Published on October 9, 2007
Slide1: Soil Fertility 101 With a focus on wheat producing areas by Clain Jones, Extension Soil Fertility Specialist [email protected]; 406 994-6076 Questions: Questions How many of you use a crop adviser for making fertilizer decisions? How many do your own soil sampling? Slide3: Goals Today Introduce basics of soil fertility Focus on nitrogen, phosphorus, potassium, and sulfur cycling and differences in their plant-availability Show nutrient deficiency symptoms and ‘test’ you Introduce soil sampling and explain yield response curves Show how to use Fertilizer Guidelines and soil lab results to estimate fertilizer needs Have you determine fertilizer rates given a soil test report Identify some differences between conventional and air drills HELP your bottom line! Slide4: There are 14 mineral nutrients that have been found to be essential for growth of most plants: The macronutrients are simply needed in larger amounts by the plant than the micronutrients. Nutrient deficiencies of the bolded nutrients have been observed in Montana Slide5: Mobility in soil of selected nutrients Why important? Can affect optimum fertilizer placement Slide6: Effect of subsurface banding urea compared to broadcast urea in Golden Triangle on small grain yield Kushnak et al., 1992 Slide7: Banding Phosphorus Banding P is much more effective than banding N, because P is much more immobile in the soil. Slide8: For more information on soil fertility and plant nutrition, refer to Nutrient Management Module 2, and for more information on Fertilizer Placement, look at Module 11: http://www.montana.edu/wwwpb/pubs/mt4449.html Nutrient Reactions and Cyling: Nutrient Reactions and Cyling Will focus on N, P, K, and S because these have best chance of limiting yield and protein. Slide11: The N Cycle Slide12: ‘Mineralization’ Release of minerals as organic matter (O.M.) is oxidized, releasing available N Organic-N Plant-Available N ‘Immobilization’ Incorporation of available N into microbial cells or plant tissue Plant-Available N Organic-N If have higher than normal O.M. (>3%), can back off on N fertilizer by 20 lb/ac. If leave more than ½ ton stubble, increase N fertilizer by 10 lb/ac. Slide13: If you want more information on N cycling, go to MSU Extension’s publication on the topic at: http://www.montana.edu/wwwpb/pubs/mt44493.pdf Slide14: P Cycle Why simpler than N cycle? Movement of P is largely through erosion/runoff, NOT leaching. Why? No gas phase P binds strongly to soil Slide15: Soluble P concentrations in soil are generally very low (0.01 – 1 mg/L) due to: Precipitation and low solubility of calcium phosphate minerals. This is very relevant in this region. 2. Strong sorption to manganese, aluminum, and iron oxides and hydroxides (example: rust). This process increases at low pH and is more of an issue in the Southeast U.S. At what pH levels would you likely need to fertilize with more P? Slide16: The effect of soil pH on P retention and availability. From Havlin et al. (1999). pH Slide17: If you want more information on P cycling, go to MSU Extension’s publication at: http://www.montana.edu/wwwpb/pubs/mt44494.pdf Questions so far?: Questions so far? Potassium (K): Potassium (K) Needed in Montana? Which crops have largest K needs?: Which crops have largest K needs? How might K, or lack of K, affect an alfalfa-hay field? : How might K, or lack of K, affect an alfalfa-hay field? Potassium Forms: Potassium Forms Potassium Cycling: Potassium Cycling Sulfur (S): Sulfur (S) Responses seen in Montana? Note: Yield increased 30% at Moccasin (Wichman, 2001) Effect of S on Protein in Wheat: Effect of S on Protein in Wheat % of Total N Effect of S on Canola Seed Yield: Effect of S on Canola Seed Yield Insert Figure 3 S Seed yield (lb/ac) Available N (lb/ac) 0 lb S/ac 40 lb S/ac 20 lb S/ac Sulfur cycling: Sulfur cycling Questions so far?: Questions so far? Nutrient Deficiency Symptoms: Nutrient Deficiency Symptoms Nutrients that are mobile in plant will affect lower leaves first: Nutrients that are mobile in plant will affect lower leaves first Mobile nutrients (in plant) Nitrogen Phosphorus Potassium Chloride For nutrients that are sometimes deficient in Montana crops Slide31: Pseudo-deficiencies What else can cause symptoms that look like nutrient deficiency symptoms? Herbicides Disease Insects Moisture stress Salinity How verify nutrient deficiency?: How verify nutrient deficiency? 1. Soil Testing 2. Tissue Testing 3. Apply fertilizer test strip Slide33: What else would you look at other than shoot tissue? Roots – healthy (white), distribution? Soil – compacted, texture, moisture? Distribution on field – near edges, patchy, in strips…? ? Factors decreasing N availability: Factors decreasing N availability Low organic matter Poor nodulation of legumes (ex: alfalfa) Excessive leaching Cool temperatures, dry In general, N, especially nitrate, is very mobile in soil. N Deficiency Symptoms: N Deficiency Symptoms Pale green to yellow lower (older) leaves Why lower leaves? Stunted, slow growth Yellow edges on alfalfa Spring Wheat Corn N is MOBILE in plant Alfalfa Phosphorus (P): Phosphorus (P) Why often deficient in Montana soils? Binds with calcium to form poorly soluble calcium phosphate minerals Factors decreasing P availability: Factors decreasing P availability Soil pH below 6.0 or above 7.5 Cold, wet weather Calcareous soils Leveled soils Highly weathered, sandy soils P Deficiency Symptoms: Alfalfa P Deficiency Symptoms Dark green, often purple Lower leaves sometimes yellow Upward tilting of leaves may occur in alfalfa Often seen on ridges of fields Lettuce Low P Adequate P Wheat Factors decreasing K availability: Factors decreasing K availability Cold, dry soils Poorly aerated soils High calcium and magnesium levels Sandy, low clay soils Low soil organic matter, or high amounts of available N K deficiency symptoms: K deficiency symptoms Alfalfa – white spots on leaf edges Corn and grasses – chlorosis and necrosis on lower leaves first. WHY? Weakening of straw-lodging in small grains, breakage in corn. 4. Wilting, stunted, shortened internodes. K is mobile in plant Factors decreasing S availability: Factors decreasing S availability Irrigated with low S in irrigation water Sandy, acidic, or low organic matter soils Cold soils Soils formed from minerals low in S or far from industrial sources S deficiency symptoms: Upper leaves light green to yellow. WHY? Small, thin stems Low protein Delayed maturity No characteristic spots or stripes S deficiency symptoms S is immobile in plant Questions so far?: Questions so far? What nutrient is deficient?: What nutrient is deficient? Options: Nitrogen, Phosphorus, Potassium, Sulfur SULFUR What nutrient is deficient?: What nutrient is deficient? Options: Nitrogen, Phosphorus, Potassium, Sulfur NITROGEN What nutrient is deficient?: What nutrient is deficient? Options: Nitrogen, Phosphorus, Potassium, Sulfur PHOSPHORUS What nutrient is deficient?: What nutrient is deficient? POTASSIUM Options: Nitrogen, Phosphorus, Potassium, Sulfur See Nutrient Management Module 11 for more info on Nutrient Deficiency Symptoms : See Nutrient Management Module 11 for more info on Nutrient Deficiency Symptoms Let’s take a 5 minute break: Let’s take a 5 minute break Soil Testing: Soil Testing Slide51: Advantages of soil testing (even if only occasionally) Allows you to optimize fertilizer rates, especially in case where soil nutrient availability has been depleted or is in excess Can increase yield and/or save on fertilizer costs (which have gone up in last year) Why are more samples better when it comes to soil sampling?: Why are more samples better when it comes to soil sampling? Variability can be large! Slide53: Nutrient Variability Insert chart Source: Dan Long Location: Liberty County Why is N tested to 2 feet and P and K to only 6 inches?: Why is N tested to 2 feet and P and K to only 6 inches? N can easily move to 2 feet (and beyond) and the lower depths often have substantial amounts of N. P and K fertilizer generally stay in upper ½ foot and amounts are often very low below there. What do ‘Olsen P’ and ‘soil test K’ mean on my lab results?: What do ‘Olsen P’ and ‘soil test K’ mean on my lab results? They are measures of ‘plant-available’ P and K and are determined by adding extractants to the soil and measuring P and K in solution. The result is the sum of soluble nutrient PLUS weakly bound nutrient. Why is ‘soluble’ N measured, rather than extracted like P and K?: Why is ‘soluble’ N measured, rather than extracted like P and K? Nitrate-N is so soluble, that the concentration in solution is about equal to what is plant available (‘with N, what you see is what you get’). Why is soluble N tested but a ‘soil test’ used for P and K?: Why is soluble N tested but a ‘soil test’ used for P and K? N fertilizer can easily move to 2 feet (and beyond) and these lower depths often have the majority of N. P and K fertilizer generally stay in upper ½ foot and are often very low below there. Generalized Crop Yield Response Curve: Generalized Crop Yield Response Curve FINALLY!!!!: FINALLY!!!! How do I determine N fertilizer amount? First, need yield potential. How determine? Average yield from past records, can be adjusted for soil moisture Average yield x 1.05 (optimistic or realistic?) From available water: Available water = April soil water + growing season rain Determining Available Soil Water: Determining Available Soil Water Generally done in late March to mid April Soil water depends on soil texture. How determine texture? NRCS Soil map Lab measurement Hand texture Texture-Available Water Relation: Texture-Available Water Relation Example Texture: sandy loam Moist soil depth (determined by Brown probe): 3 ft. Soil water = (1.5 in./ft) x 3 ft.= 4.5 in. How determine depth of ‘moist soil’?: How determine depth of ‘moist soil’? Precipitation Maps: Precipitation Maps Slide64: From MontGuide 8325 Plant-Available Water = April soil water + growing season rain Slide65: EB 161: http://www.montana.edu/wwwpb/pubs/eb161.pdf Slide66: Example Winter wheat Yield potential = 40 bu/ac Soil test N = 54 lbs/ac (top 2 ft.) If 50 lbs per acre of N needed, how much urea (46-0-0) is needed?: If 50 lbs per acre of N needed, how much urea (46-0-0) is needed? The 46-0-0 means this fertilizer is 46% N, 0% P2O5, and 0% K2O. So the fraction of N in urea is 0.46 (46/100). N fertilizer = (50 lbs/acre) 0.46 = 109 lbs urea/acre Slide68: Phosphorus Phosphorus: Phosphorus Example Winter wheat Olsen P = 10 ppm P2O5 needed = 42.5 lb/ac How much MAP (11-52-0) do you need to get 43 lb P2O5/ac? : How much MAP (11-52-0) do you need to get 43 lb P2O5/ac? MAP = 43 lb P2O5/ac 0.52 The 52 means MAP is 52% P2O5 so fraction is 0.52 MAP needed = 85 lb/ac Potassium table (Table 19) and calculations are essentially identical to P Questions so far?: Questions so far? Your turn!!!: Your turn!!! Use Fertilizer Guidelines-Keep in mind these are guidelines-may need to adjust for your region and field history. (If you know you won’t use again, please return) Crop: Spring wheat Yield pot. = 50 bu/ac Soil N = 35 lb/ac Olsen P = 14 ppm Soil test K = 200 ppm 130 25 40 www.agry.purdue.edu/mmp/webcalc/fertrec.asp : www.agry.purdue.edu/mmp/webcalc/fertrec.asp If you would rather use a web based calculator (avoids needing to interpolate), Montana fertilizer guidelines are at: Conventional vs. Air drills: Conventional vs. Air drills Conventional: place seed in a single narrow row (less than 3 inches) Air drills: can spread seed (and fertilizer) out by up to about 8 inches depending on opener Biggest problem Grant Jackson has seen with air drills is planting seed too deep, reducing stand. Need to check seed depth for each seed row frequently. Slide75: Wide Band Width Narrow Band Width What advantages can you think of for wide banding of seed? Any disadvantages? Deep Banding of Fertilizer near seed: Deep Banding of Fertilizer near seed Advantage – fast uptake in spring Disadvantage– dry out soil and can cause poor germination Solution: With low amounts of P (< 20-30 lb P2O5/ac, can place fertilizer directly with seed) Effect of opener width on stand reduction: Effect of opener width on stand reduction Premise: Fertilizer is salty and can prevent germination if too close to seed A larger opener spreads out fertilizer, decreasing salt concentrations Conclusions: Conclusions Nitrogen is much more soluble and mobile than phosphorus and potassium. Nitrogen levels are largely dependent on breakdown of organic matter (and fertilizer). Phosphorus levels are low in Montana due to insoluble calcium-P minerals. Fertilizer needs can be determined if know soil test levels of N, P, and K, and yield potential. Air drills with large (> 6 in.) openers can increase yield due to less germination problems when fertilizer is applied with the seed, increased efficiency of fertilizer use, and decreased weed pressure.