Use of by-products for agricultural benefit

Crop protection, including weed management, is a critical issue in agriculture. Mulching, which consists of covering the soil surface with organic or inorganic materials, is used to control soil moisture, soil temperature, nutrient loss, salinity, erosion, soil structure, etc. Its benefits for the growth and yield of annual and perennial crops have long been recognised. Although it is an age-old practice for managing weeds, mulching has largely dwindled since the widespread use of herbicides; however, now it is gaining importance in the context of sustainable agriculture. Different mulching materials have been used in different crops in different climatic environments for weed management, and results vary according to the chosen approach, growing practices, conditions and species. These materials include crop residues, non-degradable plastic films, and also biodegradable films. The lifetime of an agricultural mulch varies considerably (i.e., months to years) depending on the nature of the material, its application, its thickness, and the environmental conditions.

Plastic mulching has become widely used, but plastic mulches have the potential to alter soil quality by shifting the edaphic biocoenosis, accelerate C/N metabolism, eventually depleting soil organic matter stocks, increase soil water repellency, and favour the release of greenhouse gases. Also, non-degradable films must be removed from the fields, and the recovery is labour-intensive and has economic costs. Moreover, adverse effects may arise from plastic additives, with enhanced pesticide runoff and plastic residues likely to fragment into remaining microplastics. Active research has been done worldwide in recent years to find biodegradable alternatives, such as biodegradable films or paper mulches.

Paper mills are the most common end users of recovered paper, which is employed as a feedstock to manufacture recycled paper and other paper products. One possible application for recovered paper and cardboard is to produce, mixed with other lignocellulosic products, biodegradable materials that are applied as slurries, which maintain their integrity throughout the growing season and provide broadleaf and grass weed control. 

Hydromulch can be defined as a mix of water with some sort of lignocellulosic material or polymers, plus other additives suited for the particular purpose, that is applied not as a film but as liquid. Hydromulch has been used in many land rehabilitation services, for instance to mitigate post-fire runoff and erosion, and has been used experimentally for fruit orchards. Hydromulch can be an effective weed control method with much scope particularly for perennial crops, because it can be applied around already planted trees, where mechanical and chemical weeding is difficult. It has the potential to last for a long time on the soil, although its lifetime is influenced by several environmental factors, among them the frequency and intensity of rain and the amount of solar radiation. It is vital nowadays to make agricultural production sustainable, and in this respect, one of the new objectives of many governments is the transition to a more circular economic model with products, processes and business models that are designed to maximise the value or utility of resources while at the same time reducing adverse health and environmental impacts. 

The use of low-cost and available organic agricultural residues has been proposed to compound biodegradable mulch materials as a way to make weed management practices cost-effective, labour-saving, and environmentally sound. To begin with, hydromulch would provide an outlet for recovered paper. Furthermore, agricultural waste materials such as rice husk or used mushroom substrate have a potential to be used for hydromulches that could be interesting choices for weed management. 

The physical mixture of two materials with different properties can lead to the formation of a new material, called a composite, the properties of which can be the result of a synergy between the characteristics of the original materials. Unlike other types of mixtures such as alloys, in composites the original materials keep their initial properties intact. 

Scientists at the Polytechnic Univeristy of Catalonia have published work on which this blog post is based:  

• Mechanical characterisation of blends containing recycled paper pulp and other lignocellulosic materials to develop hydromulches for weed control
• The effect of a prototype hydromulch on soil water evaporation under controlled laboratory conditions

Using an evaluation test of several blends developed as prototypes to be used as biodegradable hydromulches, whose common and main component is paper pulp from a paper mill. In order to improve the structure and consistency of the pulp several additives were tested, but without losing its characteristic as a liquid mixture suitable for spraying onto the soil surface of the field. 

They used their TA.XTplus Texture Analyser to perform penetration tests on hydromulch samples as shown below. Tension and punching tests were performed to determine the mechanical characteristics of the blends. Two main manners were presumed in which recently germinated weed seedlings can overcome the hydromulch layer: penetrating directly or lifting after breaking it. Punching tests could inform about the resistance of hydromulch to being penetrated by the weed seedlings and tension tests could provide information about the tensile strength of the hydromulches, and consequently their potential capacity to control the emergence of weed seedlings through a lifting mode.

A – Texture Analyser prepared to perform the punching and the traction tests. 

B – Probe used for traction tests. 

C – Probe used for punching tests; the specimen is held between the circular metallic plaque and the PMMA support; the steel cylinder has a diameter of 7.86mm. 

Meanwhile, researchers from the Federal University of São Carlos have been evaluating new environmentally friendly particulate soil fertilisers based on agroindustry waste biopolymers and sugarcane vinasse. They used their TA.XT2 Texture Analyser to measure the compressive strength of particles. Biobased particles with vinasse additives showed the potential to be applied as soil fertiliser as an alternative to use and disposal of this expressive wastewater from sugar and alcohol industries. Read more

It is vital nowadays to make agricultural production sustainable, and in this respect, one of the new objectives of many governments is the transition to a more circular economic model with products, processes and business models that are designed to maximise the value or utility of resources while at the same time reducing adverse health and environmental impacts. 

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