レンゲ草生マルチを活用した不耕起直播水稲作における雑草の発生消長  [in Japanese] Changes in Weed Communities in Direct-Seeded Paddy Fields Under Astragalus sinicus L. Living Mulch and No-Tillage Cultivation During Three Years  [in Japanese]

レンゲ冬作による草生マルチと不耕起を基軸としたLISA水稲直播栽培試験を実施している水田2筆において, レンゲ群落, 発生雑草, および水稲収量の推移を3年間にわたり調査した。またレンゲ草生マルチの夏生雑草に対する抑草効果を評価するためにマルチ除去実験を行った。本栽培試験の初年度はレンゲはよく繁茂し冬生雑草の発生も少なかった。湛水後は, 前年の慣行栽培時に多数発生したコナギが消滅したほか, 他の草種の発生も少なく, また水稲収量も470kg/10a以上を得た。しかし2年目以降, レンゲ群落の衰退に伴い雑草の発生数は著しく増加し, 水稲収量も減少した。しかしレンゲ草生マルチをレンゲ開花期の5月上旬に除去すると, 湛水後に一年生のカヤツリグサ科を主とした水田一年生の雑草密度が顕著に増加したことから, レンゲマルチによる抑草効果が推察された。

Changes in the Astragalus sinicus L. community, density of lowland weeds and rice grain yield were investigated in two adjacent direct-seeded paddy fields under A. sinicus living mulch and no-tillage cultivation without the use of pesticides and fertilizer during three years. In the first year of cultivation, A. sinicus community in both paddy fields grew thickly and few winter weeds occurred in the mulch community. However in the second or third year, the population of other species, such as Alopecurus aequalis Sobol. var. Amurensis (Komar.) Ohwi, Geranium carolinianum L., Stellaria alsine Grimm. var. Undulata (Thunb.) Ohwi increased along with the decline of the A. sinicus community (Table 1, Fig. 1). Althought the density of summer weeds after flooding was reduced in comparison with conventional culture in the first year, the density of weeds remarkably increased, particularly Echinochloa in the second year (Fig. 2). The population of perennial weeds, such as Rumex crispus L. ssp. japonicus (Houtt.) Kitam. and Ranunculus cantoniensis DC. ssp. cantoniensis Kitam. and anemochore population also increased when mulch and no-tillage cultivation was applied (Table 2). Rice yields had gradually decreased under this cultivation system as time pass-ed, whereas rice yields recovered by the application of glyphosate before sowing of rice and topdressing of fertilizer (Table 4). On the other hand, to evaluate the suppression of summer paddy weeds by A. sinicus living mulch, mulch was removed in May and July. Mulch removal led to a significant increase of the density of summer annual weeds, especially Cyperus and Lindernia (Table 3). These results, suggest that if the A. sinicus community grows thickly and becomes stabilized every year, A. sinicus living mulch is effective to suppress weeds in the case of rice cultivation without tillage as a form of low input and sustainable agriculture.