III Modelos de determinação não-destrutiva da área foliar em girassol

*Resumo -O efeito da temperatura do ar sobre o desenvolvimento das plantas pode ser representado usando-se o método da soma térmica. Para o cálculo da soma térmica é necessário conhecer-se a temperatura base, abaixo da qual o desenvolvimento não acontece ou acontece a uma taxa desprezível. O objetivo deste trabalho foi estimar a temperatura base para emissão de nós, bem como comparar as datas de cultivo para a variável plastocrono para a cultura da melancia. Três experimentos em campo foram conduzidos em Santa Maria, RS, com oito datas de semeadura durante os anos Crimson Sweet" aleatorizado em blocos ao acaso com quatro repetições por época. O número de nós acumulados na haste principal (NN) da melancieira foi observado em três plantas por parcela, três vezes por semana. O plastocrono foi estimado pelo inverso do coeficiente angular da regressão entre NN e soma térmica acumulada. A temperatura base estimada usando a metodologia do menor valor de Quadrado Médio do Erro (QME) foi de 7,0 °C. O plastocrono em melancieira não diferiu entre as datas de plantio nos três anos agrícolas, sendo em média 23,4 ºC dia nó -1. A implicação para a modelagem é que um único valor de plastocrono pode ser usado para estimar a emissão de nós da cultivar "Crimson Sweet", independente da data de semeadura. Palavras-chave -Citrullus lanatus. Desenvolvimento vegetativo. Soma térmica.Abstract -The air temperature effect on plant development can be represented using the thermal time approach. In order to calculate the thermal time, the base temperature, below when development stops or takes place at very low rates, is needed. This work was carried out to estimate the base temperature for node appearance and compared dates for cultivation for variable plastochron in watermelon crop. Three field experiments were conducted in Santa Maria, RS, Brazil, with eight sowing dates during the 2006-2007 growing season (05/09/2006 and 21/09/2006), 2008/2009 (20/09/2008, 06/10/2008, and 20/10/2008) and 2009/2010 (20/09/2009, 21/10/2009, and 30/11/2009). The cultivar "Crimpson Sweet" was used in a randomized block design with four replications per sowing dates. The accumulated number of nodes on the main stem (NN) of watermelon was observed in three plants, three times a week. Plastochron was estimated by the inverse of the slope in the linear regression of NN against accumulated thermal time. The temperature base estimated using the least Mean Square Error (MSE) approach was 7.0 °C. The plastochron in watermelon was not different among sowing dates during the three growing seasons, with an average of 23.4 ºC day node -1 . From a modeling perspective, the implications of these results are that a single plastochron value can be used to simulate node appearance of the "Crimpson Sweet" cultivar, regardless of the sowing date.

This paper explores different models of non-destructive leaf area estimates for Solanum melongela L. by the measure of leaf length (C) and blade width (L). The methodology involved eggplant cultivation in the greenhouse from March to June. Plant leaves were sampled at random throughout the growing season, totalizing 186 leaves, of which 98 were used to estimate the model parameters and 88 were used for model validation. The samples covered wide spectrum of leaf dimensions, in order to minimize root mean square error (RMSE). Leaves were sampled at 71, 79, 81, 85, 92 and 99 days after transplanting. The highest possible numbers of leaf discs were obtained with a 25mm auger. Correlations were computed between the leaf area obtained by the discs method and the linear dimensions of L and C, the product of both (CL) and the square length multiplied by the width (C Estimativa da área foliar da berinjela em função das dimensões foliares ResumoEste trabalho explora diferentes modelos não destrutivos de estimativa da área foliar de Solanum melongela L. através de medidas do comprimento (C) e largura (L) do limbo foliar. Para tanto, um cultivo de berinjela em estufa plástica foi conduzido no período de março a junho de 2007. Amostraram-se folhas de plantas em momentos aleatórios totalizando 186 folhas, sendo 98 utilizadas na estimativa dos parâmetros dos modelos e 88 para sua validação. As amostragens abrangeram amplo espectro de dimensões foliares, visando minimizar a raiz do quadrado médio do erro (RQME) ) apresentaram melhores estimativas, com R 2 de 0,964 para ambos e RQME de 33,2 e 34,4, respectivamente. Com a medida apenas de uma dimensão foliar, o modelo quadrático (Y = -63,5+10,492L+0,2822L 2 ; R 2 = 0,937; RQME = 44,1) apresenta-se como alternativa, pouco afetando a precisão da estimativa..Palavras-chave: Solanum melongela L., índice de área foliar, modelagem.

The aim of this study was to identify soybean sowing dates on which there was low water surplus risk. The crop was raised on a Haplic Planosol soil in the Central Depression of Rio Grande do Sul, Brazil. Soybean development simulations and daily water balances were calculated for different sowing dates from August 1968 to July 2012. Water surplus data was subjected to BoxPlot analyses and Scott-Knott tests at a 5% error probability. Exponential, gamma, lognormal, normal and Weibull functions were tested and the best fits to the data were obtained for both subperiods and total cycle. The highest number of fits for the development cycle and subperiods were obtained using the gamma and weibull functions, respectively. For sowing carried out after November 1, there was a low water surplus risk in the sowing-emergence subperiod. The risk of water surplus during the development cycle decreased with the advance of the sowing date.

Sunflower crops are grown in different regions worldwide. However, the stress caused by water excess in the soil impairs this crop growth and yield. The aim of the present study was to determine the response of sunflower plants to long periods of water excess during initial development stages. Water excess treatments were applied at the initial development of these plants at the sowing day, three days after sowing, at plant emergence, and at V2 and V4 stages. The treatments had different duration periods (0, 48, 96, 144, 192, and 240 hours) and were applied at three sowing dates. The current experiment is factorial and was carried out according to a completely random design. Two plant pots, treated under greenhouse conditions, made up the experimental units. Plant emergence, leaf area, plant height, shoot dry mass, maximum root length, main root length and root dry mass were herein assessed. Water excess is more harmful to sunflower plants during the sowing-emergence period. It substantially reduces emergence, plant density, shoot and root growth, even after 48-hour stress. Moreover, water excess leads to the formation of adventitious and secondary roots.