Papaya plant growth as affected by soil air oxygen deficiency

Lack or insufficient soil air O₂ may lead to reduce plant growth, photosynthesis and plant production materials. Excess or stagnant water replace soil air O₂ and create soil air O₂ deficiency at the plant root zone. To remain healthy, the papaya plant needs regular rainfall or irrigation with good drainage while flooding for 48 hours is fatal. A balance between soil water and soil air O₂ is important for root growth of papaya. In this study, a new method of soil air O₂ measurement, soil air O₂ deficiency creation technique and effect of soil O₂ deficiency on the papaya plant growth were evaluated. Five wooden boxes filled with air dry soil (385 kg/box) were connected with PVS pipes. Six galvanized batteries (KE-25F4) were calibrated and set at the entrance of the first box and at the end of the five boxes. Entry of air was stopped from the surface. Air supply was allowed through the first box, released through the end of the fifth box and a pump sucked internal air. Galvanized batteries measured mili volt, converted to O₂ percentage, showed that soil air O₂ was within the normal air oxygen (21%). Precise measurement of the in situ soil air O₂ using the battery was therefore, successful and created soil air O₂ deficiency that is essential for studying soil air O₂ deficiency on plant growth. Considering the first sensor (standard), examination of relative reduction of soil air O₂ showed that it decreased remarkably at each point. Soil air O₂ deficit conditions affected the papaya (cv. 'Tai No 2') plant growth. Soil air O₂ deficiency reduced the big or small root growth of papaya, leaf chlorophyll content, photosynthesis rate and finally the dry matter of papaya plant. Higher photosynthetic rate under the ambient soil air O₂ condition was conducive for higher carbohydrate production and better root development than deficit soil air O₂ condition. Declining chlorophyll content reduced photosynthesis rate and buildup of carbohydrate thus reducing root and shoot dry matter of papaya. Further studies are necessary to ascertain the extent of papaya yield and quality reduction as affected by the soil air O₂ deficiency.