Correcting manganese deficiencies in eastern NCby Bob Edwards, NCDA&CS Regional Agronomist
Manganese deficiency is a common occurrence in North Carolina crops grown on coastal plain soils. Symptoms have been observed on corn, cotton, small grains, soybean, tobacco, and several vegetable crops. As a rule, deficiencies occur on soils that are inherently low in manganese or have been overlimed. Manganese deficiency is rarely observed on crops growing in piedmont and mountain soils because of the naturally high manganese content of these soils.
In general, a manganese-index (Mn-I) value of less than 25 on a soil test report indicates a manganese deficiency. However, a deficiency can occur on soils that contain adequate amounts of manganese (Mn-I>25) if the soils have been overlimed. The critical pH where deficiencies start to occur is 6.2. As pH increases above 6.2, manganese changes into a chemical state that is unavailable for plant uptake. In such cases, the manganese index can be greater than 25 while the manganese-availability index (Mn-AI) is less than 25.
Soil test data for 84,000 samples collected from July 1, 1997, to June 30, 1998, from 18 coastal plain counties have been summarized. Mn-Iwas <30 (4.8 ppm) for 31.5 percent of the samples and <25 (4.0 ppm) for 20.8 percent. The largest percentage of samples with critically low Mn-I values came from Pitt County (41.4 percent); the fewest came from Wayne County (9.1 percent). With regard to pH, 12.4 percent of the samples had a pH>6.2. The percentage of high-pH samples by county ranged from 6.6 for Greene County to 22.2 for Sampson County.
Recommendations for correcting a manganese deficiency depend on pH and soil manganese content. If deficiency is due to low soil manganese content (pH<6.2 and Mn-I<25), two treatment options are available: 1) apply 3 lbs/acre manganese banded in the row or 2) broadcast 10 lbs/acre of water-soluble manganese. The latter treatment should show residual benefit for several years.
If deficiency is due to high pH (Mn-I>25 but Mn-AI <25 and the pH>6.2), growers also have two choices: apply a band of 3 lbs/acre water-soluble manganese with an acid fertilizer or an apply 0.5 lb/acre water-soluble manganese to the foliage of the growing crop. Either method will correct the deficiency for the current crop but may not meet the needs of a subsequent crop.
The best long-term option for correcting a recurring deficiency is to apply 10 lbs/acre of water-soluble manganese. If the Mn deficiency is due to high pH (e.g., Mn-I>30 and pH>6.2), using an acid-forming fertilizer in the row will increase manganese availability for the crop. If overliming has occurred, you can apply acidulants to lower soil pH. Research has shown that compounds containing sulfur and manganese can lower soil pH.
In eastern North Carolina, soybeans and small grains are the most widely grown crops sensitive to manganese. On these crops, fertilizer is usually broadcast rather than banded. When soil manganese is low and pH is above 6.2, foliar applications of manganese have been required to correct any deficiency.
The ideal solution would be to broadcast or band a granular source of manganese under any soil pH condition and have it be available to the crop the entire growing season without adverse effects on growth or yield. For a manganese material to be effective when broadcast on a soil with pH>6.2, it would have to be acid enough to bring soil pH below 6.2. Research indicates that sulfur/manganese compounds may be suitable for this purpose.
Tisdale and Bertramson (1949) showed that oxidized sulfur reduces manganese oxides (Mn+++) to a form (Mn++) that is more readily available for plant uptake. Ludwick et al. (1968) studied the effects of S/Mn compounds on the uptake of manganese by oats grown on loamy sand. Their work indicates that S/Mn compounds will supply adequate manganese for several months, or possibly years, depending on granular size of the product.
Agri-Business Technologies in Albany, Georgia, makes two granular products that contain elemental sulfur and manganese oxide. These materials acidify manganese, making it available for plant uptake. They have been used in Florida on calcareous soils to reduce pH and supply manganese to sugar cane, citrus and vegetable crops. The two products—Agri-Man (80% S, 5% Mn) and Agri-Mans (70% S, 15% Mn)—are marketed to be blended with other fertilizers for soil application.
Materials and Methods
The test site selected in Jones County was a field adjacent to a state road covered with marl. The land is part of Thigpen Farms, the cooperator in this study. The dust from the marl had blown onto the field for a period of years. As a result, the soil pH next to the road was in the range of 6.8 to 7.2.
A 500-ft section of the field next to the road was selected for the study. A randomized complete block design was used. Plots were 25-ft wide by 50-ft deep. Four rates of manganese—2.5, 5.0, 10.0, and 20.0 lbs/acre—and a control were replicated four times. Agri-Man (80% S, 5% Mn) was the S/Mn material applied.
The treatments were hand applied to existing wheat on 2/26/98 (Table 1). Soil and nematode samples were taken prior to treatment application. Wheat tissue samples were taken on 4/24/98. The wheat was harvested in June, but yield data were not taken. Soybeans were no-tilled into the wheat stubble. Soil, plant and nematode samples were taken from the plots on 8/19/98. A 25×25-ft section of each plot was harvested with a combine on 11/2/98. Yields were recorded and corrected to 13 percent moisture. The data were analyzed using ANOVA and the t-test for significance at the 5% level.
Table 1. Plot treatments Treatment # Treatment lbs S/Mn Material 1 control 0 2 2.5 lbs Mn 50 3 5.0 lbs Mn 100 4 10.0 lbs Mn 200 5 20.0 lbs Mn 400
Results and Discussion
Because the S/Mn material is acid forming, change in pH was monitored from 2/25/98 (initial sample and S/Mn application) to 8/19/98 (final soil sample). There was no change in pH in any of the treatments (Table 2).
Table 2. Soil pH (average of 4 replications) Treatment (lbs Mn) 2/25/98 8/19/98 0 6.9 7.1 2.5 7.0 7.1 5 7.0 7.0 10 7.1 7.0 20 7.1 6.9
Soil analyses of samples taken 8/19/98 indicate that the 10- and 20-lb applications of manganese significantly increased soil Mn levels. The 5-, 10- and 20-lb rates of manganese, but not the 2.5-lb rate, significantly increased soil manganese availability levels (Table 3).
Table 3. Soil analyses * Treatment
2/98 8/98 2/98 8/98 0 49 a 49 a 26 a 22 a 2.5 45 a 52 a 21 a 25 a 5 51 a 58 a 26 a 29 b 10 ** 45 a 71 b 21 a 38 b 20 ** 49 a 102 b 23 a 57 c * Average of four replications
** Only these treatments showed a significant increase in Mn-I and Mn-AI over time [from 2/98 to 8/98].
The Mn-I values for wheat plant samples taken on 4/24/98 showed no significant differences among treatments. Because oxidation of elemental sulfur requires warm temperatures, it is possible that the chemical process did not have time to progress sufficiently before plant samples were taken in April (Table 4).
Table 4. Wheat plant analyses (average of 4 replications) Treatment (lbs Mn) Mn-I 0 17 a 2.5 16 a 5 16 a 10 18 a 20 19 a
Soybean plant samples were taken on 8/19/98. Mn-I values differed among all treatment levels, except between the 5- and 10-lbs/acre rate. It appears there is enough variation in the 5.0-lb treatment to exclude any significance (Table 5).
Table 5. Soybean plant analyses (average of 4 replications) Treatment (lbs Mn) Mn-I 0 14 a 2.5 24 b 5 50 c 10 53 c 20 61 d
Soybeans were harvested on 11/2/98, and yield/plot was determined and corrected to 13 percent moisture. There was a 10- to 13-bushel/acre increase in yield between the control and all manganese treatments. These increases were significant between the control and all manganese treatments except the 5.0-lb rate. It appears too much variability excluded any significance at this rate (Table 6).
Table 6. Soybean yield (average of 4 replications) Treatment (lbs Mn) Yield (bu/acre) 0 16 a 2.5 26 a 5 25 ab 10 27 b 20 29 b
Summary and Conclusions
Soil manganese index levels were significantly increased by the 10- and 20-lb rates of the S/Mn material. Soil manganese availability rates were significantly increased by the 5-, 10- and 20-lb rates of the S/Mn material.
All levels of the S/Mn material used in this study significantly increased soybean tissue manganese levels above the control. All treatments, except the 5.0-lb/acre rate, significantly increased soybean yields. The 5.0-lb/acre treatment gave the same yield increase over the control but was not significant because of variability among plots in this treatment.
None of the treatments increased Mn-I values for wheat tissue. This finding may have been due to limited oxidation of the sulfur since the S/Mn material was applied in February during cold weather. It is possible adequate manganese would be released for the wheat crop if the material were applied during the warmer months of September or October.
This study was carried out only on one site and for one year. However, it does show the potential for effective use of this material in eastern North Carolina. The study will continue at the Jones County site in 1998–99, using a no-till wheat/double crop soybean rotation.
Tisdale SL, Bertramson BR. 1949. Elemental sulfur and relationship to manganese availability. Soil Sci Soc Amer Proc 14:131–7.
Ludwick AE, Sharpee KW, Attoe OJ. 1968. Manganese-sulfur fusions as a source of manganese for crops. Agron J 60:232–4.
Edwards B. 1999. Correcting manganese deficiencies in eastern North Carolina. In: Allen JL, editor. Proceedings of the 42nd annual meeting of the Soil Science Society of North Carolina; 1999 Jan 19–20; Raleigh (NC). Raleigh (NC): Soil Science Society of North Carolina. p 35–9.