Monitoring and modeling of water flow and solute transport under different manure amendments in Hawaii

Sweet corn (Zea Mays L. subsp. mays) is one of the most popular and economically important crops in the world. However, its cultivation requires high inputs of nutrients through commercial fertilizers and/or organic manure amendments. Organic amendments (OA) improve soil fertility and other chemical and physical properties necessary to enhance crop production. Not enough information is available on the effect of OA on Hawaii soil water movement and nutrient concentration within and below crops root zone. The objectives of this study were to evaluate the effect of different OA types (chicken and dairy), rates (0, 168, 336, and 672 kg ha-1 total N equivalent), and number of applications (one and two time application) under sweet corn on: (1) macro- and micro-nutrient concentration within and below the root zone, (2) dry weight, macro- and micro-nutrient concentration in plant roots and shoots, (3) the values and relationship between nitrate (NO3--N) concentration within and below the root zone and relative chlorophyll content (RCC) in plant leaves, (4) sweet corn root distribution, and (5) the performance of Everglades Agro-Hydrology Model (EAHM) under Hawaii conditions. Three field experiments were conducted (one at Poamoho and two at Waimanalo Research Stations of the University of Hawaii) under Randomized Complete Block Design (RCBD) and Strip Plot Design with three replications. Real-time soil water content was monitored at 15 minutes intervals using multisensor capacitance soil water content monitoring system at 10, 20, 30, and 50 cm depths. Suction cup lysimeters were used to collect soil solutions from 30 and 60 cm depths. Soil solutions collected six times during each growing season, were analyzed for macro- and micro-nutrients, electrical conductivity (EC) and pH. Plant roots and shoots were sampled at the end of two growing seasons (Waimanalo trials only) and were analyzed for macro- and micro nutrients. Results showed a significant effect of OA types and rates on nutrient concentration within and below the root zone compared to define treatment at the two locations and during the three growing seasons. Two time application (TTA) of OA significantly increased NO3--N concentration within and below the root zone compared to one time application (OTA). Results showed a significant positive correlation between NO3--N concentration and EC of the soil solution. For the two Waimanalo trials, there was a significant effect of OA types, rates, and number of application on plant root and shoots dry weights, macro- and micro-nutrient accumulation in plant root and shoot tissues. Plant growth and nutrient accumulations were significantly higher for chicken manure (CM) under high application rates and TTA treatment. The application of CM and dairy manure (DM) increased the corn leaves RCC and NO3--N concentration within and below the root zone compared to control treatment. The results revealed a significant positive correlation between NO3--N concentration within the root zone and RCC, especially at certain growth stages. Sweet corn root distribution was significantly affected by the application of OA types and rates. There was significantly higher root density, total roots mass per plant, and percent root in soil under CM and DM compared to control treatment. The EAHM model performed reasonably well under Hawaii condition for soil water and NO3--N within and below the root zone. The simulated soil water content was slightly underpredicted compared to observed soil water content.