RESPONSE OF SUGAR BEET AND WINTER CEREALS TO REDUCED TILLAGE IN THE HARSTE LONG TERM EXPERIMENT

Reakce cukrové řepy a ozimých obilnin na redukované zpracování půdy v dlouhodobém pokusu v Harste

H.P. König, N. Stockfisch, H.J. Koch

Institut für Zuckerrübenforschung, Göttingen

Summary: Reduced soil tillage can be an effective means of environmentally friendly cultivation of field crops. Farmers often criticize such systems having a negative effect on crop yields. Since 1993 two tillage systems (plough = mouldboard ploughing before each main crop to a depth of 30 cm; mulch = shallow tillage to a maximum depth of 10 cm) are compared in a long term trial to evaluate the effects of tillage on yield and yield components of sugar beet, winter wheat and winter barley. Additionally, the nitrogen fertilizer application is varied in four levels. Effects of the mulch treatment were found in sugar beet resulting in a reduced white sugar yield. A distinct interaction of tillage systems and nitrogen dose occurred. With increasing nitrogen application the differences between yields of the two tillage treatments decreased but did not equal. On the other hand, no differences in yields were observed for winter cereals which also did not differ in yield components.

Key words: conservation tillage, sugar beet, winter wheat, winter barley

Souhrn: Redukované obdělávání půdy může být efektivním nástrojem kultivace polních plodin v souladu s ochranou prostředí. Zemědělci často podobné systémy kritizují v tom, že mají negativní vliv na výnosy plodin. Od roku 1993 byly srovnávány v dlouhodobých pokusech dva kultivační systémy (orba = orba do rozvoru do 30 cm před každou hlavní plodinou; mulč = mělké kypření do maximální hloubky 10 cm). Byl sledován jejich vliv na výnos a výnosové prvky u cukrovky, ozimé pšenice a ozimého ječmene. Navíc byla využita odlišná výživa dusíkem ve čtyřech úrovních. Vliv mělkého kypření se projevil ve snížení výtěžnosti bílého cukru. Objevili se též odlišné interakce v systémech kultivace a dávek dusíku. S aplikací vyšších dávek dusíku se snížily rozdíly ve výnosech u dvou použitých systémů. Na druhé straně nebyly zjištěny žádné diference ve výnosech u ozimých obilovin. Stejně tak nebyly pozorovány rozdíly ve výnosových prvcích.

Klíčová slova: obdělávání půdy vhodné pro uchování prostředí, cukrovka, ozimá pšenice, ozimý ječmen

Introduction

Soil degradation, compaction and erosion are severe environmental problems caused by agricultural land use. As a result, infiltration rates, water storage capacities and bearing capacities of the soil are reduced while surface runoff increases (van der Ploeg et al., 1999). In this respect soil tillage plays a major role. Cultivation systems with conservation tillage can be an effective means to protect the environment (Wegener, 2001) but these systems are often criticized by farmers to have a negative effect on the yield. In a long term tillage trial in Harste (near Goettingen, Northern Germany) the effects of conservation tillage in combination with different levels of nitrogen application on field crops are determined.

Materials and Methods

Since 1992 two tillage systems are compared. In the ”plough” treatment the soil is mouldboard ploughed to a depth of 30 cm before each main crop in autumn and in the ”mulch” treatment a shallow tillage to a maximum depth of 10 cm is performed. Nitrogen fertilizer application is varied in four levels respectively to the crop. Sugar beet is fertilized with 0, 50, 110 and 170 kg N ha-1, while winter wheat receives an amount of 0, 110, 160 and 210 kg N ha-1 and winter barley is fertilized with 0, 80, 130 and 180 kg N ha-1. Replication number is four. Yield (root yield and white sugar) and beet quality (sugar content, a -amino-N content) are determined for sugar beet. For winter wheat and winter barley yield and yield components (ear density, thousand grain weight) are determined. The experiment is carried out on a loessial loam soil.

Results

Root yield, a -amino-N content and white sugar yield of sugar beet increased with increasing nitrogen dose while the sugar content decreased (Fig. 1). Yields of sugar beet and white sugar in the plough treatment were higher for all fertilizer levels compared to those of the mulch treatment, although a significant interaction between tillage system and nitrogen fertilizer level occurred. Concerning the sugar content, this interaction was even more distinct. Without fertilizer application the sugar content in the plough treatment was higher than in the mulch treatment. Increasing fertilizer levels lowered the sugar content much more in the plough than in the mulch treatment, resulting in similar sugar contents for both at high nitrogen doses. The a -amino-N content of the sugar beets in the mulch treatment was lower than in the plough treatment and revealed an interaction between tillage systems and fertilizer levels as well.

Figure 2 presents the grain yields of winter wheat and winter barley. Both tillage systems increased in yields with increasing fertilizer amounts but the slope of the graph declined with higher nitrogen levels. Visually, there was almost no difference between the two tillage treatments. Ear density also increased with increasing nitrogen fertilizer levels but similar to the grain yields no visual differences between the tillage treatments occurred. Thousand grain weight of winter barley was neither affected by nitrogen fertilizer level nor by soil tillage. In contrast, without nitrogen fertilizer winter wheat exhibited a reduced thousand grain weight. Soil tillage did not affect the thousand grain weight. Interactions between tillage systems and fertilizer levels could not be detected for the yield components of both winter cereals.

Figure 1: Effects of soil tillage and nitrogen fertilizer application on root yield, sugar content, a -amino-N and white sugar yield of sugar beet (1993-2001)

Figure 2: Effects of soil tillage and nitrogen fertilizer application on grain yield of winter wheat and winter barley (1993-2001)

Conclusions

In sugar beet the observed interaction between soil tillage and nitrogen fertilizer application partly led to a compensation of the yield depression due to the mulch treatment with increasing nitrogen levels. Corresponding to the root yield, the negative effect of the mulch treatment on the white sugar yield was compensated by an increasing nitrogen dose. For the white sugar yield this effect was more pronounced than for the root yield. Responsible for this more distinct compensation in white sugar yield is, that sugar content and a -amino-N content are also subject to an interaction between tillage systems and nitrogen fertilizer levels and hence strengthen the compensatory white sugar yield gain. Thus, on this site at low fertilizer levels and with continuously reduced soil tillage an increased nitrogen application can aid to maintain acceptable yield levels in sugar beet.

Obviously, almost no tillage effects on the yield and yield components of winter cereals could be detected although the results of the statistical analysis display significant differences. Increasing grain yield (with increasing nitrogen application) was mainly due to an increase in ear density whereas the thousand grain weight remained almost constant.

References

van der Ploeg, R.R.; Ehlers, W.; Sieker, F., 1999: Floods and other adverse environmental effects of meadowland area decline in former West Germany. Naturwissenschaften 86, pp. 313-319.

Wegener, U., 2001: Dauerhafte Boedenbearbeitungsverfahren in Zuckerrübenfruchtfolgen - Ertragsbildung, Rentabilität, Energiebilanz und Bodenerosion im Vergleich. Dissertation, Universität Göttingen, Cuvillier Verlag, Göttingen.

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