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In-season nitrogen (N) nutrition diagnosis and N requirement (NR) estimation are critical to precision management of crop fertilization. Although many studies focus on the diagnosis of in-season crop N nutrition, few of them associated the N status with crop NR or topdressing N fertilizer. The objective of this study was bridging the gap between crop N nutrition status and crop NR for easy implementation of precision fertilization. Field experiments were conducted with different N levels and six rice (Oryza sativa L.) varieties in eastern China during 2010–2014. Rice in-season NR and N nutrition index (NNI) were calculated with plant chemical analysis and pre-established critical N dilution curve. Results showed a significant linear relationship between in-season rice NR and NNI based on the long-term field experiment, and the NR-NNI regression slope changed with days after transplanting (DAT) in a regular pattern. Based on this data changing pattern, a novel NR estimation model was established with three easy-obtained independent variables (DAT, N-fertilizer recovery efficiency and NNI). Independent model validation results showed very good performance on different rice varieties and growth stages, with root mean square error (RMSE) of 5.93, 6.96, 8.74 and 6.43 kg ha−1 for three japonica rice and one indica rice varieties, respectively. This model will significantly facilitate the estimation of in-season rice NR and provide strong technical support for the precision management of N fertilization.

Overestimation of nitrogen (N) uptake requirement is one of the driving forces of the overuse of N fertilization and the low efficiency of N use in China. In this study, we collected data from 1 844 site-years of rice (Oryza sativa L.) under various rotation cropping systems across the Yangtze River Valley. Selected treatments included without (N0 treatment) and with N application (N treatment) which were recommended by local technicians, with a wide grain range of 1.5–11.9 t ha−1. Across the 1 844 site-years, over 96% of the sites showed yield increase (relative yield>105%) with N fertilization, and the increase rates decreased from 78.9 to 16.2% within the lowest range 6.5 t ha−1. To produce one ton of grain, the rice absorbed approximately 17.8 kg N in the N0 treatment and 20.4 kg N in the N treatment. The value of partial factor productivity by N (PFPN) reached a range of 35.2–51.4 kg grain kg−1 with N application under the current recommended N rate. Averaged recovery rate of N (REN) was above 36.0% in yields below 6.0 t ha−1 and lower than 31.7% in those above 6.0 t ha−1. Soil properties only affected yield increments within low rice yield levels (

We tested the hypothesis that by reducing the application of N, based on the decrease in evapotranspiration (ET) expected due to increase in soil salinity, it is possible to reduce N loss without causing N deficiency or further yield loss in salt-stressed maize plants. We tested four levels of salinity of irrigation water (S1 = 0.5; S2 = 2.5; S3 = 5.0; and S4 = 7.5 dS m−1) and four N rates using outdoor soil columns with five replicates. The N rates were as follows: N1: N recommendation for maize (2.6 g per column); N2: 0.3 times the N recommendation (0.78 g per column); N3: reduction in N1 based on the decrease in ET caused by salinity; and N4: reduction in N2 based on the decrease in ET caused by salinity. The amounts of N for N3 and N4 were reduced (in relation to N1 and N2) by 7 %, 15 % and 30 % for 2.5, 5.0 and 7.5 dS m−1, respectively. Salinity caused NO3− accumulation in the soil, plant growth inhibition and stomatal closure. The low rates of N (N2 and N4) did not meet the N demand of maize plants, especially for low levels of salinity (control and 2.5 dS m−1). On the other hand, based on the available growth data, physiological responses and nutritional status, one can conclude that plants under N1 and N3 had the same potential for final yield. For these N rates, reduction in N application according to ET (N3 rate) not only allowed plant growth and maize physiological responses, but also increased N-use efficiency and greatly reduced soil nitrate accumulation compared to N1 rate, at the same levels of salinity. We conclude that reduction in N application, based on reductions in ET, is a good strategy to reduce both the risk of ground water contamination by NO3− leaching and fertilization costs, without causing additional damage to plant development under salt stress.

Published in Agron. J. 104:1208–1216 (2012) Posted online 15 June 2012 doi:10.2134/agronj2011.0369 Copyright © 2012 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. C bentgrass (Agrostis stolonifera L.) is presumably the most widely planted C3 turfgrass on golf course putting greens due to its wide range of temperature adaptation, aesthetic qualities, and superior playability. ‘Penncross’ has long been the standard selection for creeping bentgrass putting greens dating back to the 1950s. In the mid-1990s, cultivars L-93, Crenshaw, SR1020, and Penn offered improvement in terms of heat tolerance and overall quality (McCarty, 2009). The newest generation of creeping bentgrass cultivars offer golf course superintendents many new and improved features, including enhanced salt (Wang and Zhang, 2010) and drought tolerance (McCann and Huang, 2008). Superintendents operating in today’s environmentally conscious climate must base cultivar selection beyond just dark color and improved turfgrass quality attributes. Desirable cultivars require less input but still maintain a commercially acceptable appearance and playability. Water restrictions and use of recycled water are becoming a reality in certain geographical regions of the country. Although turfgrasses have been shown to minimize N leaching (Engelsjord et al., 2004), fertilizer use in the industry has come under scrutiny as several states have restricted the use of P-containing fertilizers, with Minnesota being the first state to issue strict regulations (Rosen and Horgan, 2005). Although N use is currently not restricted, many golf course superintendents are reducing fertilizer applications due to budget cuts (personal communication, 2009). A reduction in N can have several negative agronomic consequences. Improper N fertilization, whether excessive or inadequate, can lead to increased weed (Busey, 2003) and disease pressure (Inguagiato et al., 2008; Kaminski and Dernoedon, 2005), as well as reduced tolerance to abiotic and biotic stresses (Baldwin et al., 2009; Bunnell et al., 2005; Hoffman et al., 2010). Although putting greens comprise the least amount of managed land area on golf courses, they often have the highest management requirements in terms of fertility, chemical, and mowing inputs. Adequate N fertilization is important because N is directly tied to turfgrass color, density, recuperative ability, and overall plant health (Liu et al., 2008). Nitrogen is also a constituent in numerous plant compounds, including proteins, chlorophyll, nucleic acids, and secondary metabolites (Liu et al., 2010). Turfgrass N use has been extensively examined in the literature; however, large-scale field trials of creeping bentgrass cultivar N requirements have received little attention. Researchers from the transition zone to the North Central Midwest have reported creeping bentgrass requires N rates ranging from 146 to 390 kg ha–1 yr–1 to maintain an acceptable appearance (Koeritz and Stier, 2009; Moeller 2008; Schlossberg and Karnok, 2001; Totten et al., 2008). All of these rates are generally in the range of what superintendents in the United States reported in 2006 regarding annual N use rate (Throssell et al., 2009). The new generation of creeping bentgrass cultivars (released after 2000) possess numerous unique traits, including better disease tolerance, improved salt tolerance, darker green genetic color, increased density, enhanced drought tolerance, and ABSTRACT

Leaf colour chart (LCC) guides fertilizer nitrogen (N) application to rice as per requirement of the crop on the basis of a critical leaf colour. We evaluated need-based N management in on-farm experiments at 350 locations in the Indian Punjab during 2002 – 2005. Following LCC-based N management, from 9.4 – 54.2 kg N ha−1, with an average of about 25% less fertilizer N was used, without any reduction in yield as compared to the practice of farmers of applying blanket N at fixed time intervals. Application of fertilizer N when colour of the first fully expanded leaf was less than LCC shade 4, increased nitrogen use efficiency from 48 – 65 kg grain kg N−1. Nitrogen requirement of rice was site-specific both in terms of time and the amount of fertilizer N applied. In 36% of the experiments, a dose of fertilizer N was applied 55 days after transplanting (DAT) of rice. Also there were cases where only one top dressing of N was required. The study reveals that practice of applying N at fixed growth sta...

In order to avoid nitrogen overfertilization, fertilizer rates must be adjusted to meet crop requirements. Two field experiments with sunflower (Helianthus annuus L.) were performed in the western part of the Pampas, Argentina, to: (i) assess nitrogen fertilization effects on seed yield, grain oil content, and plant lodging, (ii) determine N requirement per unit of yield, crop recovery of fertilizer N, and whether these two parameters were affected by N and other nutrient additions. Nitrogen fertilization increased the seed yield only by 17% at one site. Crop nitrogen requirement per unit yield (b-value) increased from 37 to 42 kg Mg − 1 due to nitrogen fertilization only at the site where there was not a yield response. Therefore, if a yield response is expected, it is not necessary to use different b-values for non fertilized or fertilized crop. Reduction of seed oil content due to N addition was relatively small (2–5%), and was overcompensated by the seed yield increase at the responsive site. Recovery of fertilizer 15 N was of 51%. This efficiency of absorption should be considered for making fertilizer recommendations. Application of further nutrients including P and K had no influence on seed yield. © 2002 Elsevier Science B.V. All rights reserved.

In this study, multi-site crop response data were examined so as to improve guidelines for crop nitrogen requirement and efficient fertiliser use on winter wheat over a range of soil types. The parameters which had most individual effect on nitrogen requirement (the economic optimum amount of fertiliser N (Nopt)) were soil type and previous cropping. Interactions between soil type and soil N supply as measured by soil mineral nitrogen analysis were also important. Yield had no effect. Descriptive models were developed for Nopt. The simplest, based on N index, rainfall and soil type, accounted for 40% of the variation in Nopt. This was improved to 51% by adding spring analysis of soil mineral nitrogen. The model could be improved by inclusion of measured yield or a seasonal term, but the precision of predicted Nopt was not improved significantly, 41% of cases being within ±25 kg ha -1 of the optimum without yield and 42% with yield. The study showed that some of the inputs currently used to determine N requirement need to be revised and additional terms added. However, even the best estimates have poor predictive precision. Le lien entre le rendement et les besoins en azote d'une culture peut conduire a des applications excessives de fertilisants. Cette etude examine les besoins en azote et les fertilisants efficaces utilises sur le ble d'hiver pour differents types de sols. Les parametres ayant l'effet le plus important sur le besoin en azote sont le type de sol et la culture precedente. Cependant, les meilleures estimations restent tout de meme imprecises.

SUMMARYIn a 2-year field study, leguminous fodder crops (cowpea (Vigna unguiculata) and cluster bean (Cyamopsis tetragonoloba)) responded more to P than did nonleguminous fodder crops (maize (Zea mays), sorghum (Sorghum bicolor) and pearl millet (Pennisetum americanum)). The local cultivar of tall wheat, C306, yielded more when sown after fallow or legumes than after nonlegumes. Wheat sown after fallow or legumes produced more ear-bearing tillers and more grains per ear than when sown after nonleǵumes. Wheat sown after fallow or legumes responded to N application of up to 20 kg/ha, while when sown after nonlegumes it responded linearly to the highest rate of 60 kg/ha. Thus, preceding fallow, cowpea and cluster bean reduced the N requirement of wheat by 20–40 kg/ha compared with preceding maize, sorghum and pearl millet. Nitrogen increased grain yields only at applications of up to 40 kg/ha because lodging occurred at the higher rates. A cluster bean-wheat cropping sequence proved the most profitable.

SummaryA 2-year field study indicated that pearl millet yielded more when sown after fallow, cow pea and green gram than after maize. Preceding fallow, cow pea and green gram reduced the nitrogen requirement of pearl millet by 40 kg/ha compared with maize. Pearl millet responded linearly up to the highest rate of nitrogen (80 kg/ha). N applied to millet had no residual effect on the subsequent crop of chickpea. The chickpea yield followed the order fallow > green gram ≥ cow pea > maize. Chickpea responded to phosphorus up to 40 kg/ha. Green gram-pearl millet-chickpea proved the most profitable cropping sequence. Continuous cropping and application of nitrogen and phosphorus improved the organic carbon and available phosphorus but decreased the available potassium status of the soil.

SUMMARYUreaform, applied twice a year, in early spring and late summer, was compared with poultry manure and (NH4)2SO4 top dressings as nitrogen suppliers in a banana plantation. No significant differences between the treatments were obtained in any of the plant criteria, but nitrate concentrations in the soil were higher in the ureaform treatment at the standard nitrogen level than in the standard treatment, within the root zone as well as below it. The spring application of ureaform affected the nitrate concentration in soil for 8 months and was better utilized by the crop than the autumn application, which left a greater residual effect. It therefore seemed that one spring application might be sufficient to meet the banana's nitrogen requirement.

SummarySeventy-four field experiments on the nitrogen requirement of sugar beet were made in eastern England in. 1966 to 1974. Considerable differences in sugar yield response to nitrogen were found between the six soil types used, and these differences were found (on five of the six soils) to be related to sugar yield. Nitrogen response was large on chalk and limestone soils in Lincolnshire, intermediate on East Anglian boulder clays and least on East Anglian chalk and light drift soils. On the lighter soils (limestones, East Anglian chalks and light drifts) nitrogen response was greater with high summer rainfall than with low. Fenland silt soils were very high yielding, but nitrogen response was moderate.Optimum nitrogen rates differed between soils, in the range 100 kg/ha on East Anglian chalks and light drifts to 180–200 kg/ha on Lincolnshire chalks and limestones.

SummaryThree field experiments were carried out on sandy loam soil at Levington, Suffolk, on the effect of irrigation on nitrogen requirements of sugar beet. Four nitrogen rates (0, 67, 134, 201 kg/ha) were examined with and without irrigation. Nitrogen increased sugar yield each year, as did irrigation in 1969 and 1970, but not in 1968 when the soil moisture deficit was small. There was a significant nitrogen x irrigation interaction in 1970 only, but on average there was a greater response to nitrogen with irrigation than without it.These results and other published data suggest that on sandy soils in eastern England moisture deficit can restrict nitrogen response, and that the economic optimum nitrogen rate is appreciably higher with irrigation than without it.

Ammonium salts can replace asparagine as the main nitrogen source for maize endosperm tissue culture. Although the acetate, oxalacetate and oxoglutarate are toxic, the succinate or citrate may be used.

The enzymic nitrate reduction capacity of leaves, which is defined as the rate of response to the inducing stimulus of externally added NO3 substrate to incubated leaf fragments, is proposed as a measure for assessing the nitrogen fertilisation requirement of grass crops. The assay was tested in an annual ryegrass field experiment plot, where the effect of increasing N levels was studied. The rate of response diminished from 11 to 1 and was negatively correlated with the yield and NO3 concentration in the leaves.

SummarySeventeen experiments with spring barley testing seven amounts of nitrogen were made on commercial farms in Somerset, Devon and Cornwall between 1965 and 1968. Crop measurements and determinable site factors were only partially successful in accounting for differences between sites and between years in optimal N and efficiency of N use below optimum.The actual optima were found to differ considerably from predicted N requirements based on past cropping and summer rainfall.

The effect of N-fertilizing on the yield and N-content of soybean forage was examined experimentally from 1950 to 1954, the results being as follows. 1. Most part of nitrogen stored in the cotyledons of soybean was transfer red to other parts of the plant in 2∼3 weeks after germination. Soybean seedlings had to take N compounds from soil with their roots after the cotyledon N had been exhausted, and N-fixation did not yet begin. 2. In sand culture, the forage yield of the plants supplied with N-fertilizers only for the first 5 weeks after germination, and depending upon symbiotically fixed N thereafter, was just as high as that of the plants supplied with N continuously through the entire season. 3. The effect of N-application upon the N-content of plant varied greatly according to the difference in soil conditions. Under certain conditions, such as low lime and sandy soil, the total amount of N per plant increased significantly : while in other conditions, such as loamy soil with rich lime, the increase was very small. 4. The recovery of N was greater in young stage of plant growth, and it decreased in later stages, especially after blooming. Therefore application of N fertilizers to soybean in early growth stage of the plants may be more effective than that in later stages for the forage production.