were identified during the experiment. Gliricidia seedlings were superior to "sabiá" seedlings with regard to plant height and survival rate. The highest corn green ear and grain yields were found for twice-hoed subplots, while the lowest yield was found for no-hoed or intercropped subplots. However, grain yield values in intercropped treatments did not differ from grain yield values in hoed plots. In addition, marketable husked green ear mean weights did not differ between twice-hoed subplots and subplots directly seeded with gliricidia and "sabiá". Such results indicated that corn benefited from the intercropping system, but intercropping with gliricidia and "sabiá" transplanted resulted in lower benefits than with the direct sowing of those species.

Density and sowing season of two Brachiaria species on the soybean culture

The aim of this study was to evaluate the growth and yield of soybean cultivar M-8766 in consortium with Brachiaria brizantha. BRS Piata and Brachiaria ruziziensis at different densities and sowing dates. The experimental design was randomized blocks with treatments arranged in a factorial 2 x 2 x 3 with four replications. Used as factors grass species (Brachiaria brizantha Piata and Brachiaria ruziziensis BRS) intercropped with soybean M-8766, sowing dates (12 and 24 days after soybean emergence) and three seeding rates (0, 5, 10 kg ha-1 of seed). At 71 days after soybean emergence were evaluated plant height, stem diameter, dry mass of leaves, stems and shoots, and 4 months after sowing determined the weight of 100 grains and soybean yield. The results showed that when seeded at a density of 10 kg ha-1 at 12 and 24 DAE soy, Brachiaria brizantha. BRS Piata caused reduction in yield in the order of 6.71% and 3.03% respectively, while the Brachiaria ruziziensis was one that caused a greater reduction in productivity in the order of 13.42 and 16.23%, respectively, of these values expression when considering the price of soybean sack. B. ruziziensis expressed less competitive with soybean. However, the large biomass production of this grass provides deployment system till the next harvest.

Effects of irrigated rice sowing season and imazapyr + imazapic time of application on rice grain yield and red rice management

Irrigated rice sowing season and red rice competition are among the main factors affecting grain yield. The objective of this work was to evaluate the sowing date of irrigated rice and moments of application of the herbicide imazapyr + imazapic to control red rice management and irrigated rice grain yield. Eight experiments were performed at the following dates (09/30, 10/19, 11/08 and 12/01) for the 2010/2011 harvest season and (09/27, 10/17, 11/08 and 12/05) for the 2011/2012 harvest season. The treatments were: application of the herbicide imazapyr + imazapic at doses of 105+35 g ha-1 in pre-emergence (PRE); 52.5+17.5 g ha‑1 in pre-emergence and 52.5+17.5 g ha-1 in post-emergence (PRE + POST); and 105+35 g ha-1 in post- emergence (POST), and a control without application and no weeding. The cultivar Puitá Inta CL was used and a randomized block design with four replicates. A joint analysis of the experiments was carried out. There was less emergence of red rice and higher grain yield of the irrigated rice at the early periods (09/30/10 and 09/27/11), with 10,578 and 8,653 kg ha-1, respectively. At the end of the season (12/01/10 and 12/05/11), there was greater reduction of the red rice seed bank. Sowing at the beginning of the recommended period provided more irrigated rice grain yield. The application of imazapyr + imazapic at a dose of 52.5+17.5 g ha-1 in PRE + 52.5+17.5 g ha-1 POST, and 105+35 g ha-1 only in PRE and POST was effective in the control of red rice.

Initial growth and competitive ability of yellow nutsedge and irrigated rice

Weeds cause significant reduction in the irrigated rice crop yield. Cyperus esculentus (yellow nutsedge) is adapted to irrigate environment. Information on the competitive ability of the weed to the culture, and their environmental adaptation, are scarce. In this study, we sought to determine the initial growth and competitive ability of yellow nutsedge and irrigated rice, as a function of cultivar growth cycle. Initial growth and competition studies were conducted in a randomized complete design in a greenhouse in the agricultural year 2010/11. For the initial growth study, the treatments consisted of a factorial combination of a biotype of yellow nutsedge and two rice cultivars in the function of the vegetative cycle (BRS Querência: early cycle - IRGA 424: intermediate cycle) and six evaluation times (10, 20, 30, 40, 50, and 60 days after emergence). Were evaluated: plant height, leaf area, aboveground dry biomass and root dry biomass. In the competitive ability study in the replacement series, the cultivar BRS Querência (early cycle) and yellow nutsedge were utilized and tested in different proportions of competition (100:0, 75:25, 50:50, 25:75, and 0:100). Were evaluated leaf area and aboveground dry biomass. In general, rice cultivars have an adaptive value equivalent to yellow nutsedge. IRGA 424 cultivar has less height than weed, becoming the weed control more important in this cultivar. For rice crop, intraspecific competition is more important, whereas for the weed, interspecific competition is the most pronounced.

Adaptive value of ryegrass biotypes with low-level resistance and susceptible to the herbicide fluazifop and competitive ability with the wheat culture

Ryegrass is the main weed in wheat crop, causing yield loss due to competition by environmental resources. The objectives of this study were to estimate the fitness cost of ryegrass biotypes with low-level resistance and susceptible to fluazifop and to investigate the relative competitive ability of these biotypes between themselves and against the crop. Thus, fitness cost and competitive ability experiments were conducted under greenhouse conditions. For the fitness cost experiments, the low-level resistant ryegrass biotypes and those susceptible to fluazifop were used. For competitive ability, the treatments were arranged in a replacement series, with five proportions of the wheat cultivar FUNDACEP Horizonte and the low-level resistant and susceptible ryegrass biotypes 100:0, 75:25, 50:50, 25:75 and 0:100. Competitive analysis was carried out through diagrams applied to the replacement experiments and use of relative competitiveness indices. Variables evaluated were plant height, in the fitness cost experiment, and leaf area and shoot dry biomass in both experiments. The ryegrass biotypes show overall similar fitness cost and competitive ability. The wheat cultivar FUNDACEP Horizonte is superior in competitive ability to the ryegrass biotype with low-level resistance and equivalent to the susceptible biotype.

Wild onion (Asphodelus tenuifolius) competition in rainfed chickpea-chickpea cropping system

Chickpea yield potential is limited by weed competition in typical chickpea growing areas of Pakistan where zero tillage crop grown on moisture conserved from rains received during the months of September and August. The objective of this work was to evaluate the growth and yield characteristics of chickpea grown in coexistence with increasing densities of wild onion (Asphodelus tenuifolius). The experiment was comprised of six density levels viz. zero, 20, 40, 80, 160 and 320 plants m-2 of A. tenuifolius. A decrease in chickpea primary and secondary branches per plant, pods per plant, seeds per pod, 100-seed weight and seed yield was observed due to more accumulation of dry matter per increasing densities of A. tenuifolius. The increase in A. tenuifolius density accelerated chickpea yield losses and reached the maximum values of 28, 35, 42, 50, 58 and 96% at 20, 40, 80, 160 and 320 A. tenuifolius plants m-2, respectively. The yield loss estimation model showed that chickpea losses with infinite A. tenuifolius density were 60%. Yield reduction could be predicted by 2.52% with increase of one A. tenuifolius plant m-2. It is concluded that A. tenuifolius has a strong influence on chickpea seed yield and showed a linear response at the range of densities studied.

WATER USE EFFICIENCY, GROWTH AND YIELD OF WHEAT CULTIVATED UNDER COMPETITION WITH Setaria

ABSTRACT Understanding the critical period of weed competition is indispensable in the development of an effective weed management program in field crops. Current experiment was planned to evaluate the critical growth period ofSetaria and level of yield losses associated with delay in weeding in rain-fed drip irrigated wheat production system of Saudi Arabia. Field experiment was conducted to evaluate the effect of weeding interval (07-21, 14-28, 21-35, 28-42 and 35-49 days after sowing) and drought stress (75% and 50% of field capacity) on Setaria growth, wheat yield and water use efficiency. Season long weedy check and wellwatered (100% FC) plots were also maintained for comparison. Weeding interval and drought stress significantly (p ≤ 0.05) affected the growth and yield of Setaria and wheat. Drought stress from 75% to 50% FC resulted in reductions of 29-40% in Setaria height, 14-27% in Setaria density and 11-26% in Setaria dry biomass. All weeding intervals except 35-49 DAS significantly suppressedSetaria growth as compared with control. Delay in weeding increased weed-crop competition interval and reduced wheat yield and yield contributors. Therefore, the lowest yield of 1836 kg ha-1 was attained for weeding interval of 35-49 DAS at 50% FC. Water use efficiency and harvest index increased with decreasing FC levels but reduced with delay in weeding. Correlation analysis predicted negative association ofSetariadensity with wheat yield and yield contributors and the highest negative association was for harvest index (-0.913) and water use efficiency (-0.614). Early management of Setaria is imperative for successful wheat production otherwise yield losses are beyond economical limits.

QUALITY OF PROCESSING TOMATO FRUITS IN COMPETITION WITH Solanum americanum

ABSTRACT Five experiments were conducted to evaluate the hypothesis that Solanum americanum density and time of coexistence affect the quality of processing tomato fruit. The tomato crop was established using either the direct drilling or the transplanting technique. The factors evaluated consisted of weed density (from 0 up to 6 plants m-2) and time of weed interference (early bloom stage, full flowering stage, fruit filling, and harvest time). The effects of competition on tomato fruit quality were analysed using a multiple model. Tomato variables evaluated included industrial fruit types (which depended on ripeness and disease infection) and soluble solids level(obrix). Tomato fruit quality is dependent on the factors tested. Under low densities (< 6 plants m-2) of S. americanum there was a small impact on the quality of the tomato fruits. The percentage of grade A (mature fruit with red color and without pathogen infection) tomato fruits is the variable most affect by the independent variables. The impact of these independent variables on the percentage of grade C (green and/or with more than 15% disease infection) tomato yield was of smaller magnitude and in an inverse trend as the observed for grade A. The level of soluble solids was influenced by the weed interference on only two experiments, but the impact was of small magnitude. The impact of the results on current and future crop management practices is discussed.

Wheat Yield Loss in a Two Species Competition with Emex australis and Emex spinosa

Emex australis and E. spinosa are significant weed species in wheat and other crops. Information on the extent of competition of the Emex species will be helpful to access yield losses in wheat. Field experiments were conducted to quantify the interference of tested weed densities each as single or mixture of both at 1:1 on their growth and yield, wheat yield components and wheat grain yield losses in two consecutive years. Dry weight of both weed species increased from 3-6 g m-2 with every additional plant of weed, whereas seed number and weight per plant decreased with increasing density of either weed. Both weed species caused considerable decrease in yield components like spike bearing tillers, number of grains per spike, 1000-grain weight of wheat with increasing density population of the weeds. Based on non-linear hyperbolic regression model equation, maximum yield loss at asymptotic weed density was estimated to be 44 and 62% with E. australis, 56 and 70% with E. spinosa and 63 and 72% with mixture of both species at 1:1 during both year of study, respectively. It was concluded that E. spinosa has more competition effects on wheat crop as compared to E. australis.

GROWTH AND YIELD RESPONSE OF MAIZE (Zea mays) TO INTER AND INTRA-ROW WEED COMPETITION UNDER DIFFERENT FERTILIZER APPLICATION METHODS

A field experiment was conducted for two consecutive years to study the effect of fertilizer application methods and inter and intra-row weed-crop competition durations on density and biomass of different weeds and growth, grain yield and yield components of maize. The experimental treatments comprised of two fertilizer application methods (side placement and below seed placement) and inter and intra-row weed-crop competition durations each for 15, 30, 45, and 60 days after emergence, as well as through the crop growing period. Fertilizer application method didn't affect weed density, biomass, and grain yield of maize. Below seed fertilizer placement generally resulted in less mean weed dry weight and more crop leaf area index, growth rate, grain weight per cob and 1000 grain weight. Minimum number of weeds and dry weight were recorded in inter-row or intra-row weed-crop competition for 15 DAE. Number of cobs per plant, grain weight per cob, 1000 grain weight and grain yield decreased with an increase in both inter-row and intra-row weed-crop competition durations. Maximum mean grain yield of 6.35 and 6.33 tha-1 were recorded in inter-row and intra-row weed competition for 15 DAE, respectively.