MAIZE/CORN
Scientific Name- Zea mays
Maize is the third most important crop utilized by man based on the land area devoted to the crop.
USES
Maize is used for the following purposes:
1. As a staple human food, particularly in the tropics;
2. As feed for livestock, particularly in temperate and advanced countries, providing over two third of the total trade in feed grains;
3. As a raw material for many industrial products.
4. As ornamental, the plants are occasionally grown for ornamental use in the garden
5. As biofuel, "Feed maize" is being used increasingly for heating. Maize cobs are also used as a biomass fuel source. Maize is increasingly used as a feedstock for the production of ethanol fuel. Ethanol is mixed with gasoline in order to decrease the amount of pollutants emitted when used to fuel motor vehicles.
CLASSIFICATION
Botanical: family: Graminae; Genus: Zea, Species: mays. Maize is a tall annual grass belonging to the tribe maydea. It is a cereal with a determinate growth habit and is monoecious. Monoecious means the male and female flowers are present on the same plant. Maize can also be classified as forage or silage crop due to its importance as a livestock feed.
STAGES OF MAIZE DEVELOPMENT
It is important and convenient to be able to specify the exact stages of growth for proper crop management and pest control. In maize certain stages have been identified, namely: germination; vegetative; floral initiation; flowering (anthesis and silking); physiological maturity. Biologically speaking, the period from germination to the onset of floral initiation constitute the vegetative stage. However, for management purposes, the vegetative stage continues until the appearance of the male flowers since the floral initiation is invisible to us. From flowering to physiological maturity constitute the reproductive stage. Physiological maturity: is the stage where the flow of photosynthetic products to the seeds ceases. After physiological maturity, the seed undergoes a drying process until it reaches harvestable or field maturity. At harvestable maturity, the seed is ready to be harvested.
STAGING SYSTEM FOR MAIZE DURING VEGETATIVE GROWTH
Growth and development
Staging during this period of growth is based on the number of leaves that have been fully pushed out (fully expanded). Thus, the different stages are obtained by simply counting the number of Fully Expanded leaves. A fully expanded leaf is the one in which the legule is visible from a vertical position without ripping the leaf apart. Alternatively, a fully expanded leaf is the one, which extends enough such that its tip points below a horizontal line and is also arched over.
Stage 0: plan to emergence
Growth stage 0: from planting to seed emergence
During germination, the growth point and the entire stem are about 25 to 40 mm below the Soil surface. Under warm, moist conditions seedlings emerge after about six to 10 days, but under cool or dry conditions this may take two weeks or longer. The optimum temperature range for germination is between 20 and 30 ºC, while optimum moisture content of the soil should be approximately 60 % of soil capacity. Two leaf stage: two leaves are fully expanded. The first circle of crown/nodal roots is still unbranched. The primary roots, especially the radicle are well developed and have root hairs.
Four leaf stage: four leaves are fully expanded. The second circle of crown roots lengthens. The first circle has branched and root hairs are present. The primary roots grow very little after this stage. During this stage the tassel is initiated in the growing point, which is still belowground. Thus, damage to the leaves, such as effect of hail storm or frost may not affect the plant seriously since the growing point is still below the soil surface, it might only reduce yield slightly. Water login at this stage, on the other hand could cause a serious damage since the growing point would be flooded.
After the four leaf stage the following developments takes place:
Increase in height of the plant, appearance of more leaves, development of more crown roots, development of tillers from the nodes just below the soil surface and the tassel (growing point) is pushed above the soil surface, but still in the stem and invisible externally. Cobs are initiated at the stem nodes above the soil surface but are invisible externally.
Six leaf stage: six leaves are fully expanded. Crown roots constitute major part of the root system. The third circles of nodal roots lengthen. The rowing point is level with or just above the soil surface. The plant at this stage is absorbing more nutrients and deficiencies may become obvious.
Eight leaf stage: eight leaves are fully developed. The fourth circle of crown roots extends. This stage is characterized by active leaf growth. Stem lengthens rapidly and the growing point is about 5 to 8 cm above the soil surface. Nutrient deficiency will restrict leaf growth at this stage.
Ten leaf stage: ten leaves are fully expanded. Tassel and cob develop fast and nutrient uptake is high. Moisture and nutrient deficiency at this stage onwards will hamper cob development and lead to yield loss. Damage from hail at this stage has a greater effect than previously since plants broken below the growing point will not recover.
Twelve leaf stage: twelve leaves are fully expanded. Prop roots start developing on the first nod. There is rapid accumulation of dry matter from now onwards. Moisture and nutrient deficiencies will adversely reduce ear size.
Fourteen leaf stage: Fourteen leaves are fully expanded. The stalk lengthens rapidly. The tassel has virtually reached mature size. Prop roots develop.
Sixteen leaf stage: sixteen leaves are fully expanded. The tassel appears and the silk lengthens quickly, emerging only a few days later. Moisture shortage and nutrient deficiencies will retard silk appearance and may result in poor pollination due to pollen shortage. This would result in poor yield. Complete removal of leaves by hailstorm will result in virtually total crop loss.
REPRODUCTION AND GRAIN FILLING STAGE
TASSELED: Tassel fully extended. Ear shoot exposed but no silk showing. Husks opened on the ear shoot would show the silk longer than the cob. No pollen evidence. Plant has reached maximum stature.
POLLEN SHED: Pollen shed begins 2to3 days after tasseling. Silk not yet emerged and intercept pollen. This is the fertilization period.
SILKING: Silks emerged and intercept pollen. This is the fertilization period.
SILKS BROWN: Pollen shed almost complete. 75% of silks on earshot show purple to brown color. Silks are darkening but not dry to touch.
PRE-BLISTER: Pollination complete. Silks are all brown but still not dry. Not fluid in seed coat and kernel has appearance of a pimple.
BLISTER: Kernels appear as watery blisters. Kernel is white and fluid is colourless. Removal would only leave a hull.
EARLY MILK: Beginning of roasting ear stage. Kernels contain thin layer of milk substance.
MILK: Cob has reached its maximum length. Kernel contain milk but no solids.
LATE MILK: Milky fluid thickening and solids forming in the outer portion of the kernel.
SOFT DOUGH: Kernel content becoming pasty or semi fluid-solid. First few kernel dents showing at the bottom end of ear.
EARLY DENT: Kernels on entire ear show a dent. Kernels content mostly a thick gummy substance, but milk is still easily expressed when kernel is squeezed.
FULL DENT: All kernels deeply dented. Outer ends of kernels (away from cob) are solid and dry.
HALF MILK: Kernel milk line is midway between tip and base of kernel. Kernel moisture is about 40%.
¼ MILK: Kernel milk line has moved ¾ of way from tip to base of kernel. Some milk can still be expressed from kernel base. Kernel moisture is about 35%.
MATURE: All milk has disappeared from the kernel. The black layer is usually present. Kernel moisture is 30 to 32%.
TYPES OF MAIZE
Division into different types is based on endosperm (starch) characteristics quality, quantity and pattern of endosperm composition.
Dent Maize (Zea mays indentata )
- Pericarp is medium thickness
- Dented on upper part (crown) of kernel
- Mature endosperm contains both soft and hard
- Upper part of kernel and the central core contains soft (floury) starch
- Side of the lower part contains hard (flinty) starch surrounding the soft starch
- Dent is due to shrinkage of soft starch during kernel drying
- Distribution: world wide
- Level of importance: 73% of world ‘s production. The most important of ali the maize
- Uses: human consumption (millground meal), livestock feed, industrial processing (starch)
Flour maize (Zea mays amylase)
- Very thin pericap
- Composed entirely of soft starch
- Slightly dented at the mature crown
- Easiest to grind by hand
- higher in lysine –easily moulded before harvest in wet areas.
- Distribution: Latin America, USA.
- Level of imporatnce: 12%
- Uses: direct human use for hand ground meal, direct consumption at milk stage (minor)
Flint maize (Zea mays indurata)
- Thick pericarp
- Mostly hard endosperm
- Almost impossible to grind by hand
- Soften by boiling in lime and wet grind
- Crown is hard and rounded good storage and germination abilities
- Distribution: Argentina, Southern Europe
- Level of importance:
- Uses: human food
Popcorn (Zea mays everta)
- Very thick pericarp
- Mature endosperm is hard (flinty) & kernel is small
- Crown of kernel is either rounded (pearl type) or pointed (rice type)
- Distribution: USA
- Level of importance:
- Uses: confection
Sweet corn (Zea mays saccharata)
- Thick to medium pericarp
- Endosperm is glassy (translucent)
- Crown is wrinkled
- Contains high level of simple sugars
- Normal conversion of simple sugars to starch during endosperm development is retarded-dry sugary kernels are dry and wrinkled and glassy
- Distribution: North America
- Level of importance:1%
- Uses: direct consumption at milk stage
Pod maize (Zea mays tunica)
- Each kernel is enclosed in its own glume (husk)
- Mainly an ornamental plant
CULTURAL PRACTICES IN MAIZE PRODUCTION
Cultural practices refer to all the management practices that need to be considered to ensure successful production of a crop. These include: soil preparation, choice of cultivar or variety, planting date, planting density, planting depth, fertilization, irrigation, pest and disease control, weed control, cropping practice, harvesting and storage.
SOIL PREPARATION
This is carried out through tillage practices and the method used is influence by factors such as soil type, history of cultivation, surface residue available moisture, local temperature, topography, availability of implements etc. Conventional or traditional approach involves ploughing followed by one or two disking. The plough serves to loosen the soil and bury surface residue and weed seeds. The disk provides a friable rooting zone. Residue helps to conserve moisture, maintain cooler soil temperatures and may suppress weeds in some instances. In cold regions leaving residues on the soil surface could pose some problems because of the cooler soil temperatures may delay planting and can reduce germination and emergence. Since the growing point of maize remain below the soil surface for a long time until about the sixth leaf stage, it is important to control the amount of surface residue so as not to reduce the soil temperature too much. After successive years of minimum tillage, it is important to break the cycle with one deep plough to burry surface weed seeds, which tend to build up under minimum tillage. On newly selected areas, which had been fallowed for some years, it is important to plough first. On continuously cropped area, one or two disking may be sufficient. Deep ploughing on deep slopes is not advisable as this could enhance soil erosion. Ploughing should also be minimized on sandy soils to reduce erosion (wind or water) and moisture loss.
CHOICE OF CULTIVAR
Cultivar or variety has a pronounced effect on yield of maize and therefore careful attention needs to be given when selecting a cultivar for an environment. The choice of cultivar will depend on factors such as, environmental potential of an area, yield goal, prevailing diseases and pest in the production area, managerial skills of the producer, funds, market etc. The environmental potential refers to the extent of availability of natural growth resource in the production environment. Under high production environment, high yielding cultivars should be selected. High yielding cultivars usually demand high external inputs such as fertilizer and moisture. Therefore, if these cultivars are selected for areas with low potential, more of the external inputs will be required to sustain the yield and this could proof to be expensive and less profitable. Yield goal is the yield the farmer desire to obtain at the end of the season. This is determined by the environmental potential of the area and the farmer’s ability to provide external input. Cultivars that are resistance to diseases and pests in production area must be selected to avoid complete crop loss. In very windy environment it is important to consider lodging resistance varieties.
VARIETIES OF MAIZE
1. Open pollinated variety
2. Hybrid variety
OPEN POLLINATED VARIETY
As the name implies, this variety is produced through cross-pollination where there is an uncontrolled pollen source. Thus, kernels on cob will have different pollen source for fertilization. There is a great deal of variability in the maize plant in an open pollinated field. Desirable plants are harvested and the seeds sown in the following season. Since the seeds from a selected cob were pollinated by pollen of different genetic make-up, the resulting population after planting would have a great deal of variability. Thus, the main disadvantage of the open pollinated varieties is the variability, which may reduce its market value. The advantage is that the farmer does not need to by the seeds year after a year. Small-scale farmers usually plant this type of variety.
HYBRID MAIZE VARIETY
A hybrid maize variety is a first generation offspring of a cross between parents with constructing genotype (genetic makeup of an organism). The parents are obtained from the inbred lines. Thus, crossing inbreds lines develops hybrids. There may be single, double, three-way or multiple crosses.
Guidelines for selecting maize cultivars
Cultivar choice, if correctly planned, can make a great contribution to risk reduction and should constitute an important part of production planning. Cultivars differ from one another with regard to a variety of characteristics. Therefore, every cultivar has its own adaptability and yield potential. These differences between cultivars leave a producer with alternatives that can be utilised fully. The producer should, however, first verify the reaction of new or foreign cultivars before abandoning proven cultivars.
a. Yield potential and adaptability
As a result of a wide diversity of conditions under which maize is produced in South Africa, it is essential that cultivars that are eventually planted should be adapted to specific production conditions. Cultivars with wide adaptability can be used to stabilise yields under variable weather conditions of South Africa. Together with adaptability, stability of cultivars should also be considered. Greater stability of a cultivar, leads to predict ability of yield reaction at a specific potential.
b. Length of growing season
The length of the growing season of cultivars plays an important role, especially in cooler production areas. The cooler environment causes large differences among cultivars in the period from planting to flowering and physiological maturity and accentuates differences among the various growing periods.
c. Disease resistance
Cultivars differ in their susceptibility to diseases such as ear rot, maize streak virus disease, grey leafspot, rust, cob-and-tassel smut, stem rot as well as root rots. Cultivars with the best levels of resistance or tolerance to a disease should be selected for planting where a specific disease occurs.
d. Lodging
Lodging of plants has a financial implication for the producer, because a number of ears may be laying on the soil, making it uneconomical to be picked up by hand. Good progress has been made with cultivars showing less lodging, but differences among cultivars still occur.
e. Ear prolificacy
Prolificacy can be described as the potential of a cultivar to produce more than one ear at maturity. This characteristic is linked to the adaptability of a cultivar and can be used to good advantage where lower plant populations are required or where it develops spontaneously unintentionally. Exotic varieties of maize are collected to add genetic diversity when selectively breeding new domestic strains. There is an occurrence of drought between late December and late January in most maize producing regions of South Africa so it is important to time your planting so that this stress period does not coincide with anthesis and grain fill. Check your cultivar for days to flowering and days to maturity hen planning planting date. Maize is planted in November and December under dry land conditions, but could be planted in September under irrigation. However, under dry land conditions, planting can commence as soon as groundwater and soil temperature are suitable for good germination. If a minimum air temperature of 10 to 15 ºC is maintained for seven successive days, germination should proceed normally. Virtually no germination or growth takes place below 10 ºC. Planting should be scheduled such that the most heat and water sensitive growth stage of maize (i.e. the flowering stage) does not coincide with midsummer droughts.
PLANTING DEPTH
Planting depth of maize varies from 5 to 10 cm, depending on the soil type and planting date. Under good planting depth the ideal planting depth for maize is 5 cm. Sandy soils permit deeper planting depth than soils with high clay. As a rule, planting should be shallower in heavier soils than in sandy soils. Under moisture stress conditions, deep planting may be advantageous to ensure adequate moisture for seeds. However, if temperature colds, it is better to plant shallow to ensure rapid germination.
PLANT POPULATION
Plant population and row width
Plant populations also known as plant density refers to the number of plants per unit area and it is influenced by inter row spacing (row width) and intra row spacing (spacing within rows). Row width in many parts of the country is maintained at 90 cm. The amount of water available to the crop has a great influence on plant population. In very dry regions, maize population of about 15 000 plants per hectare is recommended under rainfed conditions. Up to 60 000 plants per hectare has been reported has been reported under more favourable conditions. Plant population per unit area is more important than specific row width. Row widths under dryland conditions can vary from 0,91 m to 2,1 or 2,3 m, depending on mechanical equipment available and type of soil tillage system used. If maize is being produced for silage, a higher population can be used. Increasing plant population does not always lead to increasing yields. There is optimum density where yield is maximum.
FERTILISATION OF MAIZE
It is of the utmost importance that the correct soil sampling methods be used when submitting samples for laboratory analysis. Fertilization in maize should be based on production potential and soil nutrient status. If this is ignored high potential soils could be under fertilized while low potential soils are over fertilized. On the hand, infertile soils could be given too little fertilizer and fertile soils too much. Efficient use of fertilizer could be obtained through establishment of sound fertilizer programming. Fertilizer programme are developed on characteristics of soil, plant and climate. Maize, like any other crops requires specific rates and ratios of the essential elements; N, P, K, Ca, Mg, S, B, Fe, Cu, Mo, Cl, C, H and O.
Fertilizer application method
• Broadcast – fertilizer should be applied when moist or wet or at irrigation
• Banded – application should be deeper than were the seed is placed
• Foliar – fertilizer should be applied through the leaves
• Fertigation – fertilizer should be applied at irrigation
WEEDS
Successful cultivation of maize depends largely on the efficacy of weed control. Weed control during the first six to eight weeks after planting is crucial, because weeds compete vigorously with the crop for nutrients and water during this period. Annual yield losses occur as a result of weed infestations in cultivated crops. The annual yield loss in maize because of weed problems is estimated to be approximately 10 %. The loss occurs as a result of weed competition for nutrients, water and light. The presence of weeds during harvesting may slow the process, pollute grain with seeds, transmit odours to grain, causing downgrading, or incur additional costs for removal of seeds. Certain seeds, such as those of the thorn apple (Datura), may be poisonous when consumed by animals or humans.
Methods of weed control
a. Physical methods
Weeds can be removed mechanically, by implements or by hand. Dense stands of weeds may be burnt as an emergency measure.
b. Cultural practices
Ploughing during winter or early spring is an effective method of destroying the majority of weeds. To control weeds during the season, crops may be planted in wide rows for mechanical control. Certain problem weeds in maize can be controlled by an alternative crop where crop rotation is practised.
