The effect of leaf area reduction on corn plants during the reproduction phase

Reduction in leaf area in corn plants during reproduction changes physiological metabolism and consequently the accumulation of dry matter in grains. The aim of this work was to study changes in agronomic characteristics caused by defoliation in corn during the reproduction phase. The experiment was carried out in Uberlândia, Minas Gerais state, in the agricultural year 2007/2008. The experiment was arranged in a randomized block design, consisting of seven treatments: control without defoliation, removal of two apical leaves, removal of four apical leaves, removal of all leaves above spike, removal of four intermediate leaves, removal of all leaves below spike, and removal of all plant leaves, with five repetitions. The genotype used for the evaluations was hybrid NB 7376. Defoliation was carried out when plants were at the growth stage R2. The variables assessed were: yield, density of spikes and corncobs, root resistance and stem integrity. When all leaves above the spike were removed, grain yield was reduced by 20%. Corncob density, stem integrity and root resistance to uprooting were also affected. Spike density was only affected when all plant leaves were removed. The leaf area remaining physiologically active above the spike was found to be most efficient in terms of grain yield.

Molybdenum mixed with glyphosate and alone via foliar spray in no-tillage common bean grown on corn stover

The effect of molybdenum (Mo) on common bean grown in desiccated corn stover in a no-tillage system was evaluated under two application modes: Mo mixed with the desiccant glyphosate and Mo direct spray to the bean leaves. The treatments (four replicates) were assigned to a completely randomized block design in a split-plot arrangement with the application of Mo (0, 100, 200, 400 and 800 g ha-1) mixed with glyphosate in the main plots and Mo foliar spray (0 and 100 g ha-1) in the sub-plots. The field experiments were carried out in 2009 and 2010 in the municipality of Coimbra, Minas Gerais State, with the common bean cultivar Ouro Vermelho. Mo mixed with glyphosate had neither an effect on common bean yield nor on the Mo and N contents in leaves, however it increased the Mo and N contents in seeds. Application of Mo via foliar spray increased Mo content in leaves and Mo and N contents in seeds. The reapplication of molybdenum with glyphosate for desiccation in subsequent crops caused a cumulative effect of Mo content in bean seeds.

Spacing, population density and nitrogen fertilization in corn grown in an Oxisoil

The objective of this study was to evaluate yield components, leaf nitrogen content and grain yield in corn as affected by row spacing, plant density and nitrogen topdressing. The experiment was conducted with the single-cross hybrid AG 8021, in the municipality of Toledo-PR, in an Oxisoil under no-tillage system, in the crop year 2005/ 2006. The experiment was arranged in a randomized block design and treatments in split-split-plots, with four replications. The two row spacings (0.45 and 0.90 m) were allocated in the main plots, the two plant densities (60,000 and 80,000 plants ha-1) were allocated in the subplots and the three nitrogen rates (80, 100, 120 and 140 kg ha-1 N) were allocated in the sub-subplots. Topdress nitrogen was applied using urea as N source. The rise of the plant population from 60,000 to 80,000 plants ha-1 and the application of topdress nitrogen resulted in increased production components. The application of topdress fertilization provided increase in leaf N content and grain yield for the spacings 0.45 m and 0.90 m. Yield was higher in the spacing 0.45 m than 0.90 m. Yield was higher with 60,000 plants than with 80,000 plants at 0.90 m, while at 0.45 m there was no difference in relation to the plant density.

Use efficiency of variable rate of nitrogen prescribed by optical sensor in corn

ABSTRACT The efficiency of nitrogen fertilizer in corn is usually low, negatively affecting plant nutrition, the economic return, and the environment. In this context, a variable rate of nitrogen, prescribed by crop sensors, has been proposed as an alternative to the uniform rate of nitrogen traditionally used by farmers. This study tested the hypothesis that variable rate of nitrogen, prescribed by optical sensor, increases the nitrogen use efficiency and grain yield as compared to uniform rate of nitrogen. The following treatments were evaluated: 0; 70; 140; and 210 kg ha-1 under uniform rate of nitrogen, and 140 kg ha -1 under variable rate of nitrogen. The nitrogen source was urea applied on the soil surface using a distributor equipped with the crop sensor. In this study, the grain yield ranged from 10.2 to 15.5 Mg ha-1, with linear response to nitrogen rates. The variable rate of nitrogen increased by 11.8 and 32.6% the nitrogen uptake and nitrogen use efficiency, respectively, compared to the uniform rate of nitrogen. However, no significant increase in grain yield was observed, indicating that the major benefit of the variable rate of nitrogen was reducing the risk of environmental impact of fertilizer.

Comparative response to N, P and K of grain sorghum and corn: I. Distrophic quartz sand

The comparative response of three sorghum (E-57, TEY 101 and C- 102) and of three corn cultivars (HMD-7974, Centralmex and Piranão) to N, P and K applications was studied in a soil from Anhembi, SP, classifield as Distrophic quartz sand (AQd) was studied. Leaf analyses were made to assess the nutritional status of the two crops. Main conclusions were the following. 1. Sorghum yieldel more than corn; 2. Both sorghum and corn varieties showed different capacities to absorb N, P and K from the soil and to fertilizer application; 3. There was no response to K2O fertilization; 4. Only Piranão increased yield when suplemented with a mixture of micronutrientes; 5. Direct relationships between rates of N and P2O5 and yield and leaf content were found; 6. Direct relationships between rates of N and P2O5 and yield and leaf content were found; 7. The following leaf levels were considered to be adequate, respectively for sorghum and corn: N - 2,00 - 2,25%, 3,25 - 3,50%; P - 0,30 - 0,40, 0,45 - 0,50; K -2,00 - 2,50, 2,20 - 2,40%; Ca - 0,20 - 0,40, 0,44- 0,72% Mg - 0,25 - 0,40, 0,34 - 0,60%; S - 0,50 - 0,70, 0,72 -0,80; Cu - 7 - 10, 11 - 15%; Fe - 84 - 170, 98 - 125%; Mn - 58 - 72, 66 - 85%; Zn - 10 - 14, 18 - 22; critical levels, however, do very depending upon cultivar.

Spatial and linear correlations between soil and corn

The Technologies setting at Agricultural production system have the main characteristics the vertical productivity, reduced costs, soil physical, chemical and biological improvement to promote production sustainable growth. Thus, the study aimed to determine the variability and the linear and special correlations between the plant and soil attributes in order to select and indicate good representation of soil physical quality for forage productivity. In the growing season of 2006, on the Fazenda Bonança in Pereira Barreto (SP), the productivity of autumn corn forage (FDM) in an irrigated no-tillage system and the soil physical properties were analyzed. The purpose was to study the variability and the linear and spatial correlations between the plant and soil properties, to select an indicator of soil physical quality related to corn forage yield. A geostatistical grid was installed to collect soil and plant data, with 125 sampling points in an area of 2,500 m². The results show that the studied properties did not vary randomly and that data variability was low to very high, with well-defined spatial patterns, ranging from 7.8 to 38.0 m. On the other hand, the linear correlation between the plant and the soil properties was low and highly significant. The pairs forage dry matter versus microporosity and stem diameter versus bulk density were best correlated in the 0-0.10 m layer, while the other pairs - forage dry matter versus macro - and total porosity - were inversely correlated in the same layer. However, from the spatial point of view, there was a high inverse correlation between forage dry matter with microporosity, so that microporosity in the 0-0.10 m layer can be considered a good indicator of soil physical quality, with a view to corn forage yield.

Nitrogen fertilization (15NH4NO3) of palisadegrass and residual effect on subsequent no-tillage corn

Nitrogen is required in large amounts by plants and their dinamics in corn and perennial forages intercropped is little known. This study analyzed the efficiency of nitrogen fertilization (15NH4NO3) applied after corn grain harvest to palisadegrass (Brachiaria brizantha cv. Marandu) in intercrops sown at two times, as well as the N residual effect on the subsequent corn crop. The field experiment was performed in Botucatu, São Paulo State, in southeastern Brazil, on a structured Alfisol under no-tillage. The experiment was arranged in a randomized block design in a split plot scheme with four replications. The main plots consisted of two intercropping systems (corn and palisadegrass sown together and palisadegrass sown later, at corn top-dressing fertilization). The subplots consisted of four N rates (0, 30, 60, and 120 kg ha-1 N). The subplots contained microplots, in which enriched ammonium nitrate (15NH4NO3) was applied at the same rates. The time of intercrop sowing affected forage dry matter production, the amount of fertilizer-derived N in and the N use efficiency by the forage plants. Nitrogen applied in autumn to palisadegrass intercropped with corn, planted either at corn sowing or at N top-dressing fertilization, increased the forage yield up to a rate of 60 kg ha-1. The amount of fertilizer-derived N by the forage plants and the fertilizer use efficiency by palisadegrass were highest 160 days after fertilization for both intercrop sowing times, regardless of N rates. Residual N did not affect the N nutrition of corn plants grown in succession to palisadegrass, but increased grain yield at rates of 60 and 120 kg ha-1 N, when corn was grown on palisadegrass straw from the intercrop installed at corn fertilization (top-dressing). Our results indicated that the earlier intercropping allowed higher forage dry matter production. On the other hand, the later intercrop allowed a higher corn grain yield in succession to N-fertilized palisadegrass.

Determination of the critical period of weed control in corn using a thermal basis

Field studies were conducted over 3 years in southeast Buenos Aires, Argentina, to determine the critical period of weed control in maize (Zea mays L.). The treatments consisted of two different periods of weed interference, a critical weed-free period, and a critical time of weed removal. The Gompertz and logistic equations were fitted to relative yields representing the critical weed-free and the critical time of weed removal, respectively. Accumulated thermal units were used to describe each period of weed-free or weed removal. The critical weed-free period and the critical time of weed removal ranged from 222 to 416 and 128 to 261 accumulated thermal units respectively, to prevent yield losses of 2.5%. Weed biomass proved to be inverse to the crop yield for all the years studied. When weeds competed with the crop from emergence, a large increase in weed biomass was achieved 10 days after crop emergence. However, few weed seedlings emerged and prospered after the 5-6 leaf maize stage (10-20 days after emergence).

Influence of micronutrients on dry matter yield and interaction with other nutrients in annual crops

The objective of this work was to determine the influence of Zn, Mn and Cu on shoot dry matter yield and uptake of macro and micronutrients in upland rice, common bean and corn. Six greenhouse experiments were conducted using a Dark Red Latosol (Typic Haplusthox). Treatments consisted of application of Zn at 0, 5, 10, 20, 40, 80 and 120 mg kg-1, of Mn at 0, 10, 20, 40, 80, 160, 320 and 640 mg kg-1 and of Cu application at 0, 2, 4, 8, 32, 64 and 96 mg kg-1. Zinc increased yield of rice, Mn increased yields of corn and bean and Cu improved yields of rice and bean. Uptake of N, Ca, and Cu in rice was decreased by zinc treatment. In common bean, uptake of N, Mg, and Cu was increased by zinc application, whereas, uptake of P was decreased. Manganese increased uptake of Mg, Zn and Fe and decreased uptake of Ca, in corn. Uptake of K, Zn and Mn was increased and uptake of P and Cu was decreased by Mn application, in bean. Copper had positive and negative interactions in the uptake of macro and micronutrients, depending on crop species and nutrients involved.

Fungicide baseline for mycelial sensitivity of Exserohilum turcicum, causal agent of northern corn leaf blight

Northern corn leaf blight, caused by Exserohilum turcicum(Et), is one of the major corn diseases which can reduce grain yield and quality. The aim of this study was to determine the mycelial sensitivity of ten Etisolates, five from Argentina and five from Brazil, to six fungicides (carbendazim, captan, fludioxinil, metalaxyl, iprodione and thiram) used in seed treatment. The inhibitory concentration (IC50) was determined by using seven concentrations of the fungicides supplemented to the agar medium. The mycelial colony diameter was measured with a digital caliper. Experimental design was completely randomized with four replicates. Data on the percent mycelial growth inhibition were analyzed by logarithmic regression and the IC50 was calculated. The fungicide iprodione was the most potent, with IC50 < 0.01 mg/L, followed by fludioxonil, IC50 0.31 mg/L, and thiram, 1.37 mg/L. Carbendazim, metalaxyl and captan were classified as non-fungitoxic, showing IC50 > 50 mg/L for all isolates. Although iprodione is the most potent fungicide, it is not used for corn seed treatment. The IC50s obtained in this study can be used as baseline for future monitoring studies of Etsensitivity to fungicides.

Comparison of metering mechanisms of corn seed

It was compared the performance of the metering mechanism of corn seeds (Zea mays) in direct seeding in an area of ​​200 ha, a property in Piraí do Sul, State of Paraná - PR, in Brazil. It was seeded 4 maize hybrids, 50 ha of each, with seeds of different sieves. The experiment was conducted in a randomized block design (RBD), with 3 treatments and 9 repetitions for each corn hybrid. The treatments were the pneumatic seed of metering mechanisms, horizontal perforated disc with and without ramp®. The plots were 40 m² and were distributed at the early, middle and late sowing. The variables analyzed in each corn hybrid were initial population, faulty spacing, multiple spacing, acceptable spacing, and yield components. As there were no significant differences in the variables, it was concluded that the quality of seeding with different systems of distribution was similar in the different sieves of distributed corn seeds.

Positioning of fertilizer in corn sowing

The aim of this study was to determine whether the form of placing the fertilizer by the planter during the sowing under mulch in the no till system affects the yield of corn. The treatments consisted of placing the fertilizer during the seeding 0.05 m below and beside the seed, in front of the cutting blade and without fertilizer, in 03 farms during 03 cropping years. The experimental design at each farm was the randomized block, with 08 repetitions, whose plots had 30 m² each. The initial population and yield components were evaluated. Under the experimental conditions it is concluded that base fertilization can affect the yield. Fertilizer placement can affect the initial stand, but not the yield.

Effect of cowpea intercropping on weed control and corn yieid

Herbicides have simplified weed control, but the use of herbicides, besides being costly, resulted in the selection of herbicide-resistant weed biotypes and has become an environmental contamination factor. Herbicide use reduction is one of the goals of modern agriculture, with several alternatives being investigated, including intercropping. The objective of this study was to evaluate the effects of cowpea and corn cultivar intercropping on weed control and corn green-ear (immature ears with 80% humidity grains) and grain yield. A completely randomized block design with split-plots and four replications was used. AG 1051, AG 2060 and PL 6880 corn cultivars (assigned to plots) were submitted to the four treatments: no weeding, two hoe-weeding (22 and 41 days after planting), and intercropping with cowpea (BR 14 and IPA 206 cultivars, with indeterminate growth). The cowpea was planted (with corn planting) between the corn rows, in pits 1.0 m apart, with two plants per pit. The corn cultivars did not differ from each other as to weed density (WD), fresh above-ground weed biomass (WB), green-ear yield and grain yields. Higher WD and WB mean values were found in no weeding subplots; lower mean values in two hoe-weeding subplots; and intermediate mean values in intercropped subplots, indicating that cowpea plants had, to a certain extent, control over weeds. The no-weeded plots and the intercropped plots had lower green-ear and grain yields. Although the cowpea cultivars had a certain control over weeds (mean reductions of 22.5 and 18.3%, in terms of green matter density and weight of the above-ground part of weeds, respectively), they also competed against the corn plants, leading to yield reduction (mean reductions of 17.0 and 32% in green ear and grain yield, respectively). The cowpea cultivars did not produce grain, certainly due to the strong competition exerted by the corn and weeds on cowpea plants.

Influence of corn sowing density and gliricidia intercropping on weed control

There is interest in the identification of the best seeding density for new corn hybrids and on reduced use of herbicides for weed control. The objective of this study was to evaluate the effects of seeding density (30, 50, 70, and 90 thousand plants ha-1) and weed control on green ear yield and grain yield in corn cultivar AG 1051. A completely randomized block design was adopted with split-plots (seeding densities assigned to plots) and ten replicates. Weed control was achieved by means of two hoeings and by planting corn intercropped with gliricidia (between corn rows, in pits spaced 0.3 m apart). A "no weeding"treatment was included as well. Increased seeding density increased the total number and weight of marketable green ears and decreased the biomass of both weeds and gliricidia. In non-weeded, intercropped and hoed plots, the maximum grain yield values achieved as seeding density increased were 7,881, 7,021, and 9,213 kg ha-1, respectively, obtained with populations of 67 thousand, 74 thousand, and 67 thousand plants per hectare, respectively. Intercropping did not control weeds (26 species) and provided weed growth, green ear yield, and grain yield (at the lowest densities) similar to those obtained without hoeing, except for total number of green ears, in which no influence of weed control was observed. At densities of 70 thousand and 90 thousand plants per hectare, grain yield with two hoeings was not different from yield values obtained without weeding or in the treatment intercropped with gliricidia, respectively, indicating that increased corn seeding density as well as gliricidiamay help to control weeds.

Modeling light interception and distribution in mixed canopy of common cocklebur (Xanthium stramarium) in competition with corn

The aim of this study was to model light interception and distribution in the mixed canopy of Common cocklebur (Xanthium stramarium) with corn. An experiment was conducted in factorial arrangement on the basis of randomized complete blocks design with three replications in Gonabad in 2006-2007 and 2007-2008 seasons. The factors used in this experiment include corn density of 7.5, 8.5 and 9.5 plants per meter of row and density of Common cocklebur of zero, 2, 4, 6 and 8 plants per meter of row. INTERCOM model was used through replacing parabolic function with triangular function of leaf area density. Vertical distribution of the species' leaf area showed that corn has concentrated the most leaf area in layer of 80 to 100 cm while Common cocklebur has concentrated in 35-50 cm of canopy height. Model sensitivity analysis showed that leaf area index, species' height, height where maximum leaf area is seen (hm), and extinction coefficient have influence on light interception rate of any species. In both species, the distribution density of leaf area at the canopy length fit a triangular function, and the height in which maximum leaf area was observed was changed by change in density. There was a correlation between percentage of the radiation absorbed by the weed and percentage of corn seed yield loss (r² = 0.89). Ideal type of corn was determined until the stage of tasseling in competition with weed. This determination indicates that the corn needs more height and leaf area, as well as less extinction coefficient to successfully fight against the weed.