1. Inbred maize response to cover crops and fertilizer-N in the southern semi-arid coast of Puerto Rico MATERIALS AND METHODS Location was Mycogen Seeds Corp. research farm in Santa Isabel, Puerto Rico. Soil series are Jacaguas (Loamy-skeletal, mixed, superactive, isohyperthermic Fluventic Haplustolls) and Fraternidad (Fine smectitic, isohyperthermic Typic Haplusterts) Trial 1: Effects of two cover crops and five fertilizer-N levels on maize seed yield response (2008-2009) Experimental design was a split-plot arrangement of a RCBD with previous cover crop as the main plot and N level as sub-plot, with four replicates. Cover crop treatments of: fallow, velvetbean (Mucuna prurience) or cowpea (Vigna unguiculata var Iron Clay), summer-fall 2008. After 140 days of growth, cover crops were sprayed with glyphosate and incorporated via disking into the soil in late September 2008. Fertilizer-N levels of: 0, 112, 150, 186, and 228 kg N/ha; 50 kg N/ha pre-plant and the remainder applied via fertigation, fall-winter 2008-2009. All subplots received 67, 112, and 28 kg/ha of P 2 O 5, K 2 O and ME (minor element mixture), respectively. Inbred maize line A 1 was sown on 10 December 2008, grown to maturity and harvested at about 91 DAP. Trial 2: Effect of five fertilizer-N levels on maize seed yield (2009-2010) Experimental design was a RCBD with five treatments (N levels) and four replications. Previous cropping was maize. Fertilizer-N levels of: 0, 84, 125, 168, 211 kg N/ha; 28 kg N/ha pre-plant and the remainder applied via fertigation, winter 2010. Inbred maize line B 1 was sown on February 2010, grown to maturity and harvested at about 91 DAP. All plots received 63, 14, and 26 kg/ha of P 2 O 5, K 2 O and ME (minor element mixture), respectively. 1 - The inbred code is propietary information of Dow Agrosciences LLC Irrigation was applied via drip irrigation following farm recommendations. Soil preparation prior to maize planting included chisel plowing and disking. Agronomic data gathered included: indicator leaf N concentration, SPAD chlorophyll meter (Minolta Corp.), plant height, leaf area index, and leaf color index (color chart with scale of 1 to 4). Nutrient use efficiency indicators [difference method (DM)] AE Y -DM = (YG f – YG u )/N a AE BY -DM = (BY f – BY u )/N a ARE-DM = (NBY f – NBY u )/N a Where AE is the Agronomic Efficiency; ARE is the Apparent Recovery Efficiency; N a is the fertilizer-N applied; YG f and YG u is the grain yield in fertilized and unfertilized crop, respectively; BY f and By u is the biomass in fertilized and unfertilized crop, respectively; NBY f, and NBY u are the whole plant biomass N in fertilized and unfertilized plants, respectively. Nutrient use efficiency indicators [balance method (BM)] PFP-BM = YG f /N a PBP-BM = NG f / N a AE = NBY f /N a Where PFP is the Partial Factor Productivity; PBP is the Partial Balance Productivity; AE is the Agronomic Efficiency; NG f is the grain N uptake in fertilized crop. David Sotomayor-Ramirez* 1, Randy Huckaba 2, Ricky Barnes 2, Ronald Dorcinvil 3, Jesus Espinosa 1 1 College of Agricultural Sciences, University of Puerto Rico, Mayagüez 2 Dow AgroSciences LLC, Mycogen Seeds, Puerto Rico 3 North Dakota State University *Contact author: david.sotomayor@upr.edu This research was supported by the Univ of Puerto Rico, Agricultural Experiment Station and Dow AgroSciences LLC Table 5. Treatment means of selected N use efficiency indicator parameters of inbred maize during 2008-2009 and 2009-2010. Means with different letters are significantly different (P<0.05). OBJECTIVES Determine optimum inbred maize seed yield response to antecedent cover crop and fertilizer-N addition Assess the effectiveness of agronomic predictors of crop nitrogen (N) sufficiency status Estimate potential N losses in the inbred maize production systems Figure 1:Scatter plots of the effect of fertilizer-N on N sufficiency indicators for inbred maize during 2008-2009 (Trial 1). Table 2. Effect of fertilizer N on selected agronomic parameters of inbred maize during 2008-2009 (Trial 1). Means with different letters are significantly different (P<0.05). Table 3. ANOVA summary to examine the effect of fertilizer N levels on yields and selected agronomic parameters of inbred maize during 2009-2010 (Trial 2) RESULTS AND DISCUSSION Table 1. ANOVA summary to examine treatment effects on yields and selected agronomic parameters of inbred maize during 2008-2009 (Trial 1). ASA-CCSA-SSSA Annual Meeting, 2011 Poster # 310 CC N Level CC * N Level Contrast between control and othersFertilizer NUnfertilized control) Effect---------Significance level (P)-------------MeanSEMeanSE Seed yield (kg/ha0.016<.001ns<0.0012,72687.31,788177.5 Stover wt (kg/ha)ns<.001ns<0.0016,620107.45,690178.6 Ears/hans Harvest index0.0090.0220.090<0.0010.260.010.210.01 Plant biomass (grain + stover) dry wt (kg/ha) ns<.001ns<0.0019,346151.27,474294.1 Stover N (kg/ha)ns<.001ns<0.001107.91.983.03.8 Grain N concentration (%)ns Grain N uptake (kg/ha)0.0800.006ns<0.00139.71.525.73.0 Crop (stover + grain) N uptake (kg/ha) ns<.001ns<0.001149.32.8110.45.8 SPAD chlorophyll reading (40 DAP)ns<.001ns<0.00150.60.443.10.7 SPAD chlorophyll reading (54 DAP)0.361<.001ns<0.00153.40.450.70.5 SPAD chlorophyll reading (70 DAP)0.0090.030ns<0.00154.30.252.60.5 Leaf color index (54 DAP)ns<.0010.009<0.0014.20.13.30.1 LAI (40 DAP)ns<.0010.008<0.0011.050.020.820.04 LAI (54 DAP)ns<.001ns<0.0011.710.031.470.05 LAI (70 DAP)ns0.012ns<0.0011.640.031.400.06 Plant height (cm), (40 DAP)<.001 ns<0.00133.80.426.40.7 Plant height (cm), (54 DAP)ns<.001ns<0.00159.50.848.01.1 Plant height (cm), (70 DAP)ns0.002ns<0.00164.21.159.91.3 N levelSeed yieldStover wtHarvest index Crop (grain + stover) dry wtStover NGrain N uptake Crop (stover + grain) N uptake MeanSEMeanSEMeanSEMeanSEMeanSEMeanSEMeanSE --------------------------------------------------------------------------------------------kg/ha----------------------------------------------------------------------------------------- 01,788177.5 B 5,690178.6 B 0.210.01 B 7,474294.1 B 83.03.8 B 25.73.0 B 110.45.8 B 1122,708173.9 A 6,754176.2 A 0.250.01 AB 9,462288.6 A 108.33.7 A 39.23.0 A 149.35.6 A 1492,592173.7 A 6,488174.9 A 0.250.01 AB 9,080287.7 A 100.43.7 A 38.43.0 A 140.55.6 A 1862,727173.7 A 6,538174.8 A 0.260.01 A 9,265287.7 A 109.53.7 A 39.83.0 A 151.15.6 A 2242,875177.2 A 6,700178.3 A 0.260.01 A 9,579293.5 A 113.23.8 A 41.53.0 A 156.45.8 A EffectPr > F Contrast between control and others (P =)MeanSE Seed yield (kg/hans0.035n/a Stover wt (kg/ha)ns 4,567216.4 Ears/hans 74,5991,116 Harvest indexns 0.2690.017 Plant biomass (grain + stover) dry wt (kg/ha)ns 5,958213.2 Stover N (kg/ha)ns 51.33.4 Stover P (kg/ha)ns 13.30.8 Stover K (kg/ha)ns 99.05.4 Grain N concentration (%)ns 1.460.03 Grain N uptake (kg/ha)ns0.064n/a Grain P uptake (kg/ha)ns0.035n/a Grain K uptake (kg/ha)0.0680.012n/a Crop (stover + grain) N uptake (kg/ha)ns 68.33.4 Crop (stover + grain) P uptake (kg/ha)ns 17.80.8 Crop (stover + grain) K uptake (kg/ha)ns 103.85.4 SPAD chlorophyll reading (V5)ns 44.60.9 SPAD chlorophyll reading (R1)0.0860.009n/a Leaf color index (V5)0.0170.030n/a Leaf color index (R1)0.0970.056n/a Plant height (cm), (V5)ns 130.4 Plant height (cm), (R1)ns 390.4 N levelSeed yieldSPAD (R1)Leaf color index (V5)Leaf color index (R1) Mean SE MeanSEMeanSEMeanSE -----------------kg/ha------------ 01,181101.8 B 49.00.6 B 3.10.1 C 3.30.1 B 841,44999.4 AB 51.10.6 A 3.20.1 BC 3.40.1 B 1251,308101.8 AB 50.80.6 AB 3.20.1 BC 3.50.1 AB 1681,52299.4 A 51.40.6 A 3.50.1 AB 3.70.1 A 2111,49598.6 A 51.30.5 A 3.70.1 A 3.60.1 AB ---------------------------------------Mean of fertilized treatments ------------------------------------ 1,44656.751.10.33.410.13.60.1 AEY-DMAEBY-DMARE-DMPFP-BMPBP-BMAE-BM N levelMeanSEMeanSEMeanSEMeanSEMeanSEMeanSE --------------------------------------------------------------------2008-2009--------------------------------------------------------------------- 1129.11.6 A 16.92.0 A 0.350.05 A 24.41.1 A 0.350.02 A 1.320.03 A 1496.21.6 AB 10.52.0 AB 0.210.05 B 17.61.1 B 0.260.02 B 0.930.03 B 1865.71.6 AB 9.32.0 B 0.220.05 AB 14.91.1 BC 0.220.02 BC 0.810.03 C 2244.91.6 B 8.42.0 B 0.200.05 B 12.61.1 C 0.180.02 C 0.690.03 C --------------------------------------------------------------------2009-2010----------------------------------------------------------------- 843.40.6 A --- 1 17.50.6 A 0.210.01 A 0.810.07 A 1250.70.6 B 10.20.6 B 0.130.01 B 0.530.07 B 1681.90.6 AB 9.00.6 BC 0.110.01 BC 0.440.07 B 2111.50.6 AB 7.10.6 C 0.090.01 C 0.360.07 B mean of N levels (2010 only)1.22.30.050.03 Table 4. Treatment means of selected N indicator parameters of inbred maize during 2009-2010. Means with different letters are significantly different (P<0.05) (Trial 2). Trial 1 Maize yields (kg/ha) were highest following velvet bean (2,903) and cowpea (2,522) and the latter was similar to fallow (2189). In general, the cover crops positively influenced the agronomic indicators. Seed yield in the fertilizer-N range of 112 to 224 kg N/ha was 34% higher than unfertilized maize. No significant difference was observed among fertilizer-N levels in the range of 112 to 224 kg/ha for stover weight, harvest index, plant biomass, stover N, grain N uptake, crop N uptake, and these were higher than the control (no fertilizer-N). The SPAD chlorophyll meter, leaf color index and leaf area index were suitable indicators of N sufficiency. Trial 2 Seed yield in the fertilizer-N range of 84 to 211 kg N/ha was 18% higher than unfertilized maize. No significant treatment effects were observed for most agronomic parameters (marked in red) The SPAD chlorophyll reading at R1 growth-stage adequately separated out the control (mean of 49.0) from the fertilized plots (mean of 51.1). The leaf color index taken at both V5 and R1 growth-stage significantly identified treatment differences between the control and the fertilized plots. Explanation of terms Crop = grain N + stover N Immediate residual = crop N - fertilizer N Potential residual 1 = crop N - (fertilizer N + stover N) Potential residual 2 = crop N - (fertilizer N + stover N + soil N supply (estimated from crop N uptake) Figure 2. Nitrogen budget for 2008-2009, Trial 1 CONCLUSIONS Optimum crop response at fertilizer-N between 88 and 112 kg N/ha. Further refinement of these values should be done using varying genetic materials (possibly classified as low-, medium-, and high- yielders). N-use efficiency and N balance data shows: Low fertilizer-N use efficiency, and harvest index Crop N extraction (63 to 75 kg/ha and 110 to 156 kg/ha) High immediate and potential residual soil N that increases beyond critical fertilizer-N rate Can use agronomic plant sufficiency diagnostic tools such as plant height, indicator leaf N concentration, leaf color, SPAD chlorophyll index, possibly pre-plant soil nitrate N budget Higher nutrient uptake in Trial 1 than Trial 2 Crop N uptake was low, with grain N about 30% of that in crop. Immediate residual N, is the fertilizer-N not taken up by the crop, and is that which remains in soil after harvest. Potential residual N 1, is the immediate residual N plus that from stover N mineralization. Potential residual N 2, is the excess N in soil considering stover N mineralization, soil profile N, and soil N mineralization. Excess N increases with higher fertilizer-N.