Effect Of Plant Spacing And Intermittent Flooding On Growth And Yield Of Selected Lowland Rice Varieties In Mwea Irrigation Scheme

Paddy rice productivity in Mwea Irrigation Scheme is low partly due to water shortage, inappropriate plant spacing and low yielding varieties. There is need for water saving practices and appropriate agronomic practices to enhance paddy rice productivity. A study with the main objective of enhancing rice productivity in Mwea Irrigation Scheme through optimal plant spacing and improved water management was conducted during March to July 2015 season and August to December 2015. The specific objectives of the study were: (1) to establish farmers’ agronomic practices for paddy rice production with respect to spacing and water management; (2) to determine the effect of intermittent flooding on growth and yield of selected rice varieties; and (3) to determine the effect of plant spacing on growth and yield of selected rice varieties. For the first objective, a detailed farmer survey was conducted across five sections of Mwea Irrigation Scheme namely: Karaba, Wamumu, Thiba, Tebere and Mwea. Two hundred farmers were interviewed using a pre-tested semi structured questionnaire with 40 farmers randomly selected from each of the five sections. Data collected included: method of transplanting, age of seedlings at transplanting, number of seedlings per hole, depth of transplanting, number of years farmers had been in rice production, sizes of land owned by farmers, whether soil testing was done in the fields, net grain yield attained in the field, frequency of irrigation, stages at which irrigation was done, knowledge on when to irrigate the rice fields, depth of irrigation, whether farmers drained the fields , plant spacing used in the fields, the reasons for choice of the type of spacing and challenges in rice production. Descriptive statistics analyses using frequencies and means were performed using Statistical Package for the Social Sciences (SPSS) program version 20. The field experiment was set up in a randomized complete block design with a split-split plot arrangement and replicated three times. The treatments consisted of two irrigation regimes (intermittent flooding and continuous flooding), three varieties (Saro5, Basmati and IR-2793-80- xi 1) and four different spacing arrangements (15 cm ×15 cm, 20 cm×15 cm, 25 cm×15 cm and 30 cm×15 cm). Data on plant height, number of tillers, number of effective tillers, number of days to maturity for each variety, panicle length, grain yield adjusted to 14% moisture content and 1000-grain weight were collected. Data were analyzed using Genstat 15th edition and treatment means were compared using the least significant difference (LSD) test at P ≤ 0.05. All interviewed farmers reported that they transplanted seedlings rather than direct seeded. Over 90% of the farmers transplanted one month or older seedlings at a rate of two seedlings per hole and at a depth of 2 cm. Most interviewed farmers had been in rice cultivation for 6-20 years, owned 1-2 acres and produced 2001-5000 kg/ha. Most farmers irrigated their fields once a week at a depth of ≤ 10 cm. Majority of interviewed farmers used plant spacing of 30 × 15 cm and 20 × 20 cm which they associated with increased yields. Water shortage, high input prices and low market prices were the major challenges farmers faced in rice production. Rice variety Basmati 370 had significantly taller plants and longer panicles than IR-2793-80-1 and Saro 5. Variety IR-2793-80-1 had significantly higher number of tillers per plant and number of panicles per plant than Saro 5 and Basmati 370. In the first season, IR-2793-80-1 had significantly higher net grain yield than Saro 5 and Basmati 370 while in the second season Saro 5 had significantly higher net grain yield than Basmati 370 and IR-2793-80-1. Basmati 370 had significantly lower 1000 grain-weight than Saro 5 and IR-2793-80-1 in both seasons. Plant spacing did not have a significant effect on plant height and panicle length. Number of tillers significantly increased with increase in plant spacing. Irrigation regime had no significant effect on number of tillers per plant in the first season, but continuous flooding significantly increased the number of tillers per plant at reproductive and maturity stages. Plant spacing of 30×15 cm had higher panicles per plant than all other plant spacing arrangements in both seasons. Plant spacing of 15 × 15 cm had higher xii grain yield than all other spacing arrangements in the first and second season. Irrigation regime did not have a significant effect on plant height, panicle length, panicle number and 1000 grain-weight in both seasons. Intermittent flooding had significantly higher grain yield than continuous flooding in the second season. Variety and plant spacing interaction effects on the number of tillers per plant and number of panicles were significant in both seasons. Transplanting was the most preferred method of planting. Most farmers used plant spacing of 30 × 15 cm and practiced continuous flooding of their rice fields. Plant spacing of 15× 15 cm was the most productive in net grain yield followed by 20 ×15 cm. Variety Saro 5 and IR-2793-80-1 had the highest net grain yield in both seasons. Intermittent flooding recorded higher net grain yield than continuous flooding and saved 44.4% water. This study has therefore demonstrated that cultivation of the recently introduced variety Saro 5 and intermittent flooding have the potential to improve rice productivity in Mwea Irrigation Scheme.