Crop seed rates

Nonchemical or traditional practices, such as weed seed removal, optimal crop seeding rates, crop selection, enhanced crop competitiveness, crop rotation, and mechanical weed control are all important components of an effective weed management program (458,459). In the context of modern intensive chemical herbicide appHcation, nonchemical practices may even represent an innovative approach to weed management and should receive careful consideration. 

Crop seed rates. High seed rates and good crop establishment all help to reduce the impact of weeds. 

Harvest losses of safflower can be one to live times the recommended seeding rate. Safflower seeds have some short-term sprouting resistance but no seed dormancy, which limits persistence in the soil seed bank. This oilseed is attractive to seed predators, including small mammals and birds (personal observation), which may reduce seed density but may facilitate transport of seed from the field. The distance and amount of seed transported by animals have not been quantified, and the fate of transported seed is unknown. Volunteer populations are restricted to the first follow year in conventional fields. Although they can be controlled by conventional herbicides in subsequent crops, there is the potential for survivors to flower, set viable seed, and contribute to both PMGF and SMGF. 

Among the important points that determine the suitability for use as a green manure, aside from climate, season, and soil, are availability and cost of seed, rate and amount of growth, how well it fits into the cropping system, primary purpose for which it is grown, type of root system, ability to compete with weeds, ease of incorporation of the crop into the soil, probable effect on the subsequent crop, and many others. 

For birds and mammals, estimated theoretical environmental concentrations (ETEs) are calculated for granivorous, herbivorous, and insectivorous organisms depending on their size and different groups of crops. Seed treatments are a special item. Based on a large survey of the relevant literature, food intake rates (FIR) and expected residues on feed items (RUD) for these different groups of organisms were collected and representative numbers were fixed in the relevant... 

Herbicide safeners (also referred to as herbicide antidotes or protectants) fulfill an important role in crop protection. Safeners are chemicals that protect crop plants from unacceptable injury caused by herbicides. Either by placement on the crop seed or by way of a physiological selectivity mechanism, safeners in commercial use do not negatively impact the weed control of the herbicide. Although many herbicides have been developed for use without a safener, some of the strongest and most broad-spectrum herbicides tend towards border-line crop selectivity, which may completely preclude use in a particular crop or at least limit maximum use rates or the crop varieties that can be safely treated. It is for such situations that safeners have been developed. Several books and reviews of safeners have been written over the past 20 years [1-3]. It is not the intention of this chapter to cover in detail older safeners, but rather to focus on more recently developed commercial safeners as well as some of the older compounds still in wide commercial usage. 

Huan NH, Thiet LV, Chien HV, Heong KL. Farmers participatory evaluation of reducing pesticides, fertilizers and seed rates in rice farming in the Mekong Delta, Vietnam. Crop Prot 2005 24(5) 457-64. 

Root crops, e.g. sugar beet, swedes and carrots also kale. These crops have small seeds and so the seedbed must be as fine as possible, level, moist and firm. This is very important when precision drills and very low seed rates are used. Good, early, ploughing with uniform, well-packed and broken furrow shces will considerably reduce the amount of work required in the spring when, if possible, deep cultivations should be avoided to keep frost tilth on top, leaving unweathered soil well below the surface. 

High seed rates can help reduce weed competition. In winter cereals drilling 500seeds/m compared with 200seeds/m can halve the weed biomass. In horticultural crops it is not always possible to plant high populations as this technique can affect crop quality and lead to poor marketable yields. 

Ideally, seed potato crops should be planted with sprouted tubers and at a high seed rate to produce a good yield of seed size tubers (25-50 mm). The haulm should be destroyed chemically, to reduce the risk of blight or vims transmission. 

Time of sowing and seed rate. Early drilling of winter wheat and late drilling of winter barley and winter rye produce taller-strawed crops that are more prone to lodging. High seed rates produce crops with a narrow spread of roots that are more liable to root lodging. 

The range of crops, often with autumn- and spring-sown varieties, offers an option for most soil types, pH and crop rotations. Seasonal weather may adversely influence crop establishment, harvesting and sample quality. Home-saved seed has been an option for some of the crops but with specific quality requirements for the harvested product, and a trend to lower seed rates/plant populations, high quality seed with an appropriate treatment is advisable. 

The seed should be treated to control damping-off and drilled 1-2 cm deep into a fine, firm and moist seedbed. For auturrm-sown crops 800-950 seeds/m should be sown in late September/early October. For spring-sown crops 600-700 seeds/m should be sown in late March/early April when soil temperatures are 6-8 °C to obtain an established population of about 400 plants/m Seed rates will range from 44-60 kg/ha because of variation in seed size between varieties. 

Plant population. Winter beans require an established plant population of 18-20 plants/m post-winter and the chosen seed rate should allow for 20-25% field loss. For spring beans the requited population is about 40 plants/m with a field loss of 0-5%. Dense populations tend to increase disease problems whereas thin crops are less competitive to weeds. In some areas rooks may reduce plant populations. 

The decision on the most profitable seed rates for potatoes is complicated by factors such as cost of the seed and expected price for the crop variety and size of the seed must also be considered carefully. The figures given in Table 15.1 are for normal-sized seed (30-60 mm), but if healthy small seed (20-30 mm) is used the rate can be reduced by at least 25%. In some countries it is common practice to cut larger seeds into pieces by hand or machine before planting. The cut pieces are more likely to rot than whole seed, but they may be treated with a fungicide for fusarium control. 

Baby leaf crops are grown at high seed rates and seed cost is a significant production cost. For example spinach will be drilled at 120-140 seeds/m Crops develop quickly and can take 21-28 days from emergence to harvest. The size of the crop at harvest will dictate the market with crops grown for micro, baby and teen leaf specifications. Crops may be covered by fleece to hasten emergence at the start of the season. 

Rye and triticale are often sown speciflcally as grazing crops. Early sowing in August or September can result in a worthwhile crop for grazing as early as November. The seed rate for lye should be about 200-250 kg/ha and for triticale 180kg/ha. 

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