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«International 17 Workshop th Nitrogen The was jointly organised by Teagasc and AFBI Printed by Print Depot Suggested citation Authors, 2012. Title ...»

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3. Results & Discussion The accumulation of biomass throughout the growing season was similar for the four treatments.

There were appreciable differences in crop N uptake throughout the crop, the final total values being 119, 177, 225 and 259 kg N ha-1 for the 2, 7, 14 and 21 mM NO3- treatments, respectively, and in shoot N content (Figure 1a) which were positively related to the applied N concentration.

There were generally clear and consistent differences between NDVI values from the different treatments, with the NDVI values being positively influenced by the concentration of applied N (Figure 1b). On 43, 56 and 71 DAT, there were similar linear relationships between NDVI and the shoot N content (Table 1). The linear regression equation for the combined data (n = 12) of the

Nitrogen Workshop 2012

three dates was NDVI = 0.0424 * shoot N + 0.6484, with a coefficient of determination (r2) of

0.864. These data suggest that the relationship between NDVI values and shoot N content was relatively constant during the last month of the crop when most biomass production occurred. This suggests that during, at least, the latter phase of a melon crop that fixed NDVI values can be used to assess crop N status. An important practical consideration is the minimum height of the crop at which canopy reflectance measurements can commence.

Figure 1. (a) Shoot N content of melon crops receiving nutrient solutions with 1, 7, 14 and 21 mM NO3-, (b) NDVI values of canopy reflectance measured in treatments receiving nutrient solutions with 1, 7, 14 and 21 mM NO3-.

All values are means of four replicates

–  –  –

4. Conclusion Crop reflectance as NDVI was sensitive to shoot N content. In the last month of the melon crop when most biomass production occurred, there was a relatively constant relationship between NDVI and shoot N content.

References Cartelat, A., Cerovic, Z.G., Goulas, Y., Meyer, S., Lelarg, C., Prioul, J.L., Barbottin, A., Jeuffroy, M.H., Gate, P., Agati, G. and Moya, I. 2005. Optically assessed contents of leaf polyphenolics and chlorophyll as indicators of nitrogen deficiency in wheat (Triticum aestivum L.) Field Crops Research 91, 35-49 Samborski, S.M., Tremblay, N. and Fallon, E. 2009. Strategies to make use of plant sensors-based diagnostic information for nitrogen recommendations. Agronomy Journal 101, 800-816 Thompson, R.B., Martínez-Gaitán, C., Gallardo, M., Giménez, C. and Fernández, M.D. 2007 Identification of irrigation and N management practices that contribute to nitrate leaching loss from an intensive vegetable production system by use of a comprehensive survey. Agricultural Water Management 89, 261-274

Nitrogen Workshop 2012

Sensitivity of the ratio leaf chlorophyll to leaf flavonols measured with optical sensors to crop N status of melon Peña, M.T.a, Thompson, R.B.a, Gallardo, M.a, Gimenez, C.b aUniversity of Almeria, Department of Crop Production, Almeria, Spain b University of Cordoba, Department of Agronomy, Cordoba, Spain

1. Background & Objectives Optical sensors are a promising approach to assess crop N status (Cartelat et al., 2005; Samborski et al., 2009). Their use in situ and in real time provides the potential for N fertiliser application to be rapidly adjusted to crop N status (Samborski et al., 2009). Such corrective management would be well-suited where the combined use of high frequency, drip irrigation and fertigation enables precise N application, such as in greenhouse-based vegetable production on the south-eastern (SE) Mediterranean coast of Spain. The SPAD meter estimates leaf chlorophyll content (Samborski et al., 2009). The content of leaf flavonols was reported to be an indicator of crop N status (Cartelat et al., 2005) who suggested that the ratio of leaf chlorophyll to leaf flavonols was particularly sensitive to crop N status. The current study examined the use of the ratio of leaf chlorophyll to leaf flavonols, both estimated with hand-held optical sensors, to assess crop N status of a melon crop.

2. Materials & Methods A cantaloupe type melon crop was grown in a loam soil in a greenhouse with polyethylene cladding in Almeria, SE Spain. The crop was transplanted as 5 week old seedlings on 19 April 2010 and grown for 78 days. The crop was drip irrigated and fertigated receiving complete nutrient solutions in all irrigations. The crop was vertically supported with nylon cord. Four different N treatments were applied, commencing 23 days after transplanting (DAT), being NO3- concentrations of 2, 8, 15 and 23 mM; 0.4 mM NH4+ was applied in all treatments. The 15 mM NO3- was regarded as conventional management, the 23 mM as clearly excessive, and the 2 and 8 mM as N deficient.

Total irrigation was 146 mm; and 34, 129, 241 and 373 kg N ha-1 were applied to the 4 treatments.

Plot size was 6 m x 6 m with six rows of plants per plot and 12 plants per row; the plots were organised in a randomised block design with four replicate plots per treatment. The SPAD-502 chlorophyll meter (Konica Minolta Sensing, Inc., Japan) was used to estimate leaf chlorophyll content. The DUALEX 4 FLAV sensor (Force A, Paris, France) was used to estimate the content of leaf flavonols. Measurements were made at weekly intervals commencing 22 days after transplanting (DAT). All measurements were made on the most recently expanded leaf on 16 plants per plot, using the same plants within each plot. Five crop biomass samplings were made throughout the crop and the N content was determined. All data are means from four replicate plots.





Sensor and biomass samplings coincided on 28, 43, 56 and 71 DAT.

3. Results & Discussion The accumulation of biomass throughout the growing season was similar for the four treatments.

There were appreciable differences in crop N uptake throughout the crop, the final total values being 119, 175, 220 and 254 kg N ha-1 for the 2, 8, 15 and 23 mM NO3- treatments, respectively, and in shoot N content (Figure 1) which were positively related to the applied N concentration. The ratio of leaf chlorophyll to leaf flavonols was strongly related to the applied N concentrations throughout the crop (Figure 2). There was a consistent general relationship between ratio of leaf chlorophyll to leaf flavonols and shoot N content (Figures 1 and 2). Linear regression analysis showed strong and significant (P0.01) linear relationships between the ratio of leaf chlorophyll to leaf flavonols and shoot N content on 43, 56 and 71 DAT with coefficient of determination (r2)

Nitrogen Workshop 2012

values of 0.78 to 0.85; however, the slope and intercept values varied appreciably between each of these dates indicating that the relationship was not constant over time. The average coefficient of variation for all values of the ratio of chlorophyll to flavonols was 29%.

Figure 1. Shoot N content of melon crops receiving nutrient solutions with 2, 8, 15 and 23 mM NO3- throughout the crop after 23 DAT.

All values are means of four replicates. DAT: days after transplanting.

Figure 2. Ratio of leaf chlorophyll to leaf flavonoles of a melon crop receiving nutrient solutions with 2, 8, 15 and 23 mM NO3- throughout the crop after 23 DAT.

All values are means of four replicates. DAT: days after transplanting.

4. Conclusion The ratio of leaf chlorophyll to leaf flavonols, was sensitive to shoot N content. There was no consistent relationship between this ratio and shoot N content suggesting that threshold values for N management would need to be determined at particular growth stages for melon.

References Cartelat, A., Cerovic, Z.G., Goulas, Y., Meyer, S., Lelarg, C., Prioul J.L., Barbottin, A., Jeuffroy M.H., Gate, P., Agati, G. and Moya, I. 2005. Optically assessed contents of leaf polyphenolics and chlorophyll as indicators of nitrogen deficiency in wheat (Triticum aestivum L.) Field Crops Research 91, 35-49 Samborski, S.M., Tremblay, N. and Fallon, E. 2009. Strategies to make use of plant sensors-based diagnostic information for nitrogen recommendations. Agronomy Journal 101, 800-816

Nitrogen Workshop 2012

Site, preceding crop and N management effects on yield of organic winter oil seed rape Engström, L.a, Stenberg, M.a, Wallenhammar, A.-C.a,b, Ståhl, P.c a SLU, Department of Soil and Environment, Skara, Precision Agriculture and pedometrics, Skara, Sweden b HS Konsult AB, Örebro, Sweden c Hushållningssällskapet Rådgivning Agri AB, Linköping, Sweden

1. Background & Objectives Plant nutrient supply is a key issue in production of organic winter oil seed rape (WOR). The variation in nitrogen (N) application and yield level varies greatly. The production of organic oil seed rape is often hazardous and the grower has to expect great variations in yield levels (Wallenhammar, 2005). WOR demands high amounts of available soil N to achieve an adequate yield. The N demand is large during the vegetative stages (Schultz, 1972), and variation in yield of WOR is due to availability of N during growth and development (Rathke et al., 2006). Excess N rates in spring can, however, increase leaching in the subsequent crop (Engström et al. 2011). There is a need to improve tools used by advisors and farmers to predict the N demand. The objective of this study was to increase the knowledge of the possibilities to adjust the N application by organic fertilizers to the previous crop and site with the aim to develop N management strategies for N application in organic WOR.

2. Materials & Methods This study was carried out in 8 field experiments in south Sweden during 2009-2010. The effects of different N levels, under varying cropping history and soil type, were determined by quantifying the yield and N demand in relation to different soil parameters. The experiments were carried out in 40 plots at each site with a fully randomized two factorial design with four replicates and two levels of N application in autumn (F1) (0 or 50 kg N ha-1) and five levels in spring (F2) (0, 50, 100, 150 or 200 kg N ha-1). N was supplied in autumn as Biofer 10-3-1 (10% N, 3% P and 1% K) and in spring as Vinasse, a by-product from yeast production with on average 4% N and 4% K. Plants were sampled for analysis of dry matter yield. Soil mineral N content in 0-90 cm was quantified at sowing (August year 1), early spring and at harvest (August year 2). Seed yield and quality including seed N content was determined in each plot. Each experimental site was characterized regarding crop rotation history and several soil characteristics as soil texture, organic matter content and soil electrical conductivity. Statistical analysis of variance of treatment effects and interactions were carried out with the Mixed model procedure in SAS 9.2 (SAS Institute Inc., Cary, NC, USA).

3. Results & Discussion Seed yields differed between sites and years and ranged from very low yields, about 500 kg ha-1, to 4080 kg ha-1 in plots without N fertilization. Yield increases from the autumn application was on average 135 kg (p=0.0012) and in spring 700 kg at the highest N level compared with no N (p0.0001). Yield increases were up to 1400 kg ha-1 at the highest spring N application rate recorded at a site with a long lasting set-aside as the preceding crop. There was no response from spring N application in three of the experiments when white clover and pasture constituted the preceding crops. These crops most likely contributed to high soil N availability during growth of WOR, thus explaining the high yield level in unfertilised WOR. A small N response was obtained at two sites with white clover and green manure as preceding crop. The weak N response at one site may be due to a dry period in spring reducing mineral N availability in the soil. The highest responses from spring N fertilisation were recorded in experiments with ley (mixed grass and clover) or a set-aside as preceding crops. Economical optimum N fertilisation was determined as N

Nitrogen Workshop 2012

rate at the highest net income assuming a seed price of 6 SEK kg-1, N cost 22 SEK kg-1 and cost for transport and drying 0.2 SEK kg-1. Optimum N rate ranged from 68 to 190 kg N ha-1 and the yield increase ranged from 824 to 1393 kg ha-1. The highest N response was recorded after a 14 year old grass set-aside. Here the soil profile was likely depleted from mineral N and N immobilisation, which was considerable due to incorporation of crop residues with low N content. The high N response after the grass/clover leys may be caused by N leaching losses from sites with sandy soil and high rainfall.

N (kg ha-1) N (kg ha-1) Figure 1. Late autumn soil mineral N and above Figure 2. Spring soil mineral N and above ground ground plant N vs. seed yield in the 0N treatment of 7 plant N vs. seed yield in the 0N treatment of 7 sites.

sites.

Soil mineral N showed large variation between sites with on average almost 80 kg N in the control treatment at establishment of the crops. Despite a large N uptake during autumn there were considerable amounts of N in the soil profile in late autumn. Total N as soil mineral N at 0-90 cm depth along with above ground plant N, in late autumn (Figure 1) as well as in spring (Figure 2) showed significant (p0.05) correlation with seed yields in the 0 N treatment. Sites with high N delivery, depending on preceding crop and management history, during autumn were also the highest yielding as shown by the seed yields at the different N application rates. The variation in optimum N rate in spring could be explained best by N-uptake in autumn (x1), soil mineral N in autumn (x2) and yield level (x3) at optimum (y = 49-1.8x1–1.9x2+0.07x3; P= 0.93; p0.001).

4. Conclusion The N response of spring N fertilisation varies depending on both preceding crop and on soil type as well as weather conditions. The results indicated that N uptake and soil mineral N in autumn as well as yield level x1 should be considered when calculating optimum N-rate in spring. Autumn N fertilisation cannot be recommended to organic WOR with a good preceding crop (white clover, pasture or red clover) or with a late sowing date.

References Engström, L., Stenberg, M., Aronsson, H. and Lindén, B. 2011. Reducing nitrate leaching after winter oilseed rape and peas by optimising crop management. Agron. Sustain. Dev. 31, 337-347.



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