Abstract
This experiment was made to determienthe effect of various soil moisture contents in simulated drought conditions on different stages of rice growth. The drought conditions were developed at such three rice-growing stages as transplanting, immediately after transplanting and young ear forming. Three different lengths of drought periods, which are ten days, twenty days and thirty days, were applied for each growing stage of rice. The rice variety used this experiment is Nong-rim 29. This experiment was conducted at the university farm of the Kon-Kuk University during the period of $1968{\sim}1970$. Three reprications for each of 12 treatments and split plot design were employed in this study. Bottomless wood square boxes, $1^m{\times}1^m{\times}1^m$, were burried in the test plot and box top was covered with poloyethylene sheets to avoid natural rainfall drops. Standard plots were irrigated continuously with a water depth of 40mm/day and those of drought treatments were irrigated continuously up to the beginning of the planned drought period, and they were irrigated again with a depth of 40mm/day up to the maturing stage of rice. Other methods for rice raising followed those methods developed by the Field Crops Experiment Station of the Office of Rural Development. During this experiments, climatic conditions in regard to rainfalls, sunshine hours, and temperatures were observed. According to this observation, those values measured deviate slightly from the annual means. However the growing condition of rice plants were normal. The pH value of irritation water is nearly neutral, and soils in the test plots are relatively fertile, being similar to ordinary paddy soils. Analysis of variances for number of stalks, plan-height, ear sprouting date, length of stalks, ear length, number of ears per plant, fertility, grain weitght, weight of plant, and yield were carried out. The variances for plant height, ear sprouting date, length of stalk ear length, and yield has statistical significance under drought treatments applied at three different growing stages. The variance showing the effect of lengths of drought period is highly significant for all the treatments studied except that of grain weight. The interaction between drought periods and drought treatments at different growing stages is significant for plant height, stalk length, ear length, number of ears, fertility and yield, these results indicated that droughts at different growing stages have influence on plant height, ear length, yield, and length of drought period also has strong influence on all factors studied except grain weight. The combination of drought treatments at different rice growing stages and lengths of drought periods has different effects on various agronomic characteristics, including yield. Plant height under drought treatment practiced at transplanting stage is the lowest, and drought treatment applied immediately after transplanting resulted in the least number of stalks. The effect of different lengths of drought periods on plant height and number of stalks depends signis ficantly on increasing days of drought. Ear sprouting date tends to be delayed for one or two days undedrought treatments at transplanting period and with increasing days of drought. Better yield is secured in drought treatment applied immediately after transplanting. Adverse effect war observed when drought treatment was applied at ear forming period. These effects may be attributed to the alternation of irrigation and drought causing vigorous root activity. In general, yield linearly decreases as the length of the drought period increases. The results obtained in this study demonstrate that, in order to mimimize damage due to drought, and, to save irrigation water, paddy fields, immediately after transplanting, may be not irrigated, since there is sufficient moisture in the soil, and that sufficient irrigation water should be applied again in the ear forming stage of rice plant.
본 시험은 한발시기를 이앙적기연한발구와 적기이앙직후한발구 그리고 유수형성기한발구별로 처리하고 한천일수를 10일, 20일, 30일간 단수했을 때의 벼 생육과 수량에 미치는 영향을 구명하였다. 가. 기상상항은 평년에 비해 일반적으로 성화에 비가 많았고 일조시간은 적었으며 온도는 비슷한 편으로 벼 작항에는 별차이가 없었다. 나. 관개수질은 중성으로 양호하였다. 다. 본 시험포의 토질은 비옥토가 양호한 편으로 일반 답토양과 비슷한 성질의 것이었다. 라. 분얼기의 생육상항은 하발 유형별로 보면 이앙적기지연한발구가 다른 처리구에 비해 초장은 가장 부량하였으나 분얼수는 가장 많았고 이앙직후한발구에서 분얼수가 가장 적었다. 한천일수별에 있어서는 일반적으로 한천일수가 길수록 초장 분얼수가 현저히 부량하였다. 마. 출수상항은 이앙지연한발구가 다른 처리구에 비해 $1{\sim}2$일정도 늦은 경향이었다. 하천일수별에 있어서는 일정한 경향이 없었다. 바. 성숙기의 생육 및 수량상항에서 한발시기별을 보면 이앙직후 한발구가 다른 처리구에 비해 양호하였고 유수형성기한발구가 가장 부량하였다. 한천일수별에 있어서는 한천일수가 길수록 생육 및 수량이 현저히 감소되었다.