Wheat Development in the U.S. & Wheat Cultivation and Harvest

1. Wheat Development in the U.S.
Fig. 3: Wheat plant development scale (modified from Large, 1954)
The wheat plant itself goes through several stages of development from the time it is planted until it has reached maturity (Fig. 3). These stages are monitored and measured at each point by farmers and researchers in an effort to understand how best to improve the amount of wheat produced by each plant. This diligence combined with experience helps the farmer to make decisions about fertilizers or other chemical applications for disease and pest control. Ultimately, the goal is a large crop of high milling quality wheat produced at the least cost.

2. Wheat Cultivation and Harvest
Wheat planting practices and the labour required for planting have seen dramatic changes over the last century. Powerful technology – enhanced tractors and implements capable of working more than 120 acres (48.6 hectares) in a single day (Fig. 4) – have replaced men with mules in the field.

Fig. 4: Harvesting wheat with a modern combine (source: Kansas State University)

In some cases wheat is even planted over the top of the previous year's stubble using a method called "no-till" in an effort to preserve soil moisture, reduce soil erosion and lower the amount of fuel required per acre. Using modern farm equipment, wheat seeds are "drilled" or planted in narrow rows. As the wheat matures the space between the rows seems to fill with the growing plants, giving the appearance of a sea of grain. In North America, planting of winter wheat begins before September in the northern areas, and continues through October in the southern regions (Fig. 5). The harvest begins in May of the following year in the southern regions and continues well past July in the northern regions (Fig. 6). Spring wheat, on the other hand, is normally planted during the month of April with harvest taking place after the 15th of August of the same calendar year.
Fig. 5: Wheat planting in the United States (modified from Anon., 1993)
Fig. 6: Wheat harvest in the United States (modified from Anon., 1993)
3. Global Significance
K. Brunckhorst

Cereals are the staple food of the world's entire population, albeit with great regional differences. The main products are wheat, rice and maize, that make up about 85% of the global grain harvest of about 2 billion t per annum (Tab. 2).
 Tab. 2: Cereal growing (five-year average, 1996 - 2000)a
 At the International Wheat Congress in Saskatoon, Canada in 1998 it was estimated that wheat is the staple food of about 35% of the world's population and that the demand will be 850 to 1,050 mio t in the year 2020. On the basis of a wheat harvest of 569 mio t and a global average yield of 2.5 t/ha at that time, an increase in yield of 1.6 to 2.6% p.a. will be necessary on more or less the same growing area if this demand is to be met. The increase in yield in the developing countries between 1961 and 1994 was 2% p.a. In Western Europe and North America the yield increased by 2.7% p.a. from 1977 to 1985 and by 1.5% p.a. between 1986 and 1995. In the same periods the global increase in yield was 3% and 1.6% respectively. The conclusion to be drawn from this is that although the total wheat crop is increasing, the increase in yield is declining in both absolute and relative terms. This correlates with the results from the Netherlands, the country that achieves the highest yield per unit of area alongside Ireland. In the Netherlands it took 5 years to raise the national average yield from 5 to 6 t/ha and 10 - 12 years to raise it from 6 to 7 t/ha.

In Germany, for example, the development of wheat growing over the past few decades has been characterized by more and more intensive cultivation, chiefly in the form of shorter and more lodging-resistant varieties and the increased use of nitrogen fertilizers and highly effective fungicides. In the mid 1970s the value tests carried out by the BSA2 – the relevant public authority in Germany – to determine productivity and the resistance and quality attributes of the wheat were conducted with 50 to 140 kg nitrogen per hectare depending on the previous crop and the quality of the site, the average being 100 kg. Today these field tests are carried out on the intensive level with 160 to 220 kg/ha, with an average of 190 kg. Through this combination of high-yielding varieties and suitable cultivation and plant protection methods, the wheat achieved yield ncreases of about 0.150 t/ha per annum (Tab. 3).
Tab. 3: Development of the grain yield and baking quality of German winter wheat in the period 1976 - 2001 (three-year averages of the intensive variant in VT a 2 or 3 of the BSA 2)
 The quality results smoothed by calculating the three-year average for 15 to 30 varieties show some striking trends for the past 25 years. Grain hardness, that manifests itself as granularity and thus water absorption, has increased noticeably. The sedimentation value has risen appreciably without positive effects on baked volume. The protein content tends to be lower, the reason being the negative relationship between grain yield and protein content as the grain yield steadily increases.

Simultaneously with this development, plant breeders succeeded in programming more and more new breeds genetically for high flour and baking quality. As a result, there was no longer any need to process summer wheat or the usually valuable imported wheat from the USA or Canada for quality reasons. The names of varieties such as Diplomat, Kormoran, Monopol, Astron, Zentos, Bussard etc. are representative of this trend.

Besides the level and reliability of the yield as objectives of breeding, and also processing quality – chiefly understood as baking quality and more recently extended to include the special qualities "biscuit wheat" and "starch wheat" – selection in respect. A comparison of susceptibility to leaf and ear diseases shows that considerable progress has been made in breeding for resistance, but what has been achieved so far still leaves room for improvement (Tab. 4).
Tab. 4: Development of grain yield and agronomic and resistance properties a according to the year of approval in Germany
The interplay between the genes for resistance in the varieties and those for virulence in the disease-causing organisms is complex and differs from one disease to another. Breeding for resistance to mildew has been particularly successful. Only 10 to 20 years ago this disease was still widespread in wheat and made the use of fungicides necessary at a fairly early stage in the development of the crop. There are now a number of varieties that are practically unaffected by attack and are likely to remain healthy on a broad basis of resistance.

In the case of yellow rust the situation is similar, but with regard to its virulence the fungus is even more capable of transformation than the mildew fungus. This means that varieties that were initially resistant to yellow rust still become susceptible to the disease when a new, aggressive yellow rust strain occurs. But here, too, there are examples of long-term field resistance.

On average it has also been possible to considerably reduce susceptibility to leaf rust in the new varieties, but as there are still great differences in the degree of resistance we may expect further progress in breeding. Progress has also been achieved in respect of the other leaf diseases such as Septoria and DTR
(Drechslera tritici repentis), but compared to the above these are less obvious because the genetic variance is smaller.

Very wet weather with little sunshine in the months of June and July has caused an increase in the ear diseases of wheat in recent years. The main problem in this case is the Fusarium fungi, which form mycotoxins damaging to man and animals as well as reducing the yield. The preference for shorter and usually more lodging-resistant wheat varieties with "shortstraw genes" chiefly results in a shortening of the upper internodes; the ear comes very close to the top leaf. Short infection routes and slow drying of the ears further increase the risk of attack. Furthermore, where resistance to ear diseases is concerned we are dealing with a polygenic system. It is the combination of several smaller positive genetic effects that keeps the ears healthy. Moreover, unlike many other diseases the different Fusarium types are not specific to certain species or organs. All this makes the fusariose complex as a whole very difficult for breeders to handle. But "on the bottom line" improvements are to be seen in this field too.

Note :
2 The Bundessortenamt (BSA) in Rettmar, Hanover, is the German agency responsible for the protection of new plant varieties.

(Source : The future of Flour)

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