Hardpan effect on sugarcane [Saccharum officinarum] transpiration, growth and yield

In recent years, mechanical cultivation has been introduced widely in developing countries. Tillage hardpan is known to affect plant roots' water absorption as it limits root penetration and soil water movement within the soil profile. However hardpan studies from crop science aspects are few. Therefore the effect of hardpan on transpiration, growth and yield of sugarcane was studied in the Japan International Research Center for Agricultural Sciences (JIRCAS) Okinawa Subtropical Station in Ishigaki Island, to find means of mitigating its impact on agriculture. An open field was divided into plots of disrupted and the undisrupted hardpan. Sugarcane cuttings were planted in the field in December 2000. Transpiration was measured using sap flow gauges in September 2001 when the crop canopy fully developed. Transpiration in the disrupted hardpan plot was almost equal to its meteorological potential. However, that in the undisrupted hardpan plot was half of the potential. Transpiration in the undisrupted hardpan plot did not increase even after precipitation increased, though roots in the undisrupted hardpan plot developed greatly in the shallow soil where the water filled rapidly. This indicates that limited transpiration in the undisrupted hardpan plot was due not only to soil water deficit. An irreversible decrease in stomatal conductance led to the result, because the ratio of transpiration per leaf area was quite low in the undisrupted hardpan plot. It resulted in the crop water content in the undisrupted hardpan plot increasing. A stomatal decrease in conductance generally decreases growth and yield due to the lessened photosynthesis. Yield increased in the disrupted hardpan plot. This shows that available means for fields in which hardpan has developed are not only hardpan disruption but also cultural practices to prevent stomatal conductance from decreasing. The yield in both plots increased as stem numbers increased. This suggests that drainage and aeration during the rainy season when available stems emerge also might increase yield in the disrupted hardpan plot.