Plant growth on experimental island beds and nitrogen uptake from surrounding water

Efforts are under way to revive an ancient agricultural system, in which crops are cultivated on raised surfaces surrounded by standing water. Our experiments try to clarify the nitrogen flow in traditional and experimental systems of this type. Total N reached much higher levels in artificial ponds exposed to sunlight than in completely shaded ponds, and yet Pará grass, planted in pots that allowed the roots to extend through to the ponds, made significantly more growth in the shaded ponds than in the sunny ponds. It is concluded that the test crop could not compete effectively for N with algae, and that N in surrounding eutrophic bodies of water is readily available to crops on islands beds only if the crop roots reach channel sediments, or organic matter is transferred from the channels to the beds. Implications are discussed for traditional and experimental systems.