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Dutch sorghum: lacking nutritional value and less residual nitrogen

30 October 2020

Most sorghum varieties had lower dry matter and higher protein yields with lower digestion coefficients of the organic matter (Vcos) than silage maize in 2018.

But the residual nitrogen in the soil after harvest was also lower with low nitrogen doses than with maize, so that the chance of nitrogen leaching from sorghum was lower. This is shown by research by Wageningen Livestock Research on a number of sorghum varieties on sandy and loess soil and compared with silage maize.

Sorghum cultivation in the Netherlands is still in its infancy compared to the now large-scale cultivation of silage maize. To fill in a number of knowledge gaps, research has been conducted into sorghum cultivation on sandy soil for several years, but this was the first year for loess soil. The cultivation method, nitrogen levels, yield, nutritional value and still usable soil nitrogen after harvest (residual N) were investigated on both soil types. In addition, soil moisture measurements have been made on the sandy soil. The trial fields also served as demonstration fields for, among others, livestock farmers, advisers, employees of water boards and financiers.

Sand: higher crude protein sorghum

In Woudenberg (Utrecht), five sorghum varieties and one maize variety were sown on sandy soil at a row distance of 50 cm. The nitrogen fertilization was the same for all fields, about 76 kg N per ha. Both maize and sorghum developed well, but suffered from a moisture shortage in July and especially at the beginning of August. Yields were on average low. However, the nutritional value of maize was higher than that of the sorghum varieties. This difference is mainly due to the higher digestibility of the organic matter (Vcos) and the lower lignin content (ADL) of maize (table 1).

The nutritional value of the sorghum varieties varied considerably, but the average crude protein content of the sorghum varieties was 30% higher than that of maize. The average amount of residual N in the 0-90 cm soil layer of sorghum was significantly lower than that of maize. No differences in soil moisture percentages between maize and sorghum and between the sorghum varieties could be demonstrated. The entire test on sand is described in Wageningen Livestock Research report 1143 .

There is a lot of interest in sorghum in the Gelderse Vallei, partly due to initiatives by dairy farmers and veal calf farmers who already grow the crop and which also involve contractors and animal feed companies. The demo day in September attracted more than 70 visitors. Clients and financiers of this trial were the Vallei en Veluwe Water Board, Utrecht Agriculture and Environment (LaMi) and O-Gen.

Loess: sorghum good with low fertilization

Five sorghum varieties and one maize variety were cultivated at two nitrogen levels (70 kg / ha and 110 kg / ha) on loess soil at the Wijnandsrade trial farm (Limburg). The row spacing was 25 cm for sorghum and 75 cm for maize. Two weeks after sowing, maize emergence was good, but sorghum was moderate to poor, probably caused by crusting after a heavy rain shower. That is why all sorghum fields were sown again on 4 June.

Despite the dry and warm weather, maize on loess soil achieved a higher dry matter yield than sorghum (table 2). It should be noted that the yield (and the other nutritional values) of the maize comes from only one field per treatment, while that of the sorghum varieties is always an average of three fields per treatment. Because of badger damage, two corn fields per treatment had become unusable. Reseeding may have played a negative role in the sorghum determinations, as emergence was sometimes below the target number of plants.

When fertilizing 70 kg N per ha, the average yield of the sorghum varieties was higher compared to 110 kg N per ha. With a nitrogen application of 70 kg N per ha, the five sorghum varieties had an average of 37% less residual N per ha than with maize. The opposite was the case for the nitrogen application of 110 kg N per ha. In addition, the five sorghum varieties had on average 33% more residual N per ha than maize. The entire test on loess is described in Wageningen Livestock Research report 1149 .

More research needed for crop optimization

The trials show that more research is needed to optimize sorghum cultivation in the Netherlands. Important questions are still for optimal plant density, seedbed preparation, sowing depth, sowing time, nitrogen level, weed control and crop protection. And its influence on residual nitrogen in connection with potential nitrogen leaching and, in particular on loess soils, soil erosion. There are also questions about silage, feed intake and animal performance for the next step.




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