Indian Cardamom Research Institute,

 Regional Research Station, Spices Board, Tadong,

 Gangtok-737102, Sikkim, India 

Mulching is the practice of covering the ground with organic material, such as crop residues, straw or leaves, or with other materials such as gravel. Sikkim being an organic state, only organic materials is permitted for cultivation of any crop (Gudade et al., 2013). Large cardamom (Amomum subulatum Roxburgh), a member of the family Zingiberaceae under the order Scitamineae, is the main cash crop cultivated in the sub-Himalayan state of Sikkim and Darjeeling district of West Bengal. It is also cultivated in some other North Eastern Hill states like Arunachal Pradesh and Nagaland. Nepal, Bhutan and Myanmar are the other three countries where large cardamom is cultivated. Sikkim is the largest producer of large cardamom and constitute lion share of Indian and world market. The crop prefers humid subtropical, semi-evergreen forests on steep hills of eastern sub-Himalayan region. It is a shade loving plant (Sciophyte) grown in the tracks with well distributed rainfall spread around 200 days with a total of about 3000-3500 mm/year (Gudade et al., 2014). The climate change at Sikkim drastically reduces the production and productivity of large cardamom. The changes of rainfall i.e. number of rainy days has been reduced, coupled with the increasing in temperature up to 20C directly influences the productivity of this crop. Mulching helps to improve infiltration, protect the soil from water and wind erosion and from dehydration and increase the moisture level in the soil. Mulching with organic material increase the level of organic matter in the soil and stimulate soil micro organisms.

Fig.1 Large cardamom plant mulched with dry leaves

 Different types of organic mulches

Corn cobs, stalks, dried grass clippings, dried leaves, coffee grounds, compost, shredded bark, nut shells, peat moss, straw, chipped wood, sawdust, pine needles and coconut husk fiber (decomposed coir). Mulch generally refers to the dead vegetative material that covers the surface of the earth. It is also sometimes referred to as plant litter. Mulch can be divided into three classes that include ungrazed mature vegetation residues still attached to the plant (cured herbage), vegetation residues detached from plants covering the soil surface (ground litter), and decomposing residues partially or completely incorporated into the soil (humus). Large cardamom plants cannot thrive well under water stress conditions. The crop required watering at least once in 10 days during dry months from October to March for better growth in coming months. Mulching at the plant base with easily degradable organic materials is good for conserving both moisture and soil. Mulching helps to retain soil moisture for longer time and irrigation can be delayed for 15 to 20 days.

Advantages of organic mulches

Fig. 2 Large cardamom plantation under 50 per cent shade

Covering the ground with a mulch layer protects the soil from forming a crust. This allows the rainwater to infiltrate and thus decreases water erosion. Moreover, the mulch layer protects the soil particles from being carried away by strong winds, i.e. it decreases wind erosion. The mulch layer protects the soil from extreme rainfall, winds or drought. Together with increased infiltration, this ensures that the moisture content in the soil remains higher than in soil without a mulch layer. It will thus take longer in the dry season for crops with mulch layer to be short of water. The temperature of exposed soil can become high during the day. By applying a mulch layer, the sun is blocked and the daytime temperature is lower, subsequently night temperature will be increased, which is favourable for seed germination, the crops root growth, and for the growth of micro-organisms. Some organisms in the soil can profit so much from the higher moisture content and protection from high temperatures that they proliferate under the mulch layer. Mulching with organic materials compared to mulching with organic materials is: the decomposition of the mulch increases the level of organic matter in the soil and helping attract many species which significantly improve soil texture and soil fertility (Sam Adams 2012). Soil formation is a very slow process. A thousand years or more are required to form an inch of soil. However, several inches of soil can be lost from erosion in less than a decade under poorly controlled by rainfall. The most important part of range management is to maintain enough vegetation residues (mulch) to protect the soil from accelerated erosion.

                                                                                       Limitations of organic mulches?

Snails can multiply extremely quickly under a mulch layer. Mulching caused an increase in the population of termites. The termites can harm the crops. In such circumstances, it would be better to look for an alternative, combining the use of compost with specific steps to protect the soil from water and wind erosion. The use of crop residues as mulch can intensify the risk of pests. This is especially true with the crop residues of corn particularly if they are not grown alternatively with another crop. Damaging and harmful insects can also create problems.

How to use organic mulches?

The organic mulch has to be applied during September and January to retain soil moisture in dry season.

Function of organic mulches

Fig.4 Bumble bee (main pollinating agent) in soil

 

Each of the three mulch components contributes in a vital way to soil, plant and watershed health. Standing cured herbage retards the flow of rainfall and dislodged soil from the site.Ground litter provides a cushion between rain drops and the soil preventing “splash effect” or dislodgement of soil particles from rain drops. It also insulates the soil from the sun and reduces evaporation from the soil surface. Humus provides nutrients for plant growth and binds soil particles together. It plays a critical role in determining soil structure which governs the soil’s capability to receive and retain moisture. Overall, mulch increases the infiltration rate and moisture holding capacity of the soil, reduces rainfall impact, provides a small pool of nutrient for plants, reduces evaporation from the soil, and reduces runoff and erosion.

B.A. Gudade, P. Chhetri, U. Gupta, T.N. Deka and A.K. Vijayan (2013) Organic cultivation of large cardamom (Amomum subulatum Roxb.) in Sikkim. Popular Kheti Vol. 1 (3): 4-9.

B.A. Gudade, P. Chhetri, U. Gupta, T.N. Deka A.K. Vijayan and N.K. Bhattarai (2014) The study of eco-friendly practices of large cardamom cultivation in Sikkim and Darjeeling. Ecology, Environment and Conservation, Vol. 20(1): 119-123.