Series 22 - Practical Nutrient Management V - Nutrient Losses

Summary

This Cornell University lecture delves into nutrient cycles in soils, emphasizing how nutrients enter and leave the system. Key factors contributing to nutrient loss include soil erosion, crop removal, volatilization, and leaching. Fertile soils are more 'leaky' because they contain higher nutrient levels, meaning that losing a small amount of soil results in a larger nutrient loss. The discussion also highlights the importance of healthy crops in reducing nutrient loss and maximizing uptake. Practical solutions for minimizing nutrient loss, such as returning crop residues and timing fertilizer applications, are explored, alongside insights into nutrient management in greenhouse and potted plant systems.

Takeaways

• 😀 Nutrient loss from soils is influenced by four main factors: erosion, crop removal, volatilization of gases, and leaching.
• 😀 Highly fertile soils tend to be more 'leaky' because they contain more nutrients, which are lost during soil erosion and other processes.
• 😀 Soil erosion removes nutrients like phosphorus and nitrogen, and this process is enhanced when soil is bare and not protected by plants.
• 😀 When crops are harvested, nutrients like nitrogen (N), phosphorus (P), and potassium (K) are removed from the system, but returning crop residues can help replenish these nutrients.
• 😀 Volatilization is a process where nitrogen (often in the form of ammonia gas) escapes from the soil, particularly during the breakdown of organic matter or when burning occurs.
• 😀 Leaching refers to the loss of soluble nutrients, particularly nitrogen, sulfur, and potassium, as water moves through the soil system, carrying away these nutrients.
• 😀 Fertilizing at the right time and in the right amounts helps minimize nutrient loss through leaching, especially in the case of nitrogen fertilizers.
• 😀 Healthy plants use nutrients more effectively, producing more biomass, which anchors the soil and reduces erosion, while also taking up more nutrients, reducing loss through volatilization and leaching.
• 😀 The addition of crop residues back into the soil contributes to maintaining the nutrient pool, as decomposing residues return nutrients like nitrogen, phosphorus, and potassium to the soil.
• 😀 In controlled environments like greenhouses or potted plants, water management is critical to prevent nutrient loss through leaching, and managing water and nutrient inputs can minimize this risk.
• 😀 In potted plant systems, excess water can lead to nutrient leaching, but water can also be absorbed back into the plant system through transpiration, which can concentrate salts in the soil medium.

Q & A

What is meant by nutrient loss in soils?

Nutrient loss refers to the process by which essential elements like nitrogen, phosphorus, and potassium are lost from the soil system. This can occur due to various factors such as erosion, crop removal, volatilization, and leaching.

Why are highly fertile soils more prone to nutrient loss?

Highly fertile soils tend to be more leaky because they contain larger pools of nutrients. When soil is eroded, more nutrients are lost from fertile soils compared to those with lower fertility, even if the percentage of nutrients lost is the same.

How does soil erosion contribute to nutrient loss?

Soil erosion removes the solid materials in the soil, which contain vital nutrients like phosphorus and nitrogen. The eroded materials often end up in streams and lakes, which can lead to downstream nutrient buildup and algal growth.

What impact does crop removal have on nutrient cycles?

When crops are harvested, nutrients like nitrogen (N) and potassium (K) are removed from the soil along with the harvested plant material. This results in nutrient loss, but returning crop residues to the soil can help reduce this loss.

What is the role of volatilization in nutrient loss?

Volatilization primarily affects nitrogen in the form of ammonia, which can escape into the atmosphere during processes like ammonification or when organic matter decomposes. This loss of nitrogen reduces its availability for plants.

How does denitrification contribute to nutrient loss?

Denitrification is a process where nitrate (NO3) is converted into nitrogen gas (N2) in anaerobic conditions. This makes nitrogen unavailable to plants and contributes to nutrient loss in the system.

What is leaching and how does it affect nutrient retention?

Leaching is the movement of soluble nutrients from the soil to deeper layers or out of the soil system through water. It is particularly significant for nutrients like nitrogen, potassium, and sulfur, which are easily dissolved and carried away.

How can the timing and amount of fertilization minimize nutrient leaching?

Fertilizing at the right time and in appropriate amounts helps reduce nutrient leaching. This ensures that nutrients are available to plants when they need them and reduces the chances of excess nutrients being lost through water movement.

Why do healthy crops use nutrients better and reduce system losses?

Healthy crops produce more biomass, which means they absorb more nutrients. By maximizing nutrient uptake, less is lost through volatilization or leaching. Additionally, healthy plants help stabilize the soil, reducing erosion.

How do potted plants differ from open-field systems in nutrient loss?

In potted plants, there is typically less erosion, but leaching can occur when excess water and nutrients drain from the pot. Managing water and nutrient delivery carefully can minimize these losses, and plant transpiration can help recover some of the water.