Leandro Coelho de Araujo

Modelos empíricos para estimar o acúmulo de matéria seca de capim‑marandu com variáveis agrometeorológicas

The objective of this work was to test empirical linear regression models, to predict dry matter accumulation rates (DMAR) of Urochloa brizantha cv. Marandu, using agrometeorological variables. To generate the models, the average dry matter accumulation under rainfed conditions, between 1998 and 2002, was used. The evaluated variables were: minimum, maximum and average temperatures, global radiation (GR), degree-days, actual (AET) and potential evapotranspiration (PET) obtained from the water balance, photothermal units (PU) and the climatic growth index (CGI). Except for the PU, the univariate and multivariate regressions showed good predictive ability. The best results were for the multivariate regression, with Tmin, GR and AET: R 2 , 0.84; root mean square residual (RMSR), 14.72; and Akaikes information criterium (AIC), 222.5. In the univariate regression, the following variables stood out: corrected degree-days (R 2 , 0.75; RMSR, 17.84; CIA, 242.6), corrected minimum temperature (R 2 , 0.75; RMSR, 17.82; AIC, 244.1); and CGI (R 2 , 0.74; RMSR, 17.85; AIC, 236.9). The correction of the agrometeorological variables using the relation between real and potential evapotranspiration (AET/PET) enhances, in general, the model prediction of DMAR.

Dry matter production of Tanzania grass as a function of agrometeorological variables

o 11, CEP 13418‑900 Piracicaba, SP, Brazil. E‑mail: fcmendon@esalq.usp.br, lc_araujo@yahoo.com.br Abstract - The objective of this work was to develop and validate linear regression models to estimate the production of dry matter by Tanzania grass (Megathyrsus maximus, cultivar Tanzania) as a function of agrometeorological variables. For this purpose, data on the growth of this forage grass from 2000 to 2005, under dry‑field conditions in Sao Carlos, SP, Brazil, were correlated to the following climatic parameters: minimum and mean temperatures, degree‑days, and potential and actual evapotranspiration. Simple linear regressions were performed between agrometeorological variables (independent) and the dry matter accumulation rate (dependent). The estimates were validated with independent data obtained in Sao Carlos and Piracicaba, SP, Brazil. The best statistical results in the development and validation of the models were obtained with the agrometeorological parameters that consider thermal and water availability effects together, such as actual evapotranspiration, accumulation of degree-days corrected by water availability, and the climatic growth index, based on average temperature, solar radiation, and water availability. These variables can be used in simulations and models to predict the production of Tanzania grass.

Development of maize and palisadegrass plants cultivated in intercrop under water deficit

The objective of this work was to evaluate the development and productive traits of palisadegrass single cultivated or intercropped with corn, in addition to corn intercropped with pasture, under water deficit at different development stages of the plants. It was used a complete block experimental design with split plots and three replicates. Periods of water deficit were placed in the plots and types of cultivation were placed in the subplots. Irrigation was stopped at germination and initial tillering of palisadegrass and at V4 and V15 stages of corn and returned when soil moisture was 40% of available water capacity. Tiller density and palisadegrass height were evaluated weekly. Dry matter (DM) of fractions of herbage mass as well as leaf area of the plants were evaluated at corn tasseling and when grains reached physiological maturity. Components of corn production were determined in the second sampling. In palisadegrass, water influenced only tillering, which was reduced in the plots in which water defict was forced at the moment of germination or at the beginning of tilering, in both cultivation systems. Plant height and DM production were affected only by cultivation, reducing when intercropped with corn. Evaluated production components did not influence corn grain productivity, which was similar in all treatments (average of 10,145 kg/ha). Palisadegrass plants produce more DM in single cultivation than intercropped with corn. Water deficit during germination and initial tillering reduces tillering of palisadegrass during establishment phase. Water deficit, applied in this trial, does not reduce DM yield in palisadegrass or corn.

Características agronômicas do Panicum maximum cv. "Mombaça" submetido a níveis crescentes de fósforo

The objective of this experiment was to evaluate the effects of the addition of increasing doses of P2O5 on the height of the dossal, number of stalks, production of dry matter of leaves and the stems of the Mombaca-grass, in different ages. The experiment was implanted in an Eutrophic Red Nitossol. The experimental designs used were complete randomized block, with four replicates, five levels of P2O5 (30, 60, 90, 120, and 150kg. ha-1) and a tester. Analyzing the first and second harvest of the pasture the tillering showed positive linear response to the increasing phosphorus levels, for the third and fourth harvest, the data were adjusted to the quadratic model. Increasing P2O5 doses decreased the leaf lamina fraction of aerial part dry matter, however raised the stems fraction. In the first, second and third harvest, aerial part dry matter production increased linearly (7, 15 and 19kg ha-1 of DM for kg ha-1 of P2O5, respectively). In the fourth harvest the data were adjusted to the quadratic model of regression, the maximum production (8.3Mg ha-1 of DM) was obtained in the application of 103kg ha-1 of P2O5.

Establishment of Brachiaria brizantha cv. Marandu, under levels of soil water availability in stages of growth of the plants

The objective of this work was to evaluate yield traits and development of palisadegrass under the influence of water deficit during the establishment period. The experiment was carried out in a greenhouse, in a completely random block statistical design in a factorial arrangement and additional treatment (3 × 3 + 1). The treatments referred to the suppression of irrigation at different phases of the establishment (sowing, germination and initial tillerring) until the soil presented water content of 75%, 50%, and 25% of the moisture related to field capacity (qFC), besides control treatment with no water restriction. Evaluations of number of grown tillers per vase, green leaves per tiller and plant height were carried out weekly, for five weeks after the first tillers appeared. Biomass sampling was carried out approximately 30 days after the end of the last applied treatment, when the soil was kept close to 100% of field capacity relative moisture. Tillering and biomass yield of palisadegrass during establishment phase are reduced when water deficit is sufficient to make soil content water reach 25% of relative moisture field capacity, regardless to the season when water shortage takes place.

Critical periods of sorghum and palisadegrass in intercropped cultivation for climatic risk zoning

The objective of this work was to define critical periods for sorghum and palisadegrass cultivated on crop-livestock integrated systems under water deficit. An experiment was carried out in a completely random block design with four treatments (control and interruption of water supply in three periods) and three replicates. Water supply was interrupted until soil water humidity was close to permanent wilting point at the phases: germination of palisadegrass seeds; start of tillering of palisadegrass and initiation of panicles of shorghum; start of shorghum flowering. Water deficit starting at palisadegrass germination delayed intital development of the plants because of the reduction in tillering. Water restriction at panicle initiation phase and at sorghum flowering determined reduction of grain production. Critical periods for intercrop of sorghum and palisadegrass correspond to palisadegrass germination phase and flowering and panicle inititation phase of sorghum.

Sowing Season and Nitrogen Fertilization Rates in Two Oats Cultivars Grown Under Greenhouse Conditions

Two experiments were carried out in the experimental field of the Universidade Estadual Paulista-UNESP in Ilha Solteira, Sao Paulo state, Brazil, in a greenhouse from April to July 2015. This study aimed at evaluating the best sowing season and response to nitrogen doses for the cultivars of yellow oat Sao Carlos and black IAPAR 61. The experiments were conducted in randomized blocks designs in a factorial scheme with three replicates. The sowing seasons were April 23, May 08, and May 5 and the nitrogen doses were 0; 12.5; 25; 35.5 and 50 kg ha-1 cycle. Harvests at 30 and 60 days were conducted in order to estimate of the production of dry weight (DW), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF). For a productivity of DW, there was interaction between sowing season and oat cultivars and significant differences for CP in the second harvesting. For NDF, a significant difference was observed between harvesting. The most suitable time for sowing of both yellow oats and black oats is early May. Dry weight yield and the CP content of yellow oats increased linearly with increasing nitrogen rates while for black oats a maximum DM yield were obtained with the application of 43.5 kg ha-1 of N.