Crop establishment in Kenya is by direct seeding or random transplanting. Rainfed rice farmers sow the crop by direct seeding. Under irrigated ecologies rice seeds are first planted on a seed bed or nursery, before transplanting 21-30 days after emergence. These operations are manual and/or involve planter use depending on scale of operation.
Rainfed Rice Ecologies
Most farmers in Kenya broadcast their rice seed at planting. Broadcast planting consists of a random distribution of seed on the seed bed. Seed coverage is carried out using either oxen drawn ploughs after broadcasting or by using oxen to pull large tree branches across the seed bed. The broadcast method of sowing has been found to be disadvantageous because the seed distribution is not uniform, optimum seeding depth and coverage are not easily achieved, seed losses to birds, rodents and insect pests is high and it is difficult to weed.
There are three methods of direct planting used under rainfed ecologies in Kenya. Seeds may be planted by dibbling, drilling or broadcasting.
There are three main methods of planting dibble, drill and broadcast.
• Dibbling - rice planted in hills
• Drill - rice is planted in rows
• Broadcasting - seed is randomly thrown onto the field
Three to five seeds are direct planted per hill and latter thinned to 2-4 seedlings at 14 to 21 days old. If germination percentage is less than 80%, the seed rate should be increased. The recommended seed rate using row drill spacing is 50 - 75 kg ha-1 depending on the moisture availability. Under rainfed conditions, drilled and hill planting methods using 50 – 75 kg ha-1 attains highest net benefits and grain yield. Irrigated cultures have lower seeding rate especially under system of rice intensification.
A spacing of 25 cm x 15 cm with 3 plants per stand for dibble sowing is recommended. The seed rate works to 50 kg seed ha-1. However, drill planting is recommended at an inter-row spacing of 25 cm by drill using similar seed rate of 50 kg ha-1. In case of poor germination, gap filling is recommended. However, with use of good seed quality, germination is greatly improved.
A sowing depth of 2-3 cm is recommended. Deep placement of seeds at more than 3 cm results in poor germination and delayed growth, and low grain yield. Planting at depth of more than 4 cm will result in low and delayed seed emergence. If there is no adequate rainfall after sowing, shallow planting (less than 1.5 cm) may result in low seeding emergence due to low moisture content of the surface soil.
Time of sowing
Planting under rainfed conditions should be at onset of rainy season so that adequate moisture at critical periods and sustains good growth. The optimum yields of rainfed rice are obtained when planting is done at a time which allows peak rainfall to coincide with maximum water requirement. Planting at onset of rainy season also allows maturity to coincide with a dry harvest period. Grain yields of early, medium and late maturing varieties are likely to reduce as planting is progressively delayed from December to April. Late planting reduces number of days to maturity and lowers grain yield though increased incidence of blast disease. Peak water requirement occurs between 20 and 70 days after emergence during the time of peak tillering, flowering and grain filling stages.
Irrigated Rice Ecologies