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Influence of Long-term N-P Fertilizers, Cropping Systems, and Rainfall on Corn Yield and on Soil Properties
Dissertation Abstract:
Studies were made on Packchong clay, reddish brown lateritic soil (Paleustult) at the National Cron and Sorghum Research Center, Packchong, Nackon Ratchasima, Thailand to evaluate the effects of long-term nitrogen-phosphorus (N-P) fertilizer, cropping systems, and rainfall on corn yields and soil properties.
One study compared application of four rates of N-P2O5 (0-0, 60-60, 120-120, and 180-180 kg/ha) over a 10-year period. The other study compared seven treatments of sole corn and its rotation or intercropping with mung bean, soybean, or peanut with or without fertilization for seven years.
When the soil fertility was low, grain and stover yields did not correlate with rainfall. At high levels of N-P2O5, however, yields responded to rainfall. The highest agronomic yield occurred with the addition of 120-120 fertilizer while the best economic yield was obtained with fertilization of 90-90 kg N-P2O5.
Soil organic matter content tended to increase with the rate of N-P fertilizer. Soil N and available P likewise accumulated with continuous application of N-P2O5. All forms of hydrolyzable N fractions and inorganic P also tended to increase with rates of fertilizer application.
Soil pH and surface soil extractable calcium (Ca) and magnesium (Mg) decreased at higher levels of fertilization. The level of deficiency, however, was not yet critical enough to warrant addition of these nutrients. The concomitant increase in the level of manganese (Mn) with fertilization may be a cause for worry in that toxicity may occur later. Aggregate stability, bulk density, and carbon-nitrogen ratio tended to decrease with fertilization over the 10-year period.
The populations of mycorrhiza and azotobacter were not affected by fertilization, although this may soon change when the soil becomes acidic enough to effect these microbes.
In seven years of growing legumes, either in rotation or as intercrop with corn, the following were observed:
1) Yields of corn grown in rotation with mung bean or peanut without N-P were comparable with those of fertilized sole corn crops; however, when rotated with soybean without fertilizers, corn yields can compare with unfertilized sole corn yields.
2) Without N-P, grain yields of corn intercropped with soybean, peanut, or mung bean were comparable with sole corn crop yields. With N-P, rotation or intercropping with either of the three legumes had yields that were comparable to yield of sole corn crop.
3) Addition of fertilizer decreased soil pH which may have aggravated the Ca and Mg leaching.
4) Insignificant differences in aggregation were found among cropping systems. Degradation in aggregation were noticed when fertilizer was applied.
5) Mycorrhizal and azotobacter were highest in the corn-mung bean rotation system. The presence of legumes either as intercrops or as rotation crops increased azotobacter population. Annual application of 94-94 kg N-P2O2/ha did not affect mycorrhizal population but decreased azotobacter population.
