Study On The Regulating Effect Of Nitrogen(N) Rate And Planting Density On Production,Water And N Utilization Of Forage Maize

The shortage of forage resources is an important bottleneck limiting the high-quality development of China’s grass-fed livestock industry.Forage maize（Zea mays L.）is characterized by high biological yield,resistance to adversity,nutritional value,and good palatability.It can help promote the growth of cattle,sheep,and other herbivorous livestock.Significant development of forage maize planting,for the optimization of the structure of the planting industry,to ensure the safe supply of forage,and promote the rapid development of grass-fed animal husbandry has important practical significance.The Longdong Loess Plateau is an important area for the development of livestock in Gansu Province.Forage maize in the area has a greater potential for planting.However,the effect of N application rate and density regulate yield,water use characteristics,and nitrogen（N）use characteristics of forage maize in this region are not clear.Meanwhile,the appropriate amount of N application rate and planting density in forage maize cultivation in the study area have not been determined.In this study,the team screened and identified the high-yielding and high-quality variety‘Yu Silage 23’as the research object.And a 2-year field control trial was conducted in Qingyang Grassland Agroecosystem National Field Scientific Observation and Research Station in Gansu province from 2021-2022.Four N application rates,i.e.,0,90,180,and 270 kg N·ha^-1(referred to as N₀,N₉₀,N₁₈₀,and N₂₇₀),and three planting densities,i.e.,70,90,and 110,000 plants·ha^-1(referred to as D₇,D₉,and D₁₁)were used in the experiment.A two-factor complete implementation scheme with a randomized block group and four replications.In this study,we systematically analyzed the effects of N application rates and planting densities on dry matter yield,feeding quality,water use efficiency（WUE）,and N use efficiency（NUE）of forage maize.We hope to clarify the best way to grow forage maize in the Longdong Loess Plateau to support high-yielding and environmentally friendly production of forage maize in the region.The main results of the study are as follows:（1）As for the agronomic traits and dry matter accumulation,N application significantly increased stem diameter,Leaf area index（LAI）,normalized vegetation index（NDVI）,aboveground dry matter accumulation,and ears dry matter allocation proportion of forage maize compared to N₀,while significantly decreased stem dry matter allocation proportion.Stem diameter,LAI,and aboveground dry matter accumulation of forage maize tended to increase and then decrease,with increasing N application rates.At the harvest stage in 2021 and 2022,the stem diameter,LAI,and aboveground dry matter accumulation(22.9 and 14.3 t·ha^-1)of forage maize were highest at an N application rate of 180 kg·ha^-1,and they were significantly higher than N₀.For NDVI and ears dry matter allocation proportion of forage maize,there was no significant difference at 180 and 270 kg·ha^-1 N application rates,but they were significantly higher than N₀.Without the N application rate,the stem dry matter allocation proportion of forage maize was significantly higher than the N application treatments.There was no significant effect of planting density on plant height,NDVI,stem,and ear dry matter allocation proportion of forage maize.However,the leaf dry matter allocation proportion of forage maize at D₁₁ was significantly higher by 19.2%and 10.2%at compared to D₉at the harvest stage in 2021 and 2022,respectively.The interaction of N application and planting density did not significantly affect plant height,LAI,NDVI,and dry matter allocation proportion of each organ（stem,leaf,and ear）of forage maize.（2）As for the feeding quality,N application significantly increased whole-plant crude protein（CP）and starch content,significantly decreasing the whole-plant acid detergent fiber（ADF）content of forage maize.The whole-plant CP and starch content of forage maize at N₁₈₀ and N₂₇₀were significantly higher than N₀ and N₉₀ at the harvest stage in 2021 and 2022.As for the whole-plant ADF content,N₁₈₀ and N₂₇₀ were significantly lower than N₀ at the harvest stage in 2021 and 2022.The planting density did not significantly affect the water content and whole-plant CP content of forage maize.However,at the harvest stage in 2021 and 2022,the whole-plant neutral detergent fiber（NDF）content of forage maize at D₇ was 62.8%and 53.2%,respectively,significantly higher than that of D₉ and D₁₁.However,during the harvest periods of2021 and 2022,under D7 density,the neutral detergent fiber（NDF）content of the entire plant of silage corn was 62.8%and 53.2%,respectively,significantly higher than that of D₉and D11.The interaction of N application and planting density had no significant effect on the whole plant ADF content and plant water content of forage maize.（3）As for the WUE,N application significantly increased the dry matter WUE and the crude protein WUE of forage maize.The dry matter WUE of forage maize with an N application rate of 180 kg·ha^-1 was 65.6 and 38.2 kg·ha^-1·mm^-1 at the harvest stage in2021 and 2022,respectively,which were significantly higher by 27.9%and 38.1%,compared to no N₀.Meanwhile,the crude protein WUE at N₁₈₀ was significantly higher than that of N₀ and N₉₀.There was no significant effect of planting density on dry matter WUE and crude protein WUE of forage maize.The interaction of N application and planting density had no significant effect on soil water storage,crop water consumption,and dry matter WUE.（4）N application significantly increased the above-ground N accumulation of the forage maize and significantly reduced the N partial factor productivity（PFP）.And the above-ground N accumulation of forage maize was highest at an N application rate of180 kg·ha^-1(235.9 and 138.2 kg·ha^-1)at the harvest stage in 2021 and 2022,which was significantly higher by 57.3%and 100.7%,respectively,compared to N₀.In terms of NUE,the PFP of forage maize at N₂₇₀ was significantly lower than that of N₉₀and N₁₈₀.There was no significant effect of planting density on the stem N allocation proportion of forage maize,N agronomic efficiency（AE）,N recovery efficiency（RE）,and N physiological efficiency（PE）.However,the leaf N allocation proportion as well as the PFP of forage maize increased significantly with increasing planting density.The leaf N allocation proportion of forage maize was significantly higher by 19.0%and 11.3%at D₁₁ at the harvest stage in 2021 and 2022,compared to D₇.In terms of NUE,the PFP of forage maize at D₁₁was significantly higher by 12.3%and 6.5%,respectively,compared to D₇.The interaction of N application and planting density had no significant effect on the PFP,AE,RE,and PE of forage maize.The results of the multiple regression analysis based on a two-year trial showed the maximum economic efficiency(25682 CNY·ha^-1),maximum dry matter accumulation(19.0 t·ha^-1),and maximum WUE(51.5 kg·ha^-1·mm^-1)of forage maize were obtained with N application was 236.6,171.2,and 56.2 kg·ha^-1 and planting density was 110,000 plants·ha^-1.With an N application rate of 236.6 kg·ha^-1（the maximum economical N application rate）and a planting density of 110,000 plants·ha^-1,97%of the maximum dry matter yield,95%of the maximum grading index,and 95%of the maximum dry matter WUE of forage maize could be achieved.Therefore,it can be recommended as a cultivation measure to balance the production efficiency,dry matter yield,forage quality,and WUE of‘Yu Silage 23’forage maize in this area.