Majuro Supplemental data.xlsx

<b>Site description and conditions</b>Majuro Atoll, the capital of the Republic of the Marshall Islands, is located in the Pacific Ocean near the equator. The maximum and minimum monthly average temperatures are 27.9 to 30.5 °C and 25.4 to 25.7 °C, respectively. The average monthly and annual precipitation is 192 to 337 mm and 3,236.5 mm, respectively. (National Oceanic and Atmospheric Administration. Retrieved March 11, 2015). Coral sand has low organic matter levels (OC 0−15 cm: 46.9 g kg−1, 15−45 cm: 10.8 g kg−1) (Deenik &amp; Yost, 2006) and high percolation rates (1.4−3.5 × 10­−­3 m s−1) (Hunt &amp; Peterson, 1980).The experimental field was located at Laura Farm (7° 8' 34" N, 171° 2' 9" E), which belongs to the Ministry of Resources and Development. The field was fallow more than six months before starting the experiments. Soil water-soluble NO3-N (0-5 cm layer; 1:2.5 soil-water extraction) was 4 µg g soil−1 by a nitrate ion meter (LAQUAtwin B-742, Horiba, Tokyo). Weeds in the field were collected, chopped, and fermented for four weeks under a roof for the first experiment (experiment 1).<br><b>Plot design and management</b>The plot size was 1.2 m × 6.0 m, and the experimental field consisted of two sets of six plots. The field size was approximately 12.5 m × 7.2 m. Sweet corn (Zea mays L.) was seeded in 2 rows at 0.5 m intervals just after land preparation. No irrigation, fertilizers, or chemicals were used in any experiment. Use of synthetic fertilizer and chemicals are forbidden in this atoll to protect the underground aquifer. Hand weeding was performed at two and five weeks after seeding (except in the treatment), and the weeds were left on the plot. Some remaining plots were used for comparison of the effect of no input in experiment 1, 2-1 and 2-2.<br><b>Experiment 1: A performance of plant residue as an alternative to copra cake</b>The experimental field was divided into four parts (each part consisting of three plots) with the same fertility based on an assessment of the original weed vegetation. The first part received fermented weed chips (6.3 Mg ha−1 in fresh weight; 5.0 Mg ha−1 in dry weight) and the second part received copra cakes (10.0 Mg ha−1 in fresh weight; 5.3 Mg ha−1 in dry weight), the conventional method used by local farmers. The third part received both weed chips and copra cakes (total 10.3 Mg ha−1 in dry weight). The fourth part did not receive an input of organic material. All the fields were cultivated with a cultivator and organic materials were mixed into soils. Sweet corn was seeded on November 26, 2013, and harvested on February 11, 2014 (77 days after seeding). Weeding was not conducted.<br><b>Experiment 2-1, 2-2: Effects of crop bed, mulching, and weeding</b>All the sweet corn stems and leaves from the previous experiment were fermented for six days until fungi began to propagate prior to use for this experiment. Eight plots were used for a 3 factors × 2 levels of factorial design: crop bed, mulching (using 1/4 of the crop residue), and first weeding (second weeding was conducted for all plots). The applied residue was 5.0 Mg ha−1 in fresh weight (3.7 Mg ha−1 in dry weight). Two control plots from the previous experiment that continued to grow sweet corn without any inputs were used as controls in this experiment. Sweet corn was seeded on February 17, 2014, and harvested on May 8 (80 days after seeding).This experiment was retried exchanging first weeding treatment plots (the other treatments were fixed). The applied residue was 2.0 Mg ha−1 in fresh weight (1.5 Mg ha−1 in dry weight) Sweet corn was seeded on May 16, 2014, and harvested on July 28 (73 days after seeding).<br><b>Experiment 3: Effects of fungi propagation, cutting, scattering, and incorporation</b>The experiment used an L12 orthogonal array design (Taguchi, 1986). The factors were: fungi propagation, cutting (approximately 10 cm), scattering and incorporation (covered by soil), or soil surface application. Plots were randomly assigned. The applied residue was 4.7 Mg ha−1 in fresh weight (2.1 Mg ha−1 in dry weight). Sweet corn was seeded on August 4, 2014, and harvested on October 21 (78 days after seeding).<br><b>Experiment 4: Evaluation of the linearity for the input and output</b>Crop residues from the previous experiment (0.4-2.0 Mg ha−1) were returned to each plot by the combination of scattering and incorporating. Namely, the quantity of applied residues was proportional to the preceding yield in each plot. Sweet corn was seeded on October 28, 2014, and harvested on January 9, 2015 (73 days after seeding).<br><b>Determinations and statistical analyses</b>Whole fresh kernels from each plot were weighed. The total biomass of sweet corn was calculated from the fresh kernel weight by assuming total dry matter/kernel fresh weight as 0.36 (Miura &amp; Watanabe, 2002). The p-values were calculated as non-paired, one-sided, and with an unequal variances condition t-test. Residual effects on total dry matter of the following experiment were examined by simple correlation (Pearson product-moment) analyses.