CONTRIBUTION OF SORGHUM TO GRAIN REQUIREMENTS OF KENYA

The Kenya government outlines the challenges facing the agricultural sector in its Vision 2030 blue print and reckons that the sector can play an increasing role in economic development of the country. For example sorghum is said to contribute up to 1 % of food grain crops. It has been noted that over one million hectares of land in semi arid regions is lying idle. This huge acreage is suited to various varieties of sorghum and other dry-land crops. Sorghum can play a leading role in food security if this land is reclaimed and put under proper use.

According to Opole et al, in his research titled, Improving Ratoon Management of Sorghum for Increasing Yields in Western Kenya, There has been on steady decline of the area under sorghum. By the year 1994; 175,000 hectares were covered by sorghum which yielded 108,000 metric tons. This reduced to 123,184 ha in 1999 which yielded 90,000 metric tons. The reduction was attributed to production constraints including competition from maize, reduced farm holdings and pests and diseases. By the year 2006, after amplified promotion of the crop as a solution to beat harsh environmental conditions, the acreage increased to 123,000 hectares.

CLIMATE CONDITIONS, SOIL AND WATER MANAGEMENT FOR SORGHUM

Sorghum is adapted to a wide range of environmental conditions and will produce significant yields under conditions that are unfavorable for most other cereals. Sorghum is particularly adapted to drought. Sorghum also tolerates water logging and can be grown in areas of high rainfall. It is, however, primarily a plant of hot, semi-arid tropical environments with rainfall from 250 mm that are too dry for maize but performs best with more than 900 mm annually.

It is also grown widely in temperate regions and at altitudes of up to 2500 m in the tropics. Sorghum tolerates a wide range of temperatures. Sterility can occur when night temperatures fall below 12-15°C during the flowering period. Sorghum is killed by frost.

Sorghum can be grown successfully on a wide range of soil types. It is well suited to heavy clay soils (vertisols) found commonly in the tropics, where its tolerance of water logging is often required, but is equally suited to light sandy soils. It tolerates a range of soil pH from 5.0-8.5 and is more tolerant of salinity than maize. It is adapted to poor soils and can produce grain on soils where many other crops would fail.

HUSBANDRY OF SORGHUM

Sorghum is a rain fed crop, sown after the onset of the long rain season. Where the seed bed is not fine it is paramount to increase the seeding rate to compensate for poor seed-bed or to allow for unfavorable moisture conditions. A fine seed bed is compulsory for better seedling establishment.

The planting field should be prepared well in advance of sowing. Seed rate is 7-10 kg/ ha or 3-4 kg/acre. Dry planting is highly recommended.  When dry planted, planting depth should be 5 cm but when planting in a moist soil use planting depth of 2.5-4 cm.  Row spacing is 75 cm and distance between plants about 20 cm. For semi arid areas, row spacing should be 90 cm and the spacing between plants is 15 cm. 

Sorghum requires about 20 kg N/ha and 20 kg P/ha at planting time, which can be supplied by alternate cropping with legumes and application of compost or manure. Also intercropping with legumes is recommended with grain legumes such as beans, cowpeas, pigeon peas and green gram. Manure and compost improve organic matter content of the soil, soil moisture retention ability and soil structure.

Manure can be broad cast in the field or applied in planting furrows and mixed with soil before seeds are planted. The standard farm wheelbarrow when full holds approximately 25 kg of dry manure/compost. At a low rate, two wheel barrows are enough for a 10m by 10m area. This translates into 200 wheelbarrows or 5 tons/ha. When aiming for high seed rate, apply 400 wheelbarrows or 10 tons of manure per hectare.

PROPAGATION AND PLANTING OF SORGHUM

Sorghum is normally grown from seed. A fine seed-bed is preferable but is often not achieved. The seed is usually sown directly into a furrow following a plough, but can also be broadcast and harrowed into the soil. Optimum plant spacing depends on soil type and availability of moisture. For favorable conditions, row spacing of 45-60 cm and plant-to-plant spacing of 12-20 cm, giving populations of about 120 000 plants per ha, are normal. For drier or less fertile conditions, wider spacing and lower plant populations are usually optimal. The seed rate varies from 3 kg/ha in very dry areas to 10-15 kg/ha under irrigation. Occasionally, seedlings are grown in a nursery and transplanted into the field early in the dry season, e.g. on the floodplains round Lake Chad in Africa

SORGHUM RATOONING

Ratooning is where a farmer gets more than one harvest from a single sowing. This is achieved by cutting the sorghum stalks to the ground level without removing the rooting system. When the roots from the previous season’s crop are in contact with some moisture, they produce tillers; which grow into full size plants.

A ratoon crop compared to a newly sown crop has an established root system which will utilize the available water in the root zone for crop growth early in the season, reduce plowing and planting labor and avoid migratory quelea birds in August by maturing early. To make best use of sorghum, this practice is preferred where environmental factors prohibit continuous cropping throughout the year.

Ratooning is important because starter water is reduced i.e. very little rainfall is required for the commencement of seed germination, crop growth and development hence the crop matures earlier. Yields per unit are reduced but not significantly when compared to yield from direct sowed seeds.

HARVESTING AND USES OF SORGHUM

HARVESTING OF SORGHUM

Sorghum is usually harvested by hand when it has reached physiological maturity - which means the grain is hard and does not produce milk when crushed. Cut the heads with sickles or a sharp knife from plants in the field or cut the whole plant and remove the heads later. Sun-dry the harvested panicles to moisture levels of 12-13 % and thresh and store the grain.

USES OF SORGHUM

Sorghum is a versatile crop. Some types are boiled like rice, some milled to flour for porridge, some "malted" like barley for beer, some baked like wheat into flatbreads, and some popped like popcorn for snacks. A few types have sugary grains and are boiled in the green stage like sweet corn. The whole plant is often used as forage, hay, or silage.

The stems of other types yield sugar, syrup, and even liquid fuels for powering vehicles or cooking meals. The living plants are used for windbreaks, for cover crops, and for staking yams and other heavy climbers. The seeds are fed to poultry, cattle, and swine

Mzee Matheka who lives in a village in Kitui district of Kenya says “The high cost of Kerosene has made us to use dried stems of sorghum for cooking. I don’t know where i could have got money to buy kerosene considering the hard economic times,” such stories abound in many parts of the world and the importance of sorghum is apparent.

Sorghum plays an important role as a food security crop especially in semi arid lands of Kenya. This is because of its adaptation where it rolls up its leaves and thus decreasing transpiration. Sorghum, changing fortunes Sorghum has been viewed as a crop for the poor and marginalized communities in the drought-prone arid and semi-arid regions of Kenya.

FACTORS AFFECTING THE POST HARVEST QUALITY OF CUT FLOWERS

The most important factors affecting the life of cut flowers in addition to maturity stage include;

  1. FOOD SUPPLY

This refers to respiratory metabolites. In a cut flower, all the metabolites are channeled towards flower development. Starch sugar stored in the stem, leaves and petals provide much food needed for flower opening. Simple nourishing food for flowers is sugar but sugar is also a suitable substrate/ food for bacteria hence you need a good preservative

Vase life can be improved by supplying food (sugar) after harvest. e.g. in tuberose and gladiolus in which flowers open further up the spike, flowers are bigger and have a longer vase life when ‘pulsed’ with a preservative solution containing 20% sucrose prior to shipping.

In those flowers where foliage is part of flower quality, e.g. Alstroemeria, if supply of carbohydrates is inadequate, leaves ‘blacken’. Tuberose flowers pulsed with 20% sucrose showed an increase of florets opening from 34% to 57% and an increase of vase life from 5-11 days.

2. TEMPERATURE

This is the most important factor because it influences the factors. Flowers are living and respiring. Respiration increase exponentially with temperature; Temperature also affects the rate of water loss, growth and development, production and response to ethylene, growth of microbes.

To reduce water loss temperature must be kept low. Flowers held at 30⁰ will respire 45 times faster than flowers held at 2⁰ C. Rapid removal of field heat and optimum storage temperature for cut flowers is 0-2⁰ C for tropical flowers, e.g. anthuriums, strelitzia and orchids, storage temperature of between 10-15⁰ C.

3. WATER SUPPLY

Plants are about 80-90% water. Cut flowers have a high surface area to volume ratio, and frequently have many leaves; hence are prone to loosing water much more rapidly compared to most perishable commodities. By detaching the flower, its source of water supply is cut off. Cut flowers should be stored under high relative humidity 95% to minimize water loss; particularly during long term storage. Loss of water causes loss of quality, accelerated aging, ethylene production, flowers can be rehydrated provided there is no obstruction to water flow. Movement of water in the stems of cut flowers can be obstructed in a number of ways:

4. AIR EMBOLISMS

The water column in the xylem vessels is under tension due to transpiration. When the stem is cut, this tension is released and a small bubble of air enters each conducting tube.

The air bubbles do not move up the stem, and may restrict water flow when the stem is placed in a vase. Removal of embolism is re-cutting the stem about 2.5 cm under water. Rehydration is improved by acidifying the vase solution ph 3.5 or by heating the vase solution to 40⁰ C

5. WATER QUALITY

Alkaline water does not readily flow through the cut flowers stems. Use or hard water can therefore substantially reduce flower vase life. This problem can be overcome by acidifying to a PH of 3.5-4.0 citric acid is commonly used. HQC (Hydroxy quinine citrate) at a concentration of 250ppm is also effective.

6. BACTERIAL PLUGGING

Sugar solution enhances vase life; but it is also an excellent substrate for the growth of bacteria and fungi. Bacterial and fungal growth is further enhanced by materials that leak out of the cut stem ends. Substrates produced by the bacteria, and the bacteria and the bacteria themselves may rapidly clog the fine tubes of the water conducting system. Buckets should therefore be regularly cleaned to prevent growth of bacteria (biocides like HQC)

7. PHYSIOLOGICAL PLUGGING

When a plant is cut, wounding occurs. To protect the wound, the plant produces latex (phenolics and tannins). The exudates leak into the vase solution and are later absorbed with the water. Being gummy, they block the vascular system of the cut flower; thereby hindering free flow of the vase solution. To restore free flow, re cut the stem to remove the cemented end of the flower.

8. ETHYLENE

Certain flowers especially those of caryophyllaceace family (carnations and gypsophilla) senesce rapidly if exposed to minute concentrations of ethylene. The higher the available ethylene concentration, the sooner the flower will bloom and wilt. In general, that ethylene can induce different damage symptoms including

a) Short longevity/vase life

b) Insufficient opening of the flower bud

c) Early wilting

d) Drop of buds and petals

e) Drop of buds and petals

f ) Discoloration of the flowers

Ethylene can occur at concentrations of 1-5ppm is already detrimental to cut flowers. Flowers should be handled in areas with the least ethylene contamination. Effects of ethylene can be minimized by holding produce at low temperatures and by using ethylene inhibitors e.g. silver thiosulfate and 1MCP