Illinois
Fertilizer Conference Proceedings
January 23-24, 1990
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P.E. Fixen1
Why should we take another look at such an old concept? This is a valid question, and if it can't be answered adequately, there is no need for further discussion. However, there are a multitude of reasons why we should revisit this issue as we enter crop production in the 1990s.
Today's potentially higher yields due to generally better cultural practices and genetic material places increased nutritional demand on the crop's root system.
The reduced tillage systems now used and the additional reductions in tillage that will come in the future, cause us to reevaluate the role of subsurface banding.
Planting equipment and planter fertilizer banding attachments have been greatly improved reducing both the magnitude and importance of planting delays caused by starter use.
Increased concern over the potential environmental consequences of agricultural practices, such as soil erosion and groundwater contamination, has increased the importance of best management practices that can reduce this potential.
Some scientists suggest that we have entered a more typical weather period that is less benign and more variable than the past few decades.
Generally, farmers are faced with increasingly greater pressures to be more efficient.
The connection of some of these observations to starter use may not be obvious at this time. However, as we proceed through this discussion, the connection should become apparent.
Classically, phosphorus has been the nutrient emphasized in starter fertilizers with importance decreasing as soil test levels increase. A common belief has been that starters are not beneficial at high soil test levels. Larger starter responses have been expected only under cool, wet conditions or when especially early planting is employed.
Evaluation of the data in Table 1 indicates that farmers share that expectation. The percent of the corn acres receiving P at planting declines as we go from the northern states to the southern states across the Corn Belt.
The Nebraska - South Dakota comparison seems to be an exception that is likely caused by the greater concentration of irrigated acres in Nebraska. Recent data suggests that these beliefs may be overgeneralizations.
To understand the role of starters in crop production, one must recognize the nutrient requirements of crops through the season. Typically, we picture these on a quantity per unit area basis. Such an evaluation gives the impression that the critical period for supplying nutrients to the crop is the "grand" period of growth when the plant's dry matter is increasing most rapidly per unit time. Nitrogen uptake rates are frequently in the 4 to 6 pounds/acre/day range during this period.
Another expression of nutrient demand is referred to as inflow. Inflow is defined as the quantity of nutrient uptake required by the plant per unit of root length present per unit of time. This expression of nutrient demand is likely more important in evaluation of the need for starters than total uptake per unit area. It indicates the amount of a particular nutrient that each segment of root must take up per unit of time.
Inflow for most crops is at a maximum when the plant switches from depending on the seed for nutrition to depending on the soil and declines as the season progresses (Fig. 2.5).
The very high inflow requirement of corn is largely responsible for the reponsiveness of corn to starter fertilizer. The demand per unit of root length early in the season can be so high that the only way it can be met is with a concentrated band of nutrients placed near the young corn plant.
Recent studies in Ontario have demonstrated that the full yield potential of corn growing in high yield environments can not be achieved unless shoot P concentration at the four-leaf stage (Iowa State System) reaches 0.5 percent (Barry & Miller, 1989). In many soils, it is nearly impossible to attain this high a concentration without a starter band.
Field comparisons have indicated that the starter band should not be more than approximately 3 inches from the corn row. When the normal growth angle of seminal roots (roots originating from the seed) is considered, the standard location of 2 inches to the side and 2 inches below the seed is nearly ideal for root interception. This usually places the band about 4 inches below the surface where soil moisture conditions are likely to be favorable for nutrient uptake by roots.
As mentioned earlier, we usually expect the need for starters to decrease as soil test levels increase. Under reasonable growing conditions, no starter response has been expected if the soil test level is adequate. Long term data from northwest Iowa demonstrates this relationship (Table 2). As the soil test level increased on this soil, starter response averaged over 32 years decreased to only 1 bushel/acre.
However, a similar study in a higher-yielding environment in northcentral Iowa shows an average starter response of 4 to 7 bushels/acre at the higher soil test levels (Table 3). The highest soil test level in this study was in the medium category. It is possible that a higher soil test level would have diminished starter response.
Other studies have clearly demonstrated starter response regardless of soil test level. In Wisconsin, starter P response was measured at a soil test level of 160 lbs/a. Research in eastern South Dakota showed that in a moldboard plow tillage system, the advantage of starter P over broadcast P remained constant across a range of soil test levels from 25 lbs/a to 60 lbs/a.
In another South Dakota study conducted in 1988, a 13 bu/a starter response was measured at a 107 lb/a Bray I soil test level (Fixen, 1988). Similarly, the starter response of irrigated corn in Kansas remained constant even though soil test P levels varied from 12 to 67 lb/a. Other examples of starter responses at high soil test levels could be sited.
Few would disagree with the concept that starter fertilization is most important when soil temperatures are low. Growth chamber studies have demonstrated greater differences between band and broadcast applications at lower soil temperatures (Knoll et al., 1964a).
Starter use has been recommended for early planting due to the associated low temperatures. Indeed, a Nebraska study demonstrated a 33 bu/a response when irrigated corn was planted on May 8 and only a 7 bu/a response when planting was delayed to May 22 (Rehm, 1979).
The Wisconsin starter response at a soil test level of 160 lb/a that was mentioned earlier was partially attributed to cold, wet soil conditions as was the starter response in the moldboard system at a high soil test level in eastern South Dakota.
But there are exceptions to this low temperature-induced starter response hypothesis. Growth chamber studies where temperature was carefully controlled have also demonstrated greater P response by corn at higher temperatures than at lower temperatures (Patterson et al., 1972; Knoll et al., 1964b).
These studies have also shown that shoot:root ratios are higher at the higher temperatures. This may cause an elevated inflow requirement and under the right circumstances (perhaps a period of low or even normal temperatures preceded by a period of high temperatures) result in greater response to banded P.
Starter experiments in South Dakota during the hot, dry 1988 growing season serve as a convincing example of starter response that is not related to low temperatures. The 1988 season in this state was one of the warmest on record, particularly May and June, yet nine sites out of nine showed early growth response to starter fertilizer.
Except for a couple of sites, the drought severely limited yields and grain yield responses occurred at only one or two sites. One of the responding sites was mentioned earlier as having a P soil test of 107 lbs/a.
It would seem that a more accurate statement of environmental influences on starter response would be the following: Handed nutrients near the crop row are critical whenever environmental conditions cause plant demand to be high relative to the root system's capacity for absorption.
Conditions leading to high nutrient demand relative to plant nutrient absorption capacity include:
Cold soils. Cold soils are indeed one condition that can lead to starter responses. Root absorbing power is decreased, nutrient translocation to shoots is slowed, carbohydrate translocation to roots is slowed and ion transport to root surfaces is slowed.
Root growth restrictions. Anything that reduces total root surface area or length reduces the root system's ability to absorb nutrients. Such factors include compaction, high acidity, high salinity and herbicide carryover.
Abnormally high early shoot to root ratios. This may result when sufficient soil water is present and early soil temperatures are elevated.
Soil compaction also can impact on the importance of starter fertilization. Availability of several plant nutrients are frequently affected resulting in reductions in early growth and yield. High soil bulk density or compaction has reduced P uptake by corn in Canadian studies. Wisconsin research has demonstrated that compaction dramatically increases corn response to row K.
Greater response to starters in reduced tillage systems was initially expected due to the environmental conditions typical of reduced tillage and has been verified in many experiments. The vertical stratification of soil-immobile nutrients like P and K increases the importance of subsurface bands, at least in growing seasons where the soil surface is dry for extended periods.
Tillage and soil test P level effects on starter response in an eastern South Dakota study are shown in Figure 3 and were referred to in part earlier. In 1984, starter response was not affected by soil test level and was greater in the no-till system. In 1986, starter response in no-till increased as soil test P level increased.
The no-till starter treatments separate themselves from all other treatments showing less grain yield response at a given level of early growth response. However, as the non-band soil test level increased, these points approached the others. One can speculate that this suggests that in no-till, a critical level of non-band P exists to supply adequate P later in the season when the vast majority of the root system is outside the band.
Many farmers in corn/soybean rotations today are no-tilling corn into soybean stubble or are considering such a practice. Primary tillage is performed on cornstalks prior to soybean planting. This type of tillage program does not allow for significant incorporation of P and K fertilizer if it is applied prior to corn planting.
Since soybeans are typically more responsive to broadcast than band applications, a logical practice would be to use a starter on the corn and broadcast the non-starter P and K needs for both the soybean and corn crop, prior to tillage for the soybean crop. This would allow for greater incorporation of P and K for corn, and the higher rates applied may benefit the soybean crop. Use of a starter on corn should overcome any problems caused by not having fresh broadcast fertilizer present.
Although historically P has been the nutrient emphasized in starter fertilizers, evidence seems to be accumulating that supports use of a starter containing N, P, K and possibly other nutrients. Research demonstrating the importance of both P and K has already been discussed.
Alabama studies on a high P sandy loam soil resulted in greater response to N in the starter than to P (Touchton, 1988). Touchton concluded that a 40-20 or 60-0 (N+P2O5) starter appeared to be the best combination for high P ultisols. Numerous other studies have indicated that N, especially ammoniacal N, can enhance the response to P applied in bands. Soils with low levels of plant available N in the surface horizon are good candidates for N starters.
Early growth response to starter sulfur has been observed in soils with low levels of S in the surface horizon. Occasional growth responses to starter zinc also have been measured in low Zn soils.
Theoretically, the environmental conditions that cause uptake problems for one nutrient such as P, also can lead to problems for other nutrients. Starters should be tailored for the needs that research indicates for specific situations, however, extra insurance can usually be purchased at minimal costs by using a complete starter containing N, P, K and where soil conditions suggest, S and Zn.
The purpose of a starter fertilizer is to increase early growth. Enhanced early growth can be beneficial for at least the following reasons:
Allows for earlier cultivation.
Provides greater competition with weed escapes.
Gives quicker soil cover reducing the potential for erosion.
May result in an earlier-maturing crop and lower grain moisture content.
Increased yield in some years.
If one accepts the concept that soil fertility should be' maintained at some soil test level, a logical argument can be made to apply at least a portion of that maintenance fertilizer in a starter band. Agriculture of the next decade will focus on efficiency as we strive to increase profitability and meet the challenge of feeding a growing population in an environmentally-responsible manner. It would seem than in many situations, starter fertilization should be viewed as the nutritional insurance policy of the 1990s.
Table 1. Timing of P application for corn in 1988.
Figure 1.† Phosphorous uptake per unit of root length for three crops (after Barber, Purdue).
† Numbered as Figure 2.5 in print version
Barry, D.A.J. and M.H. Miller. 1989. Phosphorus nutritional requirements of maize seedlings for maximum yield. Agron. J. 81:95-99.
Fixen, P.E. and B.G. Farber. 1988. Effects of starter fertilization of corn under varying cultural and environmental conditions. Soil Fertility Progress Report Soil PR 88-8, Plant Science Dept., South Dakota State University.
Fixen, P.E., B.G. Farber, and M. Vivekanandan. 1987. Phosphorus Management as influenced by tillage systems in eastern South Dakota, 1984-1986. Fluid Fertilizer Foundation Symposium Proceedings. National Fertilizer Solutions Assoc., St. Louis, MO.
Foth, H.D. and B.G. Ellis. 1988. Soil Fertility. John Wiley & Sons. New York.
Knoll, H.A., N.C. Brady, and D.J. Lathwell. 1964. Effect of soil temperature and phosphorus fertilization on the growth and phosphorus content of corn. Agron. J. 56:145-147.
Knoll, H.A., D.J. Lathwell, and N.C. Brady. 1964. The influence of root zone temperature on the growth and contents of phosphorus and anthocyanin of corn. Soil Sci. Soc. Amer. Proc. 28:400-403.
Nelson, P. and M.H. Miller. 1980. Corn root growth as affected by soil texture and bulk density. P. 47-49. in Report of Department of Land Resource Science, University of Guelph, Guelph, Ontario.
Rehm, G.W. 1979. Phosphate for corn: broadcast or row-applied. Soil Science News 1:34. CES, University of Nebraska.
Schulte, E.E. 1982. Corn response to row phosphate. Better Crops with Plant Food 66(2):10-13
Taylor, H. and H. Vroomen. 1989. Timing of fertilizer applications. In Agricultural Resources: Inputs Situation and Outlook Report. ERS, U.S. Department of Agriculture, Washington, D.C. AR-15.
Touchton, J.T. 1988. Starter fertilizer combinations for corn grown on soils high in residual P.J. Fertilizer Issues 5:126-130.
Webb, J.R. 1989a. Annual progress report -- 1988, Northern Research Center, Iowa State University, p6-8.
Webb, J.R. 1989b. Annual progress report -- 1988, Northwest Research Center, Iowa State University, p3-5.
Wolkowsli, R.P., L.G. Bundy, and B. Lowery. 1987. Compaction -- K fertility interactions in corn production. Proceedings of the 17th North Central Extension-Industry Soil Fertility Workshop. Potash & Phosphate Institute.
1Paul E. Fixen is Northcentral Director, Potash & Phosphate Institute, Box. 682, Brookings, S.D.
