Soil condition, preparation of land and shade development
Large cardamom is grown in forest loamy soils having soil depth a few inches to several feet. Color of soil ranges from brownish yellow to dark brown; in most cases from dark yellowish brown to very dark grayish brown. Texture is sandy, sandy loam, silty loam or clay. In general, soil is acidic having pH ranging from 5 to 5.5 or more, and with 1 per cent or more organic carbon (). On an average, these soils are high in available Nitrogen and medium in Phosphorous and Potassium. The mean nutrient concentrations reported from one study (mg/g of soil) are: organic carbon 23.87, total nitrogen 3.30 and total phosphorous 0.75 (). As the terrain is gentle to deep slope, chances of water logging is less, however, water-logged conditions are not suitable and adequate drainage is quite essential for better stand of the crop ().
In general Large cardamom is cultivated on hill slopes, and often in terraced lands (earlier under paddy cultivation), after raising adequate shade trees. In case of land under gentle slope, cardamom is planted on the slopes and in case of medium and steep slopes, the slopes are cut into terraces before planting. Large cardamom is a shade-loving crop. It grows well under dense shade (60–70 per cent of full day light interception) to light shade (about 30 per cent full day light interception) condition (). The daylight intensity required for optimum growth of Large cardamom ranges from 5000 to 20,000 lux. Therefore, in virgin forests it is necessary to clean the under-growth; over-head shade regulation is essential in such a way that at least 50 per cent shade is maintained in the area (). In other areas having insufficient shade, planting shade tree saplings of different species isdone in June–July.
The most common shade trees are Utis (Alnus nepalensis, 600–2000 m above mean sea level (amsl)); Chilaune (Schima wallichi, 550–1515 m amsl); Panisaj (Terminalia myriocarpa, 400–1000 m amsl); Pipli (Exbucklandia populnea 900–2000 m amsl) Malato (Macaranga denticulata, 670–1515 m amsl); Asarey (Cole brookianum 850–2000 m amsl); Gogun (Saurauvia nepalensis, 1400–2000 m amsl); Karane (Symplocos ramosissima Wall 1500–2400 m amsl); Bilaune (Maesa chesia 670–1515 m amsl) etc. It is advisable to plant more than one species of shade trees commonly grown in a particular locality. In case of bare land Utis is the first choice as it is quick growing, capable of fixing atmospheric nitrogen and has faster rates of nutrient cycling. Roots of Alnus species are nodulated with Frankia as an endophyte, and are efficient in biological N2 fixation. Monoculture plantation of A. nepalensis is known to fix 29–117 kg N/ha/year. A study on dry matter production and nutrient cycling in agro-forestry system of Large cardamom grown under N2-fixing Alnus and mixed tree species (non-N2 fixing) indicates that the stand total biomass, tiller number, basal area and biomass of Large cardamom crop was much higher under the influence of Alnus. The agronomic yield of Large cardamom is increased by 2.2 times under the canopy of Alnus. Litter production and its disappearance rate is higher in the Alnus–Large cardamom stand. The Large cardamom based agro-forestry system under the influence of Alnus was more productive with faster rate of nutrient cycling ().
Depending on the altitude, planting of shade tree saplings in a row with a distance of 9–10 m is ideal. While planting the sapling, the course and direction of the sun movement and the slope of the hill are generally considered. Usually the tree rows are run along the southwest direction inside the plantation.
For planting of Large cardamom, pits are opened at spacing suitable for the variety/cultivar. In case of robust variety/cultivar such as Sawney, Varlangey, Ramsey etc., spacing followed is 150 x 150 cm while a spacing of 120 x 120 cm is used for Golsey (Dzongu). Pits are opened in April–May. The size of pits usually is 30 x 30 x 30 cm.
After the receipt of a few showers, pits are filled at least 15–20 days before planting, with top soil, decomposed cattle manure or compost or leaf mold mixed well with the top soil along with 100 g rock phosphate. The ideal season for planting is June–August depending on rains. While planting, too much soil is avoided on the base of seedling, which may otherwise cover the collar region that leads to rotting. Staking is very essential for better anchorage during the initial stage of establishment.
The plant base should be mulched with dried leaves, weeds and trashes. Mulching is done immediately after planting as well as in October–December in the existing plantation. This practice helps to cover the exposed roots, to conserve soil moisture in the ensuing dry months and helps in recycling of nutrients.
In Large cardamom, much of the nutrients are removed by leafy shoots and very less by capsules and spikes. It is observed that robust varieties like Ramsey, Sawney etc. remove almost double the quantities of nutrients as compared to non-vigorous ones like Dzongu Golsey. It is estimated that for producing about 100 kg dry Large cardamom, the robust types remove (in kg) 10.33 N: 1.95 P: 26.24 K: 19.10 Ca and 11.9 Mg; whereas Dzongu Golsey removes only about 5.74:0.99:3.54:9.18 and 5.86 of NPK, Ca and Mg respectively. Old leafy shoots, removed during harvesting are recycled as soil mulch. As this crop is grown under forest cover, manuring and application of fertilizer is not usually practiced. Being a low-volume and less nutrient-exhausting crop, it has a degree of sustenance in terms of nutrient cycling. However, to get sustainable high yield fertilizer application is necessary.
Application of NPK fertilizer in three splits, once in April–May after the first summer showers and second split in June and third in September–October before monsoon ceases increases yield. Fertilizer is applied along a circular band at a distance of 30–45 cm from the clump, with mild forking. After application of fertilizer in September/October, the fertilizer is covered with mulch and soil from the adjacent areas, so as to form a mulch-soil base. It helps to improve the physical make up of soil, with more moisture retention capacity, cover the exposed roots and help the plant to withstand the ensuing dry winter season ().
A fertilizer schedule of 18.4, 6 and 18.6 g NPK/clump produced more number of tillers and spikes/clump in Sawney. However Golsey did not respond to fertilizer application (). Soil application of NPK at the rate of 20:30:40 kg/ha (in two splits: April–May and September) was also found to increase growth and yield characters (Anonymous, 1998a). Soil application of Potassium chloride shows significant effect on growth and yield characters.
Foliar application of urea (0.5 and 1 per cent), DAP (0.5 per cent) and Muriate of potash (0.5 and 1 per cent) during February, April and October enhanced yield of Ramsey. Potassium chloride and potassium sulphate at the rate of 15 g/clump were found to be effective in increasing the yield of Pink Golsey.
Large cardamom cultivation, is a natural farming with least external inputs and interference with the soil-ecosystem. Organic recycling of nutrients is very essential for sustained productivity.
About 51 species of weeds have been recorded in Large cardamom plantations (). Depending on the intensity of weed growth, two to three rounds of weeding are required in a year. First weeding is done in February–April, before application of first split of fertilizer and just before flowering. Second and third round of weeding is done before harvesting in August–September–October along with removal of dried leaves, unproductive tillers etc. The weeded materials are used for mulching.
Most of the shade tree species are deciduous in nature and hence frequent shade regulation is not required. However during early years of shade establishment and also at 2–3 year intervals, the under growing side branches are cut to encourage straight growth and to allow the branches to spread at least 3–4 m above ground level so that moderate shade is maintained ().
Yield performance is better in plantations where irrigation is given during dry winter and summer months. Watering during November–March is found essential to maintain a sustainable good yield in the plantation. Water is tapped through pipes and is provided to plants through surface channel/hose in different directions.
Rouging and gap filling
One of the reasons for poor productivity of Large cardamom (as low as 50–150 kg/ha) is that most of the plantations have become senile and unproductive. The two viral diseases Foorkey and Chirke – have not only spread widely reducing the yield, but also made the plantations highly unproductive and uneconomical. Regular rouging of diseased and senile plants and replanting with high yielding, disease-free seedlings/suckers/TC plantlets are necessary for improving and sustaining the yield in the years to come.
Selections from the book: “Cardamom. The genus Elettaria”. Edited by P.N. Ravindran and K.J. Madhusoodanan. Series: “Medicinal and Aromatic Plants — Industrial Profiles”. 2002.