Mulching: Explore the Agricultural and Environmental Benefits

Modern agriculture, based upon high-yielding varieties, chemical fertilizers, and protection technologies has brought a manifold increase in food grain productivity in the North West Indo-Gangetic plains of India. There is no doubt that present agricultural practices have made the country self-sufficient in food grains but at the same time, their non-judicious usage also resulted in over-exploitation of our natural resource base.

Moreover, rapid industrialization and urbanization have resulted in elevated global temperature and climatic variations thus disturbing the balance of agro-ecological systems. All these factors, if not monitored judiciously will pose a big challenge for cereal-based intensive cropping systems in the states of Punjab, Haryana, Uttar Pradesh, and Rajasthan. Therefore, eco-friendly agricultural practices for sustainable food production are very much needed to combat the effects of climate change and industrialization besides conserving our natural resources. Mulching is one of the good options in this regard as it could potentially serve the purpose of providing numerous agricultural and environmental benefits.

Types of Mulches

Broadly, there are two types of mulches:

(A) Organic: They are categorized as plant and animal origins. The plant-origin organic mulches include straw mulch, crop residue mulch, trash mulch, weeds, chopped leaves, bark, sawdust mulch, and live mulches (cover crops, intercrops), etc. The animal-originated organic mulches include compost and manures.

(B) Inorganic: Generally, plastic films are used as mulch in agricultural and vegetable crops. These plastic films are further categorized based on the color of the film (black, white), degradability (Non-degradable/Photo-degradable/Bio-degradable plastic sheet), LDPE or HDPE, and wavelength-selective mulches.

Agricultural Benefits of Mulching:

1. Soil Moisture Conservation: Many factors like high winds, elevated temperature levels, and competing plantations such as weeds are responsible for the depletion of soil moisture. Mulches can reduce weed infestation, and evaporation losses and enhance the percolation and retention rate of soil.

2. Improvement in Soil Fertility: Mulching helps in improving soil fertility through nutrient recycling and soil erosion control. One ton of paddy straw contains 6.2 kg of nitrogen (N), 2.3 kg of phosphorus (P), 25.0 kg of potassium (K), and 1.2 kg of sulfur (S). This straw when used as mulch improves the soil health whereas during straw burning all the carbon, 90% of N, 20-25% of P and K, and 60% of S present in paddy straw is lost.

3. Regulation of Soil Temperature: Mulching covers the soil surface and hence, it helps regulate the microclimate such as relative humidity, soil, and canopy temperatures, etc. It prevents the sunlight from reaching the soil, alters the net radiation at the soil surface, minimizes evaporation, and checks the escape of vapors out of the soil surface. It helps to reduce terminal heat stress at the reproductive stage in winter (rabi) crops, especially in wheat.

4. Weed Suppression: Mulching is a favorable tool for controlling the weed populations in nursery as well as field conditions. When mulch is spread on the soil surface, it acts as a barrier in the passing of light resulting in reduced germination of small-seeded weed species. Mulches also act as physical obstacles in the emergence of weeds.

5. Mitigation of Salt Stress: The mulching could effectively solve the salinity problem by enhancing water retention in soil and reducing evapotranspiration. Organic mulches have been observed as more helpful for the reclamation of salt-affected soils.

6. Plant Growth, Development, and Yield: Many research studies showed the positive impacts of mulches on germination, crop growth and development, reduction in crop weed competition, and improvement in soil conditions leading to overall enhancements in crop yield and net returns as compared to un-mulched fields.

Environmental Benefits of Mulching:

1. To Check Environmental Pollution: Burning of 1 ton of paddy-straw results in the release of 3 kg particulate matter, 60 kg carbon monoxide (CO), 1,460 kg carbon dioxide (CO2), 199 kg ash and 2 kg sulfur dioxide (SO2) which leads to various health and environmental concerns. The application of paddy straw as mulch in agricultural/horticultural fields reduces the problem of straw burning besides providing other agricultural and environmental benefits.

2. Remediation of Heavy Metals: Mulches are a good source for the removal of these heavy metals from the soils.

Recommendations for Mulch Application: A large amount of paddy straw is available after the harvest of paddy crops in North India which can be easily utilized for mulching purposes in different field crops and orchards as mentioned in Table 1.

Table 1: Recommendation of paddy straw mulch in different fields and horticultural crops

S. No	Crop	Quantity (quintals/acre)	Recommendation
1	Spring Maize	30.0	Uniform spreading of paddy straw mulch immediately after sowing.
2	Spring Sugarcane	20-25	After complete germination by mid-April, uniform spreading of paddy straw/sugarcane trash between the rows reduces soil temperature, conserves soil moisture, suppresses weeds, and reduces the incidence of shoot-borer.
3	Napier Bajra Hybrid	40.0	After planting paddy straw mulch saves irrigation water.
4	Soybean	24.0	Mulch application immediately after sowing
5	Turmeric	36.0	Uniform spreading of paddy straw over the entire field at planting can also be used to control weeds.
6	Mentha	24.0	After planting, apply paddy straw mulch for water saving and higher yield.
7	Chilli	25.0	With the use of paddy straw mulch, the total number of irrigations can be reduced drastically.
8	Potato	25.0	Application of paddy straw mulch immediately after planting provides effective control of annual weeds, saves irrigation water, and improves tuber yield
9	Okra	36.0	Apply immediately after sowing
10	Radish	32.0	Apply immediately after sowing
11	Brinjal	48.0	Apply immediately after transplanting
12	Pea	40.0	Apply immediately after sowing
13	Guava	40.0	Weeds can be managed with the application of paddy straw as mulch after the application of the recommended dose of organic manure and inorganic fertilizers in May under the tree canopy.
14	Pear	55.0	In pear orchards, a 10 cm thick layer of paddy straw mulch can be applied during the second week of April mulching under the canopies of trees to suppress weeds.
15	Ber	50.0	To suppress weeds, the application of mulch should be done in the month of October after the application of the second split of inorganic fertilizers.
16	Peach & Plum	45.0	Applications of paddy straw mulch (10 cm layer) effectively check the weeds. Mulching should be done during the first week of March after application of second split doses of inorganic fertilizers.

Thus, mulching could potentially serve the purpose of reducing soil evaporation, conserving moisture, controlling soil temperature, reducing weed growth, and improving microbial activities. Additionally, mulches could provide economical, aesthetic, and environmental advantages to agriculture and landscape.