Maximizing Nitrogen Recycling in Mixed Silphie Cultivation: A Deep Dive

The Quest For Sustainable Energy Sources Continues, and mixed silphie (Silphium perfoliatum L.) emerges as a promising contender. This perennial plant, belonging to the Asteraceae family, boasts remarkable biomass production, making it an attractive alternative for biogas plants. Recent research highlights key strategies to improve nitrogen (N) recycling within silphie cultivation, directly impacting its efficiency and environmental footprint.

A New Study, part of the “Silphieguide” project, rigorously examined various fertilization techniques to enhance nitrogen recycling. the Findings reveal that providing an early nitrogen supply is crucial for optimal growth. Avoiding nitrogen losses during fertilization is equally essential to achieve a robust and productive silphie crop. However, contrary to expectations, applying nitrogen using slit technology did not yield significant advantages over conventional methods.

Optimizing Fertilization Strategies For Silphie

Autumn fertilization,conducted from mid-September to mid-October,and spring fermentation fertilization,applied once at the end of March,were both scrutinized. All fermentation residues were carefully distributed using a parcel slipper equipped with a towing hose distributor. In one experimental variant, the soil between the silphie rows (spaced 75 cm apart) was loosened with a row hoe the day before spring fertilization to improve infiltration. The Impact Of Adding A Nitrification Inhibitor was also evaluated.

It’s significant to note that, across all years of the study, the planned nitrogen supply from fermentation residues consistently fell short by 12% to 22%. When fermentation and mineral fertilizers were combined, the mineral nitrogen fertilization occurred in early March.

The Test plots were harvested in early September. Researchers meticulously recorded the fresh mass yield per parcel and collected samples from the harvest stream to determine dry matter and nutrient content. The Amount Of Mineral Nitrogen (n_min) in the soil was measured at the begining, after the harvest, and at the end of the vegetation period in selected variants. This allowed researchers to assess the impact of autumn fertilization and the nitrogen fertilization rate on nitrate leaching potential.

The silphie Vs. Corn Comparison

The Study included a comparison with corn parcels, revealing that lower nitrogen fertilization resulted in shorter plants with smaller leaves and thinner stems. This directly impacted dry matter yield. The Unfertilized Control Group yielded only 59.1 dt TM/ha (decitonne dry matter per hectare), while increasing mineral nitrogen fertilization boosted yields up to 154.0 dt TM/ha.

In Comparison To nearby TFZ (Technologie- und Förderzentrum), silphie achieved a maximum of 80% of the dry matter yield of silage corn at the test location. Over three experimental years, fermentation fertilization in spring (averaging 136 kg N_ges/ha) resulted in yields of 127.7 and 129.3 dt TM/ha without and with a chopping insert, respectively.

However, the surface of the ground often became compacted in the spring, hindering the infiltration of fermentation residues. plots with chopping inserts showed better fermentation seepage.

Autumn fertilization or the addition of a nitrification inhibitor tended to result in lower fertilization effectiveness. The results suggest that silphie thrives on a readily available supply of nitrogen in spring. Despite High Nitrogen Supply and fermentation fertilization, post-harvest n_min values were very low (averaging 16.9 kg N/ha), indicating that the nitrogen not utilized by the biomass did not remain as mineral nitrogen in the soil. It is believed that a certain amount of nitrogen contributes to the humus structure in silphie stands.

Examining Fermentation Fertilization With Slit Equipment

A field test was conducted on a silphie practice area to assess the effectiveness of slit technology for fermentation output. The experiment compared application via a slit distributor versus a towing hose distributor, with a purely mineral nitrogen fertilization variant serving as a control. To check for potential plant damage, a further mineral-fertilized variant was implemented without fermentation. The Experiment Spanned Three years, but only two years’ data could be evaluated.

Application Quantities ranged from 22 to 46 m³/ha. At the time of application, the silphie was in various growth stages: the shoot stage (2022), the two-leaf stage (2024), or the three-leaf stage (2023). Harvest and yield data were recorded using test technology.

The Slit Disc Distributor, using v-shaped slices, only created shallow slits, averaging 2 to 3 cm deep.Even in moist ground conditions, achieving the target slit depth of 4 to 5 cm proved arduous. Moreover, the applied fermentation amount exceeded the intended volume, causing the slits to become overwhelmed.

Yields of 121.6 dt TM/ha and 116.5 dt TM/ha were achieved using slit technology and towing hose, respectively.In comparison, mineral fertilization yielded 128.5 dt TM/ha,and mineral fertilization with additional slits reached 129.1 dt TM/ha. The results suggest the slit process failed to considerably reduce ammonia losses due to inadequate slit volume, leading to no detectable betterment in nitrogen recovery compared to towing hose application.

The Danger of Late Slot Application

No Significant Plant Damage attributable to the slit itself was observed, even with the later fertilization in 2023. The Mineral-Fertilized variant with a slit crossing showed no yield reduction, suggesting the application with a slit doesn’t negatively affect silphie growth. Though, damage did occur in the lanes, indicating that late fermentation output dates in silphie cultivation must be avoided.

Due to The narrower Working Width compared to towing hoses, the slit process poses greater challenges in this regard.

Conclusion: Fermentation fertilization with silphie should occur in spring as soon as field conditions allow. Given silphie’s high nitrogen requirement early in spring, adding nitrification inhibitors to fermentation fertilization is unneeded and perhaps counterproductive. Autumn fertilization should be avoided due to poorer nitrogen recovery.

It’s essential to apply fermentation in weather conditions conducive to low losses soon after application, as there’s no direct incorporation in silphie stands. This approach maximizes nitrogen recovery. Soil Loosening with a row hoe before spring fertilization can also improve fermentation incorporation in silphie stands and secure nitrogen fertilization in unfavorable weather conditions. This measure also aids weed control.

A dividing Of fertilization is unnecessary and should be avoided due to potential plant damage in the lanes during later fertilization,fertilization must be completed by the end of April. Based on the anticipated yield, supplemental mineral nitrogen fertilization can serve as a yield safeguard. Excessive nitrogen fertilization, however, can lead to lodging and harvest difficulties.

Based On The Experiance From The Research project, the benefits of slit technology in silphie stands are limited, as the required slit depth of at least 5 cm needed for full fermentation absorption was rarely achieved, especially with larger output quantities (> 25 m³/ha). This is especially true for thin, nutrient-poor fermentation residues. No Reduction In income due to plant damage from the slit was observed.

As with fertilizing other crops, in addition to nitrogen, the need for other mineral nutrients must be considered to avoid excessive nutrient surpluses or plant deficiencies depending on the fermentation composition. The investigations confirmed that silphie has a notably high potassium, magnesium, and calcium removal rate. This can hardly be balanced solely through fermentation, necessitating sufficient mineral supplementary fertilization.

Did You Know: Silphie’s deep root system helps improve soil structure and water infiltration,making it a valuable crop for sustainable agriculture.

What fertilization strategies have you found most effective for your crops? Share your experiences and questions in the comments below!