Soil Tilth & Tillage Explained: Importance & Types for Farmers

Soil is the loose surface material that covers most land. It consists of inorganic particles and organic matter, providing structural support to plants used in agriculture. It also serves as their source of water and nutrients. Soils gently vary in their chemical and physical properties.

In its natural state, soil is not ideal for growing crops satisfactorily. The surface soil where seeds are sown should be soft and friable, allowing the tender roots of germinating seeds to easily push through the soil surface.

The young roots should also penetrate the lower layers of soil in search of food, water, and air. The soil should be free from weeds, which can rob crops of water and nutrients. Furthermore, it should contain adequate water and air, essential for plant growth.

Soil Tilth

Soil tilth is a dynamic and multifaceted concept that refers to soil's suitability for planting and growing crops. Good tilth characterizes soil that is loose, friable, and well-granulated, often described as having a good self-mulching ability. In contrast, poor tilth is associated with dense, compacted soil with hard, blocky, or massive characteristics.

Poor soil tilth often results from compaction induced by factors such as wheel traffic, animal trampling, or natural soil consolidation, referred to as "hard setting behavior." Soil tilth primarily relates to soil's physical properties and processes rather than broader concepts like soil quality and soil health.

Historically, deep and extensive tillage has been considered a major technique for achieving improved soil tilth. However, this approach can lead to long-term degradation of soil structure.

Recognizing the limitations of physical manipulation, there is growing awareness of the crucial role played by soil biota in creating and maintaining soil structure. Soil biology has gained significant attention in soil science, leading to the adoption of techniques such as diversified rotations, cover crops, and crop residue management, either as standalone methods or as part of integrated systems like organic farming and conservation agriculture.

While farmers have traditionally assessed soil tilth qualitatively in the field, there are now various quantitative and semi-quantitative methods available for determining soil tilth. These methods range from simple assessments of soil cloudiness to more in-depth analyses that consider soil consistency, organic matter content, porosity, strength, and aggregate characteristics. Semi-quantitative visual soil evaluation methods have also been developed for field assessments of soil tilth, widely used in many countries.

Characteristics of Good Soil Tilth and Measurements of Soil Tilth

Good soil tilth is typically characterized by looseness, friability, and well-granulated soil. This condition is often described as having a good "self-mulching" ability. Conversely, poor soil tilth is characterized by compacted, dense soil with hard, blocky, or massive features.

Tilth encompasses two key soil properties: the size distribution of aggregates and the mellowness or friability of the soil.

a). Size Distribution of Aggregates:

The size distribution of soil aggregates refers to the proportion of different-sized soil aggregates. In irrigated agriculture, a higher proportion of larger aggregates (over 5 mm) is desirable, while dryland agriculture prefers a higher proportion of smaller aggregates (1-2 mm). Ideally, granules or aggregates should fall within the 1-6 mm size range, but this can vary depending on soil type, moisture levels during plowing, and subsequent cultivation.

b). Mellowness or Friability of the Soil:

This property relates to the crumbliness of dry soil clods. Clods should not disintegrate into dust but remain as stable aggregates of smaller size.

A soil with good tilth is porous and well-drained, with capillary and non-capillary pores in equal proportion. Stable soil aggregates resist erosion by water or wind.

Soil tilth is relatively easy to describe but challenging to measure. The ideal granule size ranges from 1-6 mm and varies by region. The study of pore space and the balanced distribution of micro and macro pores contribute to good tilth.

Different crops and soils require varying degrees of soil tilth. For example, small-seeded crops like sorghum and cotton thrive in a relatively compact seedbed, while bold-seeded crops like gram and maize can tolerate more cloddiness. Soil type also plays a role, as fine powdery soil surfaces can be problematic for heavy clay soil, leading to surface caking and runoff.

Soil Tillage

Soil tillage involves preparing land for crop cultivation through manual clearing followed by mechanized tillage. It encompasses various mechanical actions such as digging, stirring, and overturning of the soil.

Tillage breaks the hard, compact surface of the soil to a specified depth, creating favorable conditions for plant growth. It is a crucial step in agricultural land preparation.

Tillage facilitates the loosening of the soil surface crust and ensures favorable conditions for seed germination and crop growth.

a). Types of Tillage (Primary Tillage)

Primary tillage includes three types: deep plowing, sub-soiling, and year-round tillage.

i). Deep Plowing:

Deep plowing, when conducted in the summer, breaks down large clods through alternating cycles of heating and cooling, as well as sporadic summer rains. This gradual clod disintegration improves soil structure. Deep plowing also helps control perennial weeds, as their rhizomes and tubers are exposed to the hot sun. The depth of deep tillage varies depending on the crops being grown, with deep-rooted crops like pigeon peas requiring deeper tillage.

ii). Sub-soiling:

Sub-soiling involves non-inversion tillage below a depth of 14 inches. It breaks hard pans without inverting the topsoil, maintaining minimal disturbance. Sub-soiling can address hard soil particles that limit root development and are often created by repetitive plowing at the same depth.

iii). Year-round Tillage:

Year-round tillage involves continuous tillage operations throughout the year, especially in dry farming regions. These operations prepare fields for sowing, prevent weed growth during the off-season, and may continue even after crop harvesting.

b). Secondary Tillage

Secondary tillage refers to lighter or finer actions performed on the soil following primary tillage. It addresses issues like large clods, remaining weeds, and partially uprooted stubble. Harrowing is a common secondary tillage method, carried out at a shallow depth to break up clods, remove weeds, and prepare the soil surface for seeding.

Secondary tillage tools such as disc harrows, cultivators, and planks help smooth the soil surface, break up hard clods, and prepare it for seeding.

Objectives of Tillage

Tillage serves several essential objectives in agriculture:

Loosening and Aerating the Soil: Tillage makes the soil loose and porous, allowing for better water infiltration and reduced erosion. Adequate microspore (capillary) proportions retain water, while aeration supports plant and microbial activities.

Weed Control: One of the primary functions of tillage is weed control, as it reduces competition for nutrients and water, leading to higher crop yields.

Enhancing Soil Temperature: Controlling soil moisture and exposing it to sunlight can raise soil temperatures, promoting faster microbial and chemical processes.

Pest Control: Tillage can reveal insects to heat or predators, helping control insect pests and preventing infestations in the next planting season.

Air and Gas Exchange: Tillage facilitates air exchange, essential for crop growth and the removal of excess carbon dioxide produced during decomposition.

Stubble Removal: Tillage clears fields by removing crop residues and other sprouting materials.

Incorporating Organic Matter: It integrates organic manures into the soil, promoting nutrient availability.

Inverting Soil: Deep tillage helps mix upper, organic-rich soil layers with lower, less fertile layers, benefiting plant roots.

Breaking Hard Pans: Tillage can break hard pans that hinder root growth and soil drainage.

Conclusion

Soil is a dynamic and complex entity that plays a crucial role in agriculture and plant growth. Achieving good soil tilth, characterized by loose, friable, and well-granulated soil, is essential for successful crop cultivation. This involves considering factors like the size distribution of aggregates and the mellowness of the soil.

While traditional tillage methods have been used to improve soil tilth, there is a growing awareness of the importance of soil biology in maintaining soil structure. Techniques such as diversified rotations, cover cropping, and residue management are gaining prominence in modern agriculture.

Tillage itself serves multiple objectives, from improving soil aeration and temperature to weed and pest control. It also plays a vital role in incorporating organic matter and breaking hard pans. However, it's important to approach tillage with caution, as excessive or improper practices can lead to soil degradation.