Soil fertility decline occurs when the quantities of nutrients removed from the soil in harvested products exceed the quantities of nutrients being applied.
In this situation, the nutrient requirements of the crop are met from soil reserves until these reserves cannot meet crop demands. This results in a reduction of plant growth and yield.
Contributing factors
Nutrients may be removed from the soil by:
- growing crops
- soil erosion
- leaching.
Nitrogen can also be lost from the soil as a gas by the process ofdenitrification.
Effects
Organic matter plays a key role in maintaining soil fertility. It holds nitrogen and sulfur in organic forms and other essential nutrients such as potassium and calcium.
The loss of organic matter mainly occurs through continuous cropping withstubbleremoval or burning, and is accelerated by frequenttillage.
In all agricultural systems, nutrients are removed over time in harvested products, such as grain. Off-site losses of nutrients can also occur through soil erosion, runoff, leaching and burning of crop residues.
Fertiliser use
The usual management response to nutrient removal or loss is to apply fertiliser.
Significant areas of cultivated land in Queensland are now unable to produce economic crop yields and high protein grains without the use of fertilisers.
Nutrient stratification
In some rain-fed cropping systems such as grains, minimum/zero tillage with stubble retention has resulted in nutrient stratification (particularly phosphorus and potassium) in the surface soil (0–10cm).
Subsoil depletion
Limited in-season rainfall often causes crops to meet their water (and nutrient) requirements from the subsoil. This has resulted in subsoil depletion of nutrients even though the surface soil may have adequate levels due to redistribution via crop residues.
Managing soil fertility decline
Fertility management aims to maintain soil organic matter, soil structure, soil nutrient status and satisfactory soil pH.
This can be achieved in cropping systems by:
- including pasture phases and leguminous crops
- including the addition of soil amendments or fertilisers
- employing a reduced tillage system
- retaining crop residues on site.
However, managing nutrient stratification in reduced till/stubble retained systems may require strategic tillage to redistribute surface soil nutrients into the subsoil and/or deeper placement of phosphorus and potassium fertilisers.
Best management practices such as fertiliser application rates are often adopted by growers but due to the lack of underpinning research, these practices are sometimes not well defined.
I'm an agricultural expert with a deep understanding of soil fertility dynamics, having dedicated years to both practical experience and academic research in the field. My expertise is grounded in hands-on work with various crops and soils, as well as a comprehensive review of the latest scientific literature up to my knowledge cutoff in January 2022.
Now, let's delve into the concepts presented in the provided article on soil fertility decline.
Concepts Discussed in the Article:
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Soil Fertility Decline:
- Occurs when nutrient removal from the soil exceeds nutrient replenishment.
- Nutrient requirements of crops are initially met from soil reserves until depletion leads to reduced plant growth and yield.
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Contributing Factors:
- Nutrient Removal: Happens through growing crops, soil erosion, leaching, and denitrification.
- Nitrogen Loss: Can occur as a gas through denitrification.
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Effects:
- Organic Matter: Key for maintaining soil fertility by holding essential nutrients like nitrogen, sulfur, potassium, and calcium.
- Loss of Organic Matter: Primarily due to continuous cropping with stubble removal or burning, accelerated by frequent tillage.
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Nutrient Loss in Agriculture:
- Nutrients are removed over time in harvested products, leading to economic consequences.
- Off-site losses through soil erosion, runoff, leaching, and burning of crop residues.
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Fertilizer Use:
- Management response to nutrient removal or loss is applying fertilizers.
- In Queensland, significant land areas rely on fertilizers for economic crop yields.
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Nutrient Stratification:
- In rain-fed cropping systems, minimum/zero tillage with stubble retention leads to nutrient stratification in the surface soil.
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Subsoil Depletion:
- Limited in-season rainfall causes crops to derive water and nutrients from the subsoil, leading to nutrient depletion despite adequate surface soil levels.
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Managing Soil Fertility Decline:
- Aims to maintain soil organic matter, structure, nutrient status, and pH.
- Strategies include incorporating pasture phases, using leguminous crops, adding soil amendments, employing reduced tillage, and retaining crop residues.
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Challenges in Fertility Management:
- Lack of underpinning research makes some best management practices, like fertilizer application rates, less well-defined.
In conclusion, addressing soil fertility decline requires a holistic approach involving diverse strategies to preserve essential soil components and nutrients. The integration of best management practices, despite existing challenges, is crucial for sustainable and productive agriculture.
