Interactive effects of plant density and nitrogen rate on grain yield, economic benefit, water productivity and nitrogen use efficiency of drip-fertigated maize in northwest China

Abstract

Plant density and nitrogen (N) rate are two important factors affecting maize yield. However, the interacting effects of plant density and nitrogen rate on maize production and water productivity are still poorly understood, especially under drip irrigation conditions. A two-year field experiment was carried out to determine the interactive effects of plant density and N rate on grain yield, economic benefit, water productivity (WP) and nitrogen use efficiency of drip-fertigated spring maize ( Zea mays L.) in northwest China. Based on the local plant density of 80,000 plants ha -1 and N rate of 240 kg ha -1 , two plant densities (D1: 80,000 plants ha -1 , D2: 100,000 plants ha -1 ) and four N rates (N0: 0, N120: 120 kg ha -1 , N180:180 kg ha -1 , N240: 240 kg ha -1 ) were set in 2018, while a higher plant density (D3: 120,000 plants ha -1 ) was further considered in 2020. The results showed that grain yield, economic benefit, WP and nitrogen use efficiency were significantly affected by plant density, N rate and their interaction (except for economic benefit). Average grain yield increased and then decreased with increasing N rate under D1 and D2 with the maximum values under N180 in both 2018 (12,193 kg ha -1 and 16,650 kg ha -1 ) and 2020 (11,136 kg ha -1 and 15,093 kg ha -1 ), while it continued to increase as N rate increased under D3 in 2020. On average, D2 produced significantly higher grain yield than D1 in both 2018 (13,464 kg ha -1 and 10,477 kg ha -1 ) and 2020 (13,268 kg ha -1 and 9,859 kg ha -1 ), while grain yield under D2 (13,366 kg ha -1 ) was significantly higher than that under D3 (12,301 kg ha -1 ) and D1 (10,168 kg ha -1 ) in 2020. Similar trends to grain yield were also obtained for economic benefit. Overall, grain yield, economic benefit, WP and N partial factor productivity under D2N180 was significantly increased by 41.6%, 52.6%, 33.8% and 90.4% compared with those under the conventional management practice (D1N240), respectively. Based on the multiple regression and spatial analysis, the optimal ranges of plant density of 95,000∼110,000 plants ha -1 and N rate of 185∼205 kg ha - 1 were able to simultaneously obtain ≥95% of the maximum grain yield, economic benefit and water productivity. • Medium density (100,000 plants ha -1 ) produced greater yield than low and high (80,000 and 120,000 plants ha -1 ) densities. • Maize yield peaked at 180 kg N ha −1 under low and medium densities, while at 240 kg N ha −1 under high density. • Medium density with 180 kg N ha −1 improved maize yield, economic benefit and water productivity. • Comprehensive benefit was obtained with 95,000~110,000 plants ha -1 and 185∼205 kg N ha −1 .