Short-Term Excess Water Impact on Corn Yield and Nitrogen Recovery

Optimum N management for soils which can have short-term, early-season periods of excessive soil water requires farmers to balance economic and environmental concerns. The objectives of this study were to evaluate corn (Zea mays L.) yield and N fertilizer recovery following 0, 4, or 6 in. of excess soil water. Field studies were conducted from 1985 to 1988 on Cisne silt loam (fine, montmorillonitic, mesic Mollic Albaqualf), Drummer silty clay loam (fine-silty, mixed, mesic Typic Haplaquoll), and Plainfield sand (mixed, mesic Typic Udipsamment) at three Illinois locations. Water stress was imposed by applying 0, 4, or 6 in. of water to soils at field capacity (0.33 bar). Fertilizer rates ranged from 0 to 200 lb N/acre with an additional 50 lb N/acre being applied to half the plot following the water stress treatments. Isotopic ᴵ⁵N was used for the 150 lb N/acre treatment. Relative yield on Drummer decreased approximately 1% for each day soil water tension was below 0.33 bar. On Cisne, three stress days decreased yields less than 1%, but 7 d increased the loss to about 5%. Regression equations showed that even with 200 lb N/acre, 17 in. of water during May and June resulted in yields that were only 18% of those produced with 5 in. on a Plainfield sand. Fertilizer recovery averaged 88, 61, and 61% for Cisne; 83, 50, and 44% for Drummer; and 25, 8, and 13% for Plainfield soils with 0,4, and 6 in. of excess water. Denitrification was the primary loss mechanism for the Cisne and Drummer soils, while for the Plainfield sand, it was leaching. Equations developed from this study will result in more economical and environmentally sustainable N management decisions. Research QuestionResearch and farmer experience have clearly shown that unpredictable but frequently occurring heavy rains will result in significant N loss through denitrification or leaching. When this occurs, farmers and their advisors need a reliable mechanism to allow them to predict the amount of loss and, ultimately, whether or not it would be economical to apply supplemental N. The research reported in this paper was designed to evaluate the effect of soil moisture regimes on corn yield on three diverse soil types. Literature SummaryFactors associated with the two primary N loss mechanisms that occur when soils are excessively wet have been well documented in the literature. Unfortunately, little work has been done to develop a practical technique that farmers could use to predict whether the magnitude of N loss under specific conditions has been large enough to justify application of supplemental N. Study DescriptionNitrogen was applied at four rates for corn production on three diverse soil types in Illinois. Immediately after application of N, three soil moisture regimes were established across each of the N rates. After soil moisture was no longer at saturation, supplemental N was applied to one-half of each plot at a rate of 50 lb N/acre. Corn yield data were collected at harvest and used to develop a model to predict the magnitude of N loss under the different regimes. Location and soil type: Brownstown, IL—Cisne silt loam; DeKalb, IL—Drummer silty clay loam; and Havana IL—Plainfield sand. Treatments: N rates: 0, 100, 150, and 200 lb N/acre. Moisture regimes: All treatments were brought to field capacity in late May immediately after application of the N treatments. At that time, the moisture regimes of ambient, ambient plus 4-in. water over 3 d, and ambient plus 6-in. water over 8 d were imposed. Date of treatment: Corn in 6 leaf stage of growth Supplemental N: 0 and 50 lb N/acre Applied QuestionsWhat system best predicts N loss and associated yield loss? In this study, the number of days in which soil moisture content was wetter than 0.33 bar provided the best prediction of yield loss on the Drummer silty clay loam and Cisne silt loam soils (Fig. 1). On the Drummer, yields were decreased about 1% for each day that soils were saturated. On the Cisne, yield decreased at an increasing rate as the duration of saturated soils persisted. Precipitation plus supplemental irrigation in May and June provided the best indication of the amount of yield loss that occurred on the sandy soil. Yield loss as high as 20% was recorded when 8 in. of precipitation plus irrigation was received in May and June. Can corn yield be increased by applying supplemental N after soils have been excessively wet? On the finer textured soils, application of 50 lb N/acre after the soils have been excessively wet was adequate to obtain yields comparable to those obtained in treatments that did not receive excess moisture (Fig. 2). On the sandy soils, however, the same treatment was not adequate to overcome the yield decrease associated with the N loss resulting from the excessive water treatments (Fig. 3). What were the primary loss mechanisms responsible for N loss on the three soils evaluated? Based on soil N content following the period of excess moisture, it was evident that denitrification was the primary loss mechanism associated with the N loss on the finer textured soils. There was no evidence of leaching of N out of the profile on those soils. On the sandy soil, however, leaching was obviously the major loss mechanism. At harvest time, none of the fertilizer N could be detected in the 5-ft profile of the sandy soil. Even at silking, only a small concentration of fertilizer N was detected in those plots that had received excess water and that was in the lowest foot of the 5-ft profile. Fig. 1Effect of number of days that soils remain saturated with water during the early growing season on the relative yield of corn grown on a Drummer silty clay loam and Cisne silt loam soil. Fig. 2The effect of soil moisture regime and supplemental N on corn yield grown on a Drummer silty clay loam. Fig. 3The effect of soil moisture regime and supplemental N on corn yield grown on a Plainfield sand.