Runoff formation and subsequent sediment and nutrient losses are caused by many anthropogenic factors such as faulty cultivation practices, faulty cropping pattern and adoption of shifting cultivation practices in sloping lands. In Arunachal Pradesh the cultivated lands are located in hill slopes, valleys and foot hill region. The of valleys and foot hills regions vary from 2% to 10 %.
Generally, two type of cropping patterns are prevalent viz. mono-cropping and mixed cropping. The former is practised in settled areas whereas the latter is practised in settled as well as jhum areas. Kharif is the main cropping season and maize is one of the major crops sown by the farmers. However, maize is considered as soil erosion permitting crop. Growing of two or more crops in mixture with maize provides better canopy over and obstructs overland flow. Dense foliage of erosion resistant leguminous crops like cowpea and dry bean reduces soil loss by preventing the rains from beating the soil surfaces directly.
Over the past decades, numerous studies have been conducted to investigate runoff generation mechanisms worldwide. Studies are also carried out on mixed cropping of maize with rice revealed that runoff and soil loss was reduced significantly compared with maize along the slope. Rice and maize based intercropping systems such as rice+groundnut/ soybean in 3:1 row ratio and maize +groundnut/soybean in 1:1 row ratio performed well and resulted in higher net-returns in upland mid altitude of Meghalaya (Satpathy, 2003).
Study to evaluate effect of cropping practices on runoff at Pasighat
A study was conducted to evaluate the effect of cropping practices on the runoff and sediment yield in the agro-climatic conditions of the valley and foothill region of Arunachal Pradesh as shown in Figures 1, 2 and 3. The climate of Pasighat is tropical humid during summer and dry mild winter. The long-term average annual rainfall of the East Siang district is 4510 mm distributed over the year. The torrential rain causes considerable soil loss even in the foothill and valley region. One day rain fall recorded in Pasighat is about 400mm. The soil is highly porous, having low water holding capacity, high infiltration rate and high bulk density have adverse effect on soil-water-plant continuum. High permeability of soil causes low nutrient use because of downward migration of available plant nutrients away from the root zone of field crops,resulting low productivity of crops.
Maize variety RCM-76 a high yielding variety developed at ICAR-RC-NEH, Barapani for North Eastern region performed well and is normally cultivated by the farmers. Normal sowing time of this crop is March- April and harvested in the month of August-September. Recommended seed rate and spacing for maize is 12-15 kg/ha and 50×20 cm, respectively. After harvesting of cob plant parts used as green fodder. Taking this into account, maize is taken as a crop in the trial. It is known that maize is an erosion permitting crop. It is intercropped with cowpea, which is considered as erosion resisting crop. Hence, the cowpea variety (Vigna unguiculata) Khasi kanchan is used as a cover crop. Both the crops i.e. maize and cowpea were as sown the last week of March at a spacing of 45×30cm and 30×15 cm with 1-2 seeds per hole, respectively. The inter cropping was carried out at 2:4 i.e two rows maize intercropped with four rows of cowpea.
The study revealed that the treatment T4 (maize at 3% slope) resulted highest amount of runoff i.e.2198.4 litres whereas the treatment T6 (cowpea at 3% slope) resulted lowest runoff of 1120.5litres. The same trend was observed for soil loss also. Highest sediment yield was found for the treatment T4 i.e. 865.8 grams and the lowest for the treatment T6 i.e. 289.5grams, which are significantly different from each other. The trend of the results of soil sample nutrient analysis showed that higher content of N, P, and K in lower part of the runoff plots in comparison to their middle and uppers parts as shown in Table.1 and Figures 5 and 6, which show the vigorous growth of crops towards the lowest part of runoff plots.This is due to the removal of nutrient from upper part to lower part of the land along with runoff water. It is found that maize-cowpea intercropping at 2:4 (T5) resulted in 38.6 % less runoff and 30.7 % less sediment loss as shown in Figure 4.
Table 1 : Nutrient status of runoff plots at Upper, Middle and Lower parts:
|Maize + Cowpea||U||238.3||72.3||264.83||17.2|
The farmers usually cultivate maize as one of the remunerative kharif crop. This crop alone is not able to reduce soil erosion under this agro-climatic condition. The farmers can go for a intercropping of traditional maize with cowpea which can reduce the soil erosion considerably in the sloping lands. Hence, the farmers can be suggested not to go for single crop like maize instead to go for inter cropping of maize and cowpea.
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