THE INFLUENCE OF NITROGEN APPLICATION ON THE GROWTH AND MINERAL CONTENT OF TWO AFRICAN NIGHTSHADE SPECIES (SOLANUM SPP.) CULTIVATED IN KENYA

Abstract

Plant  growth,  leaf  nitrogen  and  nitrate-N,  and  chemical  content  of  two  African nightshades,  Solanum villosum  and  S. sarrachoides  under different nitrogen levels was investigated in field experiments in 2001 and 2004. Plants were supplied with 0, 1.3, 2.6 and 5.2 g N/plant.  Both African nightshade species responded similarly to  nitrogen  supply.  Leaf  area  and  dry  matter  production  of  plants  supplied  with nitrogen was 4-8 times that of plants not supplied with nitrogen. Plants  suppliedwith  nitrogen  had  significantly  higher  specific  leaf  area  but  had  a  lower  leaf  to stem ratio  (p≤0.05). Leaf nitrogen concentration was significantly higher  (p≤0.05) in  plants  supplied  with  nitrogen. However,  when  expressed  on  a  leaf  area  basis, the  differences  in  the  leaf  nitrogen  content  between  nitrogen  treatments  were minimal.  Leaf  blade  nitrate-N  tended  to  be  high  in young  plants  especially  those that  were  supplied  with  nitrogen.  The  species  showed  significant  differences (p≤0.05)  in  the  mineral  content.  It  was  concluded  that  African  nightshade responded to limited nitrogen by drastic reduction in leaf area to maintain the leaf nitrogen content.