Seeding rate, fertiliser and herbicide effects on canopy growth and productivity of direct-seeded rice (DSR) under different management practices

A low seeding rate with seed drill is a good management practice to promote good canopy growth and increase yield of direct seeding rice (DSR) in lowland rice fields. Many studies did not evaluate seeding rates in an integrated way under different management practices in smallholder farmers’ fields. Estimating canopy cover from Canopeo and normalised vegetation difference index (NDVI) may offer a non-destructive, rapid way to assess crop growth and productivity under different field conditions. On-farm field experiments were conducted comparing the yield and canopy growth in response to seed drilled seeding rates of 20, 40, 60 and 80 kg ha −1 and hand-broadcast seeding rates of 180 kg ha −1 (farmers’ practice) grown under different management conditions in Cambodia. In the first experiment, different seeding rates were compared in two villages, Kork Ton Loab (KTL) and Svay Cheat (SVC), in the 2018 growing season. In the second experiment, seeding rates and fertiliser application rates were compared at Kork Ton Loab location in the 2019 cropping season. The third experiment compared seeding rates and pre-emergence herbicide options at Oroung village in the 2018 and 2020 cropping seasons. In experiment 1, sowing at 20 and 40 kg ha −1 consistently decreased mean canopy cover with Canopeo index at Kork Ton Loab and Svay Cheat locations. In experiment 2, sowing at 80 kg ha −1 significantly increased the mean canopy cover compared with 20 and 40 kg ha −1 seeding rates with Canopeo index at 60 and 75 DAS at the Kork Ton Loab location. The low seeding rates of 60, 80 and 180 kg ha −1 increased in canopy cover at 60 DAS with NDVI compared with the lower seeding rates at Kork Ton Loab and Svay Cheat locations. Seeding rates had significant effects on grain yield and gross margin only for experiment 1 and experiment 3 in the 2020 cropping season. For experiment 1, the seed drill rates of 60 and 80 kg ha −1 did not significantly differ in grain yield or gross margin compared with broadcast of 180 kg ha −1 in both locations. Sowing at 20, 40, 60 and 80 kg ha −1 produced similar yield and gross margin at Kork Ton Loab except for the 20 kg ha −1 seeding rate that significantly reduced yield and gross margin at Svay Cheat. For experiment 3, the seed drill of 80 kg ha −1 and 180 kg ha −1 by broadcast (Farmer’s Practice) significantly increased yield up to 3.5 t ha −1 compared with 40 and 60 seeding rates in the 2020 cropping season. Increasing fertiliser rates (high fertiliser; N-100, P-80, and K-50 kg ha −1 ) by two times increased grain yield by 12.8% compared with the low fertiliser rate of N-50, P-40, and K-30 kg ha −1 . Pre-emergence herbicide application significantly increased mean grain yield by 16% and 15% in the 2018 and 2020 cropping seasons, respectively. Therefore, the seed drill of 80 kg ha −1 , high fertiliser rate and pre-emergence herbicide interventions improved uniformity in canopy growth and increased grain yield of DSR. This information can be incorporated into integrated crop and weed management programs for the productivity of direct-seeded rice in the lowland ecosystem. • Low seeding rates (60–80 kg ha -1 ) with seed drill provide similar yield and gross margin as hand-broadcast of 180 kg ha -1 . • The use of vegetation-derived information from reflectance sensors estimates canopy growth in dynamic field conditions. • Sowing at 60 and 80 kg ha -1 with seed drill reduced undesirable agronomic traits compared with hand-broadcast of 180 kg ha -1 .