Abstract
<p>We determined the effects of oat (<em>Avena sativa</em>) and hairy vetch (<em>Vicia villosa</em>) winter cover crops on subsequent maize growth, soil erosion, water run-off, and nitrate leaching. Separate or combined plots of oat and hairy vetch cover crops were grown in winter, and maize was subsequently planted in all plots in the following summer season. The half-recommended N fertilizer (50 kg ha<sup>-1</sup>) applied to zero-tillage maize produced the same biomass and yield as the control (i.e., natural fallow-maize with tillage and fertilizer application of 100 N kg ha<sup>-</sup><sup>1</sup>) when cultivated after hairy vetch (9.6 t ha<sup>-</sup><sup>1</sup>). In contrast, maize grown after oat showed 40.4% lower biomass and 65.4% lower yield. Compared to the control, runoff and soil erosion were 85.3-92.9% (<em>P</em> &lt; 0.001) and 68.6-98.7% lower with cover crop mulch irrespective of cover crop species (<em>P</em> &gt; 0.05), respectively. Cumulative nitrate leaching 60 cm below the soil surface was highest in the control, followed by (in descending order) hairy vetch-maize, hairy vetch + oat-maize, and oat-maize. NO<sub>3</sub>-N release showed a twin-peak pattern in hairy vetch-maize plots at 18 and 37 days after sowing (DAS). Meanwhile, a single peak was observed in the control at 32 DAS immediately after top dressing at 31 DAS. The synchrony of N supply and crop demand were better in hairy vetch-maize than oat-maize or conventional cultivation owing to rapid maize growth under lower rainfall conditions.<strong></strong></p>
Highlights
Ishigaki Island is a subtropical mountainous island located from 24°20′-24°36′N and 124°04′-124°20′E
This study was conducted at sloping fields of the Japan International Research Center for Agricultural Sciences (JIRCAS), Tropical Agriculture research Front (TARF), Ishigaki Island, Okinawa Prefecture, Japan
The soil used was “Kunigami mahji,” which is classified as a red-yellow soil in the Japanese soil classification system; it corresponds to Ultisol in the United States Department of Agriculture (USDA) soil taxonomy (Hamazaki 2005)
Summary
Ishigaki Island is a subtropical mountainous island located from 24°20′-24°36′N and 124°04′-124°20′E. It is approximately 35 km long and 3 km wide in the south. As in Okinawa (Sano, Shimizu, & Nose, 1984; Mucik, 1985), the coral reefs of Ishigaki are under great stress owing to human activity (Wood & Johannes, 1975). Construction work and the plowing of agricultural fields in coral regions produce extensive erosion, and municipal sewage and agricultural fertilizers cause eutrophication (Schnare, Ben, & Shields, 1984). Environmental pollution caused by the agricultural industry occurs in Okinawa, but is a widespread phenomenon in other coral regions
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