Inspections of Seed Crop

Seed crop inspection is a regular and normal requirement for seed certification. Seed regulators will visit the seed field 3-to-6 times during the season to ensure that the crop meets the standards for certification. Seed inspectors need to have free access to the seed field and to all records. Cooperation and implementation of instructions concerning the seed crop will facilitate certification.

The following are key criteria assessed in such inspections. The seed crop is grown from an approved seed source (retaining the labels is necessary to prove this).

  • The field meets the prescribed land requirements as to the previous crop.
  • The prescribed isolation standards are observed.
  • The seed crop has been planted with the prescribed ratios of female and male parents.
  • The crop is properly rogued and detasseled to national standards.
  • The crop is true to the varietal characterization.
  • The crop is harvested properly to avoid mixtures.

Maize seed harvesting

Seed germination rate and vigor (i.e., viability), improve from fertilization of the embryo to physiological maturity, when it will reach a maximum. The absolute or maximum quality of the seed at physiological maturity will have been determined by the growing conditions during seed development, but whatever this quality is at physiological maturity, it will be the maximum the seed can attain. From this point onwards, no improvement is possible in seed viability. All operations from harvesting onwards, therefore, have to be done so as to cause the least deterioration in seed viability, while ensuring that the healthy seed is separated from inferior seed and impurities (extraneous matter and weed seeds) to achieve a specified standard of seed purity.

At the physiological maturity of the crop, the seed moisture content is between 30 and 35% and the crop will still have some vestiges of green in the stems and leaves. From physiological maturity onwards, the seed dries as the environment allows. The drier and warmer the environment and the greater the exposure of the seed to the air, the faster seed moisture will decrease. The rate of field dry-down will also be increased in cases where the cobs have few husk leaves, the cobs are poorly covered by loose husks or the cob diameter is small.

Seed quality will remain relatively high and only decrease slightly, as long as environmental conditions are favorable and grain-eating pests are absent. Seed quality will decline with high air temperatures, high moisture (or high relative humidity), diseases, or grain borers. This basically means that the crop should be harvested as soon after physiological maturity as possible.

Maize ears may be harvested (but not shelled) at a seed moisture content of 25 to 30%, dried at moderate air temperatures (<35°C), and shelled when the seed moisture is less than 14%. If the crop is to be mechanically shelled at harvest, the seed moisture content must be low enough to enable shelling but not too low, to avoid chipping or breaking of the seed. With maize, the ideal seed moisture for shelling is between 11 and 14%. If the moisture is below 11%, mechanical shelling will cause damage. If the moisture content is above 15%, the seed will be bruised and chipped. Hand harvesting of seed maize is common and enables the elimination of diseased cobs at reaping. Since this is labor-intensive, it requires good management and supervision.

Various methods have been devised to make it more efficient. The simplest is reaping cobs into sacks, which are carried out of the field by hand or on trailers. If the cobs are de-husked in the field, each laborer should be able to reap 500 kg of cobs per day, whereas if there is a mechanical de-husker and the reapers simply have to remove the cobs with husks on, then the reaping output may be increased to 1,500 kg per day per laborer. Reaping output may be increased if the cobs are thrown onto an adjacent trailer in the field, rather than being put in bags. The trailer may be fitted with a hanging curtain in the center to prevent cobs from being thrown over the trailer.

With the use of such a trailer system, labor output may be increased to 600 kg of cobs per day per laborer with de-husking, or 2,500 kg of cobs with the husk intact. Mechanical harvesting of cobs with a cob picker improves efficiency. Cobs are picked after physiological maturity when the black layer has formed at the base of the seed and when seed moisture is below 30%. The cobs are collected in a trailer and transported to the conditioning plant, where they are screened and dried if seed moisture is higher than 13%. Once the seed on the cobs is below 13% moisture, shelling may occur. Combine harvesting of seed is not recommended because it can damage the seed and removing damaged or diseased kernels from the mass of seed is difficult.

Seed shelling

For maintenance of high seed quality, hand shelling is ideal but not always economically feasible. A laborer may be able to hand shell up to 100 kg of seed maize per day. Many types of mechanical shellers are available for crop seeds, but these vary in their impact on seed quality. Aggressive, high-speed shellers or combines will chip or break seed. Mechanical damage to the seed is due to abrasion and impact. Abrasion damage mainly affects the seed coat and results from seed rubbing against rough surfaces. Impact damage may affect the entire seed and is a function of the force applied to the seed. Thus, mechanical shellers need to be operated at low speeds and adjusted to minimize seed damage.

Contact edges in the threshing drum should be rounded off and smoothed to minimize the pounding of the grain. The seed should preferably be rubbed off the cobs to reduce damage. If possible, mechanical shellers should also be used to separate the seed from extraneous matter, such as cobs and sheaths.

Maize ear weights in normal 50 kg hessian bags.

  • A bag of de-husked ears weighs – 40 kg
  • A bag of ears with husks weighs – 30 kg


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