21 RELATIONSHIP BETWEEN LEAF AREA INDEX, BIOM ASS AND WINTER WHEAT YIELD OBTAINED AT FUNDULEA, UNDER CONDITIONS OF 2001 YEAR Elena Petcu 1) , Gheorghe Petcu 1) , Cãtãlin Lazãr 1) , Roxana Vintilã 2) 1) Agricultural Research and Development Institute (A.R.D.I.), 915200 Fundulea, Calarasi County, Romania 2) National Research and Development Institute for Soil Science, Agroindustry and Environment Protection, 61 Bd. Marasti, 011464 Bucharest 1, Romania ABSTRACT Several data of the ADAM (Assimilation of Data within Agricultural Models) project were used to establish the relationships between agronomic variables of winter wheat. During the campaign 2000 -2001, ten calibration units from seed production farms of A.R.D.I. Fundulea were selected based on several factors of variation, such as: the cultivar (Dropia and Flamura 85); the preceding crops, soils with different microtopography and nitrogen fertilization. Positive correlations between leaf area index and biomass of winter wheat in different developmental phases were found (from r = 0.66* to r = 0.84***). The bio- mass was correlated with yield (r = 0.65*), number of seeds and number of ears/m 2 (r = 0.63*, r = 0.72**), too. The results of regression analysis indicate that polyno- mial models gave the best fit for regression of total bio- mass and LAI (max) on harvest index and linear model for grain yield. The coefficients of determination be- tween harvest index and total biomass are smaller than those b etween harvest index and grain yield. This means that wheat crops with the highest harvest index do not necessarily have the highest biomass accumulation. In fact, the opposite can be true. The magnitude of coeff i- cient of determination for the regression of total bio- mass and grain yield on harvest index indicates that ap- proximately 0.34 % of the total variation of total biomass can be attributed to variation in harvest index of the ana- lysed wheat crop. The low correlation of this study be- tween LAI and TKW (r = 0.29) indicates that these two traits are largely independent of each other. In fact, TKW depends on the genetic background as some research- ers have reported. Key words : leaf area index (LAI), winter wheat biomass, grain yield INTRODUCTION he theory and the agricultural practice con- cerning the formation of photosynthetic systems with high productivity have shown that the high and qualit ative yield is conditioned by numerous factors. Among them, the environmental factors with direct effect on photosynthetic activ- ity, but also the physiological state during growth and development of the plants are very important. An optimal combination of these factors, is necessary, but the dependence between internal factors with environmental ones is not enough known. Recently, the leaf area index or other ind ices of vegetation have been used in agricultural mod- els for biomass estimation and yield prediction (Major et al., 1986; Tucker et al., 1980). The objective of this paper was to establish the relationship between leaf area index, biomass and wheat yield. MATERIAL AND METHODS The investigations were performed at Fun- dulea during 2000-2003 in the framework of the bilateral collaboration project with France (ADAM project). The paper presents the results of the 2000-2001 campaign, when ten experi- mental locations were sampled. The selection was achieved by combining several possible factors of variation including: cul- tivar, the preceding crop, micro-topography and the nitrogen fertilization; the wheat experimental locations were placed in Progresul 1, Tipei, Cul- turi Irigate and Ileana farms of A.R.D.I. Fundulea (Table 1). The leaf area index and biomass measure- ments were performed on about 10 day basis and the used samples corresponded to 3-4 replicates of 0.5 m on two adjacent rows randomly located. The yield and its components were also deter- mined. RESULTS AND DISCUSSION The mean and range for leaf area index (one of the most important biophysical index involved in several canopy functioning processes, Baret and Vintila, 2003) and biomass of the wheat crop in the experimental locations are presented in table 1. The variability obtained in this study is the result of the crop management. The highest leaf area index (6.34) and biomass (1534.4 g dry mat- T