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Improving Nitrogen Management in Potatoes Through Crop Rotations and Enhanced Uptake

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## Improving Nitrogen Management in Potatoes Through Crop Rotations and Enhanced Uptake

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**Improving Nitrogen Management in Potatoes Through Crop**Rotations and Enhanced Uptake Fernando Muñoz Soil & Nutrient Management Soil and Water Science Department**Background**Worldwide, agriculture has been identified as the main contributor of NO3-N to surface and groundwaters The mean annual input of N to the Gulf of Mexico from the Mississippi-Atchafalaya River basin in the period 1980-1996 was 1,568,000 t yr-1 with 61% as NO3-N The high load of N has been related with increased eutrophication and hypoxia in the Mississippi River Delta The potato production system has high potential to generate water contamination by NO3-N due to the high N rates applied to ensure profitable yield**In the Tri-County Agricultural**• Area (TCAA) in northeast • Florida 9000 ha of potato are • planted annually in early Spring • Leading supplier of fresh • potatoes for the chipping • industry in the US • Enhanced algal growth in the • St. Johns River coinciding with • peak runoff associated with the • TCAA potato season have been • reported (SJRWMD, 1996)**The soil profile is composed of a**sandy layer about 1 m deep and a clayey restricting layer beneath that resulting in a natural shallow water table – Sandy, siliceous, hyperthermic, Arenic Ochraqualfs Potato and other crops are grown using the perched water table as irrigation source –subsurface seepage irrigation Sandy soils, high N rates, and high rainfall increase the risk of nitrate leaching and runoff**Rationale**Crop rotations with cover crops may reduce the risk of N leaching/runoff by acting as green manure to substitute for part of the soluble fertilizer and as a catch crop to recover the residual N applied to potato Increased uptake efficiency of nitrogen applied to potato may be achieved by optimum placement in the root zone, decreasing at the same time the risk of leaching/runoff to the water bodies**Our research work addressed two main aspects**-The study of potato yield and NO3-N concentration in the water table under potato bedsas influenced by crop rotations and N rates -Characterization of potato root distribution to be used as a tool to enhance N uptake by optimized fertilizer placement**NO3-N concentration in the water tableas influenced by**Crop Rotations and Nitrogen rates Specific objectives: - Identify and quantify elevations in NO3-N concentrations in the perched water table under potato beds due to leaching -To study the introduction of legume crops as possible rotation alternating with potato on minimizing nitrate leaching maintaining high marketable potato yield**Block 1**Block 2 Block 3 Block 4 3 2 1 4 3 4 3 1 0 kg/ha N 224 kg/ha N 168 kg/ha N 280 kg/ha N 0 kg/ha N 168 kg/ha N 280 kg/ha N 224 kg/ha N 112 kg/ha N 280 kg/ha N 0 kg/ha N 224 kg/ha N 112 kg/ha N 168 kg/ha N 112 kg/ha N 224 kg/ha N 112 kg/ha N 0 kg/ha N 112 kg/ha N 224 kg/ha N 280 kg/ha N 0 kg/ha N 0 kg/ha N 168 kg/ha N 280 kg/ha N 168 kg/ha N 224 kg/ha N 168 kg/ha N 112 kg/ha N 224 kg/ha N 112 kg/ha N 280 kg/ha N 0 kg/ha N 112 kg/ha N 168 kg/ha N 0 kg/ha N 168 kg/ha N 280 kg/ha N 280 kg/ha N 224 kg/ha N 3 2 2 4 2 1 4 1 224 kg/ha N 168 kg/ha N 280 kg/ha N 168 kg/ha N 280 kg/ha N 280 kg/ha N 112 kg/ha N 0 kg/ha N 168 kg/ha N 280 kg/ha N 0 kg/ha N 168 kg/ha N 112 kg/ha N 224 kg/ha N 112 kg/ha N 280 kg/ha N 224 kg/ha N 0 kg/ha N 224 kg/ha N 0 kg/ha N 280 kg/ha N 112 kg/ha N 168 kg/ha N 0 kg/ha N 112 kg/ha N 112 kg/ha N 224 kg/ha N 0 kg/ha N 168 kg/ha N 0 kg/ha N 224 kg/ha N 112 kg/ha N 224 kg/ha N 168 kg/ha N 280 kg/ha N 280 kg/ha N 112 kg/ha N 224 kg/ha N 0 kg/ha N 168 kg/ha N Rows 1 - 8 Rows 9 - 16 Irrigation furrow Spring Fall crop Code Main Plot Summer cover crop Sub-plot size: 8 m x 16 m Area:128 m2 Sorghum sudan Fallow PSF Potato 1 Potato Sorghum sudan Green beans PSG 2 Potato Cowpea Fallow PCF 3 Cowpea 4 Potato Green beans PCG**Main plot factor - Crop rotations**Sub-plot factor - Nitrogen rates applied to potato**Studied variables**-Nitrate-N concentration in water samples from wells and lysimeters -Nitrate-N concentration in soil samples at different times during the crop rotation cycles -Total Kjeldahl Nitrogen in potato tissue at full flowering -Total Kjeldahl Nitrogen in cover crops tissue sampling before soil incorporation**2001**Potato Sorghum & Cowpea Bush green bean 2002 Potato Sorghum& Cowpea Bush green bean Rainfall (cm) 25 25 25 20 20 20 2003 Water (well) 15 15 15 Water (lysimeter) Soil 10 10 10 Potato Sorghum &Cowpea Bush green bean Tissue 5 5 5 Root sampling Side-dress N 0 0 0 Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Sampling schedule**2001**Potato Sorghum & Cowpea Bush green bean 2002 Rainfall (cm) Potato Sorghum& Cowpea Bush green bean 25 25 25 20 20 20 2003 Water (well) 15 15 15 Water (lysimeter) Soil 10 10 10 Potato Sorghum &Cowpea Bush green bean Tissue 5 5 5 Root sampling Side-dress N 0 0 0 Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb**)**) ) ) 1 1 1 1 - - - - N (mg.kg N (mg.kg N (mg.kg N (mg.kg - - - - 3 3 Soil NH4 Soil NH4 Soil NO Soil NO B 2001 R 2 =0.08* 2002 R 2 =0.25** 2003 R 2 =0.13** Predicted NO3-Nand NH4-Nconcentrations in soil 70 70 A A 2 2001 R =0.64** 2 2001 R =0.53** 60 60 2 2003 R =0.55** 2 2003 R =0.57** 50 50 40 40 30 30 20 20 10 10 0 0 0 112 168 224 280 0 112 168 224 280 70 70 B 2 2001 R =0.51** 60 60 2 2002 R =0.26** 50 50 2 2003 R =0.17** 40 40 30 30 20 20 10 10 0 0 0 112 168 224 280 0 112 168 224 280 NO3-N NH4-N - 1 ) N rate (kg.ha A- Three weeks after side-dressing with ammonium nitrate B- Twelve weeks after N side-dressing in 2001 and 2002(at sorghum and cowpea planting). Seven weeks after N side-dressing in 2003**120**2 2001 R =0.36** N uptake by the cover crops 2 2002 R =0.36** 100 2 2003 R =0.42** ) 80 1 - 60 N uptake (kg.ha 40 20 0 0 112 168 224 280 Cowpea - 1 N rate (kg.ha ) Sorghum**112 kg.ha-1**280 kg.ha-1 224 kg.ha-1 168 kg.ha-1 0 kg.ha-1 July 2001 Sorghum growth due to N residual effect of N applied to potato in April 2001**40**0 kg.ha 1 N - 35 168 kg.ha 1 N - 30 280 kg.ha 1 N - 25 ) 1 - mg.L 20 N ( - 3 15 NO 10 5 0 Cowpea Sorghum Cowpea Sorghum Cowpea Sorghum First sampling Second sampling Third sampling Vertical lines are Confidence limits at 0.95 NO3-N Concentration in the water table under sorghum and cowpea in 2003**12**a a 10 8 PCG NO3-N (mg.kg-1) PCF b 6 a PSG c a a PSF 4 a 2 0 GB harvest 2001 Potato Planting 2002 12 10 8 PCG PCF NO3-N (mg.kg-1) a 6 PSG a a PSF 4 a a b c d 2 0 GB harvest 2002 Potato Planting 2003 Effect of crop rotation in soil NO3-N concentration at potato planting**35**2 R =0.38** 2001 30 25 20 NYmax = 164 15 10 5 0 224 0 112 168 280 35 2002 2 PCF R =0.81** ) 30 1 2 PCG R =0.48** - 2 PSF R =0.72** 25 PSG R 2 =0.91** 20 Marketable Yield (Mg.ha 15 NYmax = 196 10 NYmax = 208 NYmax = 210 5 NYmax = 215 0 224 0 112 168 280 35 2003 2 PCF R =0.79** 30 2 PCG R =0.92** 2 PSF R =0.84** 25 2 PSG R =0.86** 20 15 NYmax = 189 10 NYmax = 205 NYmax = 219 5 NYmax = 234 0 224 0 112 168 280 - 1 N rate (kg.ha ) Predicted N rate for maximum potato yield**Conclusions**- Fertilization at potato planting generated increased NO3-N concentration in the water table under fertilized plots - The amount of rainfall after potato planting determined the magnitude of the increase in NO3-N concentration in water table - Green bean increased soil NO3-N but its persistence until potato planting was determined by the rainfall - Higher fertilization rate than IFAS recommendation did not result in increased yield - Catch crops (non-legumes) with high demand of N may reduce the possibility of nitrate leaching in summer - Side-dressed fertilizer resulted in a second flux of NO3-N leaching in summer**Potato root distribution as a tool to enhance N uptake by**improved fertilizer placement Objectives: - To propose and test a new methodology to obtain a representative sample of potato root system for studying the spatial distribution -To study the effect of three N rates on the root distribution of potato (var. Atlantic) -To generate information on optimum fertilizer placement for increased N uptake efficiency and at the same time minimizingrisk of nitrate leaching**Block 1**Block 2 Block 3 Block 4 * * 3 2 1 4 3 4 3 1 0 kg/ha N 224 kg/ha N 168 kg/ha N 280 kg/ha N 0 kg/ha N 168 kg/ha N 280 kg/ha N 224 kg/ha N * 112 kg/ha N 280 kg/ha N 0 kg/ha N 224 kg/ha N 112 kg/ha N 168 kg/ha N 112 kg/ha N 224 kg/ha N * 112 kg/ha N 0 kg/ha N 112 kg/ha N 224 kg/ha N 280 kg/ha N 0 kg/ha N 0 kg/ha N 168 kg/ha N * * 280 kg/ha N 168 kg/ha N 224 kg/ha N 168 kg/ha N 112 kg/ha N 224 kg/ha N 112 kg/ha N 280 kg/ha N 0 kg/ha N 112 kg/ha N 168 kg/ha N 0 kg/ha N 168 kg/ha N 280 kg/ha N 280 kg/ha N 224 kg/ha N * 3 2 2 4 2 1 4 1 224 kg/ha N 168 kg/ha N 280 kg/ha N 168 kg/ha N 280 kg/ha N 280 kg/ha N 112 kg/ha N 0 kg/ha N 168 kg/ha N 280 kg/ha N 0 kg/ha N 168 kg/ha N 112 kg/ha N 224 kg/ha N 112 kg/ha N 280 kg/ha N * 224 kg/ha N 0 kg/ha N 224 kg/ha N 0 kg/ha N 280 kg/ha N 112 kg/ha N 168 kg/ha N 0 kg/ha N 112 kg/ha N 112 kg/ha N 224 kg/ha N 0 kg/ha N 168 kg/ha N 0 kg/ha N 224 kg/ha N 112 kg/ha N * 224 kg/ha N 168 kg/ha N 280 kg/ha N 280 kg/ha N 112 kg/ha N 224 kg/ha N 0 kg/ha N 168 kg/ha N Rows 1 - 8 Rows 9 - 16 Irrigation furrow Spring Fall crop Code Main Plot Summer cover crop Sorghum sudan Fallow PSF Potato 1 Potato Sorghum sudan Green beans PSG 2 Potato Cowpea Fallow PCF 3 * Cowpea 4 Potato Green beans PCG Plots used for the root study**D**Root Distribution Study A- Slicer 50.8 cm high 101.6 cm long 10.2 cm wide A B B- Slicer buried into the ridge 36 cm deep C C- Slice of the ridge D- Splitting the slice**B**A C D**A**B C**A**B D C**Root Variables**In terms of root length -Root Length Density (cm root / cm3 soil) -Specific Root Length (cmroot / mg dry-matter) In terms of root surface area -Root Surface Area Density (mm2 root surface/ cm3soil) -Specific Root Surface Area (cm2root / mg dry-matter)**Soil characteristics related with root growth**Total Root Length and Total Root Surface Area**Increase in root**thickness**B**P T2 T3 T1 T4 T2 T3 0.384 0.656 0.585 T1 T4 bcd ab ab 0.384 0.656 0.585 0.304 cde M1 M3 bcd ab ab M2 M2 M4 M1 M4 M2 M3 0.838 0.812 0.467 bc a a a 0.838 0.812 0.497 0.467 bc B1 B2 a a bc B3 B4 B5 B6 B1 B2 B3 B4 B5 B6 0.019 0.070 0.038 0.038 0.007 e de e e e 0.019 0.070 0.038 0.007 0.030 0.053 de 0.294 e de e e e de b 0.387 a Root Length Density (cm root / cm3 soil)**T3**T2 T1 T4 21.98 14.23 13.34 19.56 ab a bc bcd M1 M4 M2 M3 15.59 14.12 17.01 15.59 bc bc abc bc B5 B6 B1 B3 B4 B2 13.29 17.12 7.21 5.73 12.06 16.51 cd abc de e cd bc Specific Root Length (cmroot / mg dry-matter)**B**T2 T3 T1 T4 2.53 4.34 3.82 3.06 efgh efgh defgh efgh M1 M4 M2 M3 4.22 9.60 7.04 4.08 efgh abcd bcdef efgh B1 B2 B3 B4 B5 B6 0.15 0.37 0.25 0.07 0.24 0.50 h gh h h h gh P T2 T3 T1 T4 3.53 9.70 7.63 1.85 fgh efgh abc bcde M1 M4 M2 M3 10.39 13.06 5.61 5.08 cdefgh ab a bcdefg B1 B2 B3 B4 B5 B6 0.27 1.68 1.05 0.14 0.59 0.66 h gh gh h gh gh Root Surface Area Density (mm2 root surface/ cm3soil)**B**T2 T3 T1 T4 1.575 1.313 1.268 1.538 bcd bcd cd cd M1 M4 M2 M3 1.666 1.905 1.741 1.426 bc bc bc bcd B1 B2 B3 B4 B5 B6 1.291 2.700 0.415 0.315 1.266 1.356 cd ab d d cd cd P T2 T3 T1 T4 1.291 1.791 1.444 1.542 cd bcd bc bcd M1 M4 M2 M3 1.816 3.698 1.849 1.782 bc bc a bc B1 B2 B3 B4 B5 B6 1.362 1.916 2.036 1.225 2.206 1.517 cd bc bc cd bc bcd Specific Root Surface Area (cm2root / mg dry-matter)**Conclusions**- The proposed sampling methodology performed satisfactorily, therefore could be used for future studies under conditions similar to Hastings • Potato root distribution was not affected by nitrogen rate • under the study conditions, therefore differences in N • uptake may be due to the variation in uptake rates of the • roots - Spatial differences in soil exploration around the potato plant could be used to enhance N uptake by improved placement of the fertilizer - High soil strength and bulk density could be a limiting factor for potato root development, and therefore for optimum potato yield**Overall Conclusions**-Fertilization at potato planting generated increase in NO3-N concentration in the water table. The magnitude of the increase was determined by the amount of rainfall. -Fertilization when potato has not established its root system increase the risk of N leaching-runoff. Therefore, timing and availability are critical factors to enhance N uptake -Fertilizer placement in zones with high uptake capacity should increase N uptake efficiency. Detailed studies of water movement in the root zone should be done to optimize fertilizer placement - Controlled N sources programmed to liberate nutrients when the potato root system is established may enhance N uptake reducing the need of side-dressed N -Summer cover crops (non-legumes) with high demand of N should be used as N catch crops to reduce the risk of nitrate leaching. Legumes may increase N availability at potato planting but also may increase the risk of N leaching under high rainfall conditions.**Future Research**-Determine the effect of sub-soiling on the root distribution, N uptake and potato yield -Study of the water movement from and toward the water table and its role in nitrate movement -Testing of other non-leguminous catch-crops to ensure maximum N recovery after potato harvest -Depending on C/N ratio of the catch crops different times of incorporation should be tested -Study of the effect of reduced N rates and/or controlled N sources allocated in sites of the root zone with high scavenging capacity should be studied -Determination of the root diameter fraction implied in N uptake should be studied**Acknowledgments**Dr. Rao Mylavarapu Dr. Chad Hutchinson Dr. Thomas Obreza Dr. Yuncong Li Dr. Kenneth Portier Dr. Jim Chambers and Dr. Nick Comerford Pam Solano and Doug Gergela at the Hastings REC Joseph Nguyen and Marty Anderson Jaime Sanchez, Daniel Herrera, Leighton Croft Walker Soil and Water Science Department