Research report from OSU's North Willamette Research and Extension Center
Delbert Hemphill, T. Jackson, and D.W. McAndrew
Oregon State University
Sweet corn yields in the Willamette Valley are known to increase with application of lime and banded P fertilizers, even in the presence of a high P soil test. However, the interaction of applied P fertilizers and lime, which increases availability of soil P, has not been explored in detail. Surveys in commercial fields and experiments at the North Willamette Station indicated possible Cu deficiencies in corn leaf tissue. Application of large amounts of P could induce a Cu deficiency by making soil Cu less available. The objectives of the 1981 experiments were to study the effects of 1) combinations of broadcast and banded P at four soil pH levels at two planting dates, 2) broadcast P and Cu in combination with three (banded) P carriers, on yield and nutrient content of sweet corn. The objectives of the 1982 experiments were to study the effects of 1) three rates of banded P fertilizer and Cu with and without application of lime, and 2) four P carriers at two rates of P with and without lime on yield and nutrient content of 'Jubilee' sweet corn.
Methods
In 1981, Willamette silt loam main plots of 0, 4.5, 9.0, and 13.5 MT/ha of lime (pH 5.6, 6.0, 6.6) were split by a broadcast, incorporated application of 0 and 76 kg P/ha. These subplots were split again by application of 33 or 76 kg P/ha banded 5 cm beneath and 5 cm to the side of the seed line. Plots were seeded on May 11 and a second set on June 3. Monocalcium phosphate was the P carrier for all treatments and all plots received 200 kg N/ha. The second experiment involved a 2x2 factorial combination of broadcast P at 0 or 76 kg/ha and Cu at 0 or 5.5 kg/ha. The Cu x P factorial was split by banded application of urea phosphate (17-44-0; N-P205-K20), diammonium phosphate (18-46-0), or monocalcium phosphate (0-45-0) at 33 or 76 kg P/ha. All plots received a total application of 220 kg N/ha. Planting date was May 27.
In 1982, lime was applied at rates of 0 or 6.7 MT/ha. In the first experiment, P was applied at planting on May 5 as a band treatment of 11-51-0 at 33 kg P/ha or 33 kg P/ha as 11-51-0 plus 43 kg P/ha as 0-45-0. Copper at 11 kg/ha was applied before seedbed preparation only in combination with the high rate of P. The lime main plots were split by the four Cu-P treatments in randomized block design. In the second experiment, the lime plots were split by banded P application, at 0, 33, or 76 kg/ha, in the form of 12-51-0 (ammonium polyphosphate), 16-41-0 (urea phosphate), 17-44-0 (urea phosphate), or 18-46-0 (diammonium phosphate). Seeding was done on June 2. All plots received a total of 200 kg N/ha.
Results - 1981
In the first experiment, the major yield responses were to lime and P. At the early planting date, mature ear yield and cutoff yield increased with the higher rate of banded P only on unlimed soil. Liming increased yield with the low rate of P, but not at the higher rate of P. At the late planting date, the yield response to P was of greater magnitude than at the earlier planting date. Response to banded or broadcast P was strongest at low soil pH. Leaf tissue P levels generally increased with increasing soil pH and either banded or broadcast P treatment. Leaf copper content decreased with application of lime or P. Leaf Zn and Mn content also decreased with application of lime. In the second experiment, application of Cu increased leaf Cu content but had no effect on ear yield or cutoff yield. Form of applied P (carrier) had no effect on any yield parameter.
Results - 1982
In the first experiment, application of lime had no effect on yield of mature ears or total ear yield when averaged over P-Cu treatments, but lime did increase the cutoff ratio (weight of kernels/weight of ears) from 0.46 to 0.49. Copper and P had no effect on any yield parameter when averaged over lime rates. At zero lime application, P increased yields of mature ears by 5 MT/ha and cutoff yield by 3 MT/ha. Application of P had no effect on yield of corn grown on limed soil. In the absence of applied P, lime increased yield of mature ears and cutoff yield.
Leaf P concentration increased with P but not lime treatments. Leaf Cu content decreased with P application but was partially restored by application of P+Cu. Leaf Zn content decreased with P or lime application and Mn content decreased with lime application.
In the second experiment, the form of P fertilizer (P carrier) had no consistent effect on any yield parameter or on leaf nutrient content. Lime had no significant effect on yield when averaged over P rates and carriers, but did increase mature, total, and cut-off yield, and cutoff ratio in the absence of banded P. Mature ear yield, total yield, and cutoff yield were increased by P application, with yields at 76 kg P/ha higher than yields at 33 kg P/ha.
Leaf P content was increased by the high P rate but not by the low P rate. Lime tended to increase P content, but the differences were not statistically significant. Leaf Cu content decreased with P application. Leaf Cu, Mn, and Zn content decreased with lime application.
Discussion
Maintaining an adequate soil pH near 6.0 and use of P fertilizers are key factors in achieving maximum yields of sweet corn. Earliness, as reflected in yields of mature ears, is greatly promoted by available P. Phosphorus availability can be increased either by banding P fertilizer or by liming, preferably both. However, lime has little effect on yield in the presence of large amounts (175 kg P205/ha) of banded P. The formulation of N-P fertilizers (carrier effect) has little effect on yield. High rates of P reduce leaf Cu content slightly but addition of Cu did not increase yields in these experiments. Apparently, induction of Cu deficiency by high rates of P fertilization should not be a problem in sweet corn production on Willamette soil.