Relationship between growth duration and grain yield of rice plants

Transcription

1 Soil Science and Plant Nutrition ISSN: (Print) (Online) Journal homepage: Relationship between growth duration and grain yield of rice plants B. S. Vergara, A. Tanaka, R. Lilis & S. Puranabhavung To cite this article: B. S. Vergara, A. Tanaka, R. Lilis & S. Puranabhavung (1966) Relationship between growth duration and grain yield of rice plants, Soil Science and Plant Nutrition, 12:1, 31-39, DOI: 1.18/ To link to this article: Published online: 29 Mar 212. Submit your article to this journal Article views: 1487 View related articles Citing articles: 6 View citing articles Full Terms & Conditions of access and use can be found at

2 (Soil Science and Plant Nutrition, Vol. 12, No. 1, 1966J RELATIONSHIP BETWEEN AND GRAIN YIELD OF RICE PLANTS* B.S. VERGARA, A. TANAKA, R. LILIS, AND S. PURANABHAVUNG The International Rice Research Institute Los Banos, Laguna Manila, The Philippines RECEIVED APRIL 12, 1965 Rice varieties differ greatly in the time required from sowing until harvest. These periods often are strongly influenced by planting date and maturation in five months or more after seeding is common in the tropics. Obviously, a short duration crop would have several advantages over a long duration crop, even with equal total grain yields. A short duration crop would require less water per crop; would be less exposed to hazards such as insects, pathogenic organisms, drouths and typhoons: and would increase the time the land would be available for subsequent plantings of rice or other crops. It is possible that the varieties now commonly grown in the tropics have unnecessarily long growth durations (13-2 days). Considerably earlier varieties might yield as much or more. It should, therefore, be determined if there is an optimum growth duration for producing maximum grain yield under certain field conditions and following certain cultural practices, such as spacing and nitrogen application. Field experiments were thus conducted during the wet and dry seasons to study the relationship between growth duration and grain yield. Materials and Methods Experiment 1. Dry season Planting. Forty varieties whose growth durations (number of days from sowing to harvest) ranged from 92 to 193 days were used. The early varieties were mostly japonicas from Japan and the later varieties were indicas from Malaysia. The seeds were sown in December on wet seedbeds and transplanted 2 days later in the field at a spacing of 25 x 3 em, using one plant per hill. Forty kg./ha. each of N, P,o. and K,O were added to the field before transplanting. Experiment 2. Wet season planting. Forty-nine varieties were used. Their growth durations ranged from 1 to 2 days, the early varieties coming mostly from Taiwan and the late varieties from Malaysia. The seeds were sown in June and the cultural practices followed were similar to those of Experiment 1. Experiment 3. Effect of spacing on the optimum growth duration during the dry season. Ten varieties were selected from those used in Experiment 1 : Fujisaka 5, Hakkoda, Sukwel 2, Nang Quot, Cuon Trau, Tjere Mas. Peta, , Acheh, and Serayap. Their growth duration ranged from 8 to 15 days. In Experiment 1, the grain yields of these varieties tended to increase with an increase in growth duration. The seeds were sown in December and transplanted 16 days later in the field, using one plant per hill. Fifty kg./ha. of N and 4 kg./ha. each of P,O. and K,O were added to the field before trans planting. The spacing used were: 1 x. 1, 25 x 25, and 5 x 5 em. Experiment 4. Effect of nitrogen level on the optimum growth duration during the dry season. The same varieties were used as in Experiment 3. The seeds also were sown in December and transplanted 16 days later at a spacing of 25 x 25 em, using one plant per hill. Forty kg./ha. each of P,O. and K.O and,5, and 15 kg.fha. of N were added to the field before transplanting. In all the experiments, leaf area and light trans mission ratio were measured at 5 percent flowering. Leaf area was measured by blue printing. The light intensity above the plants and at the ground surface inside the plots was measured with a Toshiba light meter. At harvest, yield, components of yield, height, and straw weight were recorded. The nitrogen content of the panicles and straw was determined by the semi microkjeldahl method. The carbo hydrate content at flowering and at harvest of plants from Experiments 3 and 4 was determined by the Somogyi method. Results Experiment 1. Dry season planting. Grain yield tended to increase with an increase in growth duration up to 14 days and then de- *Submitted as IRRI Journal Series No. 4 by the International Rice Research Institute. Mail Address: Manila Hotel, Manila, Philippines. 31

3 B.S. VERGARA, A. TANAKA, R. LILIS, AND S. PURANABHAVUNG.. c o LAI o LTR s Days 2 16 = 12 Total plant weaght o P/S ratio a " l!;; :: < :: t- <;;- d z.5 a: Fig. 1. Grain yield, total plant weight and panicle straw ratio of 4 varieties with different growth durations planted in the dry season. creased. The optimum growth duration, under the conditions of this experiment, was days (Fig. 1). Within the range of 9 to 16 days, total plant weight increased with increased growth durations, while durations of more than 16 days were associated with little or no further increase in dry weight (Fig. 1). The paniclestraw ratio decreased as the length of the growth period increased. The panicle-straw ratios were highest in plants with high grain yields. The failure of growth durations longer than 16 to result in further increase in plant weight is attributed to two factors. One is the limitation in nutrient supply to the plants, especially nitrogen. Nitrogen content of straw at harvest decreases with the increase in growth duration and remains at around.5 percent with a further increase in growth duration (Fig. 2). The other factor is the limitation in space for leaf expansion involving the leaf area index (LAI) of the plant and 32.. t-.,. < t-., t- ;::: I Days 2 Daya Fig. 2. Leaf area index, light transmission ratio at flowering stage and nitrogen percentage of straw at harvest of 4 varieties with different growth durations planted in the dry season. the light transmission ratio CL TR). In this experiment, the LAI increased with the increase in growth duration, while the L TR in the plant population decreased (Fig. 2). After a certain growth duration, the increase in leaf area and the decrease in L TR began to level off in spite of the new leaves that were constantly being formed. This resulted from the death of the lower leaves. The two above-mentioned factors decrease the growth rate after a certain period, i.e., the general activity weakens at the later stages of growth, especially with the long duration varieties. This may result in a small paniclestraw ratio. The number of panicles per plant varied markedly with growth duration; however, it decreased when the growth duration Was especially long (Fig. 3). The number of spikelets per panicle tended to be largest in the plants with growth durations of 13 to 17 days.

4 3 RELATIONSHIP BETWEEN AND GRAIN YIELD OF RICE PLANTS, :.. ' WI 16 IMO 2 Days un :::2 ton ' f = loll tho 2 Days 1611 IKO 2fiU llavfl Days '! L..JIO_O!; :. 2 ' 8. I.:) 1 : L...LI- IJ_2 :_1:-'41-I,---:-: :1:7;:M;------=2 Oays ' I.L2--=-' :-:16::------:1-::K;------:2;:. Days Fi&'. 3. Yield components of 4 varieties with different growth durations planted in the dry season. The short and long growth duration varieties gave the highest percentage of sterility while growth durations associated with maximum yield gave the lowest (Fig. 3). The number of grains per panicle changed with growth duration as a result of the changes in the spikelet number per panicle and the percentage of sterility. It increased with the increase in growth duration up to the optimum growth duration, then decreased. The mean grain weight, which is relatively constant in most varieties, showed no correla tion with growth duration (Fig. 3). The regularity of flowering seems important in determining the yields of the early and very late varieties. Flowering was not uniform in the very early varieties: there were many immature panicles at harvest. In the very long l!iu 2UU l>anl GROll Til Ill" RATIO Fig. 4. Grain yield, weight of total plant and dead leaves and panicle-straw ratio of 49 varieties with different growth durations in the rainy season. duration varieties, several tillers within a hill or even entire hills did not flower at all. Experiment 2. Wet season planting. The varieties used had growth durations of 1 to 2 days, while those of the previous experi ments had 9 to 2 days. The results of the rainy season planting showed no optimum growth duration. Although grain yield varied from 2, to about 5, kg./ha., no particular growth duration was as sociated with the high yields (Fig. 4). Total plant weight increased with an in crease in growth duration (Fig. 4). As noted earlier, however, this increase in dry matter did not result in an increase in grain yield. A great part of this increase went into leaf production as evidenced by the increase in the amount of dead leaves with the increase in growth duration. This relationship between dry matter production and grain yield was also shown in the panicle-straw ratio. During the rainy season, the panicle-straw ratio was generally lower, and it decreased with the 33

5 B.S. VERGARA, A. TANAKA, R. LILIS, AND S. PURANABHAVUNG increase in growth duration (Fig. 4). Data from the wet season planting suggest that a short growth duration is preferable to a long one. Although grain yield is more or less the same in plants with growth durations of 1 to 2 days, short growth duration plants,would be more efficient in grain production per unit of time. In the rainy season there was a tendency for the LAI to decrease with increased growth duration, the reverse of the relationship found with the dry season planting (Fig. 5). In the wet season planting, even the early varieties had a high LAI ( wet season, dry season), indicating a more rapid leaf area production. The ceiling LAI is probably reached earlier during the rainy season so that the increase in growth duration does not further increase the LAI. For similar reasons, the L TR curve starts at a low level compared to the dry season planting. The percentage of nitrogen in the straw at flowering decreased with the increase in growth duration and then leveled off (Fig. 5). Most of the vatieties had less than.7 percent ni- trogen which might be below the level for maintaining active photosynthesis; thus, these varieties probably produced only a small a mount of carbohydrates during the ripening phase. The grain yields, however, were just as high as the early varieties that had adequate nitrogen. Presumably, carbohydrates were accumulated to a great extent during the vegetative phase. Experiment 3. Effect of spacing on the optimum growth duration during the dry season. Figure 6 shows the yield response curves of varieties with varying growth durations planted at different spacings. The highest grain yields were obtained at 1X1 em. spacing. The slopes and the intercepts of these curves differed notably at the three spacings. At lox 1 em, the curve was almost horizontal and started at a high level (5,-6,5 kg./ha.), while at 5 X 5 em, the curve was steep and started at a low level (1,-2, kg./ha.). The three curves showed a tendency for the optimum growth duration to be reached earlier at a closer spacing. LTR LAI 1 8 I. i;j ;:: z 2 t:.'1em 25x25nt ')( 5x52cm 4 a o o : x--x::== xx )(>t Day Flr. 15. Leaf area index, light transmission ratio and nitrogen percentage of straw at flowering of 49 varieties with different growth durations planted during the rainy season Fig. 6. Grain production per crop and per day at different spacings of 1 varieties with different growth durations planted in the dry season.

6 RELATIONSHIP BETWEEN AND GRAIN YIELD OF RICE PLANTS The data clearly suggest that the greater the spacing, the longer should be the growth duration. However, at close spacing, yield was not greatly affected by growth duration as was also the case in the wet season planting. At loxlo em spacing, the early varieties gave a very high production efficiency (Fig. 6). Under ordinary spacing (25X25 em), productivity did not tend to increase or decrease with growth duration. At wide spacing, however, productivity increased with growth duration. This productivity is in a way related to the number of tillers per unit area which increases up to a certain growth duration, above which productivity is inversely correlated with growth duration. The large number of panicles per unit area accounted for the high yields at close spacings. The number of panicles per unit area, however, did not increase with growth duration (Fig. 7). In fact, it tended to decrease slightly... toxloc 25X25eat )( 5><5em-;;-- '"!!!1 w '2 7 IOxiOem o 25x25cm 5 lc 5x5em i. L_ 3 1 -X ---x !5 GRO\\TH DURATION Fii. 1. Number of panicles per square meter of 1 varieties with different growth durations planted in the dry season. The leaf area indices at loxlo em, 25X25 em, and 5 X 5 em spacings increased steadily with the increase in growth duration. However, the LAI at loxlo em was much higher than at the other two spacings, suggesting a rapid leaf area production at this close spacing. The nitrogen content of the plants at flowering decreased with the increase in growth duration at the three spacings used (Fig. 8). However, the nitrogen level increased with the increase in spacing. The long growth duration had a nitrogen level below the critical required for maintaining photosynthesis. At close spacing (loxlo em) lack of nitrogen may prevent higher grain yields. If the nitrogen applied to the soil was increased, higher yields might have been obtained at close l&o o.,.. LROWTH DURATION Fig. 8. Leaf area index, nitrogen percentage of straw at flowering and carbohydrates produced at flowering as percentage of the total carbohydrates at maturity of 1 varieties with different growth durations planted in the dry season at different spacings. spacing. Regardless of spacing, the early growth duration varieties produced a great amount of carbohydrates during their flowering and ripening phases while the late varieties produced a greater percentage before flowering (Fig. 8). The first three early varieties had at flowering 1 to 2 percent of the total carbohydrates at harvest while the latest varieties had 4 to 8 percent. The longer the growth duration, the more the dead leaves at flowering (Fig. 9). The amount of dead leaves also increased.with closer spacing. The lower nitrogen content in the plants at closer spacing may have contributed to this increase. Experiment 4. Effect of nitrogen level on the optimum growth duration during the dry season. As with spacing, growth duration affected the response to nitrogen. High grain yields were attained earlier at high nitrogen levels than

7 B.S. VERGARA, A. TANAKA, R. LILIS, AND S. PURANABHAVUNG f l Q 9 e lox o 25X X 5X Days Fig. 9. Dry weight of dead leaves at flowering of the 1 verieties planted at different spacings during the dry season Days Fl. 1. Grain yield at different levels of nitro gen of 1 varieties with different growth durations planted in the dry season. at low nitrogen levels (Fig. 1). The yield curve angle at different nitrogen levels be came less steep with the increase in nitrogen. As shown in Experiment 3, wider spacing required longer growth duration varieties and vice versa. In the present experiment, at N added to the soil, the relatively long growth duration varieties gave higher yields than the short duration varieties. This suggests that relatively long growth duration varieties may be better adapted to low nitrogen situations than short growth duration varieties and, perhaps, partially explains their widespread use in tropical regions. At high nitrogen levels (15 N). growth duration had less effect on yield - a result similar to that obtained at close spacing or wet season planting. The yields at high nitrogen level, however, were lower than those at close spacing (loxlo em). The LAI curve at 15 N increased rapidly, and the indices were high, similar to the LAI at 1X1 em spacing, suggesting again a rapid 36.., too -.- ;;:.. - i '.....,..----Q)I.... 2'-----,..,,-----'--.,"::--:-':::---...,..,-= Daya Fig. 11. Leaf area index, nitrogen percentage of straw at flowering and carbohydrates produced at flowering as percentage of the total carbohydrates at maturity of 1 varieties with different growth durations planted in the dry season at different nitrogen levels. leaf area production (Fig. 11). At and 5 N, LAI increased steadily with the increase in growth duration. The nitrogen content of the plants at flowering decreased with the increase in growth duration (Fig. 11). The percentage of nitrogen of the straw was more or less the same in the long growth duration varieties regardless of the nitrogen level in the soil at the start of the experiment. The carbohydrate content at flowering and at harvest showed a trend similar to that in : Experiment 3 (Fig. 11). Regardless of the nitrogen level, the short growth duration varieties produced more carbohydrates during the flowering and ripening phases, while the late varieties produced less. As in the previous experiments, the amount of dead leaves increased with growth duration. At N, the increase in number of dead leaves

8 RELATIONSHIP BETWEEN AND GRAIN YIELD OF RICE PLANTS was probably influenced by low nitrogen level. On the other hand, at 15 N the increase was probably related to lack of light, induced by heavy mutual shading (Fig. 12) !3!5 -l Q A 9 3 Oi'l o SON X!SON X !5 Daya GROWTH PURAT1N Fig. 12. Dry weight of dead leaves at flowering of the 1 varieties planted at different nitrogen levels during the dry season. Discussion YAMAKAWA and co-worker (1,2) pointed out the existence of an optimum growth duration in obtaining high grain yields. Under greenhouse conditions, VERGARA et al. (3) obtained high grain yields and found them to be associated with certain optimum growth durations. They observed that plants with growth durations shorter than the optimum produced fewer panicles and less spikelets per panicle. On the other hand, plants with growth durations longer than the optimum produced fewer spikelets per panicle, but the number of panicles per plant was the same as that of the plants with optimum growth durations. Field experiments using several varieties of different growth durations and varying nitrogen levels, spacing and planting season showed different optimum growth durations. The optimum growth duration actually involves a balance of growth processes throughout the life of the plant. This balance should result in the production of the maximum number of matured panicles, field spikelets, and mean grain weight. The balance which would result in high grain yields also may be achieved not only by getting high values for the three yields components but also by increasing one yield component to a high degree and at the same time decreasing slightly the other components. This means that the number of panicles may be very high but the number of grains per panicle could decrease slightly or vice versa. The balance of growth can be achieved by adjusting or manipulating such factors as nitrogen and spacing. Temperature, light intensity and daylength are factors difficult to manipulate except by adjusting the season of planting. Since the pattern of growth changes with season and varieties ( 4), the use of spacing and nitrogen in obtaining the balance of growth also changes with the materials used and the date of planting. Under field conditions, two factors, nitrogen supply and space limitations, seem to be mainly responsible for limiting the occurrence of the optimum growth duration. 37 A certain amount of nitrogen in the plant is necessary for efficient photosynthesis. A certain nitrogen level is also associated with carbohydrate accumulation. VERGARA et al. (3) have shown that, with short growth duration plants, almost no carbohydrates (starch and sugars) were accumulated during the vegetative and reproductive phases. With optimum growth duration plants (high yielding) small quantities were accumulated during the vegetative phase, large amounts during the reproductive phase and sizeable amounts during the ripening phase. With long duration plants, much carbohydrate was accumulated before flowering. Similar results were obtained in the present field experiments. Under field conditions, high nitrogen content in the plant decreases the percentage of filled spikelets (5). Since all the nitrogen applied in these experiments was added before transplanting, the short growth duration varieties had a higher nitrogen content than the long growth duration varieties, even at harvest. This may have accounted for the low percentage of filled spikelets and consequently, the smaller number of grains per panicle. Plants with optimum growth duration have an adequate nitrogen level to produce enough spikelets and at the same time have a high percentage of filled spikelets. On the other hand, plants with growth durations longer than the optimum apparently have a low nitrogen level, resulting in fewer spikelets and

9 B.S. VERGARA, A. TANAKA, R. LILIS, AND S. PURANABHAVUNG grains per panicle. The other factor affecting the optimum growth duration, space limitations, is reflected in LAI, L TR and the rate of leaf area production. At flowering, plants that were to give high grain yields showed relatively high LAI's. It does not necessarily mean, however, that plants with high LAI at flowering would give high grain yields. If a high LAI is obtained as early as the tillering stage, this condition may not be beneficial to the subsequent growth of the plant. In any case, leaf area production, L TR and nitrogen level are important in determining the optimum growth duration for a certain cropping season. Leaf area production and nitrogen content can be manipulated by using different levels of nitrogen and spacings. Under field conditions, these two limiting factors decrease the growth rate after a certain period as the relative growth activity at the later stages weakens (6). At close spacing (1X1 em) or at high N level (15 kg.jha. N) during the dry season, the leaf area production rate (LAI/t) was high. This resulted in a high LAI even for the early varieties. Net assimilation rate increases with the increase in LAI up to a certain point; it may then decrease with the further increase in LAI (7). The high LAI for early varieties planted at close spacing resulted in high production of carbohydrates at all stages of growth. KANDA and SA TO (7) showed the existence of an optimum LAI for rice plants. This optimum LAI is probably a major factor in determining the optimum growth duration. Close spacing seems a more effective way to attain a high LAI than increasing the nitrogen level or the wet season growing of early varieties. It should be pointed out here that a very high LAI at flowering does not always mean a high net assimilation rate or that high grain yields will be obtained. At a low nitrogen level or at wide spacing, the low leaf area production per unit area in the field and, hence, the poor utilization of sunlight per unit field area, seems to be a major factor in the low yields of the early growth duration varieties. At close spacing (1X1 em), an optimum growth duration was not evident during the dry season (from 8 to 15 days). At wider spacings, yield increased with growth duration. At higher nitrogen levels, high grain yields were obtained even with short growth durations. A significant point shown by the experiment is that at a low nitrogen level the longer growth duration varieties yielded more grain per crop than did the short duration varieties. This is a possible reason for the popularity of long growth duration varieties in the tropics where generally, a minimum a mount of nitrogen is applied to the soil. That the longer growth duration varieties yield better than short duration varieties may not, however, be true in soils with extermely low or extremely high nitrogen levels. The results showed that during the wet season growth durations had little or no relation to yield, and that grain yields were much lower than those obtained in the dry season. As grain yields during the wet season were more or less the same in the different vatieties used, short duration plants would appear to be preferable. In shifting the optimum growth duration to an earlier time, closer spacing is of primary importance; at the same time, higher levels of nitrogen are necessary. Summary Experiments were conducted to study the relationship between growth duration and grain yield under field conditions. During the dry season, maximum grain yields were associated with certain critical growth durations. On the other hand, the wet season planting showed no critical or optimum growth duration. Varying the spacing and nitrogen level during the dry season resulted in different optimum growth durations. Earlier optimum growth durations are possible by closer spacing and higher nitrogen levels. Under field conditions, two factors seem to be mainly responsible for the occurence of optimum growth duration, limitation in nitrogen supply and limitation in space. 38

10 RELATIONSHIP BETWEEN AND GRAIN YIELD OF RICE PLANTS Referances 1) YAMAKAWA, Y. and NISHIYAMA, H.: Agr. Bull. Saga Univ., 7, 1-48 (1958) 2) YAMAKAWA, Y. : Agr. Bull. Saga Univ., U, (1962) 3) VERGARA, B. S., Litis, R. and TAN AKA, A.: Soil Sci. Plant Nutrition, 1, (1964) 4) TANAKA, A.: Symposium on the Mineral Nutrition of the Rice Plant. p.37, Johns Hopkins Press (1965). 5) MA TSUSHIMA, S. : Theory and techniques of rice cultivation. Dept. Agr., Kuala Lumpur, Malaya. 257 p. (1961). 6) TANAKA, A. and KAWANO, K.: Plant and Soil (In Press) 7) KANDA, M. and SATO, F.: Sci. Repts. Res. Inst. Tohoku Univ.,Ser. D. Agr. U, (1963) 39