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Animal Powered Tillage Translocated Soil Affects Nutrient Dynamics and Soil Properties at Claveria, Philippines.

ABSTRACT: Intensive tillage in a humid tropical setting on uplands in Claveria, Philippines moves soil downslope, often creating unfavorable soil conditions for crop production. This field study, conducted on Oxisols with slope gradients ranging from 16-22%, evaluated nutrient dynamics for four ox-powered contour tillage systems: 1.) contour moldboard plowing (CMP); 2.) contour ridge tillage (CRT); 3.) contour natural grass barrier strips plus contour moldboard plowing (GCMP); and 4.) contour natural grass barrier strips plus contour ridge tillage (GCRT). The four management systems (treatments) were replicated three times on two sites. Eight corn (Zea mays L) crops were grown from 1992 to 1996. Corn residues, vegetative materials, and inorganic fertilizers (80 kg N, 30 kg P, and 30 kg K [ha.sup.-1]) were applied uniformly to all systems. Lime at 3 Mg [ha.sup.-1] was applied in 1992. Soil sampling was conducted within plots initially, and in 1996, was systematic at equally divided compartments along transects . Overall, from 1992 to 1996, the concentration of total C slightly increased, total N slightly decreased, and extractable Ca, K P, Cu, and Zn increased significantly in all systems. During the four year period, generally, the concentration gradients of extractable P, K, and Ca within treatments became steeper, with the higher concentrations occurring at the lower elevation of the CRT and CMP plots and at the lower elevation of individual terraces of GCMP and GCRT plots. In contrast, concentration gradients for Cu and Zn increased linearly from the lower to higher elevation. Soil pH immediately downslope from the grass strips was significantly lower compared to pH in the grass strips. The changes in pH and chemical concentration gradients across the plots and terraces are attributed primarily to tillage translocated soil downslope due to moldboard plowing. Installation of contour grass barrier strips in conjunction with ridge tillage reduced the rate of soil translocation and, thus, the rate of chemical gradi ent change.

Keywords: Concentration gradients, divided compartments, intensive tillage, translocated soil

Translocation of soil downslope has been reported for tillage operations by power machinery (Lindstrom et al. 1990, 1992; Lobb et al. 1995; Govers et al. 1994), animal-pulled tillage implements (Thapa et al. 1999), and manual tillage (Turkelboom et al. 1997). Regardless of whether tillage operations occur on the contour or up and downslope, net soil movement is downslope. For example, soil material moved by a tillage operation in an open, sloping field (Figure 1A) is displaced downslope; this soil material, however, is replaced by soil material moving downslope from the region above it. On the other hand, for alley cropping (Kang and Wilson 1987), that is, for a field with a series of parallel contour vegetative strips or barriers of trees, shrubs, or grasses, the soil translocation process is somewhat different (Agus et al. 1997; Thapa et al. 1999). Figure 1B shows the upper area of each terrace eroded as successive tillage operations transport soil material downslope.

This material, or much of it, eventually is deposited and accumulates near the grass strips at the lower elevation of the same terrace. This process led to terrace formation. The term "terrace" used in this study is equivalent to the term "alley" in discussions of "alley cropping' in the agroforestry literature.

Recently, tillage induced soil translocation has been considered to affect nutrient dynamics and crop production. In one study in the Philippines, gradients in soil physical properties developed across the terraces within three to four years after alley cropping practices were imposed on a Rhodic Hapludox (Agus et al. 1997). Measured differences in soil properties after three years were found for bulk density, soil transmissivity to water, and plant available water. Concentration gradients across the terraces of extractable P, K, and Ca in the Ap horizon were also observed.

Ridge tillage has been advanced to reduce tillage induced soil transport on steeplands in the humid tropics (Thapa et al. 1999). Ridge tillage is defined as a tillage system in which ridges are reformed atop the planted row by cultivation, and the ensuing row crop is planted into ridges formed the previous growing season. Thapa et al. (1999) reported soil translocation on hillsides under four management systems, two of which involved ridge tillage on a highly acid, P-deficient Oxisol in the Philippines. Mean downslope soil tracer displacement over a two year period for corn production ranged from 3.3 m for continuous contour moldboard plowing to 1.5 m for continuous ridge tillage in conjunction with multiple grass strip barriers. Tillage induced soil movement (63 Mg [ha.sup.-1] [yr.sup.-1]) by conventional contour moldboard plowing of an Oxisol was reduced by 53% using a combination of ridge tillage and contour natural grass barrier strips. Corn production was greater for the latter system (Thapa et al. 2000 ). Data from this experiment provides an opportunity to evaluate the effect of soil translocation on nutrient dynamics for four tillage regimes.

The objective of this study is to evaluate the effects of four soil management systems, two involving contour ridge tillage and two involving contour moldboard plowing, on nutrient dynamics and soil fertility changes over a four year period.

Materials and Methods.

This study on nutrient dynamics was part of a large tillage experiment and was conducted at two sites, the Ane-i and Patrocinio, from June 1992 to January 1996 at Claveria, Philippines (Thapa et al. 1999). Elevation at both sites is about 500 m. The soil at the Ane-i site is a Lithic Hapludox with 2.1 cmol + [kg.sup.-1] exchangeable Al below the 37 cm depth. Aluminum saturation based on effective CEC was 56% at this depth. The Rhodic Hapludox at the Patrocinio site has an Al saturation value of 69% or higher below the 48 cm depth. Clay content exceeded 69% and bulk density was less than 1 Mg [m.sup.-3] at all depths for both soils (Thapa et al. 2000). Table 1 shows the relevant soil macro and micro element concentration information for the two soil profiles in 1996 at the end of the study. The Patrocinio site had higher total C and total N at comparable depths compared to the Ane-i site, whereas extractable P, K, and Ca concentrations were higher at Ane-i. Extractable Mg, Mn, and Cu were slightly higher on t he surface horizon at Patrocinio.

At Claveria a moisture deficit exists from January to May. The wettest months are June, July, and August. Annual rainfall in 1992, 1993, 1994, and 1995 were 1561, 2099, 2020, and 1901 mm, respectively. Claveria has an isohyperthermic temperature regime with daily air temperature nearly constant throughout the year. The mean 10 day maximum temperature ranges from 25 to 28[degrees] C; the mean 10 day minimum temperature, 19-21[degrees] C.

Description of nutrient management systems. Three replicates of four soil management systems (treatments) were laid out in a randomized complete block design at two sites. The treatments were: 1.) contour moldboard plowing (CMP), the farmers' conventional practice in the region; 2.) contour soil barriers formed by ridge tillage (CRT); 3.) contour barriers formed by natural grass strips plus moldboard plowing (GCMP); and 4.) contour barriers formed by a combination of ridge tillage and natural grass strips (GCRT). Four of these treatments were imposed in 1992 and evaluated for tillage induced soil translocation (Thapa et al. 1999) and corn production (Thapa et al. 2000).

For the CMP system, a single ox-pulled, single blade moldboard plow and a harrow in separate operations prepared the soil for seeding. The moldboard plow was also used to make furrows for seeding and to maintain ridges with a nominal 10 cm height (i.e., for the two "hilling up" operations), as the row crop grew. For CMP, these 10 cm high ridges were destroyed during land preparation for the next crop.

The CRT system was managed similarly to CMP initially in 1992, but during the second hilling up operation, 20 cm high ridges spaced 60 cm apart, the distance between adjacent corn rows, were constructed on the contour using an ox pulled doubleblade moldboard plow. After their initial formation in 1992, the ridges were maintained. Thus, the intensity of tillage for CRT was lesser than the CMP.

During the initial phase of the experiment, the GCMP and GCRT systems were similar to CMP and CRT, respectively, except that five 0.5 m wide unplowed strips were left at contour intervals based on a 1.5 m vertical drop in elevation. Native grasses grew on these unplowed strips. All grass strips were effective barriers against downslope soil movement. As a result of rapid soil accumulation above each strip, four terraces formed, each 9-10 m wide depending on slope (Figure 1B).

The GCRT system utilized a combination of CRT practices in addition to the contour grass strips described above. The grasses were pruned each 45 days and the material uniformly applied across the terrace. Each management system received 3 Mg [ha.sup.-1] lime initially in 1992 and inorganic fertilizers (80 kg N, 30 kg p, and 30 kg K [ha.sup.-1]) during each of the eight corn crops.

For the purpose of sampling, each of the four terraces in each GCMP and GCRT experimental plot was divided into five equal compartments for a total of 20 compartments per plot. Similarly, the CMP and CRT plots had 20 sampling compartments per plot. Of all the plots, compartment 1 was at the lowest elevation (Figure 1).

In June 1992, soil samples from the 0-20 cm depth in two replicate plots (replicate 1 and 3) were taken with a hand auger (the sampling protocol is depicted in Figure 1). Soil samples were taken from compartments 1, 5, 10, 15, and 20 for treatments CMP and CRT, and from compartments 1, 2, 3, 4, 5, 16, 17, 18, 19, and 20 for treatments GCMP and GCRT. Each compartment sample was a composite of three random subsamples.

The soil samples were air dried, placed in two layers of polyethylene bags, and stored at ambient temperature in the laboratory until analyzed at a later date. In January 1996, the second set of soil samples was collected using the previous protocol. In addition, for treatments GCMP and GCRT, soil samples were taken in grass barrier strips GS 2 and GS 4, and at distances of 0.15 m downslope and 0.15 m upslope from the lower and upper edges of these grass barrier strips (Figure 1).

In March 1996, all soil samples collected in 1992 and 1996 were ground to pass a 2 mm sieve, packed into polyethylene containers, and shipped to the Soil Science Service Laboratory at North Carolina State University (NCSU) where they were analyzed. Total N and C were determined using a Perkin-Elmer PE 2400, CHN elemental analyzer. Phosphorus, K, Ca, Mg, Cu, Mn, and Zn were extracted using the Mehlich-I procedure (Mehlich 1953; Nelson et al. 1953); 5 g of soil and 25 ml of extracting solution (0.05M HCl in 0.025M H2SO4) were used. Extractable P was determined using the colorimetric molybdate blue procedure (Murphy and Riley 1962). The remaining chemical species were analyzed using an ion coupled plasma (ICP) technique.

Statistical analysis. Compartment is the lowest factor analyzed. For each compartment in each plot, the 1992 concentration of total C and the measured macro and micro elements (chemical species) was subtracted from the corresponding concentration measured in 1996. The difference between the 1996 concentration and the 1992 concentration is called "change in chemical species concentration."

The 1996 chemical species concentration data and the change in chemical species concentrations were analyzed separately using the general linear model (GLM) procedure (SAS 1988). Site, replication, treatment, terrace, and compartment within terrace are sources of variation for the combined factorial analysis. Replication and site are considered as random effects and treatment, terrace, and compartment are fixed effects. Linear regression of concentration of various chemical species and pH against compartment and terrace were made.

Results

A brief summary of the previously cited tillage translocation study (Thapa et al. 1999) is pertinent to interpret the chemical species data. Mean downslope soil tracer displacement over a two year period beginning July 1994 was 3.3 m for CMP, 1.8 m for CRT, 2.2 m for GCMP, and 1.5 m for GCRT. During this period, the last four corn crops out of eight were grown. Soil would have been displaced downslope by tillage at faster rates for GCRT and GCMP during the two year period following establishment of the experiment in 1992 because the terrace slope was greater at that time. The rate of tillage induced soil movement downslope was slope dependent.

Table 2 shows a summary of the analysis of variance for the change in concentration of each chemical species. Significant differences exist for the following variables: site, site by management treatment (s x m), site by terrace within management (s x t/m), and compartment within management by terrace (c/m x t). The analysis of variance results for the 1996 chemical species concentration data were similar to the changes reported in Table 2 and are not shown.

Site and treatment effects. Table 3 shows the mean change in various chemical species concentrations from 1992 to 1996 and the 1996 chemical concentration data for each site. The extractable P concentration in 1996, when averaged across management systems, replications, terraces, and compartments, was significantly greater at Patrocinio than at Ane-i (5.9 vs. 4.3 [micro]g [g.sup.-1]). During the experiment, the increase of extractable P concentration was less at Ane-i (+2.7 [micro]g [g.sup.-1]) compared to Patrocinio (+4.4 [micro]g [g.sup.-1]).

Total C and total N underwent little change in concentration after four years of corn production, but the tendency was for total N to decrease at both sites. Concentrations of extractable Ca, Cu, and Zn increased and Mg decreased during the four year period at both sites. The extractable K concentration increased at Ane-i and decreased at Patrocinio.

Soil management system (treatment) on chemical concentration change was not significant for any species (Table 2). Although the interaction of management with site (s x m) for the various chemical species was significant at various probability levels, it has little relevance to the discussion on terrace and compartment effects.

Terrace and compartment effects. The corn crop for the GCMP and GCRT systems was grown in terraces between adjacent contour grass barrier strips (Figure 1). Effects of terrace (position on the landscape) within management, which is averaged across the five compartments within each terrace for treatments GCMP and GCRT, were significant at the 0.10 probability level for P and Cu concentrations (t/m in Table 2). Of more interest is the interaction of site by terrace within management (s x t/m in Table 2) for C, N, Ca, Mg, and Zn concentrations (P [less than] 0.1 to 0.001).

Measurement of chemical species concentrations within each of the five compartments in a terrace allowed us to examine the "soil fertility" gradient across the terrace. Figures 2-7 show the observed chemical species concentrations in the surface soil (0-20cm depth) versus compartment, that is, across the landscape of the "open field" plots (CMP and CRT) and individual terrace of management with grass barrier strips (GCMP and GCRT).

The total C concentration distributions across the entire plot in 1996 for treatments CMP and CRT, and for individual compartments in terraces 1 (footslope) and 4 (shoulderslope) for treatments GCMP and GCRT, are shown in Figure 2. A gradient in total C existed across the treatments without grass barriers (Figure 2A, 2B). Total C decreased with increase in elevation (increasing compartment number).

When the contour grass strip was combined with contour moldboard plowing, the slope of the regression equation in terrace 1 of GCMP increased to 0.50 (Figure 2C), indicating a greater change in total C concentration across the terrace. For GCMP (Figure 2D), the slope of the equation relating total C concentration versus compartment in terrace 4 of GCMP (Figure 2D) is seven times greater than the slope of the equation for terrace 1, indicating a greater change in total C across the terrace at the higher elevation. The observed relationships suggest that total C concentration changes faster across individual terraces than across open field plots.

Tillage translocation of soil from higher to lower elevations within each individual terrace is likely the major factor affecting this total C distribution. However, surface water runoff also could have contributed to the transport of soil materials and their deposition above the grass strips, but further research on experimental quantification of this water induced soil translocation is needed. Comparison of the regression slopes in Figure 2E and 2F with that in Figure 2B leads to a similar conclusion for GCRT for terrace 1, but not for terrace 4.

Extractable P concentration versus compartment number in 1992 before fertilizer was applied, and again in 1996, are compared for all four systems in Figure 3. In 1992, the P concentration was nearly constant across each plot (CMP and CRT) or terrace (GCMP and GCRT), being [less than or equal to] 2 [micro]g [g.sup.-1] soil. In 1996, the levels were higher, but nearly constant across the CMP and CRT plots (Figure 3A and 3B). For GCMP terraces 1 and 4, the P concentration decreased with increasing elevation.

This 1996 P distribution results from soil translocation of Ap horizon soil material and adsorbed P by tillage from the higher elevation to the lower elevation in each terrace. Even though P was added uniformly for each crop and pruned grasses uniformly spread as mulch across each terrace, the periodic tillage associated with each crop moved P toward the lower elevation, increasing P concentration at compartments 1 and 16 while reducing concentrations upslope. The P concentration in the terraces of treatment GCRT was higher and more variable because the soil was not mixed each year by moldboard plowing.

The relationship between extractable K concentration and compartment for all systems were linear in 1992 and 1996 (Figure 4). In 1996, the negative regression slopes for GCMP were 6-9 times steeper than for CMP (compare Figure 4A, C, D) whereas the negative regression slopes for GCRT in 1996 were about 3-4 times steeper than CRT (Figure 4B, 4E, 4F). The relationships for CRT (1996) and GCRT (terrace 4) were not significant for linear fit. Overall, the same type of relationship observed for P concentration existed for K concentration, although the changes over the four year period were not as great, with the exception of terrace 4 for GCMP and GCRT.

Extractable Ca concentration (Figure 5) in 1996 was greater than in 1992. The concentration decreased with increase in elevation. No differences in slope were found between 1992 and 1996. The extractable Mg concentrations showed no predictable pattern in 1992 or 1996 (data not shown).

The general trend for both Cu (Figure 6) and Zn (Figure 7) was for concentration to increase with increase in elevation in the terraces (GCMP and GCRT) and open fields of CMP and CRT. The higher concentration of Cu and Zn in 1996 compared to 1992 is attributed to the mixing of subsoil rich in these elements with topsoil containing lower concentrations of these elements. The soil Cu and Zn attained higher concentrations in the upper part of the terrace because, as soil was gradually translocated from the upper to lower part of the terrace, more Cu and Zn enriched subsoil was incorporated into the topsoil in the upper portion of the terrace.

Soil acidity. Soil pH in 1996 versus compartment is shown for CMP and CRT in Figure 8A. The relationship for CMP is described by a linear function of compartment, but CRT is not well described by a linear curve. In general, there is a trend for pH to decrease as compartment number (elevation) increases. The pH versus compartment relationship is periodic for GCMP and GCRT (Figure 8C). If, however, we look at compartments within terraces, the relationship is linear (Figure 8B).

The pH shown for the lower compartment identified by "1" is the mean pH value measured for compartments at the lowest elevation (compartments 1, 6, 11, 16) in all four terraces. The pH was lowest for upper compartments (5, 10, 15, and 20 in Figure 8B). All of these compartments are located immediately downslope from the grass strip, and at the highest elevation within each terrace. Loss by downslope translocation of soil with adsorbed Ca and Mg occurred at the upper part of the terrace. In addition, the subsoil with pH 3.6 (Agus et al. 1997) and over 60 % aluminum saturation (Thapa et al. 2000) was incorporated by tillage into the plow layer in the upper area of the terrace as time progressed.

Compartments 1, 6, 11, and 16 (lower part of terrace in Figure 8B), immediately upslope from the grass strips, were depositional areas, which received and trapped soil materials and basic cations moving from the upper area of respective terraces. Soil pH was highest in the lower part of the terraces and in the grass strips (Figure 8D).

To our knowledge, the observed soil acidity increase in the upper portion of an individual terrace has not been considered as a possible factor for yield decline near the contour barrier strips. The soil acidity increase in the surface soil may have secondary effects on nutrient availability and chemical toxicity.

Discussion

Published data on soil nutrient gradients across terraces or broad slopes is rare. In this study, the gradual downslope translocation of soil over a four year period gave rise to concentrations in extractable P, K, and Ca which generally decreased with elevation (increasing compartment number) in the CMP and CRT treatments, and across the terraces of treatments GCMP and GCRT. Agus et al. (1999) reported for a Rhodic Hapludox in the Philippines that a gradient in several soil chemical species was present three to four years after establishing a contour Gliricidia hedgerow system. Extractable P and Ca concentrations and pH decreased with increase in elevation across the terrace, whereas Mg and Al concentrations increased with elevation.

Gradients in several soil physical properties were also reported for the same study (Agus et al. 1997). Soil bulk density was lower and soil transmissivity was higher in the lower portion of terraces compared to the upper portion of terraces. Plant available water retained in the 0-15 cm thick surface layer in a terrace was 0.16, 0.13, and 0.08 [m.sup.-3] [m.sup.-3] for the lower, middle, and upper positions, respectively.

These observed differences in soil chemical and physical properties were ascribed to the formation of terraces between adjacent hedgerows by soil translocation. No soil chemical concentration or physical property data at the beginning of the study were reported. Nevertheless, the reported results for the chemical analyses after four years agree with the results found in the current study.

Garrity et al. (1995) reported from a Senna spectabilis hedgerow study that organic C varied from 1.7% in the upper part of the terrace to 2.8% in the lower part of the terrace. Similarly, concentration of available soil P was twice as high in the lower part of the terrace compared with the upper part. These concentration differences could be explained by soil translocation downslope by intensive moldboard plowing. Once again, the observations agree with those for total C and extractable P measured across the terraces between contour natural grass strips in the present study.

Conclusion

A four year study evaluating four soil management systems for growing corn on sloping, highly acid, P deficient soils was conducted in a Philippine upland. Samples of the surface soil were systematically collected from the bottom to the top of the slope within each experimental plot at the beginning in 1992 and at the end of the experiment in 1996. Analyses of the soil samples showed that chemical species concentration gradients were present in the soil initially, but the gradients intensified for P, K, Cu, and Zn, especially for the systems with moldboard plowed contour grass barriers, during the four year period.

The extractable P concentration gradient became steeper for management systems utilizing grass barriers, with the highest concentrations at the base of the terrace. In general, extractable K and Ca showed the same response, but was not as consistent as for P.

Gradients of extractable Cu and Zn increased during the four year period, but the concentrations were greatest in the upper part of the terrace because the subsoil provided a source of these elements. Finally, pH developed a periodic relationship with distance in the contour grass barrier strip treatments, as a result of translocation of soil calcium from the upper to lower portion of the terrace, and concomitant incorporation of acidic subsoil into the surface soil in the upper portion of the terrace.

We believe that the observed soil fertility gradients that develop across open fields and within terraces between grass barrier strips, and that induce variable rates of crop production, should be considered in the management of these lands for sustainable agricultural production. Currently P fertilizer, if available, is applied uniformly across a terrace.

One possible management scheme might be to apply higher rates of P in the upper part of the terrace than in the lower part of the terrace. Application of P fertilizer in this manner could conceivably increase overall crop production on a terrace without increasing the amount of fertilizer applied based on traditional uniform application. In addition, digging a portion of nutrient rich soil trapped in the grass strips and incorporating it in the upper part of the terrace would enrich the soil. Vegetative residues and pruned grasses used as surface mulch could be added in greater amounts on the upper part of the terrace.

Bir B. Thapa is a researcher in the Department of Crop Science and D. Keith Cassel is a professor in the Department of Soil Science at North Carolina State University. Dennis P. Garrity is an agronomist and coordinator for the Southeast Asian Regional Research Program in Bogor, Indonesia.

REFERENCES CITED

Agus, F., D.P. Garrity, and D.K. Cassel. 1999. Soil fertility in contour hedgerow systems on sloping Oxisols in Mindanao, Philippines. Soil and Tillage Research 50:159-167.

Agus, F., D.K. Cassel, and OP. Garrity. 1997. Soilwater and soil physical properties under contour hedgerow systems on sloping Oxisols. Soil and Tillage Research 40:185-199.

Garrity, D.P., A. Mercado Jr., and C. Salem. 1995. Species interference and soil changes in contour hedgerows planted on inclines in acidic soils in Southeast Asia. Pp. 351-365. In: B.T. Kang et al. (eds). Alley farming research and development. Ibadan, Nigeria: International Institute of Tropical Agriculture.

Govers, G., K. Vandacle, P. Desmet, J. Poesen, and K. Bunre. 1994. The role of tillage in soil redistribution on hillslopes. Europcan Journal of Soil Science 45:469-478.

Kang, B.T. and G.F. Wilson. 1987. The development of alley cropping as a promising technology. Pp. 227-243. In HA. Steppler and P.K.R. Nair (ed.s). Agrofotestry: a decade of development. Nairobi, Kenya: International Council for Research Agroforestry.

Lindstrom, M.J., W.W. Nelson, and T.E. Schumacher. 1992. Quantifying tillage erosion rates due to moldboard plowing. Soil and Tillage Research 24:243-255.

Lindstrom, M. J., W. W. Nelson, T. E. Schumacher, and G. D. Lemme. 1990. Soil movement by tillage as affected by slope. Soil and Tillage Research 17:255-264.

Mehlich, A. 1953. Determination of P, Ca, Mg, K, Na, and [NH.sub.4]. Mimeograph. North Carolina: Soil Test Division.

Lobb, D.A., R.G. Kachanoski, and R.H. Miller. 1995. Tillage translocation and tillage erosion on shoulderalope landscape positions measured using 137Cs as tracer, Canadian Journal of Soil Science 75:211-218.

Murphy, J. and J.P. Riley. 1962. A modified single solution method for the determination of phosphate in natural waters. Analysis of Chemistry 27:31-36.

Nelson, W.L., A. Mehlich, and E. Winters. 1953. The development, evaluation, and use of soil rests for phosphorus availability. Pp 153-188. In: W.H. Pierre and A.G. Norman (eds). Soil and fertilizer phosphorus. Agronomy: a series of monographs. Vol. IV. New York: Academic Press, Inc.

Statistical Analysis Software Institue, Inc. (SAS). 1988. SAS/STATR users' guide. 6.03 ed. Cary: SAS Institute Inc.

Thapa, B.B., D.K. Cassel, and D.P. Garrity. 1999. Ridge tillage and contour natural grass barrier strips reduce tillage erosion. Soil and Tillage Research 51:341-356.

Thapa, B.B., D.P. Garriry, D.K. Cassel, and AR. Mercado. 2000. Contour grass strips and tillage affect corn production on Philippine steepland Oxisols. Agronomy Journal 92: 98-105.

Turkelboom, F., J. Poesen, I. Ohler, K. Van Keer, S. Ongprasert, and K, Vlassak. 1997. Assessment of tillage erosion rates on steep slopes in northern Thailand. Catena 199:1-16.
                       Soil macro and micro element
                   concentrations in January 1996 at the
                    [Ane.sup.-1] and Patrocinio sites.
   Soil         Total     Total        P [+]        K  Ca  Mg Cu  Mn Zn
 Depth cm         C         N
  Ane-i:
            g [kg.sup.-1]       [micro]g [g.sup.-1]
    0-18         19        1.6          2.4         72 680 26  9 135 2.9
   18-50         12        1.0          0.5         31 507 47 25  37 6.9
   50-70          7        0.6          0.5         16 342 61 27  17 8.2
  70-100          5        0.4          0.5         15 255 25 29  14 8.0
Patrocinio:
     0-9         25        2.0          0.6         33 304 80 10 146 3.2
    9-23         23        1.9          0.5         27 197 45  9 127 2.8
   23-38         21        1.8          0.5         10 131 31 15  29 2.5
   38-84          8        0.7          0.5         23 210 40 11 170 5.0
  84-116          6        0.5          0.5         10  76 15 18  24 2.4
(+.)P. K. Ca. Ma. Cu. Mn. and Zn are extractable.
     Mean squares and significance levels for the analysis of variance
        for change in concentrations of total soil carbon and macro
        and micro nutrients in the 0-20 cm depth from 1992 to 1996.
                  Mean Squares
Source of              Df      Total C      Total N        P
Variations
Site (s)               1         0.508 [*]  0.000019 [ns]  207.9 [#]
Replication (r)/s      2         0.022      0.000429        18.1
Soil Management        3         0.063 [ns] 0.000261 [ns]   60.8 [ns]
System (m)
s x m                  3         0.372 [*]  0.001670 [ns]   72.5 [***]
r x m/s                6         0.242      0.001522         7.6
Terrace (t)/m          2         0.053 [ns] 0.000586 [ns]   76.2 [#]
s x t/m                2         0.840 [**] 0.007121 [***]   4.9 [ns]
Compartment           36         0.148 [*]  0.000988 [#]    24.4 [***]
(c)/m x t
s x c/m x t           36         0.076 [ns] 0.000632 [ns]    3.7 [ns]
Pooled error          76         0.133      0.000881        10.769
Source of         K           Ca           Mg           Cu         Zn
Variations
Site (s)          3692.6 [ns] 21137.6 [ns] 8987.9 [***]  9.8 [ns]  16.9 [#]
Replication (r)/s  872.7      17466.8         7.74      22.6        1.3
Soil Management   1099.3 [ns] 10932.9 [ns]  736.4 [ns]   9.2 [ns]   0.8 [ns]
System (m)
s x m             2862.1 [*]  55048.8 [#]   359.7 [*]   22.9 [***]  3.0 [**]
r x m/s            403.7      68906.1        53.83       7.9        1.2
Terrace (t)/m     1047.2 [ns] 47584.7 [ns]  191.9 [ns]  23.2 [#]    1.2 [ns]
s x t/m            650.8 [ns] 68192.2 [#]   665.6 [**]   1.7 [ns]   2.7 [**]
Compartment       1271.9 [**] 63189.1 [**]  304.2 [**]   8.5 [***]  0.8 [ns]
(c)/m x t
s x c/m x t        492.2 [ns] 26068.6 [ns]  107.2 [ns]   2.9 [ns]   0.6 [ns]
Pooled error       834.9      22746.8       116.1        3.5        0.6
The symbols (***.), (**.), (*.) and (#.)indicate significance levels
of 0.001, 0.01, 0.05, and 0.1, respectively
(ns.) = not significant.
               Mean change in chemical species concentration
                from 1992 to 1996 at Ane-i and Patrocinio,
                  Claveria, Philippines. A positive value
                indicates an increase and a negative value
                indicates a decrease in nutrient level from
            1992 to 1996. The 1996 data are given as reference.
                                    Change in
                                  Concentration
Chemical Species                      Ane-i      Patrocinio
Total C (g [kg.sup.-1])              -0.04 a [+]    +1.00 a
Total N (g [kg.sup.-1])              -0.06 a        -0.07 a
Extract. P ([micro]g [g.sup.-1])      +2.7 b         +4.4 a
Extract. K ([micro]g [g.sup.-1])     +11.0 a         -1.0 b
Extract. Ca ([micro]g [g.sup.-1])   +202.0 a       +225.0 a
Extract. Mg ([micro]g [g.sup.-1])     -2.0 a        -18.0 b
Extract. Cu ([micro]g [g.sup.-1])     +1.5 a         +1.3 a
Extract. Zn ([micro]g [g.sup.-1])     +1.4 a         +0.8 b
                                  Concentration in 1996
Chemical Species                          Ane-i         Patrocinio
Total C (g [kg.sup.-1])                  20.4 A             18.5 B
Total N (g [kg.sup.-1])                   1.8 A              1.7 B
Extract. P ([micro]g [g.sup.-1])          4.3 B              5.9 A
Extract. K ([micro]g [g.sup.-1])         91.0 A             46.0 B
Extract. Ca ([micro]g [g.sup.-1])       744.0 B            870.0 A
Extract. Mg ([micro]g [g.sup.-1])        33.0 B             50.0 A
Extract. Cu ([micro]g [g.sup.-1])         8.6 A              5.9 B
Extract. Zn ([micro]g [g.sup.-1])         3.9 A              2.4 B
(+.)Site means that for change in a given chemical species concentrations
followed by the same letter are not significantly different at the
P = 0.05 level. Likewise for chemical species concentrations in 1996.
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Author:Thapa, B.B.; Cassel, D.K.; Garrity, D.P.
Publication:Journal of Soil and Water Conservation
Article Type:Statistical Data Included
Geographic Code:9PHIL
Date:Jan 1, 2001
Words:5606
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