Growth effects of corn in rotation with rice.

Abstract

The growth and development of upland crops after rice (Oryza sativa L.) in the Lower Mississippi River Valley is frequently disappointing. We hypothesized that ponded rice water on weakly structured silty-textured soils' further weakens the soil structure, fostering the slaking of the fine silt and clay separates into the remaining pore space. The degrading of the soil structure augments' soil compaction, leading to a higher bulk density, reduced pore space, decreased aeration and limited root proliferation. A two year experimental design involving corn (Zea mays L.) after rice consisted of tillage as the main treatment and nitrogen and phosphorus as sub and sub-sub treatments. Soil fertility treatments were not significantly different. The tillage treatments consisted of raised beds (hipped beds) and flat beds' (direct planting on zero grade land). The hipping treatments increased the root and top biomass; as well as, the yield in both years. Measurements of selected soil properties inferred that oxygen diffusion into the root zone was a limiting factor and future research into tillage practices that augment oxygen diffusion into the rooting zone is likely to be beneficial.

Key Words: Corn (Zea mays L.), rice (Oryza sativa L.), tillage, oxygen diffusion, soil

1. Introduction

Corn (Zea mays L.) grown after rice (Oryza sativa L.) in the Lower Mississippi River Valley frequently experiences yield reductions, greater lodging problems, and overall reduced vigor. There is no clear consensus that exists to explain corn's poor performance following rice; however, the alteration of the soil's physical properties because of rice flooding is likely an important aspect. Recently, numerous research efforts have been directed towards understanding the interplay between soil organic matter (SOM) content and soil structure's resiliency in promoting a favorable root zone (Baldock and Nelson, 2000; Kay and Angers, 2000, Burke et al., 1998; Cambardella and Elliot, 1993; Franzluebbers and Arshad, 1997).

Soil structure is defined as the arrangement and organization of the primary soil particles (Hillel, 1980). The primary soil particles may be present in various quantities, sizes, shapes, and orientations. Their incorporation into aggregations may be complex, producing natural aggregates that differ in size, shape, strength (Hillel, 1980). These aggregates may be strengthened by SOM and other cementing agents (Beare et al., 1994ab; Bowman et al., 1999).

The value of soil structure revolves around the creation of soil porosity, thereby augmenting aeration, water holding capacity and root expansion. Soil structure is profoundly affected by climate, biological activity of the soil, crop rotations, and management practices (Al-Darby and Lowery, 1987; Bruce et al., 1990; Hill, 1990; Merrill et al., 1996). Agricultural practices that may reduce benefits afforded by the soil structure include: (1) tillage operations and (2) crop rotation and (3) irrigation.

Gas exchange in soils is important in supplying oxygen for root respiration and reducing potentially toxic soil C[O.sub.2] concentrations. Soil structure provides pore space for this gas exchange; however, the total porosity is only one factor in the overall efficiency of the gas exchange process. Oxygen diffusion in air is [10.sup.4] times more effective than oxygen diffusion in water (Kramer and Boyer, 1995), thus water-filled pores hinder effective gaseous exchange. Secondly, soil aeration is advanced in soils having a continuous network of interconnected soil pores. The gas composition of a soil commonly includes [N.sub.2], [O.sub.2], C[O.sub.2], trace gases and water vapor. Oxygen and C[O.sub.2] levels are largely determined by the intensity of root and microbial respiration and the degree of interaction with the atmosphere.

The partial pressure of atmospheric C[O.sub.2] is approximately 3.4 [10.sup.-4] atm, whereas the partial pressure of C[O.sub.2] in the soil atmosphere may reach concentrations approaching 3 [10.sup.-3] atm. At this level C[O.sub.2] could become phytotoxic (Hillel, 1980). Oxygen consumption in the soil environment may exceed the supply of [O.sub.2] from the atmosphere, resulting in [O.sub.2] depletion and the onset of anaerobic conditions. Root surfaces generally require [O.sub.2] flux rates of 0.4 mg [O.sub.2] x [cm.sup.-2] x [min.sup.1] for normal physiological functioning, whereas [O.sub.2] flux rates below [O.sub.2] mg [O.sub.2] x [cm.sup.-2] x [min.sup.-1] are considered limiting (Hillel, 1980).

The root system of a plant provides many important physiologic functions essential to the proper growth, development, and functioning of a plant. These functions include: anchorage, hormonal synthesis, nutrient and water uptake, and carbon storage (Kramer and Boyer, 1995). Reduced aeration affects hormonal synthesis in the root system, resulting in reduced production of exportable cytokinins and gibberellins and enhanced production of abscissic acid (Kramer and Boyer, 1996). The nutrient uptake of P, K, and other elements is restricted because of a reduced respiratory rate (Tisdale et al., 1985).

Many soil and climatic factors limit root function, with soil water extremes, soil acidity and reduced aeration being the most important. Typically, plants that experience reduced oxygenation of their root systems are associated with poorly drained and fine-textured soils; in which, a large percentage of the pore space contains water and the air-filled pores present a torturous pathway for oxygen diffusion. Typical symptoms include a reduced and shallow root system, anoxic conditions in the stele, stunting, reduced nutrient uptake, a proliferation of adventitious roots near the soil surface, thin culms, and reduced crop yields (Kramer and Boyer, 1996).

The purpose of this research is: (1) to determine the effect of flooding associated with rice production on the physical and fertility properties of the soil, and (2) to estimate if these soil changes are detrimental to the subsequent growth of corn.

2. Materials And Methods

Experiments were conducted to assess corn growth and development because of tillage treatments and the nature of the previous crop. In particular, for corn following rice, tillage treatments involving soil hipping (raised beds) are a better tillage option than no-till planting. Secondly, we wished to assess corn growth on land that had been previously planted to: (i) soybeans (Glycine max. L), (ii) drill-seeded rice, and (iii) water-seeded rice. The goals of these experiments are designed to determine: (1) whether the nutrient status of the soil is different because of the treatments, and (2) whether the culture of rice predisposes the soil to lower yielding upland crops in succeeding years after rice. Lastly, we wish to infer the exact mechanism responsible for crop yield reductions following rice.

a. Experiment One: Raised Beds (Hipping) versus No-till Planting (Flat)

An experiment evaluating corn growth on hipped and flat seedbeds was conducted at the Missouri Rice Research and Demonstration Farm near Glennonville, MO on a somewhat poorly drained Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualfs) during 2000 and 2001. Soil testing demonstrated that the soil had a satisfactory soil fertility level during 2000 and was somewhat P and K deficient during 2001 (Table 1). The experimental design consisted of replicated blocks for the hipped and flat beds with individual plots established after stand development. Raised and flat beds had a row spacing of 36 inches (0.914 m) and were planted with hybrid corn to establish 20,300 plants [acre.sup.1] in 2000 and 26,000 plants [acre.sup.-1] in 2001. Urea was applied according to soil test (120 lbs N x [acre.sup.-1]) at planting in 2000 and at emergence in 2001. The crop was furrow irrigated.

After planting, the bulk density and the saturated hydraulic conductivity were estimated in triplicate for the raised bed, the flat bed, and the underlying subsoil (Carter, 1993). The soil aggregate size distribution was estimated using dry sieving. In this procedure, bulk soil samples were dried at 110 C and gently sieved (4, 0.8 and 0.25 mm openings) to roughly assess if the tillage program altered the distribution of the aggregates (DeFreitas et al., 1996).

Tissue testing in 2000 was performed five times [22 May (fully emerged leaves from 20 plants), 6 June (fully emerged leaves from 20 plants), 27 June (uppermost fully-developed leaf from 10 plants), 17 July (leaf one node above first-developing ear from 10 plants)]. Tissue testing in 2001 consisted of a mid-July sampling involving leaf sampling, one node above the developing ear, from 10 plants. Nitrogen was determined using semi-micro Kjeldahl, whereas S, P, K, Ca, Mg, Na, Al, Fe, B, Mn, Cu and Zn were determined by inductive-coupled plasma-emission spectroscopy (ICP-AES) after ignition at 500 C in a controlled temperature furnace, followed by uptake in 5% HN[O.sub.3]. Roots were similarly collected (6 June and 17 July) and washed repeatedly in distilled water before tissue testing.

Total plant biomass was assessed twice during the 2000 growing season and once during the 2001 growing season. Four (2000) and eight (2001) visually representative plants were selected for analysis from each plot. The plant and its allotted soil volume were excavated and transported to the laboratory. The soil was carefully washed from the root system after soaking of the soil-root mass in large tubs of water for several days. Roots, stems (culms), leaves, tassels, and ears were separated and dried at 70 C for several days. Plant dry weight (mass) was obtained by weighing.

b. Experiment Two: Corn after Soybeans, Drill Seeded Rice, and Water Seeded Rice

Experiment two was conducted in a commercial field in 2000 where corn was planted after previous crops of soybeans, drill-seeded rice, and water-seeded rice. The soil type was a somewhat poorly drained Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualfs). Soil testing demonstrated that the soil had a satisfactory soil fertility level (Table 3). Fertilization consisted of 90 lbs of urea, 90 lbs of a (0-23-30) mixed fertilizer at planting and 200 lbs of liquid N after emergence. Planting dates for corn were 7 April (soybeans and drilled seeded rice plots) with a 29 inch row spacing for the soybean plot and an emergence count of 1.4 plant row-[foot.sup.-1] and a 31 inch row spacing and an emergence rates of 1.3 plants row-[foot.sup.-1] for the drill seeded rice plot. Corn was planted on 13 April for the water seeded rice plots, consisting of 31 inch row spacing and an emergence rate of 1.3 plant row-[foot.sup.-1]. Irrigation was furrow irrigation. All methods are similar to those described for the above experiment.

3. Results Involving Corn Planted on Hipped versus Flat Beds

a. Soil Fertility and Physical Measurements

Soil test results in 2000 suggest that the plots have reasonable soil fertility and soil fertility differences between the plots are minor (Table 1). Phosphorus is somewhat P deficient (P value of 30 lbs P [ac.sup.-1] is considered adequate for rice, whereas a value of 45 lbs P [ac.sup.-1] is adequate for corn). Soil-test results for 2001 indicate that P and K are somewhat deficient. The level of soil fertility was roughly equivalent throughout the study area and differences in soil fertility are not sufficient to influence or bias tillage treatments.

The soil bulk density is low, indicating a pore space of approximately 58% for the hipped and flat surface soil layers (Table 1). The bulk density of the subsoil is appreciably higher, indicating a more compact soil layer and a reduced total pore space. The pore space of the subsoil, if air-filled and consisting of connected pores, should be sufficient to support root development. However, the moisture content and the fine soil texture suggest that the soil pores are small and frequently water saturated. The soil structure of the subsoil immediately below the seedbed is composed entirely of moderate, very fine to medium platy structures, suggesting a torturous pathway for water and air transmission. Additionally, the compact subsoil has the likelihood of restricting the developing root system of corn because of reduced soil temperatures, wetness, and physical hindrance of the elongating roots.

The aggregate size analysis indicates that the majority of the A horizon in the seed-bed is composed of very fine spherical aggregate and non-aggregated material, suggesting that the water culture of the earlier rice crop has "slaked" the natural aggregates and promoted the potential for compaction, filling of pores with silt, and reducing the diffusion of oxygen to the developing root system.

The saturated hydraulic conductivity for the hipped plots averages 1.05 x [10.sup.-4] cm x [s.sup.-1], whereas the flat plots averaged 2.65 x [10.sup.-5] cm x [s.sup.-1]. The flat plots have a significantly reduced infiltration capacity, indicating that water flow and presumably air flow have been compromised by the lack of large connected pores (Table 1). The saturated hydraulic conductivity of the subsoil is (2.39 x [10.sup.-6] cm x [s.sup.-1]) is very low, suggesting appreciable water and air resistances.

b. Tissue Testing of Corn Planted in Hipped and Flat Beds following Rice

Tissue testing demonstrates that the nutrient levels for corn are appropriate and that soil fertility has not limited plant growth (Table 2). Nutrient levels decline with later sampling dates, a trend that is consistent with a normal corn growth pattern (Tisdale et al., 1985). Root tissues have smaller macronutrient concentrations than leaf tissues; however, Fe and Mn are appreciably more concentrated in root tissues, indicating root accumulation that is consistent for a soil with an acidic pH. Nutrient levels between the hipped and the flat tillage designs are equivalent, indicating that any yield differences between these two treatments are not likely attributable to soil fertility. Tissue testing in 2001 suggests that K is slightly low and B was low; however, differences in these nutrients between treatments were not significant (Table 3).

c. Biomass and Yields for Corn Following Rice

The total plant biomass and the distribution of the biomass among the root system, stem, leaf, and ear in 2000 indicate differences because of the tillage treatments (Fig. 1). Total biomass, stem and root growth are appreciably greater in the hipped system. In 2001, the total biomass was greater for the hipped system (Fig. 1); however, the distribution of the biomass was roughly equivalent between the tillage systems. The leaf to root ratio for the hipped system (mean = 1.24, standard deviation = 0.08) was significantly smaller than the flat system (mean = 2.0, standard deviation = 0.8). Average plant height (not measuring tassel length) was significantly greater for the hipped system (mean = 67 inches, standard deviation = 7.5 inches) than the flat system (mean = 58 inches, standard deviation = 4.7 inches). Yield estimates indicate that the hipped system in 2000 returned 5,900 lbs [acre.sup.-1], whereas the flat system returned 4,700 lbs [acre.sup.-1]. Yield estimates in 2001 for the hipped treatment averaged 5,670 lbs [acre.sup.-1], whereas the flat treatment averaged only 3,920 lbs [acre.sup.-1]. Thus the yield potential of hipped system was consistently and substantially greater.

[FIGURE 1 OMITTED]

4. Results Involving Corn after Soybeans, Drill-Seeded, and Water-seeded Rice

a. Nutrient Concentrations of Corn Following Soybeans, Drill-seeded Rice, Water-seeded Rice

Soil-test results suggest that the plots have reasonable soil fertility for rice culture and soil fertility differences between the plots are minor. Tissue testing demonstrates that the nutrient levels for the corn plant are appropriate, suggesting that the soil fertility has not hindered plant growth (Table 5). Nutrient levels decline with later sampling dates (data not shown), a trend that is consistent with a normal growth pattern of an annual crop (Tisdale et al., 1985). Root tissues are generally lower in the macronutrients than the leaf tissues; however, selected micronutrients such as Fe and Mn are appreciably greater in root tissues, indicating root accumulation. Nutrient levels in the root systems and the leaves among the soybean, drill seed and water seeded designs are largely equivalent, indicating that any yield differences between these three treatments are not likely attributable to soil fertility.

b. Biomass and Yields for Corn Following Soybeans, Drill-Seeded Rice, Water-Seeded Rice

The total plant biomass and the distribution of the biomass among the root system, stem, leaves, and ears indicate differences because of the previous crop (Fig. 2). Total biomass, ear, stem, leaves, and root growth are appreciably greater in corn-after-soybean systems than either of the corn-after-rice systems. The corn after drill-seeded rice produced a greater total biomass and greater biomass among the root system, stem, leaves, and ear than the corn after water-seeded rice (Fig. 2). The leaf to root ratio for the corn after soybean system (mean = 1.76, standard deviation = 0.52) was similar to the leaf to root ratio for the corn after rice systems (mean = 1.8, standard deviation = 0.48). Average plant height (not measuring tassel length) for the corn after soybean system (mean = 68.5 inches, standard deviation = 6.1 inches) was roughly equivalent to the corn-after-drill-seeded rice (mean = 71.3 inches, standard deviation = 8.7 inches) and significantly greater than the corn-after-water seeded-rice (mean = 52.5 inches, standard deviation = 3.0 inches).

[FIGURE 2 OMITTED]

Yield estimates indicate that the corn-soybean system returned 8,571 lbs [acre.sup.-1] and the corn-drill-seeded rice system returned 8,686 lbs [acre.sup.-1], yields that are roughly equivalent. The yield of the corn-water-seeded rice system was significantly and negatively impacted by the previous water-seeded rice system, returning only 5,828 lbs [acre.sup.-1].

5. Summary

The following conclusions appear valid:

(1)Soil fertility did not appear to be a deciding factor in the development of corn between rotations involving corn-soybeans and corn-rice.

(2)Physical properties of the soil suggest that the total pore space is normal for a silt loam soil; however, the distribution of the pores, the average moisture content and the platy soil structure is such that the majority of pores are small and the movement of water and air is difficult. Slaking of the soil structure during flooding of the previous rice crop weakened the expression of the granular or blocky soil structures and fostered a large percentage of smaller pores.

(3)Hipping promoted corn growth and yield, suggesting that the tillage system provided a more suitable rooting environment and gas exchange. Perhaps subsoiling may promote a deeper soil aeration capacity.

(4)It is the consensus of the research team that oxygen diffusion from the atmosphere to the developing root system of corn is a limiting factor. Future research should address the augmentation of oxygen diffusion in soil.

Table 1. Soil Chemical and physical property characterization of hipped
and non-hipped corn planted after rice.

Treatment    pH      SOM     Phosphorus    Ca      Mg      K
                      %       lbs P/ac     [cmol.sub.p(+)] x kg
                                             x [soil.sup.-1]

2000                                       Exchangeable Cations

Hipped       5.00    1.70         23.00    4.45    2.08    0.20
Flat         5.00    1.70         16.00    4.32    1.94    0.20
2001         7.10    1.50         27.00    5.61    1.38    0.17

             Exchangeable Cations

Treatment    K       Na      CEC
             [cmol.sub.p(+)] x kg
               x [soil.sup.-1]

2000
Hipped       0.20    0.15    10.00
Flat         0.20    0.15    10.00
2001         0.17    0.32     7.48

Treatment         Bulk          Pore         Hydraulic
                 Density        Space       Conductivity
             g x [cm.sup.-3]      %       cm x [s.sup.-1]

Hipped          1.1 (1.0)          62    1.05 x [10.sup.-4]
Flat            1.1 (1.1)          58    2.65 x [10.sup.-5]
Subsoil         1.4 (1.4)          46    2.39 x [10.sup.-6]

                   Aggregate Distribution

Treatment    5 to 1   1 to 0.25    Finer than
               mm        mm          0.25 mm
               %         %             %

Hipped           26          53            21
Flat             28          55            17
Subsoil          --          --            --

Table 2. Nutrient concentration in the developing corn crop (2000).

Treatment        Plant     N       S       P       K       MG      Ca
                 Part
                                               %

Normal levels
High Range                5.00    0.40    0.40    4.00    0.40    1.00
Low Range                 1.00    0.10    0.10    1.00    0.10    0.20

                                             6 June

Hipped           leaf     3.46    0.26    0.16    2.93    0.49    0.80
Flat             leaf     3.53    0.23    0.18    2.59    0.51    0.67
Hipped           root     2.21    0.16    0.11    0.90    0.32    0.60
Flat             root     1.97    0.18    0.08    0.65    0.28    0.47

                                            17 July

Hipped           leaf     3.39    0.27    0.34    0.85    0.67    0.59
Flat             leaf     3.05    0.26    0.27    1.16    0.35    0.45
Hipped           root     1.82    0.10    0.12    0.37    0.24    0.58
Flat             root     1.32    0.26    0.14    0.73    0.20    0.26

Treatment         Fe     Mn     B     Cu    Zn

                         mg x [k.sup.-1]

Normal levels
High Range        250    500    18    20    150
Low Range          50     20     6     5     25

Hipped            2.7    150    10     8     45
Flat              2.6    132     9     9     48
Hipped           2237    208     6    12     40
Flat             2367    231     5     9     69

Hipped            122    221     7    14     58
Flat              109     85     8    12     44
Hipped           2337    493     5    21     21
Flat             1955    175     1    40     21

Table 3. Tissue test results for corn having hipped and flat bedding
systems.

Treatment         S       P       K       Mg      Ca

                                    %

Normal Levels
High Range       0.40    0.40    4.00    0.40    1.00
Low Range        0.10    0.10    1.00    0.10    0.20
Mean
Hipped           0.23    0.26    1.31    0.43    0.69
Flat             0.21    0.25    1.42    0.34    0.69
Standard Deviation (n=8 samples)
Hipped           0.03    0.08    0.25    0.19    0.17
Flat             0.05    0.08    0.08    0.05    0.14

Treatment         Fe      Mn      B      Cu      Zn

                            mg x [kg.sup.-1]

Normal Levels
High Range       250     500     18     20      150
Low Range        50      20      6      5       25
Mean
Hipped           168     162     4.7    10.1    33.5
Flat             165     159     5.7    9.7     32.7
Standard Deviation (n=8 samples)
Hipped           33.4    29.3    1.4    2.2     12.5
Flat             27.4    31.1    0.9    1.7     13.2

Table 4. Soil chemical and physical property characterization for corn
grown after soybeans, drill seeded rice and water-seeded rice.

                                            Exchangeable Cations

Previous Crop   pH    SOM   Phosporous    Ca     Mg     K      CEC

                                           [cmol.sub.p(+)] x kg x
                       %     lbs P/ac          [soil.sup.-1]

Soybeans        6.4   2.7           59   9.86   3.31   0.36   14.11
Drilled rice    6.8   2.3           46   7.66   2.99   0.36   11.65
Water-seeded    7.0   1.9           27   9.53   3.11   0.33   13.87

SOM = soil organic matter by loss on ignition

Table 5. Tissue test results for corn following soybeans, drill-seeded
and water-seeded rice (2000).

Treatment Plant Part      N       S       P      K       Mg      Ca

                                             %

Normal levels
High Range              5.00    0.40    0.40    4.00    0.40    1.00
Low Range               1.00    0.10    0.10    1.00    0.10    0.20

                                           17 July

Soybean   leaf          3.17    0.22    0.31    1.71    0.29    0.60
Drill     leaf          2.95    0.20    0.26    1.90    0.19    0.49
Water     leaf          3.24    0.22    0.31    1.72    0.26    0.49
Soybean   root          1.14    0.13    0.09    1.54    0.13     026
Drill     root          0.93    0.19    0.08    1.77    0.14    0.25
Water     root          1.28    0.28    0.13    1.48    0.24    0.46

Treatment         Fe      Mn     B    Cu     Zn

                        mg x [kg.sup.-1]

Normal levels
High Range        250    500    18    20    150
Low Range          50     20     6     5     25

                             17 July

Soybean           190    122    31    17     24
Drill             149    158    26    14     42
Water             153    130    37    14     28
Soybean          1908    317     4    41     14
Drill            1221    218     4    19     12
Water            2247    244     4    26     11

Tissue concentrations for 3 June and 27 July are similar and are not
shown.

6. Literature Cited

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Donn Beighley, Wesley Mueller and * Michael Aide Southeast Missouri State University and David Dunn and Gene Stevens University Missouri Delta Center, Portageville, Missouri April 2004

* Corresponding author ([e-mail])