Enquiries SEED News - nov/dec 2008 This section is coordinated by the professors from the Federal University of Pelotas-Brazil, with the objective of answering the inquiries sent by the readers. Send your question to e-mail: silmar@seednews.inf.br I'm planning to establish a maize crop with a stand of 70,000 plants per hectare, to which purpose I need assistance to determine the seed spacing within the row. For a stand of 70,000 plants per hectare (a figure indicative of the relevance of the spatial arrangement of plants for efficient light capture and use of soil water and nutrients) a row spacing of 0.45 m must be considered. With 90% germination, the quantity of seeds to be sown is of 78,000/ha and since one hectare is equivalent to 10,000 mē and the row spacing of 0.45 m, there'll be in total 22,200 meters of rows. Considering the potential 78,000 seeds/ha, the number of seeds per row meter will be of 3.06, i.e. the spacing between two successive seeds of the same row will be of 32.6 cm. In the region were I grow soybean seeds harvest coincides with the rain season. I had a seed crop ready to be harvested (13% moisture) when heavy rainfall occurred. Can it still be considered apt to be graded as a seed lot? Soybean seeds are especially sensitive to heavy rainfall when ready to be harvested. A rule of thumb is for harvest to start as soon as soybean seed moisture reaches 18%, so that the chances to preserve seed quality are high. Something to bear in mind: a seed crop with 18% moisture is less susceptible to heavy rainfall than that with 13% moisture content. I found the article on production of hybrid maize seed from the last SEED News issue very interesting. The production of high quality seed is indeed a sophisticated process. I'm curious to know why, when producing seeds from three-way hybrids, the female is a single-cross hybrid whereas the male is an inbred line. The hybrid maize seed industry has evolved to deliver the highest quality possible to the growers. Within this context, the fact that the female is a single-cross hybrid is due to its higher yield potential in relation to inbred lines. This helps to reduce the cost of the seed produced. I have read several articles regarding the production of forage seed from Brachiaria grasses. They coincide in that the seed which is collected from the soil shows the highest quality. I find this quite strange so that I will appreciate your comment on this aspect. As strange as it may sound, Brachiaria seeds "harvested" from the soil surface show the highest physiological quality. This is because in this species seed maturation is extremely uneven and shattering is high; as soon as seeds mature they fall onto the soil so that when the last batch completes maturation and the seed is shattered, harvest is ready to proceed. Two basic reasons explain why these seeds are of the best quality: in the first place, seed maturation in this species coincides with the dry period and secondly, when seeds fall onto the soil they are dormant, thus minimizing deterioration. If seeds were not harvested from the soil surface, their yield would be as low as 40% of the potential seed yield. However, for Brachiaria humidicola, due to its stoloniferous habit it is harder to harvest the seeds directly from the soil, so that the current trend for this species is to harvest the seeds directly from the plant. Soybean seed production has to deal with losses caused by stink bug, mechanical damage and excess moisture. I would like to know what is the upper tolerance limit in order to accept seed delivery to the processing unit, considering all three loss factors. The most important losses are caused by excess moisture, indicating that deterioration has occurred in the field. The other two loss sources can be important also, since they can significantly reduce seed viability. Considering all three, it is advisable that losses do not go beyond 10%, since damaged seeds are hard to separate during processing.