INTERCROPPED POTATO (SOLANUM SPP) - EFFECT OF SHADE ON GROWTH AND TUBER YIELD IN THE NORTHWESTERN REGOSOL BELT OF SRI-LANKA

The effect of various shade treatments on growth and tuber yield of potato was evaluated at the Agricultural Research Station, Kalpitiya (8°N, 0-5 m a.s.l.) during five Maha (October-March) seasons. Shading experiments consisted of: (a) use of live perennial shade of Ipil Ipil (Leucaena leucocephala); (b) relay cropping with maize and soybeans; and (c) use of artificial and live shade at different growth stages of potato. Ipil Ipil, planted in avenues of 1-m and 2-m width, increased the tuber yield per plant in the first two seasons by 20%, when fully shading the potato crop for one month after planting and two weeks before harvest. In the two successive seasons, yield per plant was reduced in shaded treatments compared to the yield of unshaded controls, although the number of tubers per plant remained the same. This suggests that, as Ipil Ipil matures, competition with potato increases in successive seasons, especially at closer avenue spacings. Avenues 3 m wide, introduced in the last season, improved tuber yield per plant compared to 1-m and 2-m avenues of the same age. In relay-cropping combinations using maize or beans (soybean or polebean) as companion crops, shading during the first four weeks improved tuber yield by 20% whereas shading for up to 6 or 8 weeks after planting the potato reduced the potato yields by 25 and 35%, respectively. Artificial shade (suspended coconut leaves intercepting 50% of the incoming irradiance) during the first four weeks after planting potato, improved total tuber yield by 15% and 20% respectively over live shade (Ipil Ipil or Crotalaria sp.) or unshaded potato yields. However, shading throughout the potato crop, either with live or artificial shade, reduced tuber yield significantly compared to sole potato yields. The benefits of late-season shading were variable, and apparently dependent upon the degree of shading experienced by the potato plants. © 1990.