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<strong>AGRONOMIJAS</strong> VĒSTIS (Latvian Journal of Agronomy), No.10, LLU, 2008tool in modeling plant growth and dry matter accumulation, especially in canopy, where there is nolimitation of development due to unavailability of water or mineral nutrients, and eventually toother unfavorable climatic conditions, diminishing value of RUE (Stockle and Kiniry, 1990;Runyon et al. 1994; Ruimy et al., 1995). The RUE depends mainly on the crop, developmentalphase, intensity of CO 2 assimilation, nitrogen nutrition of plants, occurrence and severity ofeventual droughts, temperature and degree of plant infestation with diseases (Faber, 2000,Reynolds et al. 2000). It is strictly joint to the canopy architecture, being according to Ross (1981)‘a set of features involving shape, size, geometry and external structure of plant’. A reciprocal ofRUE is used in Varlet-Grancher formula.A substantial progress in breeding cereals has been observed last years in Poland. Formswith reduced contribution of hulls to grain in the case of hulled species (barley, oat) weredeveloped. Such new forms are called hulless (barley) or naked (oat), in the literature (Nita, 1999).Developing of these forms may increase both nutritional and forage value of grain. Newlyintroduced to the national register oats cultivars differ among others in the view of needs to fertilizethem with nitrogen. Apropriate nitrogen fertilization enables this crop to develop and maintain theadequate for effective PAR absorption canopy, thus affecting the yielding. Recognition ofphysiological responses of plants forming oat canopy to differentiated nitrogen fertilization willenable much better exploitation of yielding potential of newly registered varieties.The aim of investigation was to evaluate a capacity of solar energy absorption and its usefor biomass production in two oat morphotypes (hulled or naked) cultivated under differentiatednitrogen fertilization.Materials and MethodsTwo factorial field experiment in randomized blocks with 4 replications was conducted inDepartment of Agronomy of Warsaw University of Life Sciences experimental field Chylice. Thesoil was a degraded black earth formed from clay sand of ice accumulation on light burden clayand was that of rye good complex. There were two oat cultivars investigated: Chwat (hulledmorphotype) and Akt (naked one). Nitrogen was provided as ammonium nitrate at 5 rates (0, 30,60, 90 and 120 kg N ha -1 ). The all rates 30 and 60 kg N ha -1 were applied two days presowing(27.03), whereas in the case of rates 90 and 120 kg N ha -1 , first 60 kg N ha -1 were provided alsopresowing, while the remaining 30 or 60 kg N ha -1 at culm growth (30.05). Thus, with two cultivarsand 5 rates of nitrogen fertilization there were 10 experimental combinations resulting in 40 plots(20 for each cultivar). Plot area was 30 m 2 (12 m x 2,5 m).During vegetation on five occasions 1.05 (32 day after emergence DAE, according toZadocks et al., 1974), 16.05 (47 DAE), 28.05 (59 DAE), 13.06 (75 DAE) and 28.06 (90 DAE)above ground plant dry mass (g m -2 ) to calculate maximum dry matter biomass and PARtransmission to the bottom of canopy were determined. The latter was done one directly abovecanopy, then three times at its bottom with two replicates, using AccuPAR Model PAR-80(Decagon Inc., USA). Grain yield was determined at harvest.Taking into account data characterizing global radiation reaching the canopy (R s ) measuredat experimental field Chylice meteorological station, PAR recorded by ceptometer and cropbiomass, the following indices (Varlet-Grancher et al. 1993) were calculated: e b = CdW c /PAR c -biological efficiency of transformation PAR intercepted by canopy, e c = 1- PAR c /PAR i - efficiencyof PAR absorption by the canopy, RUE, e - energy yield being a product of e b , e c , e r and R s ;assuming the e r fraction of R s global solar radiation in the PAR range as 0.476 (according to stationand ceptometer instructions) and C - free energy released during hydrolysis of chemical bonds ofphotosynthetic products as 17 KJ g -1 (Varlet-Grancher et al., 1993); dW c - biomass formed in giventime period. Obtained data were analyzed using two-way ANOVA (Statgraphics 3.1). First orderfactor was cultivar, second one – rate of nitrogen fertilization.ResultsDifferences in above ground dry matter biomass of oats were much smaller as comparedfor that in grain yield (Table 1). It points to much better distribution of assimilates in cv. Chwatthan cv. Akt. On average, naked morphotype yielded worse by 52.8 % as compared to traditionalone.162
<strong>AGRONOMIJAS</strong> VĒSTIS (Latvian Journal of Agronomy), No.10, LLU, 2008Table 1. Grain yield in dependence on cultivars and nitrogen fertilization, t ha -1Cultivars Nitrogen rate, kg N ha -1 Biomass d.m., g m -2 Grain yield, g m -20 3260 275530 3652 3058Chwat60 4465 318890 4580 3266120 4018 3058Mean 3995 30650 3240 138530 4083 1429Akt60 3806 174190 3747 1853120 4153 1836Mean 3806 1649In the case of hulled morphotype nitrogen fertilization up to 90 kg N ha -1 increased bothbiomass dry matter and grain yield, while with the hulless one although the effect of this rate wasthe same in the case of grain yield, the 30 kg N ha -1 was quite enough for canopy growth.Efficiency of PAR absorption by the oat canopy fertilized or not fertilized with applied inexperiment nitrogen rates was higher in traditional cultivar Chwat (Table 2, significance ofdifferences see Table 4). Nitrogen fertilization affected efficiency of PAR absorption by the canopy(e c ) as well as that of biological transformation of intercepted radiation in both studied oatmorphotypes.Table 2. Indices of energetic analysis in dependence on cultivars and nitrogen fertilizationCultivars Nitrogen rate, kg N ha -1 Indices of energetic analysise c e b0 0.596 0.03430 0.617 0.038Chwat60 0.656 0.04690 0.668 0.047120 0.651 0.042Mean 0.638 0.0410 0.559 0.03430 0.604 0.042Akt60 0.625 0.03990 0.622 0.039120 0.624 0.043Mean 0.607 0.039e b – biological efficiency of transformation PAR intercepted by canopy,e c – efficiency of PAR absorption by the canopy, RUE,e r – 0.476 the fraction of global solar radiation in the PAR rangeValue of e c for cv. Chwat, was increasing with fertilization rate up to 90 kg N ha -1 , whileefficiency of PAR absorption in cv. Akt canopy increased with fertilization rate up to 60 kg N ha -1 .Efficiency of biological transformation of PAR absorbed by the canopy (e b ) was similar for controltreatment of both cultivars. In the case of cv. Chwat taken across the combinations it was a bithigher in cv. Chwat as compared to cv. Akt (0.041 vs 0.039). The e b in this cultivar increasedfollowing nitrogen fertilization till the rate of 90 kg N ha -1 . In naked morphotype fertilization with30 kg N ha -1 caused substantial increment of e b by 0.009 as compared to the control. Combinationsfertilized with 60 or 90 kg N ha -1 characterized with a bit less e b values comparing to that fertilizedwith 30 kg N ha -1 . The combination of naked morphotypes given the highest fertilization rate ofnitrogen (120 kg N ha -1 ) showed maximum biological efficiency of PAR transformation. Analysisof energy yield (e) of studied cultivars showed again cv. Chwat prevailed over cv. Akt in thisrespect (Fig. 1).163
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