How Does Nitrogen Application Rate Affect Plant Functional Traits and Crop Growth Rate of Perennial Ryegrass-Dominated Permanent Pastures?

High doses of nitrogen (N) fertiliser input on permanent pastures are crucial in terms of N surplus and N losses. Quantitative analyses of the response of plant functional traits (PFT) driving crop growth rate (CGR) under low N input are lacking in frequently defoliated pastures. This study aimed to understand the significance of PFTs for productivity and N uptake in permanent grasslands by measuring dynamics in tiller density (TD), tiller weight (TW), leaf weight ratio (LWR), leaf area index (LAI), specific leaf area (SLA), as well as leaf N content per unit mass (LNCm) and per unit area (LNCa) in perennial ryegrass (Lolium perenne)-dominated pastures, in a simulated rotational grazing approach over two consecutive growing seasons. Annual N application rates were 0, 140 and 280 kg N ha−1. The phenological development of perennial ryegrass was the main driver of CGR, N uptake and most PFTs. The effect of N application rate on PFTs varied during the season. N application rate showed the greatest effect on TD, LAI and, to a lesser extent, on SLA and LNCm. The results of this study highlight the importance of TD and its role in driving CGR and N uptake in frequently defoliated permanent pastures.

Forage intake by heifers on alexander grass (Urochloa plantaginea (Link.) Hitch) fertilized with different levels of nitrogen

This work was conducted to study the efficiency of using nitrogen on Alexander Grass (Urochloa plantaginea (Link.) Hitch) through information about the characteristics of the pasture and forage intake of beef heifers. The experiment was carried out at the Federal University of Santa Maria (Universidade Federal de Santa Maria, UFSM) in Santa Maria, Rio Grande do Sul, Brazil, from January to April of 2014. The treatments consisted of doses of zero, 150, or 300 kg/ ha nitrogen (N) in the form of urea. The study used a rotational pasture method and 16 Angus heifers with a mean initial age and body weight (BW) of 15 months and 276 ± 17.4 kg, respectively. Forage intake was evaluated by treating two picketed test heifers with chromium oxide (Cr2O3) for eleven days as an external indicator of fecal production. The experimental design was completely randomized, and the measurements were repeated over time with three treatments and two repetitions per area. Crude protein content was 3.4% higher under 300 kg/ha nitrogen fertilization compared to 150 kg/ ha (18.7%). Independent of the N application rate, the heifers ingested 2.2 ± 0.09 kg DM 100/ kg BW of forage. Nitrogen fertilization of Alexander grass modified the structure of the pasture, increasing the quality and total production of the forage. Heifers pastured on Alexander grass fertilized with 300 kg/ha nitrogen harvested forage with higher levels of crude protein. The structural change in the canopy let the heifers reduce their consumption of forage at the end of the Alexander grass life cycle.

Reducing N Application by Increasing Plant Density Based on Evaluation of Root, Photosynthesis, N Accumulation and Yield of Wheat

(Aims) To clarify the mechanisms though which dense planting could alleviate the negative effect of the reducing N rate on yield, (Methods) an experiment with four nitrogen levels—0 (N0), 120 (N1), 180 (N2) and 240 (N3) kg N ha−1—and three plant densities—180 (D1), 240 (D2) and 300 (D3) × 104 basic seedlings ha−1—was conducted. (Results) Increasing plant density decreased the root length, root volume, root surface area and root tips of individual plant while it enhanced the aforementioned root traits in population. The chlorophyll content, photosynthetic rate, stomatal conductance and transpiration rate of the individual plants were decreased with the increase in plant density and enhanced with the increase in N level. The increasing density and N application rate enhanced the leaf area index, photosynthetic high-efficiency leaf area and canopy photosynthetically active radiation of population. N accumulation per plant was decreased with increasing density and was enhanced with an increasing N application level. Within the same N level, the N accumulation in the population, N production efficiency and N recovery efficiency were consistently D3 > D2 > D1. A high N application rate with high density was not conducive to improving the NR (nitrate reductase), GS (glutamine synthetase) and GOGAT (glutamate synthase) activities. The yield could be maintained as stable or improved if decreasing by 60 kg N ha−1 with increasing 60 × 104 basic seedlings ha−1 within the range of N application in this experiment. (Conclusions) These results indicated that the yield of wheat could be improved with less N application by adjusting the compensatory effects from the plant density in populations.

Effects of Nitrogen Application Rate on Protein Components and Yield of Low-Gluten Rice

Low-gluten rice cultivar D105 was grown in the field under five nitrogen (N) treatments (N0: 0, N90: 90, N135: 135, N180: 180, and N225: 225 kg·hm−2) to investigate the effect of N application rate on the yield and the resulting dynamic changes in protein content, grain processing quality, and relative content of each component protein. The results indicated that the number of effective panicles, seed setting rate, the number of solid grains, dry matter, leaf nitrate reductase and glutamine synthetase activities, and yield increased with N application rate ranging from 0 to 180 kg·hm−2. However, the seed setting rate and the number of solid grains decreased under N225 treatment, leading to a decline in yield. At maturity, 35 days after flowering, no significant differences between albumin and gliadin in the rice grain were found among the N treatments, while globulin and gluten differed among treatments, indicating that the effect of N application rate on the former was slightly the opposite to that observed on the latter. Further, the N application rates did not change the proportions of component proteins relative to the total protein content in the grain. Processing and taste qualities of D105 low-gluten rice were optimal in the N135 and N180 treatments, and the overall rice quality decreased under the N225 treatment. Therefore, the optimal N application rate for yield and processing quality of D105 low-gluten rice is N180: 180 kg·hm−2.

Nitrogen fertilizer reduction in combination with Azolla cover for reducing ammonia volatilization and improving nitrogen use efficiency of rice

Background Excessive nitrogen (N) application rate with low N use efficiency (NUE) caused a considerable amount of N losses, especially ammonia volatilization (AV). Proper N fertilizer reduction (RN) could significantly reduce AV. However, continuous RN led to a nutrient deficiency in the soil and therefore negatively impacted the NUE and rice yield. Paddy Azolla, a good green manure, is considered as a promising measure to decrease AV and improve NUE and grain yield of rice. However, there is limited information on the integrated effects of RN and Azolla cover on the AV, NUE, and rice yield, especially in the highly fertilized rice-growing systems. Methods The experiment was conducted including eight treatments: the control (without N fertilizer and Azolla cover), Azolla cover without N fertilizer (A), farmer’s N application rate (FN), FN + Azolla cover (FNA), 15% RN from FN (RN15), RN15 + Azolla cover (RN15A). 30% RN from FN (RN30), RN30 + Azolla cover (RN30A). The integrated effects of N fertilizer reduction and Azolla cover on AV, NUE, and rice grain was evaluated. Results RN15A and RN30A substantially reduced total AV by 50.3 and 66.9% compared with FN, respectively, primarily due to the lower surface water ammonia concentrations and pH. RN improved the efficiency of Azolla cover on reducing AV, with 4.1–9.9% higher than for FN. Compared with the FN, RN15A and RN30A enhanced apparent N recovery efficiency (ANRE) by 46.5 and 39.1%, which might be responsible for the lower NH3 emission and the increased total N uptake / total chemical N applied. Furthermore, RN15A and RN30A reduced yield-scaled volatilization by 52.3 and 64.3% than for FN, respectively. Thus, combining 15–30% RN with Azolla cover may be a way to reduce AV and improve ANRE without decreasing rice grain yield.

Nitrogen Fertilizer Rates can be Lowered without Compromising Cotton Yield under Drip Irrigation System

The effects of reducing N fertilizer use on soil NO3--N content and cotton yield were studied through a three-year (2015 to 2017) field experiment in South Xinjiang of China. Cotton was sown under drip irrigation system using five N fertilizer reduction treatments as: conventional N application rate (N100), N application rate reduced by 16.67% (N-16.67), 33.33% (N-33.33), 50% (N-50), and 100% (N-100). The data were recorded for changes in soil NO3--N content, and the SPAD value of cotton leaves was recorded at the peak bolling stage. The total N content of the plant was recorded at the boll formation stage, while yield was recorded at maturity. The results revealed that the soil NO3--N content in N-16.67, N-33.33, N-50, and N-100 treatments decreased by 10.8, 45.5, 60.7 and 72.3% compared to N100 treatment, respectively. The SPAD values of N-16.67 and N-33.33 treatments were significantly higher than those of N100 treatment, while the SPAD values of N-50 and N-100 treatments were significantly decreased. The total N content of cotton was significantly decreased with the increase in the proportion of N fertilizer reduced. The seed cotton yield in N-16.67 and N-33.33 treatments increased by 9.2 and 7.9% compared to the N100 treatment, respectively. However, the cotton yield decreased significantly when the N application rate was reduced by 50 and 100%. The relationship between the N fertilizer reduction rate and cotton yield suggested that the N application rate can be reduced by 18.47–45.50% without compromising the cotton yield in South Xinjiang of China. © 2021 Friends Science Publishers

Optimizing Water and Nitrogen Application System to Improve Nitrogen use Efficiency and Ensure Sustainable Yield of Summer Maize (Zea mays L.)

Exploring the optimal method of water and fertilizer application and N application rate for summer maize is important for achieving the high water and N efficiency in the North China Plain. We tested that the hypothesis that optimizing water and nitrogen application system could improve nitrogen (N) use efficiency and water productivity, and ensure sustainable yield of summer maize. The results showed that: the 216 kg N ha-1 of drip irrigation (DI) and micro-sprinkling irrigation (SI) could obtain the high grain yield compared with 270 kg N ha-1 of flooding irrigation (FI), which was achieved by maintaining a high 1000-grain weight and kernel number. However, the grain yield of 162 kg N ha-1 would be decreased significantly. Irrigation methods and N application rates had significant effects on the ammonia volatilization rate and ammonia volatilization accumulation of soil, N harvest index (NHI), N partial productivity and water productivity. Compared with FI, DI and SI could reduce the ammonia volatilization rate through applying little fertilizer-N by times, and reduce the ammonia volatilization accumulation of 19.5%-54.9%. In addition, under the same irrigation method, the NHI reached the maximum when the N application rate was 216 kg ha−1. Considering comprehensively, under the condition of this experiment, 216 kg N ha−1 is the best N application rate under DI or SI for maize.