Farming

Crop Establishment

The establishment of a crop is one of the most important stages since decisions taken at sowing will affect the entire life cycle of the crop. Usually, the seed company will provide planting recommendations for a hybrid. At this stage, the following points are noteworthy.

  • Know and implement the recommended planting split between the female and male. This will be specified in the planting instructions for the hybrid, and may require more than one sowing of the male in some cases.
  • Apply a field-marking system to identify which rows are planted to the male and female. If mechanical planters are used, clearly mark the male seed box. If hand planting is used, know the row ratios and which are the male and female rows. At sowing, place markers on the field edge at each male row so that these may be identified by laborers and throughout the growing period to ensure that only the female rows are detasselled.
  • Apply any special treatments, such as chemical seed dressings or fertilizer, to the parents and be sure to use only recommended herbicides. In some instances either or both parents may be susceptible to certain diseases or pests and will therefore require chemical control measures to assure a good harvest.
  • Ensure that planting equipment is thoroughly clean from contaminant seed before sowing Examples of foundation (basic) seed of female (single-cross) and male (inbred) parents. Note the different colored seed bags to assist in field identification of the two parental components.
  • After crop emergence, take plant stand counts to determine whether the desired plant density has been achieved. If plant densities are well below recommendations, re-planting may be required. Note that it is not advisable (or allowed in most certified seed regulations) to “gap-fill” plant stands that have inadequate numbers of plants at emergence. This is because differential growth and flowering will make it difficult to assure adequate seed quality.

Roguing: removal of off-types

During the vegetative growth of the seed crop, regularly inspect the field for pests, weeds, and diseases and control these as necessary. From the 6- to 12-leaf stage and before tassels emerge, remove off-types from both male and female rows. Off-types are usually clearly identifiable as taller or smaller, earlier- or later-flowering, or plants with characteristics distinctly different from the norm.

Descriptions of the distinguishing characteristics of the parents should be available from the seed company and will include aspects such as the angle of the leaf blade to the stem coloration of the leaf sheath and stem, and the shape of the tassel. Persons who conduct roguing must become familiar with these characteristics so that only off-type plants are removed. Off-type plants should be completely destroyed. Beware that in some cases, after cutting the off-type plant at the base, side shoots may grow and produce an undesirable cob and tassel. Thus, it is best to uproot off-type plants.

For efficient roguing, note the following recommendations.

  • Limit the roguing team to 10-12 people including the supervisor, because larger groups get easily distracted. If more people are needed to rogue the fields, divide into several groups and assign them to different parts of the field, giving specific responsibilities for specific sections.
  • Select responsible people for the roguing team and provide training on the identification and removal of off-type plants.
  • The team should start in a corner of the field and work through it slowly, walking parallel to and in the same direction down the rows.
  • Each member of the roguing team should have a narrow zone to observe. For maize consider a maximum of two adjacent rows.
  • Use large stakes to mark areas of the field that have been rogued.
  • The position of the sun and wind movement can affect the team’s ability to identify undesirable plants.
  • After several hours of roguing, a person tires and becomes less efficient. Thus it is advisable to rogue relatively few hours per day. Roguing teams may work most efficiently during the early morning or
  • late afternoon.
  • The supervisor should concentrate on overseeing and inspecting roguing team activities, than actually roguing.

When to rogue

Roguing should be conducted before genetic or physical contamination occurs and during times favorable for visual identification.

  • Rogue volunteer plants; these are easily identified by size and position out of the rows (post emergence).
  • During vegetative development, rogue off-type plants that deviate from the given genotype with respect to root and stalk development, plant type, pigmentation, leaf and stem pubescence, etc. Effective roguing during this period will help reduce the work load during the critical flowering period.
  • At the flowering stage, important agronomic and morphological characteristics can easily be identified. This is the critical stage to prevent genetic contamination of crop. Roguing on male plants must be complete before pollen shedding begins. Roguing on female plants should be complete soon after silk-emergence.

Detasseling

In hybrid maize seed production, detasseling of the female plants must meet the required standard and be conducted in a timely fashion. Any delays in detasseling or inadequate detasseling that result in tassel-stubs or missed plants will seriously diminish the genetic purity of the hybrid seed and might result in rejection for certification.

Note the following.

  • The tassels on the female plants must be removed before they begin to shed pollen.
  • Detasseling must commence when the top 3-4 cm of the tassel is visible above the leaf whorl.
  • Detasseling must continue every day until complete, come rain or shine.
  • Some female parent plant types are more easily detasseled than others.

For example, some female parents have tassels that are physically hard to pull out, others break easily and some begin shedding pollen before fully emerging from the upper leaves. Tall female plants, especially when the female is a single-cross hybrid, are difficult to detassel. In top-cross or varietal cross hybrids, where the female is an open-pollinated variety, the time of tassel exertion in the female population will vary. Lastly, with some parents, silks emerge much earlier or later than pollen shed. All these situations may be compounded and make for difficult detasseling supervision and potential management problems. Close supervision of the field is crucial.

Detasseling involves the removal of the tassel from female plants before pollen shedding.

  • Detasseling may take two to three weeks, depending on the field size, uniformity of the crop and labor availability.
  • About six people can detassel one hectare per day, but this rate will be a function of the difficulty of detasseling.
  • Individual workers may be allocated specific sections of the field to detassel, so as to give responsibility and accountability. However, monitoring each person’s detasseling effectiveness will be necessary to ensure that one or more laborers do not spoil the entire field.
  • Removal of more than one leaf with the tassel will reduce yields.

Mechanical detasseling to cut or pull female tassels improves efficiency but will require manual follow-up to remove any remaining tassels or stubs. Mechanical detasseling is not always possible on three-way hybrids because the females may be too tall for the machines to drive over the crop. Mechanical detasseling usually cuts or removes one to three of the uppermost leaves, which will reduce yields.

Synchronization of male and female flowers

Ideally, the male plants should begin shedding pollen when the first female silks begin appearing and they should shed pollen for as long as it takes for all the female silks to emerge. However, male and female plants do not always take the same time to reach flowering, due to different growth rates and environmental variations. Furthermore, the duration of pollen shedding may be shorter than the time for females to reach full silk emergence.

Any mistiming of male and female flowering will reduce yields and expose the female seed parent to contamination from foreign pollen. Pollen shedding and silk emergence may take place over 7 to 14 days and may not coincide, even if the male and female parents are planted on the same date. For example, the silks on the female may begin to emerge before the males begin to shed pollen. Indeed, the silks in the example were shown for five days before significant pollen shedding occurred, thereby exposing the female to possible contamination from foreign pollen. The time to 50% silking of the female occurred 64 days after planting, and the time to 50% pollen shedding on the male occurred 67 days after planting. To achieve a perfect nick (male-female flowering synchrony) in this case, the male would need to be planted three to five days earlier than the female.

If a male parent is an inbred line with a weak growth habit, or if it has a short pollen shedding period or does not produce a profuse amount of pollen, it is advisable to sow male plants on two (or even three) consecutive dates a few days apart, so that the pollen shed period covers the whole period of silk emergence. The split-planting of the male is usually done in two adjacent rows. To reduce the land required, the two split-planted male rows may be seeded relatively close together, compared to the female rows.

For example, if the normal row spacing is 90 cm, the two split male rows could be sown 45 or 60 cm apart, but 45 to 60 cm away from the adjacent female rows. Where the male does not produce an abundance of pollen, the female-to-male ratio should not be more than 3:1, whereas if the male is a profuse pollen producer (as in the case of a double-cross hybrid), the female-to-male ratio may be increased to 6:1 or even 8:1. In some cases, even with single- and three-way cross hybrids, a ratio of 6:2 may be planted, but the male must be a prolific pollen producer. In single-cross hybrid seed production, where the male and female inbred parents are of similar vigor and stature, a “squeeze-row” configuration may be feasible.

In this arrangement, the male row is planted at half the normal row spacing between alternate rows of females, which are planted at the normal row spacing. For example, if the female rows are planted in their normal row spacing, say 90 cm, then in every second female row-space, the male is planted at 45 cm from the female. Thus, the female: male ratio is 2:1, but effectively the female covers the entire field and the land is optimally used. However, it is important in this system to remove the male immediately after pollination, to reduce competition with the female.

Other methods of improving synchronization, especially where there is a small difference between the times of flowering of males and females, include the following.

  • Soaking the seed in water for 12 to 24 hours prior to sowing may advance flowering by 1 to 2 days. Soaked seed absorbs water and begins to germinate. It is therefore vulnerable to damage if mishandled. Water soaking only works with hand sowing into wet soil. Sowing soaked seed into dry soil will likely lead to poor germination and emergence.
  • Clipping the two-to-four whorl leaves of the male plants when four to six leaves have fully emerged (determined by the presence of leaf collars) is effective in delaying pollen shed by 2 to 3 days. However, if the plants are clipped too severely they may produce small tassels and less pollen than if not clipped. If clipped too late, there will be little effect on the time of pollen shedding, but tassel size may be reduced.
  • Burning male plant leaves with herbicide or flame at the three-to-five leaf stage may delay tasseling and pollen shed by 2 to 3 days. This has proven to be effective if burning is not excessive.
  • Adding extra phosphate and nitrogen fertilizer in the planting furrow of the male or female may hasten plant growth, particularly in soils that are not very fertile. But the hastening of plant growth may only cause flowering to occur one to two days earlier than if no fertilizer were applied or if fertilizer were broadcast.

Irrigation applied one to two weeks before flowering will ensure that the silks emerge at the expected time, especially if the weather is hot and dry at that time. In cases where male plants are insufficient due to germination failures, pollen may be collected from remaining plants, bulked into “pepper pots” and applied to the silks of female plants. Alternatively, or in addition, walking through the field at pollen shed with motorized mist-blowers can blow the pollen across the female rows and improve pollination.

Early detasseling can hasten the emergence of silks on females by one or two days. Cutting back the sheath on the ear can advance silk emergence by two to three days, but as the cob grows, it may extend out of the cut sheath leaves, exposing the tip to insects, birds, and diseases.

Male removal

As soon as possible after pollination, remove the males from the field. Male plants are cut at the base and either removed from the field or left to rot in the row. Removing males soon after pollination ensures that there will be no mixture of male and female seeds at harvest. Male removal also improves the yield of the female by allowing more light penetration into the female rows and reducing competition for moisture. Note that weeds will take advantage of the free ground and will need to be controlled.

Effect of poor synchronization on yield and grading of seed maize.

1. Pollen too early or silking late relative to pollen

  • The base of the cob will be pollinated, with the tips empty.
  • Depending on the percent seed set, yield loss is usually low, since kernels at the base of the cob are usually larger and compensate better than the normally smaller kernels at the tip.
  • Expect a higher proportion of large round seed compared to other seed grades.

2. Silking too early or late pollen shed relative to silks

  • The tips of cobs will be filled, with blind butts.
  • Yield loss is usually high, since large butt kernels missing but small kernels on tip present.
  • The seed will comprise mostly small round and thick grades, with a small proportion of medium flat seed.

3. Inconsistent or insufficient pollen shed

  • The filling of the cob is irregular, with empty cobs when pollen is not available.
  • Yield loss is high due to reduced kernel number.

President

The divine scriptures are God’s beacons to the world. Surely God offered His trust to the heavens and the earth, and the hills, but they shrank from bearing it and were afraid of it. And man undertook it.
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