Sarhad J. Agric. Vol.25, No.1, 2009

RESPONSE OF WHEAT GENOTYPE ‘MSH-14’ TO DIFFERENT LEVELS/RATIOS OF NITROGEN AND PHOSPHORUS PARVEZ KHAN, MUHAMMAD IMTIAZ, MUHAMMAD YOUSUF MEMON and MUHAMMAD ASLAM Soil Science Division, Nuclear Institute of Agriculture, Tando Jam, Pakistan ABSTRACT A wheat genotype MSH-14 was investigated for two consecutive years i.e. 2005-06 and 2006-07 for its response to different ratios of nitrogen (N) and phosphorus (P). Four levels of N (0, 90, 120 and 180 kg ha-1) and eight levels of P2O5 (0, 23, 30, 45, 60, 70, 90 and 135 kg ha-1) along with 60 kg K ha-1 in ten combinations were employed in different ratios i.e., (4:1, 4:2 and 4:3). Results indicated that the agronomic parameters like plant height, number of grains/spike, spike length and 100-grain weight were influenced significantly by the application of N and P2O5. The maximum biological yield was recorded with 180 kg N and 90 kg P2O5 ha-1, which was statistically at par to that produced by 120 kg N and 90 kg P2O5 ha-1. The yield trend at both years clearly indicated that application of N and P2O5 at 4:3 ratio improved their utilization efficiency. Since the test genotype (MSH-14), produced maximum yield at 120 kg N and 90 kg P2O5 ha-1, hence it could be adopted as the most economical dose for obtaining the maximum yield of wheat under the agro-climatic conditions of Sindh. Key Words: Balanced fertilization, Nitrogen, Phosphorus, Wheat Citation: Khan, P., M. Imtiaz, M.Y. Memon and M. Aslam. 2009. Response of wheat genotype “MSH-14” to different levels/ratios of Nitrogen and Phosphorus. Sarhad J. Agric. 25(1): 59-64. INTRODUCTION The foundation of good fertilizer stewardship rests on the principles of using the right source at the right time and with right placement (Roberts, 2007). Use of essential elements (NPK) in appropriate combination is imperative to enhance crop productivity in Pakistan as continuous cropping of high yielding crop varieties has caused rapid mining of essential nutrients from the soil resulting in poor soil fertility (Sadiq, 1992). One of the major challenges in agriculture is to increase crop production in a sustainable way by improving soil fertility. To maintain soil fertility and to realize our food security goals, use of fertilizers is one of the most important factors. If nutrients depleted through crop removal are not replaced, soil fertility level will go gradually down creating a stress soil environment. This situation exists in many crop-producing regions of the country, seriously affecting crop production (Ahmad, 2002). Fertilizer application practice in Pakistan is predominantly in the favour of N only, which is further accentuating nutrient deficiencies particularly of P2O5 and results in poor yield potential of crops (Saleem et al., 1986). Balanced fertilization is one of the most important components of the modern production technologies that refers to the supply of plant nutrients not only in proper amounts but also in balanced proportions. Balanced fertilization minimizes the possibility of environmental pollution. Balanced fertilization is not an expense; it is an investment in the future of soil (Khalid and Malik, 2002). Whenever, a plant breeder develops a new variety it is essential to plan its production technology particularly with reference to the requirement of N and P2O5, as the nutritional requirements of different cultivars of the same crop species may vary, depending on their yield potential, plant architect and agro-climatic conditions of the region (Imtiaz et al., 2003). The present studies were undertaken to assess the effect of different N and P2O5 ratios on the performance of a wheat cultivar ‘MSH-14 evolved at NIA, Tando Jam for obtaining maximum yield and economical returns. MATERIALS AND METHODS Field studies were conducted on fixed layout for two consecutive years at Nuclear Institute of Agriculture (NIA), Tando Jam to study the response of wheat crop to N and P fertilizer application. The experimental site was silty clay in texture, non-saline in nature (ECe, 0.66 and 0.58 dS m-1), low in organic matter (7.2 and 8.1 g kg-1), Kjeldahl N (0.04 and 0.046 %) and Olsen’s P (6.2 and 6.8 mg kg-1). Four levels of N (0, 90, 120 and 180 kg ha-1), eight levels of P2O5 (0, 23, 30, 45, 60, 70, 90 and 135 kg ha-1) along with 60 kg K ha-1 in ten combinations were employed in (4:1, 4:2 and 4:3 N:P ratios). The experiment was laid out according to randomized complete block design (RCBD) with four replications. The plot size was 4m x 4m in both years. Phosphorus in the form of triple super phosphate was applied at the time of sowing according to the quantity required for each treatment. The

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required quantity of N in the form of urea was applied in two splits; half at sowing and the remaining half at the time of first irrigation. Pre-sowing soil samples upto 30 cm depth were collected and analyzed for their physico-chemical properties such as soil texture (Koehler et al., 1984) Soil pH(1:5) (Mclean, 1982) using 105 Ion Analyzer pH meter), soil organic matter (Nelson and Sommers, 1982), P by Spectrophotometer “Spectronic 21” using required standard solutions. Total nitrogen in soil and plants was determined using Kjeldahl distillation procedure as described by (Bremner 1996). The seed of the candidate wheat variety MSH-14 developed by plant Genetics Division of NIA, Tando Jam was used for the evaluation of nutrient requirements prior to its release. The wheat was sown with single row hand drill at inter-row spacing of 30 cm with the seed rate of 150 kg ha-1. The requisite agronomic and plant protection measures were adopted uniformly for all the treatments during the entire growing period. At maturity the data were recorded for biological yield after harvesting the crop. The plant samples were then collected randomly from each treatment and separated into grain and straw. Both of these plant parts were dried at 70 oC in an oven at a constant weight for determination of N and P2O5. A uniform sub portion of the dried material was ground in Wiley’s mill and a known quantity of the ground material was digested by modified Kjeldahl’s method in which N is converted in NH4+ form by digestion with H2SO4. The NH3 is distilled into boric acid and determined by titration with standard H2SO4 (Jackson, 1962). Total P was also determined by digesting the plant material in HNO3: HClO4 mixture prepared in 5:1 ratio. The digested material was analysed for total P by metavanadate yellow colour method as described by Jackson (1962). The results obtained were subjected to statistical analysis using standard method of analysis (Steel and Torrie, 1986). The differences among the treatment means were compared by using DMR test. RESULTS AND DISCUSSION Plant Height The data regarding plant height have been depicted in Table-1. The plant height increased significantly with the application of N and P. The lowest plant height (72.5 cm) was recorded in control plot while the maximum plant height (98.0 cm) was observed with 180 kg N and 135 kg P2O5 ha-1 which was statistically identical to that of 120 kg N and 90 kg P2O5 ha-1. The results are in close agreement to those reported by Malik (1990) while working with no till dry land winter wheat. Grain Number Spike-1 The data regarding the number of grains/spike are presented in Table I. Fertilizer application significantly increased the grains per spike. The lowest number of grains per spike (45.0) was found in control while the maximum grain per spike (82.0) was recorded with 120 kg N and 90 kg P2O5 ha-1. Successive increase in P2O5 at each level of N showed a tendency to increase the number of grains per spike indicating the effectiveness of P2O5 towards seed formation and grain filling (Kaishtha and Marwahs, 1977). Table I. Effect of different fertilizer levels and ratios on agronomic parameters of wheat genotype MSH-14 Treatments (N- P2O5 kg ha-1) Control 90: 23 (4:1) 90: 45 (4:2) 90: 70 (4:3) 120: 30 (4:1) 120: 60 (4:2) 120: 90 (4:3) 180: 45 (4:1) 180: 90 (4:2) 180:135 (4:3)

Number of Grains Spike-1

Plant height (cm) 2005-06

2006-07

Mean

2005-06

2006-07

Mean

72 d

73 d

72.5 d

45e

45 f

45.0 f

82 c 84 c

82 c 84 c

82.5 c 84.0 c

70 cd 72 bc

70 de 73 cd

70.0 cd 72.5 bc

90 b 90 b 92 b 96 a 96 a 98 a 98 a

89 b 90 b 92 b 98 a 97 a 98 a 98 a

89.5 b 90.0 b 92.0 b 97.0 a 96.5 a 98.0 a 98.0 a

75 b 66 d 68 d 82 a 79 a 79 a 80 a

76 bc 66 e 68 e 82 a 81 a 80 ab 81 ab

75.5 b 66.0 e 68.0 de 82.0 a 80.0 a 79.5 a 80.5 a

Means followed by different letters in the same column are significantly different from each other at 5% level of significance.

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Spike Length (cm) Escalating response of spike length to the application of N and P has been presented in Table II. It’s linearly increased with subsequent increase in each unit of N and P2O5 however, response was comparatively higher at 4:3 N and P2O5 ratio and lower at 4:1 ratio. The maximum spike length (13.7 cm) was observed when N and P2O5 were applied at 120 kg and 90 kg ha-1. The control gave significantly lower spike length of 9.3 cm. Our findings are in close agreement with those reported by Ahmad and Rashid (2003) and Singh and Singh (1991). Hundred Grain Weight (g) A similar impact of fertilization was observed on 100 grain weight (Table II) as on spike length. The lowest 100-grain weight of 3.07 g recorded in the control was enhanced significantly with the successive increments in the application rates of N and P. The highest grain weight (4.62 g) was recorded with the application as N and P2O5 at 120 and 90 kg ha-1 and it was significantly different from the other treatments. Singh and Singh 1991 and Vaughan et al., 1990, have also reported similar findings, who studied the impact of irrigation time and N level on wheat and suggested that N and P2O5 in balanced proportion are vital for formation and development of grains. Table II. Effect of different fertilizer levels and ratios on agronomic parameters of wheat genotype MSH-14 Treatments (N- P2O5 kg ha-1) Control 90: 23 (4:1) 90: 45 (4:2) 90: 70 (4:3) 120: 30 (4:1) 120: 60 (4:2) 120: 90 (4:3) 180: 45 (4:1) 180: 90 (4:2) 180:135 (4:3)

Spike length (cm) 2005-06 9.7 e 11.2 d 12.3 c 13.0 abc 13.2 ab 12.7 bc 13.8 a 13.3 ab 13.2 ab 13.4 ab

2006-07 9.0 d 11.9 c 12.4 bc 13.1 ab 13.1 ab 13.2 ab 13.6 a 13.3 ab 13.4 ab 13.4 ab

100 grain weight (g) Mean 9.3 e 11.5 d 12.4 c 13.0 ab 13.1 ab 13.0 bc 13.7 a 13.3 ab 13.3 ab 13.4 ab

2005-06 3.06 c 3.97 b 4.09 b 4.34 ab 4.02 b 4.14 b 4.61 a 4.01 b 4.00 b 4.10 b

2006-07 3.09 d 4.04 bc 4.00 c 4.44 ab 3.95 c 4.22 bc 4.62 a 4.18 bc 4.14 bc 4.16 bc

Mean 3.07 d 4.01 c 4.05 c 4.39 ab 3.99 c 4.18 bc 4.62 a 4.10 c 4.07 c 4.13 bc

Means followed by different letters in the same column are significantly different from each other at 5% level of significance. Biological yield The crop showed obvious response to various levels of N and P2O5 fertilizers when applied at different ratios (Table III). Generally yield increased with increasing N and P2O5 levels but different ratios of N and P2O5 influenced biological yield more significantly. The highest biological yield of 11.72 t ha-1 obtained with 180 N and 135 kg P2O5 ha-1 was statistically identical to that produced by 120 N and 90 kg P2O5 but different from rest of the fertilizer treatments. The better growth and higher biological yield with increasing N levels can be attributed to the most important functions of the N, in enhancing the vegetative growth (Ma et al., 2004). Phosphorus seems to have an additive effect on crop growth provided it is supplied in a balanced proportion to that of applied N (Bhatti et al., 1988 and Brink, 2001). Our findings are in close agreement to those reported by Ahmad et al., (1992). Grain yield As noted for biological yield, similar response of N and P2O5 fertilization was also recorded for grain yield (Table III). The highest grain yield of 4.99 tons ha-1 was recorded where N and P2O5 were applied at 120 and 90 kg ha-1. The yield trend clearly indicated that application of N and P2O5 at 4:3 ratios improved their utilization efficiency. Since “MSH-14” the test cultivar produced maximum yield (4.99 t ha-1) at 120 kg N and 90 kg P2O5 ha-1, hence the fertilizer treatment was enough to satisfy the crop nutrient requirements (Villar-Mir et al., 2002 and Bhatti et al., 1988). Thus it may be considered as a balanced and economical dose for the said cultivar. Kumar et al., (2002) and Das and Yaduraju (1999) have reported that each increment in P2O5 level resulted in higher grain yield of wheat.

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Value Cost Ratio (VCR) Value cost ratio is an important criterion which relates to the economics of commodity produced and determines the net profit for the farmer. In this particular study, different values of VCR were calculated with the addition of different fertilizer levels. The highest VCR of 3.99 was calculated for the treatment where N and P2O5 were applied at 120 and 90 kg ha-1, while the lowest VCR value was recorded in the treatment where the fertilizer inputs were applied at the highest level indicating that unnecessary application of higher fertilizer doses with marginal yield increases are neither economical nor profitable. It is thus necessary to use the costly inputs at judicious levels to earn more profit. Table III. Effect of different fertilizer levels and ratios on the yield of wheat MSH-14 Yield (tons ha-1)

Treatments (N- P2O5 kgha-1) 2005-06 Control 90: 23 (4:1) 90: 45 (4:2) 90: 70 (4:3) 120: 30 (4:1) 120: 60 (4:2) 120: 90 (4:3) 180: 45 (4:1) 180: 90 (4:2) 180:135 (4:3)

Biological 2006-07

Mean

2005-06

VCR Grain 2006-07

Mean

7.27 d

7.19 e

7.23 e

2.77 e

2.70 f

2.74 f

Mean (2 years) -

8.98 c 10.08 bc 10.31 bc 10.23 bc 9.69 c 10.00 bc 10.31 bc 12.19 a 11.17 ab

9.14 d 10.08 cd 10.63 c 10.16 cd 10.00 cd 12.97 ab 13.13 ab 13.91 a 12.27 b

9.06 d 10.08 c 10.47 c 10.20 c 9.84 cd 11.49 b 11.72 b 13.05 a 11.72 b

3.32 d 3.87 c 4.26 bc 3.87 c 4.14 bc 4.95 a 3.98 bc 4.10 bc 4.43 b

3.48 e 4.01 d 4.49 bc 4.16 bcd 4.12 cd 5.02 a 4.14 bcd 4.28 bcd 4.57 b

3.40 e 3.94 d 4.37 bc 4.01 d 4.13 cd 4.99 a 4.06 cd 4.19 bcd 4.50 b

2.94 3.85 3.87 3.92 3.02 3.99 3.74 3.42 2.58

Nitrogen and Phosphorus Uptake The uptake of both nutrients was significantly affected by their respective fertilizer application rates (Table IV and V). Nitrogen uptake by wheat was escalated from 40.3 to 156.0 kg ha-1 when N application rate was increased from 90 to 180 kg ha-1. Our findings are in close agreement with those reported by (van Keulen and Stol, 1991). Successive increments in P2O5 fertilization at each N dose significantly improved the efficiency of N usage, which reflects strong synergism between both elements. Phosphorus harvests also increased linearly with the corresponding increase in P2O5 application rates. The highest P2O5 uptake of 17.34 kg was recorded with 135 kg P2O5 ha-1 and the lowest (4.14 kg) in the control treatment. The results of the present study are similar to those recorded by Brink et al., (2001), who reported that appropriate proportion of nutrients in the soil facilitate their uptake by plants. Table IV. Nitrogen uptake as influenced by different N and P application rates and ratios Treatments (NN uptake (kg ha-1) -1 P2O5, kgha ) Grain Straw 2005-06 2006-07 Total 2005-06 2006-07 Control 38.6 e 31.9 f 35.2 g 4.0 f 6.1 e 90: 23 (4:1) 74.8 d 73.8 e 74.3 f 10.6 e 18.0 d

Mean Total 5.05 f

40.3 e

14.31 e 88.6 d 90: 45 (4:2) 89.0 cd 90.0 cd 89.5 de 12.5 de 19.6 d 16.02 e 105.6 c 90: 70 (4:3) 99.3 bc 97.6 cd 98.5 cd 14.6 d 20.9 d 17.71 e 116.2 c 120: 30 (4:1) 84.4 cd 86.6 d 85.5 e 17.8 c 28.6 c 23.16 d 108.7 c 120: 60 (4:2) 89.2 cd 90.8 cd 90.0 de 20.4 c 29.8 c 25.14 d 115.1 c 120: 90 (4:3) 116.0 ab 111.5 ab 113.8 ab 23.6 b 38.9 b 31.28 c 145.0 ab 180: 45 (4:1) 110.2 ab 98.3 cd 104.3 bc 24.2 b 55.5 a 39.88 a 144.1b 180: 90 (4:2) 109.8 b 99.7 bc 104.8 bc 23.6 b 52.0 a 37.83 ab 142.6 b 180:135 (4:3) 127.2 a 113.0 a 120.1 a 27.1 a 44.7 b 35.93 b 156.0 a Means followed by different letters in the same column are significantly different from each other at 5% level of significance.

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Table V. Phosphorus uptake as influenced by different N and P application rates and ratios Treatments P uptake (kg ha-1) (N- P2O5 kg ha-1)

2005-06

Control

3.98 f 90: 23 (4:1) 7.35 e 90: 45 (4:2) 8.90 de 90: 70 (4:3) 12.63 b 120: 30 (4:1) 8.55 de 120: 60 (4:2) 10.58 c 120: 90 (4:3) 15.25 a 180: 45 (4:1) 9.75 cd 180: 90 (4:2) 12.73 b 180:135 (4:3) 14.00 ab Means followed by different letters in significance.

Grain 2006-07

Total

2005-06

Straw 2006-07

3.85 e 3.91 g 0.17 b 0.30 f 7.93 d 7.64 f 0.34 b 0.55 ef 9.25 cd 9.08 de 0.51 b 0.85 d 13.05 b 12.84 b 0.56 b 0.88 d 9.18 cd 8.86 e 0.40 b 0.70 de 10.63 c 10.60 c 0.58 b 0.85 d 15.68 a 15.46 a 0.84 b 1.43 c 10.25 c 10.00 cd 0.49 b 1.28 c 13.43 b 13.08 b 0.74 b 1.83 b 15.45 a 14.73 a 2.37a 2.88 a the same column are significantly different from each

Mean Total 0.234 e 4.14 g 0.446 de 8.08 f 0.681 cde 9.75 de 0.716 cde 13.56 b 0.551 de 9.41 e 0.712 cde 11.33 c 1.131 e 16.60 a 0.884 bc 10.90 cd 1.284 b 14.33 b 2.623 a 17.34 a other at 5% level of

CONCLUSION The genotype (MSH-14) performed well with the increasing N and P2O5 levels and their ratios. The maximum yield was produced with optimum inputs of 120 kg N and 90 kg P2O5 ha-1. Hence, it can be considered as the most economical dose for this genotype when grown in agro-climatic conditions of Sindh. ACKNOWLEDGEMENT The authors acknowledge the contribution of Mr. Mehboob Ali Sial, Principal Scientist for providing the seed of wheat genotype “MSH-14”. REFERENCES Ahmad, N. and M. Rashid. 2003. Fertilizer and their Uses in Pakistan. NFDC. Planning and development Div. Islamabad. 17p. Ahmad, N., M. W. Thakar, N. A. Malik, M. L. Shah and S. Ahmad. 1992. Effect of NPK on growth, yield and yield components of Sunflower. J. Agric. Res. 30(1):20-24. Ahmad, N. 2002. Soil fertility management: Key to food security and poverty alleviation. Proc. 9th Nat. Congr. Soil Sci., March 18-20, 2002, NIAB, Faisalabad 17p. Bhatti, H. M., M. Rashid, M. Y. Nadeem and M. T. Siddique. 1988. Micronutrient fertilization and wheat yield in Punjab. In Micronutrients in Soils and crops in Pakistan; Proc. Natl. Seminar Agric. Univ. Peshawar. pp. 208-217. Bremner, J. M. 1996. Nitrogen-Total. P. 1085- 1122. In: Methods of Soil Analysis. Part 3 Chemical methods. D. L. Sparks (eds.). SSSA and ASA,. Madison, WI. USA. Brink, G.E., G.A. Peterson, K.R. Sistani and T.E. Fairbrother. 2001. Uptake of selected nutrients by temperate grasses and legumes. Agron. J. 93:887-890. Das, T. K. and N. T. Yaduraju. 1999. Effect of weed competition on the growth, nutrient uptake and yield of wheat as affected by irrigation and fertilizers. J. Agric. Sci. 133(1): 45-51. Imtiaz, M., K. H. Shah, P. Khan, S. H. Siddiqui, M. Y. Memon and M. Aslam. 2003. Response of wheat genotype ‘SI-91195’ to increasing N and P levels and their ratios under agro-climatic conditions of Sindh. Pak. J. Soil Sci. 22: 58-63. Jackson, M. L. 1962. Soil Chemical Analysis. Prentice Hall Inc., Englewood Cliffs, N. J. pp 151-185. Kaishtha, B. P. and B. C. Marwahs. 1977. Response of Sonalika wheat to graded doses of P in acid soils of different available P status at Palampur. Fert. Tech. (India) 14: 235-239. Khalid, B. Y. and M. A. Malik. 2002 Balance fertilization and its benefits in Agriculture Proc. 9th National Cong. Soil Sci., March 18-20, 2002, NIAB, Faisalabad 17p. Koehler, F.E., C.D. Moudre and B.L. Mcneal. 1984. Laboratory manual for soil fertility. Washington State Univ. Pullman, USA. Kumar, S., R.S. Singh and S. Kumar. 2002. Phosphorus management in rice–wheat-cropping system. J. Res., Birsa Agric. Univ. India 13(1):51-56. Ma, B. L., W. Yan, L.M. Dwyer, J. Fregeau-Reid, H.D. Voldeng, Y. Dion and H. Nass. 2004. Graphic analysis of genotypes, Environment, Nitrogen Fertilizer and their interaction on spring wheat yield. Agron. J. 96: 169-180. Malik, M.A. 1990. No till dry land winter wheat (Triticum aestivum L.) as influenced by fertilizer placement methods. USA Dissert. Absts. Int. Biol. Sci. Engg. 51:160-161. Mclean, E.O. 1982. Soil pH and lime requirement. P 199-208. In: Methods of soil analysis. Part 2: 2nd Edition. A.L. Page, R.H. Miller and D.R. Keeney (Eds.) Amer. Soc. Agron., Madison, WI. USA.

Parvez Khan et al. Response Of wheat genotype ‘Msh-14’ to different levels of nitrogen and phosphorus…

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Nelson, D.W. and L.E. Sommers. 1982. Total carbon, organic carbon and organic matter. P. 574-577. In: Methods of soil analysis. Part 2: 2nd edition A.L. Page, R.H. Miller and D.R. Keeney (Eds.) American Society of Agronomy, Madison, WI. USA. Roberts, T. I., 2007. Right products, right rate, right time, and right placement the foundation of best management practices for fertilizer. Pp 29-32. Fertilizer best management practices, general principles, strategy for their adaptation, and Voluntary Initiatives vs Regulations Proc. Of IFA International Workshop 7-9 March 2007, Brussels, Belgium. International Fertilizer Industry Association. Paris France. Sadiq, M. 1992. Role of Soil testing in improving fertilizer use efficiency in Pakistan. Proc. 4th National Cong. Soil Sci. Islamabad, May 24-26. pp. 107-113. Saleem, M.T., H. Nabhan and C. de Bie. 1986. Fertilizer management and crop production in rainfed areas in Pakistan. In: Proc. IMPHOS Seminar on Crop Prod. Techniques and Fertilizer: Management in Rainfed Agriculture in Southern Asia. New Delhi, 22-25 Jan. 1986. Singh, S. P. and W. B. Singh. 1991. Effect of irrigation time and nitrogen level on wheat under late sown conditions of western Utter Paradesh. Ind. J. Agron. 63:41-42. Steel, R.G.D. and J.H. Torrie. 1986. Principles and Procedures of Statistics 2nd Ed. McGraw Hill, Book Co. Inc, New York. 187p. Van Keulen, H. and w. stol. 1991. Quantitative aspects of nitrogen nutrition in crops. Fert. Res. 27: 151-160. Vaughan, B., D.G. Westfall and K.A. Barbarick. 1990. Nitrogen rate and timing effects on winter wheat grain yield, grain protein and economics. J. Prod. Agric. 3:324-328. Villar-Mir, J.M., P.V. Claudio-stocckle, F. Ferrer and M. Aran. 2002. On farm monitoring of soil nitrate-nitrogen in irrigated cornfields in the Ebro Valley (Northeast Spain). Agron. J. 94: 373-380.