Lecture 8 Current Issues
Determining Sowing Rates for Seed Crops
Introduction to Sowing Rates
When determining the appropriate sowing rate to achieve optimal crop population for seed production, it is essential to analyze classical yield response curves. The relationship between density and yield is depicted through two significant graphs:
Graph 1: Density per square meter vs. Relative Seed Yield
The peak performance illustrates a point (density) where the yield is maximized. Beyond this density, yield declines due to decreasing productivity per plant.
Graph 2: Per plant yield diminishes with increasing density; this highlights the necessity to balance the number of seeds per plant and seeds per unit area.
Optimal Density for Different Crop Types
Cereal Crops vs. Forage Crops
Cereal Crops: The optimum density for grain production aligns with that for seed modification.
Forage Crops and Leafy Vegetables: The optimal density for seed production is considerably lower than that required for forage production.
Example:
Rye Grass: 15 to 20 kilos per hectare for forage, whereas only 2 to 10 kilos per hectare is used for seed production.
Red Clover Pasture: 6 to 8 kilos per hectare for forage; half that rate for seed.
Farmers typically use around 8 kilos per hectare for diploid crops.
Techniques for Managing Sowing Rates
Manipulating Sowing Rates
Adjusting Seed Amount: Reduce the amount of seed sown.
Increasing Row Width: This alteration can facilitate lower seed density while maintaining adequate spacing.
Measuring Pure Live Seed
Definition of Pure Live Seed: Pure live seed (PLS) is calculated as follows:
Sowing rate recommendations are based on a norm of 98% purity and 90% germination. Lower germination rates necessitate increased sowing rates to ensure adequate plant establishment.
Seed Characteristics and Implications
Seed Conditioning and Coating
The weight of pelleted seeds varies, from minor micro-coating to coatings that may double seed weight, affecting the sowing strategy accordingly.
Ploidy Levels: Tetraploids necessitate higher seeding rates due to increased weight and doubled chromosomes.
Row Width Implications
Density Consideration: The sowing of 10 kilos per hectare in 15 cm rows will differ from the same rate in 30 cm rows due to density within the row.
Optimal row width for crops like white clover tends to be 30 cm to allow for stolon movement and flower production.
Wider rows may lead to harvest challenges, where cut crops lie flat on the ground, potentially impacting soil moisture retention and contamination risks.
Disease Management
Blind Seed Disease
Defined as a disease affecting grass wherein the spores spread easily if rows are too wide, leading to contamination and ultimately non-viable seeds despite normal appearance.
Trial Design for Density Studies
Nedler Radial Design
This innovative trial design enables a more efficient use of space while studying optimum density, requiring significantly smaller area compared to conventional methods.
Economic Considerations
Seed Pricing and Availability
High-quality seed (breeder seed) is significantly more expensive than basic seed, thus justifying lower sowing rates to manage costs and maximize yield potential.
Establishment effectiveness is critical — take into account seedling vigor, pest threats, disease risks (such as damping-off), frost lift risks, herbicide residues, and soil moisture conditions.
Environmental and Temporal Factors
Sowing Date Impact
Each autumn presents different soil moisture conditions and temperatures; understanding these factors is critical to timing sowing accurately.
Older seedlings are prone to frost lift if temperature drops significantly post-sowing.
Herbicide Residues
Chemicals such as trifluralin (Treflan) can linger in soil, potentially affecting subsequent sowings of other crops; careful planning of planting rotations is crucial.
Weight Conversion and Yield Measurement
Yield Metrics
Converting measurements from grams per square meter to kilos per hectare is straightforward and crucial for farmers.
For instance, yield in grams multiplied by 10 gives kilos per hectare, an easier metric for farmers to comprehend.
Peas and Other Crops Analysis
Peas and Density Dynamics
Research indicates that with increased density, the number of pods per plant decreases, while the total number of seeds in a pod remains relatively constant, emphasizing the relationship between density and yield.
Comparisons with Other Crops
Trials measure density impacts in different crops (e.g., sunflowers) and emphasize the role of germination rates in calculating viable plant emergence.
Roguing and Off Type Management
Importance of Roguing
Roguing refers to the practice of removing off-type plants to maintain seed quality and uniformity. Higher densities complicate roguing practices.
Seed Quality Considerations
Impacts on Quality
Relation between primary umble production and seed quality — higher density can lead to less uniformity in maturity, affecting seed integrity and performance.
Conclusion
Adjustments in sowing rates informed by these factors can enhance seed crop yields and quality. Understanding these principles allows farmers to optimize planting while effectively managing risks and maintaining high standards in seed production.
Future Discussions
Upcoming lectures will expand further on current issues in seed production and delve deeper into the seed certification process.
Questions
Open for questions, with an invitation to continue discussing these critical concepts in future seminars.