The Influence of Phosphorus Application Rate and Deep

Tillage on Rice Yields After Land-Forming

Annual Report - MS-10F

T.W. Walker1, J.E. Street1, W.L. Kingery2, M.S. Cox2, and J.L. Oldham2

1Delta Research and Extension Center – Stoneville, MS

2Department of Plant and Soil Sciences – Mississippi State, MS

Introduction:

Best management practices (BMP’s) have not been clearly determined for restoring the production of deep cut areas of precision-leveled soil. Yield-limiting factors are often site-specific and can be a combination of more than one factor. This study was designed to test the effects of two factors that can cause yields to be lower in deep cut areas when compared to neutral areas, or areas where fertile topsoil was used to fill low-lying areas. The objectives of this study were to: 1) determine the optimum rate of fertilizer-P for a newly-leveled field composed of soils from the Forestdale series (fine, smectitic, thermic Typic Endoaqualfs) that varied from silt loam to silty clay loam in texture prior to leveling; and 2) determine the effects of deep tillage following precision-leveling on rice grain yields.

Materials and Methods:

A production field in Boyle, MS, was precision-leveled in the summer of 2001. An area within the deep cut area of the field was chisel-plowed to a depth of 18 inches in February of 2002. Cocodrie rice was planted on May 22, 2002, and emerged on May 29th. On June 8th, 0- to 6-inch soil samples were randomly collected from within both the chiseled and non-chiseled area, prior to hand-broadcasting the P2O5 treatments on the 6’ x 15’ plots. The field was flush-irrigated on June 10th. A permanent flood was established on June 17th. Y-leaf and flag leaf tissue samples were collected on July 5th and August 3rd, respectively. Tissue samples were analyzed by the Mississippi State University Extension Service Soil Testing and Plant Analysis Laboratory. Three center rows from each plot were harvested with Suzue plot combine. The plot weights were determined and adjusted to 12% moisture.

The experiment was arranged in a split plot design with two tillage treatments and five P2O5 rates. The chiseled and non-chiseled areas served as the main plot units and the five P2O5 rates (0, 20, 40, 60, and 80 lbs. P2O5 A-1) served as the sub-plot units. Tissue and yield data were subjected to analysis of variance and tested for interactions among fixed effects using a mixed model approach (SAS, 1999). Standard errors of differences in least square means were used to calculate the LSD for mean separation. A significance level of 0.05 was used for all statistical tests.

Results and Discussion:

Soil test results from the chiseled and non-chiseled areas are summarized in Table 1. According to MSU-ES recommendations (Table 2), no P2O5 would have been recommended for either area. Figure 1 and Figure 2 indicates that visual P-deficiency symptoms were pronounced approximately 8 days after permanent flood establishment as vegetative growth was greater in plots were higher rates of P were applied. Figure 3 indicates that plant development is delayed where P is limiting. Tissue-P concentrations were maximized when 60 lbs. P2O5 A-1 were applied (Table 3). Yields were affected by a P2O5 rate and tillage interaction (Table 4). A yield increase of 24 bu A-1 was obtained when 20 lbs. P2O5 A-1 was added to the chiseled area; however, yields were not increased until 40 lbs. P2O5 A-1 were applied for the non-chiseled area. The 60 lbs. P2O5 A-1 treatment further increased yields in the non-chiseled area followed by a decrease in yields with the 80 pound treatment. In the chiseled area, average yields were unchanged after the initial increase from the 20 pound treatment; however, the trend indicated that an 80 pound rate would produce higher yields than the 20 pound rate.

Summary:

This study indicates that a revision in P2O5 recommendations may be needed for rice. Currently, no fertilizer-P recommendation is made for medium testing soils. The increased P-solubility and P-diffusion under flooded conditions is the basis for not recommending P on medium testing soils. However, as some of the figures depict, it is important for the rice roots to be able to absorb and store P in the early vegetative growth stages. Phosphorus promotes root development and tillering, which both contribute to overall yield potential. In Mississippi, fields are typically not flooded until after the plant has initiated tillering. It is important that our recommendations are made to address the needs of the plant throughout the entire growing season. A second observation is that even when relatively high rates of P were applied (60-80 lbs. P2O5 A-1), y-leaf and flag leaf tissue concentrations were below the optimum range of 0.2 to 0.4% as reported by Dobermann and Fairhurst (2000). Tissue analyses did indicate that when all plots within a tillage treatment were averaged, sulfur concentrations were slightly above the critical level of 0.16% at tillering; however, the average S concentration in the flag leaf for the non-chiseled and chiseled area was 0.08% and 0.07%, respectively, both of which are below the critical level of 0.10%. Sulfur was broadcasted across the entire field in the form of ammonium thiosulfate (12-0-0-26) at a rate of 10 gallons per acre at planting. However, as the tissue analyses indicate, as well as some yellowing of the new leafs after the plant began the reproductive phase (Figure 4), a sulfur deficiency may have impacted the yield results. This study will be repeated in 2003, and either midseason or increased early season S will be applied to alleviate the possible problems associated with S.

Tables and Figures:

Table 1. Soil test levels prior to application of the P2O5 treatments.

Tillage / Ca / K / Mg / Na / P / S / Zn / pH / OM / CEC
Lbs. A-1 / %
Chiseled / 5464 / 477 / 3362 / 389 / 20 / 57 / 11.6 / 5.5 / 0.40 / 34.7
Non-chiseled / 5704 / 494 / 3079 / 344 / 27 / 50 / 12.4 / 5.4 / 0.35 / 34.6

Table 2. Soil test-P categories and the corresponding P2O5 recommendations.

Category / VL / L / M / H / VH
Range (lbs. P A-1) / 0-9 / 9-18 / 18-36 / 36-45 / 45+
Recommended lbs. P2O5 A-1 / 80 / 40 / 0 / 0 / 0

Table 3. Tissue-P concentrations for P2O5 treatments averaged across tillage treatments at PD and B.

P2O5 (lbs. A-1) / 0 / 20 / 40 / 60 / 80
Tissue-P %
Time
PD / 0.08 / 0.13 / 0.14 / 0.16 / 0.16
LSD (0.05) / 0.02
C.V. % / 13.3
B / 0.11 / 0.12 / 0.13 / 0.14 / 0.14
LSD (0.05) / 0.01
C.V. % / 10.2

Table 4. Yield response to P2O5 and tillage treatments.

P2O5 (lbs. A-1) / 0 / 20 / 40 / 60 / 80 / LSD (0.05)
Tillage / bu A-1
Non-chiseled / 115 / 117 / 142 / 166 / 137 / 14
Chiseled / 110 / 134 / 135 / 138 / 147
LSD (0.05) / 14
C.V. % / 7.5


Figure 1. The effects of P2O5 on tillering approximately 8 days

after permanent flood establishment.

Figure 2. Differences in vegetative growth approximately 17 days

after permanent flood establishment.


Figure 3. Differences in internode elongation as effected by P2O5

treatments.

Figure 4. Yellowing of plants at PD.

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