Ramasamy et al. - 1997 - Yield formation in rice in response to drainage an

More documents

Recommendations

Info

14 S. Ramasamy et al. / Field Crops Research 51 (1997165-82 observed effects of drainage on each of the above intermediary processes are summarized in Table 4 and discussed below. 4. I. Yield components Yield differences between drained and undrained plots were directly related to the number of filled grains per panicle. The number of panicles per m’ and the number of spikelets per panicle were not much affected, or were even slightly smaller under drained conditions. The formation of panicles and spikelets is determined by the rate of crop growth at the tillering and early ear development stages, respectively (e.g., Yoshida and Parao. 1976; Seito et al., 1990; Islam and Morison, 1992; Hasegawa et al., 1994). The absence of differences in sink capacity due to drainage is therefore consistent with the absence of drainage effects on pre-flowering growth. 4.2. Pre-flowering growth, N uptake and leaf area Dry matter production is determined by light interception (leaf area) and light use efficiency, both of which are closely related to leaf nitrogen content (e.g. Sinclair and Horie, 1989). During the preflowering stage, drainage did not significantly affect growth in our experiments, nor did it alter the total amount of N in leaves. Leaf area was reduced slightly in response to drainage. These observations were consistent in Expts. l-3. 4.3. Post-flowering growth, N uptake and green leaf urea During the grain filling stage, biomass accumulation increased significantly due to drainage in all three experiments. In Expt. 1, however, the extra biomass production under drained conditions could account for only 20% of the grain yield increase. Miyasaka (19701 found that N uptake increased after the panicle initiation stage with improved drainage. N uptake in drained fields was indeed greater in our Expts. 1 and 3, but not in 2 (Tables 2 and 4). Because larger grain yields were, nevertheless, also attained in Expt. 2, it is concluded that yield response to drainage is not necessarily based on increased N uptake. Table 3 Effects of drainage and N application on translocation of stem carbohydrate reserves and nitrogen (N,) in race cultivar IR50 (Expt. 3) at Coimbatore, Tamil Nadu. India, during 1991 Treatments N,,, N at maturity (kg/ha) a N, (kg/ha) Wkwx Stem carbohydrates (kg/ha) a green leaves dead leaves ’ translocated (kg/ha) total h Leaves 0”.N-loo D;N150 Q-N200 42.7 I .l 14.2 (0.33) 15.9 26.8 0.63 51.1 2.1 15.2 (0.30) 17.3 33.0 0.66 57.8 2.5 18.8 (0.32) 21.3 36.5 0.63 Q-N100 D;N150 D, -N200 45.2 8.1 12.1 (0.27) 20.2 25.0 0.55 5 1.2 9.3 13.1 (0.26) 22.4 28.8 0.56 51.2 10.0 13.8 (0.24) 23.8 33.4 0.50 Stems D;NlOO D;N150 D;N200 D;NIOO D;N150 D, -N200 40. I 16.7 (0.40) 23.9 0.60 2400 53.2 18.9 (0.36) 34.3 0.64 2647 56.3 - 24.0 (0.43) 32.3 0.57 2483 57.6 - 11.3 (0.20) 46.3 0.80 2857 64.3 - II.3 (0.18) 53.0 0.82 3100 68.6 12.2 CO.18) 56.4 0.82 3187 * N,,, IS the maximum amount of N observed in plant parts (leaves. stems) at any ttme during the growth period. Calculation of N, is explained in the text. ’ Figures in parentheses are amount of N in dead tissue, relative to N mar of the corresponding organ.
S. Ramsamy et al. /Field Crops Research 51 (1997) 65-82 15 Nodal root length 8; l- ‘-. 6. E 5- &\ f 4. Aa -- D” E 3- - Dn+N Flowering / ;2- FL . -~I--- .~~ =:+, 0 20 40 60 SO 100 120 Days after transplanting Fig. 3. Effects of drainage and N application at heading on the length of nodal roots of rice cultivar IR20, Coimbatore, Tamil Nadu, India, 1991- 1992, Expt. 4. D,: undrained, D,: drained, N: nitrogen application at heading. For further treatment details see text. Alpha-naphthylamine oxidation power by roots 0 50 100 150 Days after transplanting Fig. 4. Effects of drainage and N application at heading on the oxidizing power of roots in rice cultivar IR20, Coimbatore, Tamil Nadu, India, 1991-1992. Expt. 4. 0,: undrained, D,: drained, N: nitrogen application at heading. For further treatment details see text In two experiments (Expts. 1 and 3), drainage was associated with greater green leaf area and a larger amount of bulk leaf nitrogen NL (g N per m’ ground area). To analyze whether photosynthetic activity per unit bulk leaf N increased during grain filling in response to drainage, we determined the factor fc,,, defined by the relation G=f,, .p.NL[l -e-EK/(P*v~ ‘1 (Ten Berge et al., 19961, where G (g m-* d-‘) is the crop growth rate, R is the daily incident global radiation (MJ m-’ d-l), p is the initial leaf nitrogen use coefficient (fixed at 10 g g-’ d-l) and E the initial global radiation use coefficient (fixed at 2.5 g MJ-‘1. The factor f,, is an empirical calibration coefficient, accounting for all variations in growth arising from factors other than R and N,. This coefficient was determined by fitting the growth curves G(t) calculated by Eq. (1) to the observed growth curves, using measured time series R(t) and N,(t). A significant increase of the post-flowering f,, value in response to drainage was observed in Expts. 2 and 3, but not in Expt. 1. (During the pre-flowering phase, effects of drainage on f,, were absent in all experiments.) Earlier leaf senescence was recorded in the undrained plots, but must be eliminated as the primary cause of poorer grain filling, because smaller grain yields in undrained soil were not always (Expt. 1) associated with an equivalent decrease in total dry matter production (see also Fig. 1). Leaf senescence is often viewed as the result of N extraction from leaves and translocation to growing (1) panicles (e.g., Sinclair, 1990). The present study does not fully confirm this concept, because Expt. 2 produced more grain in drained conditions, without additional N uptake, yet with less leaf senescence than in undrained plots. Moreover, N content in ‘early’ senescent leaves (just after flowering) was lower (0.3% N) than in leaves that senesced later (0.7% N near maturity); and N concentration in senescent leaves was greater in undrained plots. These observations indicate that senescence is not just the result of N extraction from leaves. This view is supported by Herzog and Geisler (1982) who proposed that leaf senescence in wheat is induced by competition (ear versus leaf) for a limited pool of growth regulators, rather than carbohydrates or N. Un-drained Drained AT PI T-F MR Fig. 5. Effect of drainage on root color in rice cultivar IR50 at Coimbatore, Tamil Nadu. India, 1991. Expt. 3. at crop stages AT (active tillering), PI (panicle imtiation). FF (first flowering) and MR (maturity). Means over all N levels. Observations in Expts. 1, 2 and 4 were similar. For treatment details see text.
Page 1 and 2: ELSEVIER Field Crops Research 51 (1
Page 3 and 4: S. Rarnrrsamy et al. /Field Crops R
Page 5 and 6: S. Ramasamy et al. /Field Crops Res
Page 9: S. Ramasamy et ~1. /Field Crops Res
Page 13 and 14: S. Rarnasanq et al. / Field Crops R

Ramasamy et al. - 1997 - Yield formation in rice in response to drainage an

Create successful ePaper yourself

Delete template?

Save as template?