Residual Effects of No-Till Crop Residues on Corn Yield and Nitrogen Uptake

The residual effects of crop residues on N availability and crop growth are largely unknown. A field experiment was conducted from 1986 through 1988 at Lincoln, NE, to determine the residual effects on no-till corn (Zea mays L.) production and N uptake of 0,50, 100, and 1509'0 of the amount of crop residues produced by the previous crop during the previous 5 yr. These effects were evaluated with and without tillage (disking), N fertilizer (60 kg N ha-'), and hairy vetch (Vwia villosa Roth ssp. villosa, 'Madison') winter cover crop. Increasing the previous crop residue rate increased organic C, total N, and NO,-N in the upper 30 cm of soil as much as 10, 12, and 66V0, respectively. Growth and N uptake by corn (3-yr average) generally increased as previous residue rate increased. Corn grain and stover production was 17 and 25% greater for the highest compared with the lowest previous residue rate. Uptake of indigenous soil N, hut not fertilizer N, also increased as previous residue rate increased. Cover crops generally increased growth and N uptake with no fertilizer, but had little effect with N fertilizer. Soil properties, crop growth, and N uptake generally were not affected by tillage or interactions among the variables. These results indicate that increasing no-till crop residue rates increased the capability of this soil to provide N to growing crops for many years. It appears this effect is somewhat self-perpetuating. C ROP FERTILIZER REQUIREMENT and soil nutrient availability are influenced by soil fertility and crop residue management. Crop residues contain appreciable plant nutrients and, therefore, have contributed to the, maintenance of soil productivity if returned to the soil (Holland and Coleman. 1987: Paul and ~uma,4981)'. Returning residues also helps maintain soil organic matter, which is important for soil structure, soil and water conservation, and soil microbial and faunal activity. Furthermore, the microenvironment in residue-covered soils is usually less oxidative than where residues are removed or incorporated (Doran, 1980). Prolonged removal or burning of crop residues usually decreases nutrient and organic matter content (Hooker and Schepers, 1984; Unger, 1973). The effects &dean tillage and soil erosion on decreased soil organic matter content and loss of productivity have been documented frequently (Prasad and Power, 1991; Unger and McCalla, 1980). These adverse effects are largely overcome by use of reduced or no tillage and by use of cover crops (Doran et al., 1984; Smith et al., 1987; Unger and McCalla, 1980). Stratification of crop residues and conservation of soil organic matter near the soil surface with reduced or no-till management are paralleled by greater soil microbial biomass in these layers, which causes greater immobilization of fertilizer N, compared with plowing M S . Maskina, Punjab Agricultural Univ., Ludhiana, Punjab, India; J.F. Power, J.W. Doran, and W.W. Wilhelm, USDA-ARS, Univ. of Nebraska, Lincoln, NE 68583. Published as Paper no. 10438, Journal Series, Nebraska Agricultural Research D~vision, Lincoln. Received 27 Apr. 1992. *Corresponding author. Published in Soil Sci. Soc. Am. J. 57:1555-1560 (1993). or shallow tillage (Carter and Rennie, 1987; Doran and Smith, 1987). In Kansas, Hooker and Schepers (1984) showed greater soil N and C and plant N availability after more than 10 yr of adding crop residues vs. burning. In Montana, Black (1973) showed that addition of wheat (Tnticum aestivium L.) straw also increased soil N and C and mineralizable N. Use of legume cover crops likewise adds organic matter to soils and affects soil N transformations (Janzen et al., 1990; Varco et al., 1989). A number of studies have been published in which the effects of tillage, cover crops, N fertilization, and soil organic matter individually influenced N availability and uptake by a crop. Some studies have also investigated the effects of combinations of several of these factors, but few have simultaneously investigated the interactions between more than two of these factors that affect N availability and uptake. In nature, however, there are numerous environmental and cultural factors operating and interacting simultaneously that affect soil N availability. Consequently, we studied the simultaneous effects and interactions of tillage, cover crop, N fertilization, and soil organic matter level on N availability and uptake by dryland corn. Differences in soil organic matter content were established in an earlier 5-yr experiment (1981-1985) in which crop residues were added to no-till plots at rates of 0, 50, 100, and 150% of the quantity of residues produced by the previous crop (Power et al., 1986; Wilhelm et al., 1986). MATERIALS AND METHODS This study was conducted from 1986 through 1988 on a Crete-Butler silty clay loam (fine, montmorillonitic, mesic Pachic Argiustoll-Abruptic Argiaquoll) near Lincoln, NE. Climatic is continental with typically 70% of the average 717 mm of annual precipitation falling between April and September. However, rainfall distribution is highly variable. The experimental site is nearly level (0.2% slope). In an earlier 5-yr experiment, we returned either 0, 50, 100, or 150% of the crops residues produced by the previous crop (either corn or soybean [Glycine m a (L.) Merr.]) to the soil surface in a no-till production system (Power et al., 1986; Wilhelm et al., 1986). In the 3-yr experiment reported here, which utilized the same plots as the previous 5-yr residue rate experiment, we discontinued the variable crop residue rates (that is, all residues produced by the previous crop were left on each plot), and we measured the residual effects of the previous no-till residue rates on crop growth and soil properties. In addition, we determined the effects of tillage (no-till and tilled), winter legume cover crop (hairy vetch), and fertilizer N (0 and 60 kg N ha-') on dryland corn production for each of the previous residue rates. The experimental units were arranged as split plots within a randomized complete block design. Main treatments were tillage, with previous residue rates as subblocks. The N fertilizer and cover crop treatments were randomized within each previous residue rate plot, in 9.1 by 9.1 m subplots replicated four times. At the initiation and several times during the experiment, soil samples were collected in the spring for laboratory char1556 SOIL SCI. SOC. AM. J., VOL. 57, NOVEMBER-DECEMBER 1993 Table 1. Monthly precipitation and mean temperature during 1986, 1987, and 1988 growing seasons at Lincoln, NE. Table 3. Effect of previous crop residue levels on growth and N accumulation in cover crops.