Abstract:This study aims to model the impacts of the frequency of cuttings of Tifton 85 bermudagrass on the dynamics of evapotranspiration (ET c ) and to derive crop coefficients appropriate for grass water management. Two seasons of experimentation were used with four different cutting treatments which provided field data for calibration and validation of the soil water balance model SIMDualKc for all treatments. Cuttings were performed after the cumulative growth degree days (CGDD) attained 124 • C, 248 • C and 372 • C, thus from short to very long intervals between cuttings. SIMDualKc adopts the Food and Agriculture Organization (FAO) dual K c approach for partitioning ET into crop transpiration and soil evaporation, thus providing for an assessment of their dynamics. All treatments were irrigated to avoid water stress. Grass ET c was modelled adopting a K cb curve to describe the ET variation for each cutting cycle, that is, using the FAO K c curve that consists of a series of K cb curves relative to each cutting cycle. Each individual K cb curve consisted of three segments constructed when knowing the K cb values at the initial, at the end of rapid growth, and at cutting, respectively K cb ini , K cb gro and K cb cut . These K cb values were first estimated using the equation relating K cb to the density coefficient (K d ), which is computed from the fraction of ground cover (f c ) and canopy height (h) at the same dates. The goodness of fit indicators relative to the calibration and validation of the SIMDualKc model were rather good, with the normalized root mean square error (RMSE) ranging from 4.0% to 6.7% of the mean available soil water. As an example, the standard K cb values obtained after model calibration relative to the cuttings treatment with CGDD of 248 • C are: K cb ini = 0.86, K cb gro = 0.91 and K cb cut = 0.96. K cb values were smaller when the frequency of cuts was larger because h and f c were smaller, and were larger for reduced cuttings frequency since h and f c were then larger. Because the soil was wet most of the time, the soil evaporation K e varied little but its value was small due to the combined effects of the fraction of crop cover and plant litter covering the soil. The values of K c = K cb +K e also varied little due to the influence of K e and the K c curve obtained a form different from the K cb curves, and a single K c value was adopted for each cutting frequency, e.g., K c = 0.99 for the treatment with CGDD of 248 • C. Results of the soil water balance have shown that, during the experimental periods, likely due to the effects of the El Niño Southern Oscillation (ENSO), runoff and deep percolation exceeded ET c . Moreover, the soil evaporation ratio was small: 14% in case of frequent cuttings and less for more spaced cuttings, thus with a transpiration ratio close to 90%, which indicates a very high beneficial consumptive water use, mainly when cuttings are not very frequent.

Deficit and water excess in maize (Zea mays L.) in greenhouse Deficit and water excess in maize (Zea mays L.) in greenhouse Maize is a culture with importance in global scenario due your function in food industry, as well as yours water requirements in the course of your cycle. Therefore, studies became important regarding the use of water resources where irrigation strategies are of great importance for water savings. This study aimed evaluate different irrigation levels (deficit and water excess) during a total maize cycle and at different specifics phenological stages of the culture. Development characteristics, production and hydric state of the plant were evaluated. The experiments were conducted at Department of Biosystems Engineering from "Luiz de Queiroz" College of Agriculture, located at Piracicaba, São Paulo State. The experimental design was a randomized block, with 12 treatments and 4 repetitions. Treatments consisted in replacement of 150, 100, 50 and 30% of water evapotranspired (ETc), applied in four subperiods of the total culture cycle: subperiod 1 (V4 to V8), subperiod 2 (V8 to Vp), subperiod 3 (Vp to R1) and subperiod 4 (R1 to R6). The experimental data were submitted to individual variance analysis, and when were possible, conjunct variance analysis, using the average data of the experiments. The first planting was carried out on 18 May of 2012 and the second, on April 21 of 2013, in greenhouse, totaling 137 and 144-day cycle, with sum-Thermal 1413 and 1444 °C accumulated degree days (ADD),respectively. Were evaluated the plant height (PH); ear height insertion (AIT.I); number of ears per plant (NE); ear weight with straw (PEP); weight of ear without straw (PED); number of grain per ear (NG); number of grain rows per ear (NFG); ear size (TE); ear diameter (dE); diameter of the cob (DS); number of between-nodes (NE) and productivity (PG). The leaf temperature was measured (Tm), also the vapor pressure deficit (VPD) and leaf water potential (Pl). Leaf water potential showed to be an efficient method regarding hydric state of the plant, there were difference between the four treatments studied (III, EEEE, D50 e D70), demonstrating variation of its value over the day. the response coefficient of the crop to water deficit (KY) were calculated, where the period of bolting and flowering were the most critical when water stress was imposed in specific phenological stages. From the productivity data and water levels applied in both experiments, was possible adjust second degree polynomials models to water productivity (WP) and culture production function. The results allowed conclude that a higher WP were obtained in the treatment D50.

EPÍGRAFE"O homem não teria alcançado o possível se, repetidas vezes, não tivesse tentado o impossível." (Max Weber)