Soil Properties and Nutrient Uptake of Corn-Legumes Intercropping Under Conservation Agriculture Practice Systems (CAPS) in a Sloping Upland Oxisol

Journal of Multidisciplinary Studies Vol. 4, No. 1, pp. 25-49, August 2015 ISSNJournal 2350-7020 of Multidisciplinary (Print) Studies Vol. 4 No. 1, pp. 25-49, August 2015 ISSN 2362-94362350-7020 (Print)(Online) doi:ISSN http://dx.doi.org/10.7828/jmds.v4i1.860 2362-9436 (Online) doi: http://dx.doi.org/10.7828/jmds.v4i1.860

Soil Properties and Nutrient Uptake of Corn-legumes Intercropping Under Conservation Agriculture Practice Systems (CAPS) in a Sloping Upland Oxisol

Apolinario B. Gonzaga, Jr.

University of Science and Technology of Southern Philippines Claveria Campus, Misamis Oriental, 9004 Philippines Corresponding author: Apolinario B. Gonzaga, Jr., email: [email protected]

Abstract

Conservation Agriculture Practice Systems (CAPS) is new agronomic innovation anchored on three main pillars: minimal tillage, continuous mulching and diversified cropping all applied in a simultaneous manner in a cropping season and area. It is a global innovation adapted by major food production countries. However, it is not yet tested under local farming landscape more so in a sloping upland production area. Influence of CAPS on changes in soil properties, nutrient uptake, and soil moisture are critical factors in its long-term sustainability and adoption among local farmers. This study aimed to conduct a field experiment involving different corn-legumes intercropping (cropping system 1 or CS1, CS2, CS3, CS4) and monocrop corn (CS5, control) to evaluate the changes in soil properties, nutrient uptake, and soil moisture in an upland oxisol for two cropping seasons. Key edaphic parameters such as internal nitrogen (N) efficiency, organic matter (OM), organic carbon (OC) and soil moisture content were determined and evaluated. A notable increase in N efficiencies, OM, OC, and soil moisture content measured at different time intervals in corn-legumes systems (corn + Arachis pintoi, corn + Stylosanthes guianensis and corn-cowpea) compared with the control (corn-corn, CS5) was observed. Corn + S. guianensis (CS2) and corn + cowpea (CS3) appeared to have more efficient N absorption trend as compared to other cropping systems imposed. Key findings provided initial merits of adoption of CAPS within the context of productivity, profitability, and soil sustainability in local corn-based farms in sloping uplands.

Keywords: edaphic, farming, nitrogen, productivity, sustainability

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Soil Properties and Nutrient Uptake of Corn-legumes A. B. Gonzaga, Jr. Intercropping Under Conservation Agriculture Practice Systems (CAPS) in a Sloping Upland Oxisol

Introduction

Presently, agriculture needs to produce more from less land area through the most efficient use of natural resources with least possible negative impact on the environment to meet the demands of the growing population. This challenge has become more intense in recent years with the sharp rise in food cost, energy and production inputs, climate change, scarcity of water, degradation of ecosystem services and biodiversity, and financial crisis (Kassam et al., 2012). Dwindling land resources, declining soil fertility and climatic abnormalities attributed to the changing climate will be the main constraints to achieving a sustainable food production. Therefore, strategies must be developed to keep with the demand and overall productivity that is sustainable over the long-term. Conservation Agriculture (CA) refers to the system of raising crops with minimal disturbance to the soil while keeping crop residues on the surface. The Food and Agriculture Organization (FAO) characterized conservation agriculture as a system that maintains a permanent or semi-permanent organic soil cover that can be a growing crop or dead mulch. Its function is to protect the soil physically from sun, rain and wind, and to feed soil biota. It is a new agricultural management system that is gaining popularity in many parts of the world (Hobbs et al., 2008). Moreover, CA aims to conserve, improve and efficiently use more the natural resources such as the soil, water, and biological resources through an integrated management combined with external inputs. It contributes to environmental conservation, as well as to enhanced and sustained agricultural production. Similarly, it is one of the many practices that can sustain agricultural productivity (Hobbs et al., 2008; Derpsch, 2008; Kassam et al., 2012). The practice can also reduce soil erosion effectively (Scopel et al., 2005; Lal et al., 2007; Baldé et al., 2011). It is a system approach to sustainable soil and water conservation, high crop productivity and profitability. Therefore, CA is a system approach to sustainable agriculture (Li et al., 2011). This practice relies on continuous cropping rotation or cropping combination, minimum soil disturbance or tillage and continuous ground cover or

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mulching. It spearheads an alternative no-till agroecological paradigm that is making an increasing contribution to sustainable production intensification (Hobbs et al., 2008; Pretty, 2008; Goddard et al., 2008). In Asia at present, there are still few adopters of CA despite gaining ground as an emerging alternative to conventional tillage-based agriculture worldwide. According to Ella et al. (2012), few countries like Cambodia, Vietnam, China and recently the Philippines conduct research on CA for future adoption. The same authors stated that in the Philippines, no research exists on the soil quality impacts of conservation agriculture in its strictest sense. In the Philippines, the last remaining frontiers for agricultural expansion are the sloping uplands. This ecosystem is fragile and vulnerable with the critical resource. Attributable to the topography, soil erosion is prevalent and excessive. At present, upland areas play a vital role as watersheds in the conservation of water resources and the maintenance of a stable agricultural ecosystem. Upland areas are also the potential expansion areas for agricultural production considering the shrinking agricultural areas due to other uses. The Philippine uplands, which constitute about 10 million hectares, are characterized by sloping and acidic soil in which about 50% of the area is less productive due to soil degradation (Mercado, 2011). Report of the Bureau of Agricultural Statistics showed that in 2014 the agricultural land area of the Philippines totalled to 9,671 million hectares divided into the arable land (4,936 M ha), permanent cropland (4,225 M ha), and forestland (0.7 M ha) (CountryStat Philippines, 2014). Cropping patterns in most sloping uplands are monocropping or multiple cropping of cereals (e.g. corn and rice), root crops (cassava and sweet potato) and vegetables (e.g. tomato, sweet pepper, cabbage, etc.) or combinations of these crops. Corn cultivation is both for food and feed while cassava production constitutes an important staple root crop in sloping farm areas. Both plants demand intensive tillage, heavy external fertilizer application, and other cultural management intensification measures. The challenge for CA for the adoption of local farmers is to evaluate the productivity of the two above-mentioned principal crops cultivated under its pillars. Similarly, CA in the country with its

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Soil Properties and Nutrient Uptake of Corn-legumes A. B. Gonzaga, Jr. Intercropping Under Conservation Agriculture Practice Systems (CAPS) in a Sloping Upland Oxisol integrated components is a new development in crop production. Hence, testing for its adaptability and efficiency in local farming landscapes is essential. This step entails the formulation of CAPS, a tailor-fitted approach for successful adoption and implementation of CA to a particular location. The concept of CA that involves minimal soil disturbance, continuous retention of residue, mulching of soil surface, and diverse and rational use of crop rotations (Erenstein et al., 2008; Sustainable Agriculture and Natural Resource Management Collaborative Research Support Program [SANREM CRSP], 2009) constitute the basis of CAPS. The systems involve optimum seed integration or seedling establishment methods, implement farm selection, crop choice for rotation, suitability of germplasm, management of mulch and fodder, and demand to produce. The systems also involve profitability, nutrient management, farmer preferences and skills, local government policies, credit availability, production inputs, labor, gender, and other various concerns. Without appropriate soil conservation techniques, upland soils become prone to erosion, and could eventually become infertile as production intensifies. Hence, sustainability of the production system, concerning crop and soil productivity, is among the crucial considerations over the long-term. This study determined the changes of soil properties and nutrient uptake of corn-legumes intercropping systems under the CAPS in a sloping upland oxisol in Northern Mindanao. Specifically, the study aimed to evaluate the effect of different cropping systems on soil properties. The paper also determined the nutrient uptake and efficiencies and measured the moisture content of the soil as influenced by the various CAPS. This study also aimed to identify locally-viable conservation agriculture practices suitable for the existing upland crop production areas in Northern Mindanao.

Materials and Methods

Place and time of the study The study area was at Bug-ong, Rizal, Claveria at 8.656550 N 124.862290 E in Misamis Oriental Province of Northern Mindanao, Philippines (Figure 1). The experiment was conducted from

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November 2011 to November 2012. The study duration covered the typical two corn croppings per year in the locality.

= Province of Misamis Oriental, Northern Mindanao, Philippines

= Location of the experimental site

Figure 1. Map showing the locale of the study (Municipality of Claveria, 2003)

Description of the experimental site The sloping upland agroforestry farm currently used as the research site for the World Agroforestry Center (formerly ICRAF - International Center for Research in Agroforestry) was the location of the study (Figure 2). The slope ranges from 20-26% based on clinometer measurement. The site was a former ranching area. Typical native vegetation growing in the landscape before the implementation of the study includes cogon (Imperata cylindrica), “tigbaw” (Saccharum spontanium), “dinog” (Antidesma ghaesembilla) and other grasses and shrubs. The area is a typical upland farm of the country and in most tropical areas in Southeast Asia.

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Soil Properties and Nutrient Uptake of Corn-legumes A. B. Gonzaga, Jr. Intercropping Under Conservation Agriculture Practice Systems (CAPS) in a Sloping Upland Oxisol

Figure 2. The experimental set-up of different conservation agriculture practice systems at Claveria, Misamis Oriental.

The topography as Agus et al. (1999) and Mercado (2007) described in previous studies, ranges from undulating land forms to incised plateau, with an elevation of 350-950 meters above sea level (masl). Around 62% of the total land area is rolling to very steep. The classification of the soil materials is acid upland soils with fine mixed isohyperthermic, Ultic Haplorthox (Mercado, 2007). The major soil series dominating the landscape is Jasaan Series with Jasaan clay loam and Jasaan clay as major soil types. Jasaan Series is under the Order Oxisol. Other Orders found in the area are Inceptisols and Alfisols (Maglinao, 1998). The estimated soil erosion rate in the area is 200-350 mg ha-1 yr-1 (Fujisaka, 1995; Mercado, 2007). Average annual

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precipitation is 3000 mm distributed throughout the year that typically peaks during the months of June and October. An earlier study of Maclean et al. (2002) revealed that the area serves as a representative site of a typical Philippine upland, formerly forested then settled by immigrants from other islands in the Philippines in the late 1940’s following the loggers. Logging and settlers’ semi- shifting cultivation resulted in the conversion of forest into croplands and grasslands. The acid clay, infertile soils (mainly Ultic Haplorthox and Oxic Dystropepts) are friable and of volcanic origin with pH from 3.9 to 5.2. Severe erosion has depleted the topsoil and reduced production potential from agriculture (Maclean et al., 2002). Thus, the foundation for improving crop productivity in this deforested area with high rainfall (2.2 m average) was stabilization of soil erosion. The experimental site plays a crucial role in upper watershed areas for 13 municipalities situated in the lower coastline. The Cabulig River and the watershed system have their origin as well as their tributaries in the uppermost part of the area. The whole watershed landscape has undulating landforms, steep valleys, and deeply incised terrains. The depressed watershed serves as the recipient of all the farming activities in the upper slope. This river and watershed provide both potable and industrial water to at least 13 municipalities situated in the lower part of the province (Australian Centre for International Agricultural Research, 2013). Thus, soil and water conservation measures in the study area will provide significant information and will serve as a model in conservation activities especially in other upland farming areas in the country.

Experimental design and treatments The experiment followed the Randomized Complete Block Design with four replications with the different CAPS plus the conventional method cropping systems used as treatments (CS1 – CS5). A 10 m x 10 m plot area, spaced at 2 m between treatments within a replication and 3 m between replications. There were different cropping combinations imposed by the operating pillars of CAPS, namely: i) minimal soil disturbance, ii) continuous mulching, and, iii) diversified crop rotations, respectively (Figure 3).

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Soil Properties and Nutrient Uptake of Corn-legumes A. B. Gonzaga, Jr. Intercropping Under Conservation Agriculture Practice Systems (CAPS) in a Sloping Upland Oxisol

CS1: Corn + A. pintoi – Corn + A. pintoi CS2: Corn + S. guianensis – Corn + S. guianensis

CS3: Corn + Cowpea – Upland rice + Cowpea

CS4: Corn + Rice bean – Corn + Rice bean CS5: Corn – Corn

Figure 3. Representative experimental plots showing the different cropping systems implemented.

Varieties and species used Planting of hybrid corn (NK Super Jumbo, Syngenta Inc.) in all treatments was done in both cropping seasons. The study used the local varieties of cowpea, rice bean and local sources of Arachis pintoi and Stylosanthes guianensis as associated legumes or living mulches component. Selection of the experimental species was based on the most common variety used by farmers in the locality while the associated

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legumes were primarily selected based on their local adaptability and availability of planting materials.

Nutrient management Fertilizer recommendation applied in all cropping systems was 120-60-60 (N-P2O5-K2O) in both growing seasons following the initial result of the soil analysis conducted before the implementation of the study. Agricultural lime (CaCO3) was applied during the first cropping season at an application rate of 3 t ha-1. Phosphorus (P) and potassium (K) in the form of ammonium phosphate (16-20-0) and muriate of potash (0-0-60) were applied as basal during planting. Nitrogen (N) in the form of urea (46-0-0) was applied at 16-21 and 30-31 days after planting (DAP), respectively.

Harvesting The harvesting of corn on all cropping systems for both seasons was at 110 DAP. The harvest time was during the typical and observed maturity period for corn in the study area. Harvesting of cowpea and rice bean was when the time the pods were mature. Final harvesting of cowpea, rice bean as well as the living mulches was at the end of the cropping season.

Data gathered

A. Soil characteristics Soil and plant tissue analyses. The soil nutrient levels of N, P, K, OM, and the pH were determined before the start of the experiment and every end of a cropping season. Soil samples were sent to the Central Mindanao University Soil and Plant Tissue Laboratory (CMU-SPTL), Musuan, Bukidnon for analysis. Soil pH was determined by 1:5 soil:water. Organic matter was analyzed following the Modified Walkley-Black method while nitrogen was determined by the micro-Kjeldahl method. The Bray No. 2 method and ammonium acetate (NH4OAc) test were used in determining the P and K, respectively.

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Soil Properties and Nutrient Uptake of Corn-legumes A. B. Gonzaga, Jr. Intercropping Under Conservation Agriculture Practice Systems (CAPS) in a Sloping Upland Oxisol

B. Nutrient uptakes and internal efficiencies of nitrogen Total N, P and K uptakes and internal efficiency due to the nitrogen of corn were determined, expressed on a hectare basis in soil samples and plant tissues in all of the cropping system treatments in both cropping seasons. The formula below determined the internal efficiency at harvest or maturity:

IE N

where GY is grain yield and N uptake is nitrogen uptake both expressed in kilogram (kg). According to Fageria and Baligar (2005), Nitrogen Use Efficiency (NUE) in crop plants is defined in many ways. In simple terms, efficiency is the ratio of output (economic yield) to input (fertilizers) for a process or a complex system (Crop Science Society of America, 1992). It has a significant positive association with grain yield in crop plants, which means that improving N use efficiency in crop plants can improve grain yield. Moreover, it can be enhanced by adopting appropriate crop management practices. Nitrogen uptake by corn plants in adequate amount and proportion is paramount for producing higher yields. On similar account, distribution of absorbed or accumulated nutrients in shoot and grain is associated with yield improvement (Fageria & Baligar, 2005).

C. Changes in soil properties Soil analyses determined the dynamics of the key soil properties such as the pH, organic matter, organic carbon, cation exchange capacity, total N, extractable P, exchangeable K, and C:N ratio. Composite samplings were carried out at the start of the first cropping (November 2011), end of the first cropping (May 2012), and end of the second cropping (November 2012). Since the experiment started in October 2010, the soil samples saved from the beginning were analyzed and used as benchmark soil data for the assessment of changes in soil properties due to imposed CAPS.

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The seven-inch probe attached in a time-domain reflectometer (TDR) (Field Scout TDR 300, Spectrum Technologies, Inc.) recorded the soil moisture content measured at 3, 6, 9 and 12 days after a rainfall. This procedure aims to evaluate the efficiency of different cropping combinations in conserving soil moisture. Measurement of soil moisture content was done every cropping season throughout the entire duration of the study. However, during the first cropping, measurements were done only at three and six days after an observed rainfall owing to the most frequent occurrence of rain in the area.

Results and Discussion

Nutrient uptakes Table 1 presents the N, P and K uptake of corn under different cropping systems during the first and second cropping. The NPK uptake (18.03, 3.85 and 16.79 kg kg-1) obtained during the first cropping was substantially higher than NPK (7.44, 1.78 and 5.59 kg kg-1) extracted during the second cropping. Reduction of 58.7 % (N), 53.77 % (P) and 66.70 % (K) was computed from the first season relative to the second cropping season. The fertilizer rate of 120-60-60 (N-P2O5-K2O) applied uniformly in all cropping systems in both seasons was the basis for the computation of the NPK data. During the first cropping, corn + A. pintoi (CS1) quantitatively had the highest NPK uptake (30.07, 5.74 and 28.40 kg kg-1) among cropping systems. On the other hand, corn + cowpea gave the lowest extracted NPK (12.46, 2.36 and 7.78 kg kg-1) among the employed CAPS. During the second cropping, variation between the uptake exists, CS5 (sole corn) had the highest N and K uptake (10.12 kg kg-1 and 8.66 kg kg-1), and CS2 (corn + S. guianensis) had the highest P uptake (2.09 kg kg-1). Similarly, CS4 (corn + rice bean) had the lowest NPK uptake (5.88, 1.36 and 5.08 kg kg-1), respectively. Decreased NPK uptake during the second cropping was probably the main reason for the subsequent decline of GY in that season.

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Soil Properties and Nutrient Uptake of Corn-legumes A. B. Gonzaga, Jr. Intercropping Under Conservation Agriculture Practice Systems (CAPS) in a Sloping Upland Oxisol

Table 1. Nutrient uptake (kg kg-1) of corn as influenced by cropping systems during two cropping seasons.

Nutrient uptake First cropping Second cropping Cropping system T N T P T K T N T P T K

% % % % % %

Corn + A. pintoi – Corn + A. pintoi 30.07 5.74 28.40 8.78 1.96 6.02 Corn + S. guianensis – Corn + S. guianensis 19.03 4.54 14.49 6.36 2.09 4.23 Corn + Cowpea – Upland rice + Cowpea 12.46 2.36 7.78 6.09 1.59 3.96 Corn + Rice bean – Corn + Rice bean 10.69 2.17 13.26 5.88 1.36 5.08 Corn – Corn 17.94 4.44 20.03 10.12 1.89 8.66

Internal efficiency of nitrogen Table 2 presents the internal efficiency of N in corn grown under different cropping systems. Internal efficiencies obtained higher values during the first cropping compared to the second cropping season. The lower internal efficiency of N in corn in the second cropping was attributed to the lower grain yield as well as NPK uptakes in the test crops’ dry matter.

Table 2. Internal efficiency of nitrogen in corn grown under different ccropping systems.

Internal efficiency of nitrogen (kg kg-1)

Treatment First cropping Second cropping

IE N % N IE N % N (kg kg-1) Rec (kg kg-1) Rec

Corn + A. pintoi – Corn + A. pintoi 51.03 0.43 38.31 0.32 Corn + S. guianensis – Corn + S. guianensis 68.08 0.57 38.73 0.32 Corn + Cowpea – Upland rice + Cowpea 65.79 0.55 39.30 0.33 Corn + Rice bean – Corn + Rice bean 57.52 0.48 32.85 0.27 Corn – Corn 56.21 0.47 46.21 0.39

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Internal efficiency reflects the amount of N absorbed in plant tissues as a proportion of the applied and indigenous N, hence the greater the amount, the more efficient an individual system. The result revealed that among CAPS, corn + S. guianensis (CS2) and corn + cowpea (CS3) appeared to have more efficient N absorption trend as compared to other cropping systems. However, N efficiency obtained was higher during the first cropping compared to the second cropping. This condition also resulted in a better yield on the first cropping than the second cropping period. Grain yield and N uptake in corn tissue constitute the basis of internal efficiency of N determined at maturity. There is a relationship between N efficiency and yield which indicates that higher efficiency would likely result in greater yield (Fageria & Baligar, 2005). The result of this study showed that corn monocrop at second cropping had the highest internal efficiencies among the various cropping system treatments. However, its value failed to reflect the obtained grain yield of that specific treatment.

Changes in soil properties due to varying cropping systems Table 3 presents the changes in soil properties due to varying cropping systems. There were changes to the pH, organic matter, organic carbon, and cation exchange capacity of soils during the two cropping seasons. Soil pH. Soil pH of plots planted to CS1, CS2, CS3 and CS4 apparently improved after two croppings (one-year cycle) from extremely acidic to strongly acidic while the soil pH in corn monocropping (CS5) continued to decrease. The addition of organic matter and prevention of leaching of soil nutrients from these treatments with sufficient soil cover as manifested by CAPS treatments can be attributed to the improvement of soil pH (Erenstein et al., 2008). In contrast, corn monocrop (CS5) had only adequate soil cover during the period of standing crop but with bare soil after the harvest period. The sloping area with high to very high annual rainfall (>2000 mm) further aggravated this condition. Leaching of nutrients and continuous monocropping are known to decrease soil pH or induce soil acidity (Cosico, 2005).

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Table 3. Soil pH, organic matter (OM), organic carbon (OC), and cation exchange capacity (CEC) of soils as influenced by cropping systems during two cropping seasons.

OM OC CEC pH (%) (%) (me/100g) Treatment Percent Percent Percent Percent Initial Final Initial Final Initial Final Initial Final change change change change

CS1 4.01 4.14 3.24 5.18 4.86 -6.18 3.01 2.82 -6.31 24.59 33.98 38.19

CS2 4.77 5.07 6.29 4.22 5.75 36.26 2.45 3.34 36.33 26.38 26.09 -1.10

CS3 4.00 4.64 16.00 5.05 5.18 2.57 2.93 3.01 2.73 21.40 29.57 38.18

CS4 4.01 4.41 9.98 4.22 4.60 9.00 2.45 2.67 8.98 24.78 32.48 31.07

CS5 4.18 4.14 -0.96 4.66 4.47 -4.08 2.71 2.60 -4.06 23.93 30.69 28.25

August 2015 Initial - before first cropping season Final - after second cropping season

CS1 = Corn + A. pintoi – Corn + A. pintoi CS2 = Corn + S. guianensis – Corn + S. guianensis CS3 = Corn + Cowpea – Upland rice + Cowpea CS4 = Corn + Rice bean – Corn + Rice bean CS5 = Corn – Corn

Soil Properties and Nutrient Uptake of Corn-legumes A. B. Gonzaga, Jr. Intercropping Under Conservation Agriculture Practice SystemsJournal of (CAPS) Multidisciplinary in a Sloping Studies Upland Vol. Oxisol 4 No. 1, pp. 25-49, August 2015

Organic matter and carbon. Cropping systems with Conservation Agriculture Practices (corn with legume intercrops) have a higher percent OM than the corn monocropping (CS5) in four sampling periods (S0-S3). Among the cropping systems, corn + A. pintoi (CS1), corn + S. guianensis (CS2) and corn + cowpea (CS3), respectively showed to conserve OM within two cropping. There is a need to validate further such results over the long-term. Meanwhile, the trend of soil organic carbon (OC) based on cropping system treatments showed a similar pattern with OM considering both parameters are highly related. Different cropping systems intercropped with associated or living legumes have higher percent OC as compared with monocrop corn. This result implies the potential of legumes intercropped with corn in the maintenance of organic matter, either as cover crops that prevent the adverse impacts of high rainfall or through the addition of litter fall that subsequently becomes part of OM pool in the soil or combinations of both factors. However, this trend is limited to the upper 0-30 cm of the soil where composite samplings were done. Cation exchange capacity. The experimental site has CEC ranging from 21.4 to 26.66 me/100g soil at the start of the first cropping that increased (23.75-33.98 me/100 g soil) after the second cropping period. The CEC values ranged from medium to high since typical soils have lowered values of 10-30 me/100 g soil or higher. The inherent high clay content of the Jasaan series (Oxisol) and its organic matter content attribute to this relatively high CEC (Agus et al., 1999). Comparably, there was a considerable increase in CEC in most CAPS treatments as compared to the corn monocrop (CS5). However, there was a decrease in CEC in corn + S. guianensis (CS2, -1.09%). Among CAPS, corn + A. pintoi (CS1) and corn + cowpea (CS3) had the highest CEC increased (38.18%). Cation exchange capacity increased after two cropping seasons, but the study cannot yet establish the influence of OM on CEC in only two cropping seasons. Theoretically, increased in OM can enhance CEC (Cosico, 2005). However, it is important to note that CEC is a stable soil property while OM is highly variable. Tillage, cropping systems, slope, and degree of soil erosion are known to affect OM content (Derpsch, 2008).

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Soil Properties and Nutrient Uptake of Corn-legumes A. B. Gonzaga, Jr. Intercropping Under Conservation Agriculture Practice Systems (CAPS) in a Sloping Upland Oxisol

Soil nutrients (NPK) Total nitrogen. Table 4 presents the changes in NPK levels after two seasons of cropping with varying cropping systems. Total nitrogen in soil increased in most of the corn-based treatments. Corn intercropped with legumes had a 26-31% increase, while a 46% increase in the monocrop corn was observed. The absence of competition from other associated crops, as seen in the treatments with intercrops can attribute to the higher observed increment in total N in pure corn (CS5). Similarly, NPK uptakes also showed almost the same trend among various cropping systems. Several workers reported that legumes intercropped with cereals can increase N absorption by the cereals (Corre-Hellou & Crozat, 2005; Hauggaard-Nielsen et al., 2003). The study of Jensen (1996) suggested that the advantage of legume- cereal intercropping is mainly the complementary use of soil mineral N. Extractable phosphorus. Extractable P increased in all cropping systems, except corn + S. guianensis (CS2) which decreased by 76%. The increasing trend in soil P could be due to the application of P2O5 fertilizer to the main crop (corn) and the possibility of residual considerations, the rates of P fertilizer application, and crop uptake. Exchangeable potassium. Exchangeable K decreased after two seasons in all of the corn cropping in the system treatments, except for corn + rice bean (CS4), having a slight increase of 8%. In CS4, the small increase in exchangeable K probably was the result of the residual effect of applied K fertilizer just superimposed on this treatment. Hence, the rest of the treatments have a decreasing trend of K. C:N ratio. The ratio reflects the rate of organic matter decomposition wherein the higher C/N ratio may imply a slower decomposition rate of soil OM. High C:N also indicates that N could be temporarily immobilized or unavailable for crop uptake. A medium level of C:N ratio was 11-20 among the cropping system treatments and decomposition of residues (corn biomass) was near the optimum level of 20/1 C:N ratio.

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Table 4. Total nitrogen, extractable phosphorus, exchangeable potassium, and C:N ratio of soil as influenced by cropping systems during two cropping seasons.

Total N,% Extr. P,% Exch. K C:N Ratio (ppm) Treatment Initial Final Percent Initial Final Percent Initial Final Percent Initial Final Percent change change change change

CS1 0.19 0.25 31.58 1.29 6.02 366.67 45.00 33.00 -26.67 15.49 11.48 -25.89

CS2 0.19 0.25 31.58 8.24 1.98 -75.97 45.00 30.00 -33.33 12.62 13.59 7.69

CS3 0.17 0.22 29.41 4.59 13.92 203.27 36.00 30.00 -16.67 17.44 13.67 -21.62

CS4 0.19 0.23 21.05 1.83 26.40 1342.62 39.00 42.00 7.69 12.65 11.48 -9.25

CS5 0.14 0.21 50.00 2.36 3.34 41.53 84.00 39.00 -53.57 19.04 12.55 -34.09

Initial - before first cropping season Final - after second cropping season

CS1 = Corn + A. pintoi – Corn + A. pintoi CS2 = Corn + S. guianensis – Corn + S. guianensis CS3 = Corn + Cowpea - Upland rice + Cowpea A. B.Gonzaga,Jr. CS4 = Corn + Rice bean - Corn + Rice bean CS5 = Corn - Corn

Journal of Multidisciplinary Studies Vol. 4, No. 1, pp. 25-49, August 2015

Soil Properties and Nutrient Uptake of Corn-legumes A. B. Gonzaga, Jr. Intercropping Under Conservation Agriculture Practice Systems (CAPS) in a Sloping Upland Oxisol

The C:N ratio decreased in all cropping systems after the two cropping seasons except in CS2. This result could be due to the incorporation of low-quality corn stover, with a typical C:N ratio of 50/1 (Cosico, 2005). Conversely, the decrease could be due to the high- quality residues from associated legumes that probably help reduce the C:N ratio, therefore, avoiding the potential temporary N immobilization by microorganisms (Sakala et al., 2000; Adu-Gyamfi et al., 2007). Grasses have higher C:N ratio than legumes (Thorup-Kristensen, 1994). The decreasing trend of C:N in almost all treatments can be due to the effect of component legumes wherein the added N in their biomass seems to have decreased the C:N ratio of most of the treatments.

Soil moisture content Figure 4 presents the water-holding capacity of the soil, measured as the residual soil moisture in various cropping system treatments. During the first cropping, residual soil moisture within three and six days after a rainfall decreased in all corn-based cropping systems. However, there was good water retention (conservation) in corn + S. guianensis (CS2). For the second cropping, residual soil moisture was retained within 3-12 days after rainfall in most cropping system treatments. The time of taking the measurement (early morning) could probably attribute to the increased residual soil moisture in all treatments by the 9th day after the rainfall. Studies of Doanh and Tuan (2008) and Kassam et al. (2012) indicated that soil cover or living mulches helped maintained moisture content in the surface especially during dry days of the growing period of the crop. At the 12th day after the rainfall, there was a reduction in soil moisture with levels similar to the level on all the corn-based cropping systems and the monocrop corn at three days after rainfall. Hence, the assumed depth was only about 12 cm soil layer across all treatments. Rainfall intensity during the first cropping (1,592.9 mm) was slightly lower than during the second cropping season (1,676.8 mm). In this study, the various cropping systems employed across seasons influenced the dynamics of soil properties. The different cropping systems imposed mostly changed the soil pH, % OM, % OC and soil water-holding capacity. Based on analyses, these parameters

42 Soil Properties and Nutrient Uptake of Corn-legumes A. B. Gonzaga, Jr. Intercropping Under Conservation Agriculture Practice SystemsJournal of (CAPS) Multidisciplinary in a Sloping Studies Upland Vol. Oxisol 4 No. 1, pp. 25-49, August 2015

increased, and the based treatments have shown to affect these parameters positively compared to the pure corn treatment (CS5). Other parameters such as CEC, NPK, and C:N ratio decreased. Findings of Ella et al. (2012) also showed similar trend on the influence of several legumes utilized as living mulches.

15 Soil moisture, Soil moisture, %

0 3 6 3 6 9 12 First Cropping Second Cropping

Days after rain

Corn + A. pintoi – Corn + A. pintoi Corn + S. guianensis – Corn + S. guianensis Corn + Cowpea – Upland rice + Cowpea Corn + Rice bean – Corn + Rice bean Corn – Corn

Figure 4. Soil moisture content at varying days after rainfall as influenced by cropping systems during two cropping seasons.

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Soil Properties and Nutrient Uptake of Corn-legumes A. B. Gonzaga, Jr. Intercropping Under Conservation Agriculture Practice Systems (CAPS) in a Sloping Upland Oxisol

Cropping systems with associated legumes have shown to enhance positive influence on soil properties. Based on the results, CS2, CS3, and CS4 appeared to have shown sustainability characteristics as compared to other treatments. However, there is a need to validate further the results over a long term since only two cropping seasons were considered in this study.

Conclusion and Recommendations

Changes in key soil properties due to the various cropping systems imposed were observed especially for percent OM and OC. Internal efficiencies of N also differed between cropping systems and seasons. Among CAPS, corn + S. guianensis (CS2) and corn + cowpea (CS3) appeared to have more efficient N absorption trend as compared to other cropping systems. Further, corn + A. pintoi (CS1), corn + S. guianensis (CS2) and corn + cowpea (CS3), respectively showed to conserve OM within two croppings. Corn-legumes appeared to have increased the soil parameters measured. Based on the results, the potential of corn-legumes intercropping imposed as CAPS could be a viable alternative to pure corn system in sloping upland production areas in Northern Mindanao. However, results obtained from this study are still inconclusive owing to the time element involved. Hence, results could not yet establish as attributable to specific CAPS employed. The locally accepted legumes such as mung bean, peanut and soybean should be potential in the future cereal-legume association. These legumes are known to adapt well to local growing condition and in association with other crops.

Acknowledgment

This study is supported by the Department of Science and Technology (DOST) through the Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development (PCAARRD). The author is also indebted to SANREM and ICRAF for administrative and logistical support and to the USTSP Administration for the completion of this research activity.

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