Irrigation and fertilizer efficiency in South Texas grapefruit production

On-farm management strategies to conserve water in the Lower Rio Grande Valley (LRGV) are of interest due to reduced water available for irrigation during periods of drought and increased demand by rapid population growth in South Texas. This study was performed in South Texas to assess the impact of drip, micro-jet spray and flood irrigation systems on yield and irrigation use efficiency (IUE) of Rio Red grapefruit (Citrus paradisi Macfad. ). Mature grapefruit trees previously flood irrigated were converted to drip and micro-jet spray irrigation. By the second year of production after adaptation to low water-use systems, the grapefruit trees under micro-jet spray irrigation out produced flood and drip irrigated trees. In the third harvest year (2005) heavy pruning and minimal irrigation resulted in decline of the trend. Overall IUE was greater by both drip and microjet spray than flood irrigated trees. Also, an organic-based fertilizer of biosolid origin called XtendRTM was compared to two inorganic-based fertilizer sources to determine their effect on crop productivity. Results showed that fertilization with XtendRTM provided statistically equivalent grapefruit production as 21-0-0 or 13-13-13 fertilizers. This suggests that long-term use of this organic-based fertilizer may provide similar crop productivity while providing slight additions of carbon over time to the soils of South Texas that are natively low in organic carbon. In juice acidity analysis flood irrigated trees produced fruit with a significantly lower acidity than the drip and microjet spray irrigated trees. Juice acidity in drip and microjet spray irrigated trees had no significant variation but drip irrigated trees had higher mean juice acidity. Compost treatment did not have a significant effect on the yield, root hair density and soil bulk density however an increasing trend was noticed in composted trees for yield, root hair density and soil bulk density. A significant difference for plant nutrients between irrigation treatments was noticed with higher N concentration in drip and microjet spray irrigation systems than flood irrigation. This suggests that low water-use systems enable better assimilation or minimal leaching of plant nutrients from the soil than the flood system. No significant difference was observed in the soil pH of the three irrigation systems, but drip irrigated soils had a low pH than the spray and flood. Corresponding to pH, soil EC also did not have any significant variations.