Planting in pits prepared well in advance of planting is a common practice in South Asia. Pitting should be done while the ground still has some moisture in it and so is soft and easy to dig. Soon after the monsoon is a good time, but it may be better to wait until after the festivals of Dasain and Tihar, that is until November and December (Mansir and Paush). If it is impossible to make the pits at this time, it is better to wait until the premonsoon rains of April and May (Chaitra and Jesth) have moistened the soil, but this is a period of fairly high agricultural activity when people are sowing maize and preparing unirrigated land (khet) for cultivation. Above 2000m, the soil dries out, and pitting is to be done from January to May (Paush to Baisakh).
The standard pit in Nepal is circular, at least 30cm deep and 30cm in diameter at the bottom. Unless the sides of the pit are vertical the diameter at the top need to be greater than 30cm. Workers should be given 30cm sticks to check the depth and diameter of the pits. On slopes the depth of the pit should be measured at its centre. The most useful tool for pitting is a modified kodali. Mattocks are also suitable.
The top-soil of upto 15cm should be dug up and placed to one side of the pit, separate from the sub-soil from below 15cm.
The optimum spacing in forest plantations depends on a number of factors. These include the rate of growth of tree, its form, the availability of nutrients and soil moisture, the effects of grass and weed competition, the danger of fire, the rotation to be used, the purpose of the plantation, the costs of plantation establishment and maintenance, etc. As for example, if fodder production is the main object of the plantation, very close spacing is preferable. Where saw-timber production is the main objective of the plantation, initially close spacing and progressively thinning them out to the final spacing desired.
Most trees grown for fodder, and fruit trees such as Juglas regia (Okhar) and Choerospondias scholaris (Lapsi) need ample space for their crowns to develop and should be planted at a wide spacing such as 5m×5m or more. In between the rows, Leucaena leucocephala (Ipil-Ipil) can be planted at very close spacing. The advantages of close spacing are as follows:
- It reduces weeding costs and fire risks
- If a few deaths occur, these do not cause large gaps in the plantation
- The trees tend to grow straighter and produce lighter branches
- The total volume of wood produced is higher, especially on short rotations.
The main disadvantage is the cost. At a spacing of 1m×1m, 10,000 plants are needed per ha; at 2.5×2.5m only 1600 plants needed. Thus, to plant 1 ha at 1m×1m will need over six times as many nursery seedlings, and will cost over six time as much in pitting, planting and initial weeding than planting at 2.5×2.5m. Hence, the spacing of 2.5×2.5m has become standard in Nepal, which has been regarded as a reasonable compromise. At Sagarmatha, the spacing is 4m×2m for Dalbergia sissooand 4m×1.7m for eucalypts. This will allow three years of crop cultivation between the trees.
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