Grass nitrogen (N) concentrations of dairy grasslands are higher on peat soil than on mineral soils. This can lead to increased N losses to air and water from dairy farming systems on peat soils. Our hypothesis was that the use of low-N perennial ryegrass (Lolium perenne L.) genotypes could be a means to lower grass N concentrations, when grown on peat soils. Our objective was to determine whether perennial ryegrass populations with different shoot tissue N concentrations, recorded on a sandy soil, would show different shoot tissue N concentrations and N use efficiencies (NUE) or N uptake efficiencies (NUptE) when grown on a peat soil. First, a pot experiment lasting 62 days was carried out with nine diploid and seven tetraploid populations, followed by a field experiment with two diploid and two tetraploid populations and a control lasting 30 months. Both experiments had three N fertilization levels. In the pot experiment, populations explained 3% of the variation in shoot tissue N concentration among tetraploids, 5 and 7% of the variation in NUE among diploids and tetraploids and 12% of the variation in NUptE among diploids. In the field experiment, populations explained 44% of the variation in NUptE. A higher NUE coincided with lower shoot tissue N concentrations among tetraploid populations in the pot experiment. We conclude that there is potential to alter the shoot tissue N concentrations of perennial ryegrass grown on peat soil, via selection for shoot tissue N concentrations and NUE.

Enhanced-efficiency nitrogen (N) fertilizers (EENFs) such as slow-release polymer-coated urea (PCU) and deep placement of urea briquettes (UBs) improve nitrogen use efficiency (NUE) by reducing N losses and increasing nitrogen uptake by plants. Multilocation field trials (81) with cauliflower were conducted across two agroecological regions covering seven districts during two crop-growing seasons between 2018 and 2020 to assess the potential of three EENFs, i.e., PCU, sulphur-coated urea (SCU) and UB for increasing curd yields, agronomic NUE (AEN) and economic benefits over conventional urea (CU). Results were compared with farmers’ current nutrient management practice (FP): applying CU at 58.5 kg N ha−1 (ranging from 33 to 88 kg N ha−1). The N rates in three EENF treatments were 33% lower (100 kg N ha−1), considering their higher N use efficiency, than for CU (150 kg N ha−1). We hypothesize that EENFs produce similar or even higher yields compared with CU. For both years, all three EENFs resulted in significantly (p < 0.05) higher curd yields than CU (36.7 ± 1.1 t ha−1). PCU, SCU and UB increased yields by 21, 21 and 24% over those for CU. The yield increment was much higher (PCU, 44%; SCU, 43%; UB, 46%) than for FP. Similarly, PCU, SCU and UB increased the partial factor productivity of N (PFPN) by 91, 90 and 94% and the AEN by 133, 129 and 138%, respectively, compared with CU. The gross margins of all three EENFs were similar: an average 25% more than with CU and 51% more than with FP. These results suggest that EENFs could help increase productivity and farmer income while considerably reducing N input, compared to use of CU. The government of Nepal should promote these EENFs by removing barriers to access for the associated fertilizers and foster their use through extension.

Deep placement of briquette urea (BU) is environmentally friendly and promotes for better nitrogen use efficiency. Nonetheless, its farm-level adoption is low. This paper contributes to the existing literature on climate-smart technology adoption by examining the factors that affect the BU adoption decision using the national representative Bangladesh Integrated Household Survey (BIHS-15) dataset consisting of 3384 rice farmers in Bangladesh. BU adoption probability is higher for farms that specialize in rice production, have more assets, use mobile phones for farming and have better access to extension services. Also, empowered women have a higher propensity to adopt BU. However, living in the feed the future zone decreases adoption probability. BU adoption probability is inversely correlated with rainfall and salinity vulnerability, while the opposite is observed for cyclone and drought vulnerability. Compared to the prilled urea (PU) users, the BU adopters applied a significantly lower amount of urea. The adopters produce more and have a relatively higher return, though the differences are insignificant. The relatively high price of BU compared to PU and the associated high labor requirement dampers the benefit of adopting the technology. Reallocation of subsidies from PU toward BU could be an effective way of promoting BU technology.

Increasing herd size and fragmented or non-uniform land challenge pasture-based milk production systems. Therefore, part-time grazing combined with indoor feeding of fresh herbage (‘cut-and-carry’) allows to maintain the advantages of fresh-herbage-based diets. However, consequences for environmental nitrogen losses, animal behaviour and ruminal metabolism are decisive for its implementation. Animal performance, nitrogen use efficiency (NUE), reticulo-ruminal pH and feeding/locomotive behaviour were compared in six cows subjected either to full-time grazing (system F) or to part-time grazing system with indoor feeding of fresh herbage and concentrate (system P). Biweekly samplings were performed on six lactating cows per treatment in spring, summer and autumn. Nitrogen (N) balance was calculated from estimated N intake and N output via faeces, urine and milk. Reticulo-ruminal pH was recorded using a wireless data recorder. Eating and locomotive behaviour were measured with noseband sensors and pedometers. In spring, but not later, herbage intake per unit of body weight was higher for system F compared to system P cows. Eating time was shorter by 15% in P compared to F cows. Across systems, NUE declined from spring to summer/autumn from about 300 to 200 g milk protein N/kg N intake. Reticulo-ruminal pH was more variable under part-time grazing conditions, with a pronounced decrease subsequent to offering the herbage indoors. The part-time grazing system resulted in similar or higher NUE than full-time grazing. Additional studies with larger numbers of experimental units are required to be able to develop comprehensive recommendations for the improvement of the two grazing systems.

Ruminants fed high-forage diets usually have a low feed efficiency, and their performances might be limited by methionine (Met) supply. However, the INRA feeding system for growing cattle does not give recommendation for this amino acid (AA). This study aimed to assess the effects of Met-balanced diets on animal performance and N metabolism in young bulls fed high-forage diets formulated at or above protein requirements. Four diets resulting from a factorial arrangement of two protein levels (Normal (13·5 % crude protein) v. High (16·2 % crude protein)) crossed with two Met concentrations (unbalanced (2·0 % of metabolisable protein) v. balanced (2·6 % of metabolisable protein)) were tested on thirty-four fattening Charolais bulls for 7 months before slaughter. Animal growth rate was greater in Met-balanced diets (+8 %; P = 0·02) with a trend for a greater impact in High v. Normal protein diets (P = 0·10). This trend was observed in lower plasma concentrations of branched-chain AA only when Met supplementation was applied to the Normal protein diet (P ≤ 0·06) suggesting another co-limiting AA at Normal protein level. Feed conversion efficiency and N use efficiency were unaffected by Met supplementation (P > 0·05). However, some plasma indicators suggested a better use of AA when High protein diets were balanced v. unbalanced in Met. The proportion of total adipose tissue in carcass increased (+5 percent units; P = 0·03), whereas that of muscle decreased on average 0·8 percent units (P = 0·05) in Met-balanced diets. Our results justify the integration of AA into dietary recommendations for growing cattle.

Polyphenol oxidase (PPO) in red clover (RC) has been shown to reduce both lipolysis and proteolysis in silo and implicated (in vitro) in the rumen. However, all in vivo comparisons have compared RC with other forages, typically with lower levels of PPO, which brings in other confounding factors as to the cause for the greater protection of dietary nitrogen (N) and C18 polyunsaturated fatty acids (PUFA) on RC silage. This study compared two RC silages which when ensiled had contrasting PPO activities (RC+ and RC−) against a control of perennial ryegrass silage (PRG) to ascertain the effect of PPO activity on dietary N digestibility and PUFA biohydrogenation. Two studies were performed the first to investigate rumen and duodenal flow with six Hereford×Friesian steers, prepared with rumen and duodenal cannulae, and the second investigating whole tract N balance using six Holstein-Friesian non-lactating dairy cows. All diets were offered at a restricted level based on animal live weight with each experiment consisting of two 3×3 Latin squares using big bale silages ensiled in 2010 and 2011, respectively. For the first experiment digesta flow at the duodenum was estimated using a dual-phase marker system with ytterbium acetate and chromium ethylenediaminetetraacetic acid as particulate and liquid phase markers, respectively. Total N intake was higher on the RC silages in both experiments and higher on RC− than RC+. Rumen ammonia-N reflected intake with ammonia-N per unit of N intake lower on RC+ than RC−. Microbial N duodenal flow was comparable across all silage diets with non-microbial N higher on RC than the PRG with no difference between RC+ and RC−, even when reported on a N intake basis. C18 PUFA biohydrogenation was lower on RC silage diets than PRG but with no difference between RC+ and RC−. The N balance trial showed a greater retention of N on RC+ over RC−; however, this response is likely related to the difference in N intake over any PPO driven protection. The lack of difference between RC silages, despite contrasting levels of PPO, may reflect a similar level of protein-bound-phenol complexing determined in each RC silage. Previously this complexing has been associated with PPOs protection mechanism; however, this study has shown that protection is not related to total PPO activity.

Animal proteins are naturally 15N enriched relative to the diet and the extent of this difference (Δ15Nanimal-diet or N isotopic fractionation) has been correlated to N use efficiency (NUE; N gain or milk N yield/N intake) in some recent ruminant studies. The present study used meta-analysis to investigate whether Δ15Nanimal-diet can be used as a predictor of NUE across a range of dietary conditions, particularly at the level of between-animal variation. An additional objective was to identify variables related to N partitioning explaining the link between NUE and Δ15Nanimal-diet. Individual values from eight publications reporting both NUE and Δ15Nanimal-diet for domestic ruminants were used to create a database comprising 11 experimental studies, 41 treatments and individual animal values for NUE (n=226) and Δ15Nanimal-diet (n=291). Data were analyzed by mixed-effect regression analysis taking into account experimental factors as random effects on both the intercept and slope of the model. Diets were characterized according to the INRA feeding system in terms of N utilization at the rumen, digestive and metabolic levels. These variables were used in a partial least squares regression analysis to predict separately NUE and Δ15Nanimal-diet variation, with the objective of identifying common variables linking NUE and Δ15Nanimal-diet. For individuals reared under similar conditions (within-study) and at the same time (within-period), the variance of NUE and Δ15Nanimal-diet not explained by dietary treatments (i.e. between-animal variation plus experimental error) was 35% and 55%, respectively. Mixed-effect regression analysis conducted with treatment means showed that Δ15Nanimal-diet was significantly and negatively correlated to NUE variation across diets (NUE=0.415 −0.055×Δ15Nanimal-diet). When using individual values and taking into account the random effects of study, period and diet, the relationship was also significant (NUE=0.358 −0.035×Δ15Nanimal-diet). However, there may be a biased prediction for animals close to zero, or in negative, N balance. When using a novel statistical approach, attempting to regress between-animal variation in NUE on between-animal variation in Δ15Nanimal-diet (without the influence of experimental factors), the negative relationship was still significant, highlighting the ability of Δ15Nanimal-diet to capture individual variability. Among the studied variables related to N utilization, those concerning N efficiency use at the metabolic level contributed most to predict both Δ15Nanimal-diet and NUE variation, with rumen fermentation and digestion contributing to a lesser extent. This study confirmed that on average Δ15Nanimal-diet can predict NUE variation across diets and across individuals reared under similar conditions.

Over-application of nitrogen (N) in rice (Oryza sativa L.) production in China is common, leading to low N use efficiency (NUE) and high environmental risks. The objective of this work was to evaluate the ability of the CERES-Rice crop growth model to simulate N response in the cool climate of Northeast China, with the long term goal of using the model to develop optimum N management recommendations. Nitrogen experiments were conducted from 2011–2015 in Jiansanjiang, Heilongjiang Province in Northeast China. The CERES-Rice model was calibrated for 2014 and 2015 and evaluated for 2011 and 2013 experiments. Overall, the model gave good estimations of yield across N rates for the calibration years (R2=0.89) and evaluation years (R2=0.73). The calibrated model was then run using weather data from 2001–2015 for 20 different N rates to determine the N rate that maximized the long term marginal net return (MNR) for different N prices. The model results indicated that the optimum mean N rate was 120–130 kg N ha–1, but that the simulated optimum N rate varied each year, ranging from 100 to 200 kg N ha–1. Results of this study indicated that the CERES-Rice model was able to simulate cool season rice growth and provide estimates of optimum regional N rates that were consistent with field observations for the area.

Weeds that respond more to nitrogen fertilizer than crops may be more competitive under high nitrogen (N) conditions. Therefore, understanding the effects of nitrogen on crop and weed growth and competition is critical. Field experiments were conducted at two locations in 1999 and 2000 to determine the influence of varying levels of N addition on corn and velvetleaf height, leaf area, biomass accumulation, and yield. Nitrogen addition increased corn and velvetleaf height by a maximum of 15 and 68%, respectively. N addition increased corn and velvetleaf maximum leaf area index (LAI) by up to 51 and 90%. Corn and velvetleaf maximum biomass increased by up to 68 and 89% with N addition. Competition from corn had the greatest effect on velvetleaf growth, reducing its biomass by up to 90% compared with monoculture velvetleaf. Corn response to N addition was less than that of velvetleaf, indicating that velvetleaf may be most competitive at high levels of nitrogen and least competitive when nitrogen levels are low. Corn yield declined with increasing velvetleaf interference at all levels of N addition. However, corn yield loss due to velvetleaf interference was similar across N treatments except in one site–year, where yield loss increased with increasing N addition. Corn yield loss due to velvetleaf interference may increase with increasing N supply when velvetleaf emergence and early season growth are similar to that of corn.

Field experiments were conducted to study the competition effect of winter wheat planted in a square arrangement and Italian ryegrass planted randomly on biomass yields of both species, ryegrass seed yield, N use efficiency, and progeny seed germination. Increases in wheat density up to 800 plants/m2 reduced ryegrass seed yield by 87% but increased its harvest index up to 42% compared to its monoculture yield. Species densities and their interactions accounted for 66 to 73% of the total variation in per-unit area biomass of species, and their association was more favorable to ryegrass biomass than wheat. Seeds of each species had three times greater nitrogen percentage than did shoots. Intra- and interspecific competition increased nitrogen percentage in wheat seeds. In Italian ryegrass, only interspecific competition increased N percentage in seeds. Although total nitrogen uptake by winter wheat was three times greater than in Italian ryegrass, Italian ryegrass was two times more efficient than wheat at producing biomass per unit of N taken up and specific leaf area at heading stage in mixture. Germination percentages of progeny seeds of both species in mixtures were greater in presence of high densities of the companion species than in their monocultures. Nitrogen was not the main limiting factor for competition between winter wheat and Italian ryegrass in this study.

Leaf and grass canopy photosynthetic rates were measured in a West African humid savanna during several stages of the early growing season. The results obtained on the dominant grass species Hyparrhenia diplandra and data published previously show that C4 savanna grasses exhibit a remarkably high leaf photosynthetic capacity despite their low nitrogen content. A variation of leaf photosynthetic capacity in relation to leaf rank on stems is observed which is interpreted by ageing and shading effects within the canopy. Seasonal variations of the canopy CO2 assimilation rate is explained in relation to variations of leaf area index and canopy nitrogen content. Despite low nitrogen content or low leaf area index, maximum canopy net photosynthesis was high (24 μmol CO2 m-3 s-1 for LAI = 1.5). The high photosynthetic nitrogen use efficiency exhibited by leaves of humid savanna grass species is a major attribute explaining high photosynthetic rates of the grass canopy in this environment. This result sustains the emerging opinion that tropical savannas could be highly productive despite the generally low nutrient status they experience.