Agronomy Journal Grow Your Career With ASA
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (13)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Jeranyama, P.
Right arrow Articles by Harwood, R. R.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Jeranyama, P.
Right arrow Articles by Harwood, R. R.
Agricola
Right arrow Articles by Jeranyama, P.
Right arrow Articles by Harwood, R. R.
Related Collections
Right arrow Economics
Right arrow Other Cropping Systems
Right arrow Crop Systems
Right arrow Soil Fertility and Productivity
Agronomy Journal 92:239-244 (2000)
© 2000 American Society of Agronomy

INTEGRATED AGRICULTURAL SYSTEMS

Relay-Intercropping of Sunnhemp and Cowpea into a Smallholder Maize System in Zimbabwe

Peter Jeranyamaa, Oran B. Hestermanb, Stephen R. Waddingtonc and Richard R. Harwooda

a Dep. of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824 USA
b IFS Program, W.K. Kellogg Foundation, One Michigan Ave. East, Battle Creek, MI 49017 USA
c CIMMYT-Zimbabwe, P.O. Box MP 163, Mt. Pleasant, Harare, Zimbabwe

rharwood{at}pilot.msu.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
The rising real prices of purchased inputs is driving smallholder maize (Zea mays L.) production towards lower levels of inorganic fertilizer. Legume intercrops are a source of plant N that can be produced locally and offer a practical complement to inorganic fertilizers. Field experiments conducted on a loamy sand (Typic Kandiustalf) soil evaluated the impact of relay-intercropping two legume crops, cowpea (Vigna unguiculata L.) and sunnhemp (Crotolaria juncea L.) into smallholder maize in Zimbabwe. The objectives were to quantify: (i) biomass and N yield of intercropped legumes, (ii) the impact of the legumes on companion maize yield and N uptake, and (iii) the response of a subsequent maize crop to legumes. Dry matter yield ranged from 0.6 to 4.6 Mg ha-1 for cowpea and 0.9 to 2.9 Mg ha-1 for sunnhemp, over two years. At the most, cowpea and sunnhemp produced 154 and 82 kg N ha-1, respectively. Companion maize grain yields were not reduced when the legumes were relay-intercropped into maize fertilized at 0 to 60 kg N ha-1. However, maize yields were reduced 18 to 31% when maize + legume intercrops were fertilized at 120 kg N ha-1. In the subsequent year, maize grain yields were increased by 8 to 27% following maize + legume when no fertilizer N was applied, compared with maize following maize. Legumes reduced fertilizer needs of a subsequent maize crop by 36 kg N ha-1. Intercropped annual legumes and small amounts of inorganic fertilizer offers a strategy to meet the N needs on smallholder farms.

Abbreviations: PAR, photosynthetically active radiation • RCBD, randomized complete block design • FRV, fertilizer replacement value


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 
DECLINING maize yields in the smallholder subhumid cropping systems of northern Zimbabwe present the need to develop a more sustainable production system. At current fertilizer costs, most smallholders in sub-humid Zimbabwe grow maize with little N–P–K fertilizer. Maize dominates the cropping system, although some grain legumes, particularly groundnut (Arachis hypogaea L.), are grown as loose rotations with maize (Metelerkamp, 1988). Maintaining maize production in these southern African smallholder systems will require using inorganic fertilizers in combination with a range of available organics such as cattle manure, miombo leaf litter, herbaceous legume plant residues, and compost (Kumwenda et al., 1996; Waddington and Heisey, 1997; Snapp et al., 1998). Legume intercrops are potential sources of plant nutrients that complement/supplement inorganic fertilizers. Legume intercrops are included in cropping systems because they reduce soil erosion (Giller and Cadisch, 1995), suppress weeds (Exner and Cruse, 1993), and fix biological N (Giller et al., 1994). In addition, certain legume crops can provide food to humans and or livestock. The integration of small amounts of inorganic fertilizer N along with organic material and N from annual legumes offers a strategy to meet the N needs of smallholder farms (Waddington and Heisey, 1997).

Legume green manures are not new to the region. They were heavily researched in Zimbabwe from the 1920s to 1940s (Metelerkamp, 1988), and large-scale commercial farms (the second sector in a dichotomous agriculture) used green manures widely. There were informal reports that some smallholders used some green manures such as sunnhemp to maintain soil fertility (Hikwa et al., 1998). This practice continued until the cost of inorganic fertilizers fell in the 1950s and green manures became uneconomical (Tattersfield, 1982). Rising real prices of inorganic fertilizers in the 1990s and concerns about the sustainability of current smallholder cropping systems have renewed interest in green manures and related legume technologies (Hikwa and Mukurumbira, 1995).

There is a potential to integrate more legumes in the existing cropping systems as intercrops because growing sole legume crops or green manures in fallow has been rejected by smallholders due to labor and land constraints (Kumwenda et al., 1996). If legumes are intercropped in a timely manner, competition with the maize crop for light, water, and nutrients can be minimized while legume herbage N can be accumulated and production increased. If food legumes are not to be a net drain on N from the system, those with a low N harvest index (N in harvested grain per unit total above-ground N), such as indeterminate types of cowpea, will be most valuable, as they are associated with less N removal from the field in harvestable grain. A relay-intercropped legume is not likely to directly benefit the companion maize crop, but has potential to increase the yields of a subsequent maize crop (Jeranyama et al., 1998). In Zimbabwe there have been few studies on soil fertility effects of intercropping annual legumes with maize (Natarajan and Shumba, 1990). Recent work by Muza, reported in Giller et al. (1998), showed that both cowpea and sunnhemp sown 28 d after maize can produce large amounts of biomass without reducing the yield of the companion maize crop.

The objectives of this study were to: (i) quantify legume herbage biomass and N accumulation of food and forage legumes relay-intercropped into maize; (ii) evaluate the impact of relay-intercropped legumes on the companion maize crop; and (iii) determine the response of a subsequent maize crop to relay-intercropped legumes and compare this with the response to fertilizer N.


   Materials and methods
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
Results and discussion
 Conclusions
 REFERENCES
 
This study was conducted over three years (1996–98) on the Agricultural, Technical and Extension Services (AGRITEX) training center farm at Domboshava (elevation approx. 1500 masl), 31 km north east of Harare in a sub-humid unimodal rainfall zone. The field has a Typic Kandiustalf loamy sand soil that is moderately fertile but shows good response to the application of N fertilizer. Soil properties were characterized at the beginning of the study in 1996 (Table 1) .


View this table:
[in this window]
[in a new window]
  		Table 1 Soil properties at the beginning of study at Domboshava, Zimbabwe, 1996

 
Maize (3-way cross hybrid R215) was hand-planted in late November or early December at two seeds per hill on tractor disc-plowed land. Designated plots received 22 kg N ha-1, 28 kg P ha-1, and 19.5 kg K ha-1 applied as Compound D (8–14–7 N–P–K) before planting. Also, an unfertilized plot was maintained as a control in each replication. Additional fertilizer as NH4NO3 was applied to designated plots as a surface dollop next to each station about 48 d after planting (V6 growth stage of maize; Ritchie et al., 1993) when the soil moisture level in the ground was at field capacity, so that each replication had plots with 0, 60, and 120 kg N ha-1. Maize plant spacing was 0.9 m between rows and 0.5 m within rows giving a population density of 44444 ha-1; each plot was 10 m by 6.4 m.

Weeds were removed manually whenever necessary. Cowpea (a food legume) and sunnhemp (a forage legume) were relay-intercropped into maize (two legume rows between adjacent maize rows) in 1996 and 1997. Legumes were planted as relay intercrops at about 28 d after planting maize (V4–V6 stage) (Ritchie et al., 1993) in pre-assigned plots. Legumes were seeded at in-row spacings of 0.1 m and 0.3 m away from the adjacent maize row, achieving a plant population density of 111000 plants ha-1. The legume seeds were not inoculated with Rhizobia before planting, which corresponds to local farmers' practice. Also, an unfertilized sole maize plot was included in each replication as the control.

Above-ground herbage biomass of legumes was estimated at 45, 60, and 75 d after planting from plant samples harvested from one 0.09 m2 quadrat per plot. Weeds were hand separated from legumes and legume herbage was dried at 60°C for at least 3 d to determine dry matter yield.

Photosynthetically active radiation (PAR) was measured using an LI-191SA Line Quantum Sensor meter (LI-COR, Inc., Lincoln, NE) in 1997 at 50 and 75 d after planting the legume. Readings were taken just above the maize canopy, just above the understory legume, and at the ground level under the legume.

Maize grain was harvested from a 1.8 m by 4 m section of the center two rows in each plot so that the area harvested was 7.2 m2. Grain yields were adjusted to 125 g kg-1 moisture content. To express yields as dry matter per hectare, maize stover was harvested from a single center-most row in a 0.9 m by 4 m section and dried at 60°C for at least 48 h.

In the subsequent year, maize following maize + legume intercrops was established on the same plots. This crop was fertilized with 0, 46, 92, and 138 kg N ha-1 in two split applications. At planting, 22 kg N ha-1 was applied as Compound D and the balance at the V6 growth stage (Ritchie et al., 1993) in the form of NH4NO3 in all plots except the control.

Plant and Chemical Analysis
Total N in maize grain, stover, and above-ground legume biomass was determined by a modified micro-Kjeldahl method. Dry plant materials were ground in a Wiley mill (Thomas Scientific, Swedesboro, NJ) to pass through a 2-mm screen. Plant samples of 0.1 g were digested in 4 ml of 18 M H2SO4 with 1.5 g K2SO4 and 0.075 g Se catalyst. Following digestion, total NH+4 was determined by spectrophotometry. Total N yield was calculated as the product of dry matter yield and N concentration.

Statistical Analysis
In the relay-intercropping year, the experiment was planted as a randomized complete block design (RCBD) with treatments replicated three times. Analysis of variance was used to analyze treatment differences for grain yield, total above-ground biomass, grain N content, and total N uptake of maize.

Legume above-ground biomass was analyzed as a repeated measures experiment with a first order auto-regression correlation type [AR(1)] over sampling periods in Proc Mixed of SAS (SAS Institute, 1997). Due to a significant (P <= 0.05) three-way interaction of legume x N applied x sampling period, a reduced model of herbage biomass and N yield was used within a sampling period. In the reduced model, legume above-ground biomass and N yield were analyzed as a RCBD, with treatments replicated three times.

In the subsequent year, the experiment was a RCBD with a split-plot arrangement, replicated three times. The first year cropping system (maize + first-year N or maize–legume + first-year N) were whole plots and second-year N rates were subplots. Analysis of variance using Proc GLM (SAS, 1997) was used to identify treatment effects. Responses to N fertilizer rate in the second year were determined by evaluating linear and quadratic trends from single degree of freedom comparisons. Whenever trends were significant, regression equations were calculated to determine FRVs of relay-intercropped legumes in the preceding year.


   Results and discussion
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
Conclusions
 REFERENCES
 
Legume Above-Ground Biomass
A significant legume x nitrogen interaction was observed in both years for above-ground biomass and N yield. Hence, legumes herbage biomass (as dry matter) and N yields are presented separately for each N rate (Table 2) . Above-ground biomass ranged from 0.6 to 4.6 Mg ha-1 for cowpea and from 0.9 to 2.9 Mg ha-1 for sunnhemp. These biomass yields are similar to those recorded with pigeon pea (Cajanus cajan L.) when grown alone (Kwatpata, 1984) and when intercropped with maize in Malawi (Sakala, 1994).


View this table:
[in this window]
[in a new window]
  		Table 2 Effect of fertilizer N on intercropped legume above-ground dry matter, DM and N yield at 75 days after planting in 1996 and 1997 in Domboshava, Zimbabwe

 
Response of legumes to N fertilizer was determined by evaluating linear and quadratic trends from single degree of freedom comparisons. In 1996, only sunnhemp was linearly related to N applied. Sunnhemp herbage biomass yield was positively correlated (r = 0.55, P <= 0.1) with N rate. However, cowpea and N applied were not significantly correlated (P <= 0.1), but herbage biomass was lowest at the maximum N applied (Table 2). Differences in response by the two species are mainly due to different growth habits. Cowpea will be more shaded by the high N rate maize, but sunnhemp grows up (erect) into the maize canopy and intercepts more light. In 1997, both cowpea and sunnhemp linearly responded to N applied and were negatively correlated with N rate (r = -0.55 for cowpea and r = -0.41 for sunnhemp, P <= 0.1). Above-ground biomass yield tended to decline with increase in N rate (Table 2).

The negative correlation of herbage biomass to applied N could be explained by the direct effects of shading from the maize crop on dry matter production by the legume. Because dry matter production in crops depends on the efficiency of PAR (Biscoe and Gallagher, 1977), shading of the legume understory resulted in low herbage biomass. In this study, PAR recorded in 1997 shortly before tasselling was 87, 78, and 61% for understory legume in maize–legume intercrops fertilized with 0, 60, and 120 kg N ha-1, respectively (data not shown). The PAR recorded indicated some shading in the understory legume at 120 kg N ha-1.

Legume Nitrogen Yield
Legume N yields ranged from 15 to 154 kg N ha-1 for cowpea and 23 to 82 kg N ha-1 for sunnhemp (Table 2). Giller et al. (1994) have shown that tropical legumes grown as sole crops can often accumulate 100 to 200 kg N ha-1 in 100 to 150 d. The range of N yields reported in our study are somewhat lower, partly because the legumes were intercropped and allowed to grow for a maximum of only 75 d. Legume N yields in intercrops are usually lower than those from sole legumes because intercrops occupy less land area and are subject to competition for resources, particularly for light, from the taller cereal crop (Nambiar et al., 1983).

In 1997, N yields of cowpea and sunnhemp were negatively correlated to N rate (r = -0.56 for cowpea and -0.52 for sunnhemp, P <= 0.1). Giller and Cadisch (1995) reported a decrease in N2 fixation by legumes due to excessive plant-available N. Our results suggest that N yields are reduced in the presence of an increased inorganic N pool and due to the shade effects by maize grown at high N rates (>60 kg N ha-1). Furthermore, Eaglesham et al. (1983) concluded from pot studies that fertilizer N applications in excess of 25 kg N ha-1 would be likely to inhibit N fixation of cowpea under field conditions.

Relay-Intercropped Maize Yields
Due to a significant cropping system x nitrogen rate interaction, data are presented as response of maize to cropping system and fertilizer N. Because legume x nitrogen interactions were not significant, and main effects of cowpea and sunnhemp were not significantly different, data were averaged across the two legumes.

Relay-intercropping of cowpea and sunnhemp into maize fertilized with zero or 60 kg N ha-1 was not associated with a significant maize grain yield reduction (Table 3) . However, relay-intercropping legumes into maize fertilized with 120 kg N ha-1 resulted in significant maize grain yield reductions of 18% in 1996 and 31% in 1997 (Table 3) compared with unfertilized sole maize, due to competition effects between fast-growing and well-fertilized legume crop and revenue maize crop.


View this table:
[in this window]
[in a new window]
  		Table 3 Effect of fertlizer N on grain yield and grain N uptake of maize grown alone (-L) or intercropped with legumes (+L) in 1996 and 1997 at Domboshava, Zimbabwe

 
Results for zero and 60 kg N ha-1, which are representative of the range of N rates that smallholders in Zimbabwe often use, suggest that legumes could be relay-intercropped into maize without reduction in maize grain yields. In our study, the yields were slightly improved at these N rates, although not significantly so. Also, our results are similar to those of Haizel (1974), who worked with maize–cowpea, and Andrews (1972) and Rees (1986), who worked with sorghum–cowpea intercrop systems. In these studies, neither maize nor sorghum yield suppressions or increases were observed.

Maize grain yield reductions at 120 kg N ha-1 likely resulted from competition for nitrogen by the legume. Lack of maize response to higher N rate in 1996/97 was due to incessant and excessive rainfall (758 mm) received especially in the months of January and February. The maize grain yield reduction of 18 to 31% when maize was relay-intercropped with legumes in our study corresponds to those by other researchers reporting declines in unfertilized maize yields when intercropped with cowpea of 31% (Haizel, 1974) and 18% (Ofori and Stern, 1987). However, unfertilized maize yields have been increased in some studies by 11% (Agboola and Fayemi, 1971) and 45% (Remison, 1978) in maize–cowpea intercrop systems in West Africa.

Maize Grain Nitrogen Uptake
Maize grain N uptake was similar or slightly greater with the intercrop than with the control (sole maize) when no N fertilizer was applied (Table 3). At 60 kg N ha-1, intercropped maize was associated with a significantly higher grain N uptake in 1996. Although in 1997, grain N uptake for maize with legume intercrop had a numerically low uptake, this was not significantly less than that of sole maize when no fertilizer was applied. At 120 kg N ha-1, grain N uptake in the intercrop system was reduced by 13% in 1996 and 34% in 1997 (Table 3).

In cereal–legume intercropping, the legume component is capable of fixing atmospheric N2 under favorable conditions and this is thought to reduce competition for N with the cereal (Trenbath, 1976). In the absence of an effective N2–fixing system, both the cereal and intercropped legume compete for available soil N (Ofori and Stern, 1987). Giller and Cadisch (1995) state that in the presence of adequate to excessive soil N, legumes switch off N2 fixation and use the readily available soil N. This theory seems to adequately explain the grain N uptake pattern in our study. Our results suggest that the legumes were actively fixing N2 when plots were unfertilized or fertilized with 60 kg N ha-1, but N2–fixation was reduced at the higher N rate (120 kg N ha-1). Decreased N2 fixation resulted in competition for soil N, hence the lower maize grain N uptake.

Subsequent Maize Response to Legume and Fertilizer Nitrogen
Maize Yields: No Nitrogen Applied
There was no significant legume x nitrogen fertilizer interaction on subsequent maize grain yield, grain N uptake, and total above-ground biomass. Therefore, data presented are means of two legumes (cowpea and sunnhemp). Most studies of maize–cowpea intercropping conducted in Zimbabwe have not assessed an effect in a subsequent year, in spite of reporting either an intercrop advantage (e.g., Mariga, 1990) or disadvantage (Natarajan and Shumba, 1990) in the intercropping season. Our study is an attempt to provide an assessment on effects of intercropped legumes in the subsequent season.

Maize following maize + legume intercrop was associated with a positive yield response (8–27%) (Table 4) . In 1997, grain N uptake by maize following the maize + legume intercrop was significantly higher (83%) than that of maize following maize alone (Table 4). Total above-ground biomass was not significantly affected by the presence of a legume from the previous season in 1997, but in 1998 total above-ground biomass of maize following the maize + legume intercrop produced a 42% significantly higher biomass than that of maize following a sole maize crop (Table 4).


View this table:
[in this window]
[in a new window]
  		Table 4 Percent grain yield, grain N uptake, and total aboveground biomass of non-N fertilized maize following maize + legume intercrop, relative to a monocropped maize in sequence at 100% in two years at Domboshava, Zimbabwe

 
Maize yield improvements of 33% following pigeon pea in Malawi (Kwatpata, 1984) and 21% following sunnhemp in Tanzania (Temu, 1982) have been reported. Agboola (1980), working with one season fallows of pigeon pea, mucuna (Calopogium mucunoides L.), and cowpea in a sub-humid province of Nigeria, reported increases of subsequent maize crop yields of 10 to 30%.

Maize Response to Fertilizer and Legume Nitrogen
There was a positive response of maize grain yield, grain N content, and total above-ground N uptake to fertilizer N (Table 3) and legume from the previous year (Table 4). Fitted regression equations were calculated for maize grain yield, grain N content, and total N uptake as a function of fertilizer N applied (Table 5) . However, in the second season (1998) following maize + legume intercrops the maize crop did not respond to incremental fertilizer N. Therefore, fitted regression equations are from one season.


View this table:
[in this window]
[in a new window]
  		Table 5 Regression equations for maize grain yield (GR), grain N content (GRN), total above-ground biomass (TDM), and total N in above-ground biomass (TN) as a function of fertlizer N applied (x) in the subsequent year (maize + legume–maize) in Domboshava, Zimbabwe

 
Maize grain yields were greater at all fertilizer N levels following a maize + legume intercrop compared with continuous maize, but not significantly so at the highest N level. Maximum yield benefits of the maize + legume intercrop in the subsequent year appeared to be realized when maize was fertilized with 46 to 92 kg N ha-1, while at higher N levels diminishing returns were apparent.

Fertilizer Replacement Values
For the cropping systems under study to be acceptable to both the farmers and researchers, there must be a convincing yield or N uptake improvement in the subsequent year, with no yield reduction in the intercropping season. One way to assess improvements in the subsequent year is to evaluate FRV. A FRV is the quantity of fertilizer N required to produce a yield in a crop that does not follow a legume that is identical to the yield produced by incorporation of the legume (Giller et al., 1994). For a FRV to be valid, yield of a subsequent crop following the legume should be significantly higher than that of the nonlegume control (Jeranyama et al., 1998).

Highest FRVs were calculated based on grain N content and the lowest on grain yield (36 kg N ha-1 based on maize grain N content and 18 kg N ha-1 based on maize grain yield). Because the lowest FRV of 18 kg N ha-1 was obtained with grain yield, this suggests modest residual N benefits derived from the cropping system. Singh (1983) estimated N benefits to subsequent cereal crops after cereal–legume intercrops. Nitrogen fertilizer equivalents of 3 kg ha-1 with soybean, 31 kg ha-1 with greengram (Vigna radiata L. Wilcz.), 46 kg ha-1 with grain cowpea and groundnut, and 54 kg ha-1 with forage cowpea were reported.


   Conclusions
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
REFERENCES
 
Legume above-ground biomass and N yield of intercropped legumes were influenced by N application. A high fertilizer N rate (120 kg ha-1) was associated with decline in legume biomass and subsequent N yields compared with 60 kg N ha-1, except for sunnhemp in 1996.

Companion maize grain yields were not reduced when legumes were relay-intercropped into maize, either fertilized with 60 kg N ha-1 or not fertilized. However, at 120 kg N ha-1, yields were reduced by 18 to 31%. Also, grain N uptake was not reduced at zero or 60 kg N ha-1 applied in the intercropping system but was reduced by 13 to 34% at 120 kg N ha-1.

In the subsequent year, maize grain yields were increased by 8 to 27% following legume intercrops compared with continuous maize. Maize grain N uptake following the maize + legume intercrop was increased by 83%. Legume intercrops could reduce fertilizer needs of the subsequent maize crop by 18 to 36 kg N ha-1.

This research suggests that annual herbaceous legumes have a unique niche in smallholder farms in Zimbabwe. If they are relay-intercropped into moderately fertilized (60 kg N ha-1 or less) maize the yields of companion maize can be maintained, while subsequent maize crop yields may be enhanced.

Received for publication June 4, 1999.
   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Conclusions
 REFERENCES
 




This article has been cited by other articles:


Home page
 Agron. J.Home page
C. M. Cherr, J. M. S. Scholberg, and R. McSorley
Green Manure Approaches to Crop Production: A Synthesis
Agron. J., February 7, 2006; 98(2): 302 - 319.
[Abstract] [Full Text] [PDF]

Home page
 Agron. J.Home page
K. S. Balkcom and D. W. Reeves
Sunn-Hemp Utilized as a Legume Cover Crop for Corn Production
Agron. J., January 1, 2005; 97(1): 26 - 31.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (13)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Jeranyama, P.
Right arrow Articles by Harwood, R. R.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Jeranyama, P.
Right arrow Articles by Harwood, R. R.
Agricola
Right arrow Articles by Jeranyama, P.
Right arrow Articles by Harwood, R. R.
Related Collections
Right arrow Economics
Right arrow Other Cropping Systems
Right arrow Crop Systems
Right arrow Soil Fertility and Productivity

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Crop Science Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome