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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 5, Num. 2, 1997, pp. 201-207
African Crop Science Journal
Vol.5. No.2, pp. 201-207, 1997


Effect of incorporating Cassia siamea prunings on maize yield in an alley cropping trial in semiarid Kenya


Kenya Forestry Research Institute (KEFRI), P.O. Box 20412, Nairobi, Kenya
^1 Soil Science Department, Egerton University, P.O. Box 75, Njoro, Kenya
^2 TTMI Project, Crop Science Department, University of Nairobi, P.O. Box 30197, Nairobi, Kenya
^3 TTMI Project, Department of Meteorology, Wageningen Agricultural University, Duivendaal 2, 6701 AP Wageningen, The Netherlands
^4 Forestry Department, Moi University, P.O. Box 3900, Eldoret, Kenya

(Received 29 November, 1995; accepted 30 April, 1997)

Code Number: CS97026
Sizes of Files:
    Text: 22.6K
    Graphics: Line drawings (gif) - 10.8K 


The influence of soil-incorporated Cassia siamea prunings on nutrient status of maize leaves, grain and yield was studied in an alley cropping experiment in semiarid Machakos, Kenya, during the 1988 long and short rainy seasons. The trial was established in 1983 and in all the seasons Katumani composite B maize was sown, except in the short rains of 1988 when Hybrid 511 was planted. Plots consisted of 3 cropped alleys between cassia hedges spaced at 3.6 m apart. The hedges were lopped at the beginning of every season (on-set of rains) and the prunings incorporated into the alleys one day before maize seeds were sown. The control plots had no hedges and hence no prunings were incorporated. Incorporation of prunings into the soil increased nutrient concentration in the maize leaves, grains and soil in the treatment plots compared to the controls. Maize grain yield on a per row basis was also higher in the plots that received prunings application compared to the controls. However, on an area basis, the yield increase was insufficient to compensate for the area lost to the Cassia siamea shrubs.

Key Words: Agroforestry, hedge row intercropping, cassia shrubs


L'impact des emondes de Cassia siamea inorpores dans le sol sur la production et la composition minerale des feuilles de mais et des grains a ete etudie dans une experimentation de culture en couloirs. Celle-ci a ete organisee en region semi-aride de Machakos au Kenya pendant les grandes et petites saisons pluvieuses de 1988. L'essai a ete mis en place en 1983. Chaque saison, le compose B du mais connu sous le nom de Katumani etait serre, sauf pendant les petites saisons pluvieuses de 1988 lorsque l'hybride 511 etait plante. Les parcelles etaient constituees de 3 allees cultivees entre les haies de cassia distantes entre elles de 3.6 m. Les haies etaient elaguees au debut de chaque saison pluvieuse. Les emonoles etaient ensuite incorporees dans les allees un jour avant la semence des graines. Les parcelles de contr“le n'avaient pas de haies; les emondes n'y etaient donc pas incorporees. L'incorporation des emondes dans le sol des parcelles de traitement augmentait la teneur des elements mineraux nutritifs dans les feuilles et les grains de mais. Cela n'etait donc pas le cas dans les parcelles de contr“le. La production des grains de mais par rangee s'est egalement averee plus importante dans les parcelles ou les emondes ont ete appliquees que dans celles de contr“le. Cependant, en terme de surface la croissance de la production etait insuffisante pour pouvoir compenser la perte de la surface due a la presence des arbustes de Cassia siamea.

Mots Cles: Agroforesterie, culture en cauloir, arbustes de cassia


The major constraints to food production in semiarid areas of Kenya include low and unreliable rainfall, low soil organic matter and low usage of soil inputs. Repetitive maize/bean intercroping has led to degradation And impoverishment of soils in these areas, resulting in very low crop yields. At times total crop failure, necessitating expensive famine relief intervention, has been experienced (mungai, 1992).

Traditionally, farmers mainly relied on long fallow periods to regenerate the fertility of land exhausted by cropping. This is, however, no longer possible due to increased population pressure. Other alternative measures to improve soil fertility are therefore urgently needed in these regions. Inorganic (chemical) fertilizers have been used successfully to improve crop yields in many parts of the world, but high costs and unavailability of these fertilizers at the required time limit their use by small farmers in the semiarid areas and indeed in many parts of the developing world (fao, 1990; vlek, 1990). Application of cattle manure could be another alternative for soil fertility improvement in these regions. However, the quantities produced and applied are too low to be effective (batiano and Mokwunye, 1991). Agroforestry has been proposed as one alternative low cost technology for soil and crop yield improvement in these areas. According to Nair (1984), it has the most apparent potential in marginal and in

resource-limited smallholder systems where monocultural agriculture or forestry may not be feasible or even desirable.

One form of low input agroforestry system that has been introduced in the semiarid areas of Kenya is hedgerow intercropping (alley cropping), which involves growing arable crops in between hedgerows of established shrubs (Wilson and Kang, 1991). Periodic pruning of the shrubs provide organic materials which serve as a source of nutrients for crops. The work reported here assessed the influence of soil incorporated Cassia siamea prunings in an alley cropping trial and their effects on maize nutrients and yields.


The study was conducted at the Katumani National Dryland Farming Research Centre (NDFRC) site (approximately 1 degree 3's, 37 degrees 15'e; altitude, 1560 m). The climate of the area is sub-humid to semiarid (Sombroek et al., 1982). Details have been summarised by Kibe et al. (1981) and Mugendi et al. (1994). The rainfall distribution at the site for the period January 1988 to May 1989 is shown in Table 1. This covers two rainy seasons, the Long Rains of 1988 (LR 88) (March-June) and the Short Rains of 1988/1989 (SR 88) (October-January).

TABLE 1. Monthly average rainfall (mm) for the experimental site in 1988 and 1989

Month      1988       1989    
January    144.3     127.2
February    28.9       9.1
March      125.7      86.2
April      263.9     134.2
May         15.1      61.9
June        10.8
July         0.2
August       6.1
September   24.7
October     31.8
November   147.7
December   208.7

The experimental layout had been designed and established earlier under the Dryland Agroforestry Research Project (DARP) (Mugendi et al., 1994). The trial was laid out in a completely randomised design with 3 treatments (2 treatments of within row cassia shrub spacing of 0.25 and 1.0 m and a control without trees) each replicated four times (results reported in this paper concentrated on the 0.25 m tree spacing treatment compared to the control). Plot dimensions were 10 x 10.8 m. The treatment plots consisted of 3 alleys between cassia hedges spaced at 3.6 m. Maize was sown at a spacing of 90 x 30 cm. This constituted a total of 9 maize rows in the treatment plots and 13 in control plots (each hedgerow in the treatment plot was replaced by a row of maize in the control plot). The hedges therefore occupied approximately 30% of the cropland. In the LR 88 (and in previous seasons) Katumani composite B maize was sown; in the SR 88, Hybrid 511 was mistakenly planted due to mixing up of seed.

At the beginning of every season, Cassia siamea prunings were lopped and immediately incorporated into the soil using hand hoes at the on-set of rains. Maize seeds were then sown approximately a day after the prunings had been incorporated (no inorganic fertilizer was applied to any of the plots). Twenty maize leaves from each plot were randomly sampled at the end of tasselling period close to cob setting. The leaves sampled were those opposite the cob. Maize grain yield was determined on per row basis after the crop was harvested and threshed. Twenty grain subsamples (approximately a hundred grains) from each plot were sampled for nutrient analysis after threshing. Also, twenty soil samples from the 0-20 cm depth were sampled at the end of the SR 88 growing season. Nutrient concentrations in plant material, maize grain and soil (N, P, K, Mg and Ca, and pH and C for soil) were determined following the methods outlined by Anderson and Ingram (1993). Grain yield and nutrient concentration data were subjected to ANOVA using SAS (1988) programme. Means were declared different at P<0.05.


Nutrient composition of maize leaves.

Maize leaves from the treated plots (where prunings were incorporated) had a significantly higher % concentration of all the nutrients than the untreated plots in both seasons (Table 2). The highest percentage increase was recorded for K followed by Mg in the LR 88 while Ca had the highest increase followed by Mg in the SR 88 season.

TABLE 2. Mean nutrient composition of maize leaves (%)

Season                 N        P        K       Ca       Mg
        Treatment    3.72a    0.28a    1.75a    0.98a    0.38a
LR 88   Control      3.12b    0.24b    1.25b    0.78b    0.28b
        % Increase  19.2     16.7     40.0     25.6     35.7
        Treatment    2.46a    0.17a    2.02a    0.44a    0.23a
SR 88   Control      2.21b    0.14b    1.82b    0.28b    0.17b
        % Increase  11.3     21.4     11.0     57.1     35.3
LR 88 and SR 88 = Long and Short rain seasons of 1988
Means followed by the same letter within a column for a particular season are not different (P<0.05)

Nutrient composition of maize grains.

Mean nutrient composition of maize grains for the two seasons of 1988 are presented in Table 3. As in the case of the maize leaves (Table 2), the grains had a higher concentration of nutrients in those plots that received prunings as compared to those that did not. All differences were significant except for Ca in the SR 88 season. The highest percentage increase recorded was for K and P during the LR 88 season and for Mg during the SR 88 season.

The results further indicated that there were some genotypic differences between the treated and control plots in terms of the nutrient concentration in the two maize grain cultivars. The percentage increases of all the nutrients except Mg were smaller for the Hybrid maize (SR 88) compared to the Katumani composite B (LR 88) (Table 3).

TABLE 3. Mean nutrient composition of maize grains (%)

Season                 N        P        K       Ca      Mg
        Treatment    1.47a    0.18a    0.22a    0.18a    0.14a
LR 88   Control      1.22b    0.14b    0.17b    0.16b    0.12b
        % Increase  20.5     28.6     29.4     12.5     16.7
        Treatment    1.53a    0.22a    0.23a    0.17a    0.13a
SR 88   Control      1.41b    0.19b    0.20b    0.16a    0.11b        
        % Increase   8.5     15.8     15.0      6.7     18.2
LR 88 and SR 88 = Long and Short rain seasons of 1988
Means followed by the same letter within a column in a particular season are not different (P<0.05)

Soil nutrient status.

Soil sampled at the end of the SR 88 growing season (Table 4) indicated that there was an overall increase in nutrients (including pH and organic carbon content) in the plots that received prunings compared to the controls.

TABLE 4. Mean nutrient composition of soil (0-20 cm depth) at the end of short rain 1988 season

             pH       N       C         K      Ca    Mg            P
            ---------------------     ----------------------     -----
                    in %                 in cmol/kg              mg/kg    
Treatment   6.2a    0.08a   0.82a      0.71a   5.79a   1.84a     18.0a
Control     6.0b    0.06b   0.60b      0.56b   3.38b   1.08b     12.1b
% Increase  3.3    33.3    36.7       26.8    71.3    70.3       49.0
Means followed by the same letter within a column are not different (P<0.05)

Maize grain yield.

Maize yields were compared on a per row basis (kg/row) for the two seasons. Rows in the treatment plots were compared with identical rows in the control plots. The results indicated that the treated plots significantly out-performed the control plots (3.1 vs 2.4 kg/row) by approximately 32% for the LR 88 and by 12% for SR 88 (4.3 vs 3.8 kg/row) (Fig. 1). Hybrid 511 maize (SR 88) did better than Katumani B composite (LR 88); however, the smaller difference (12%) of the Hybrid maize compared to Katumani (32%) was due to a greater increase in the Hybrid controls of 62% when the LR controls (Katumani) were compared to the SR controls (Hybrid). The treated plots for the same seasons on the other hand increased only by 38%. Thus, the yields in the control plots increased more than those of the treatment plots when the LR and SR were compared.

    Figure 1 - Maize grain yield (kg/row) for the two seasons of 1988 at Machakos, Kenya.

The two maize rows (eastern and western) next to the cassia hedge performed better than the middle row with the eastern row out-performing the western row in both seasons (Fig. 2).

    Figure 2 - Maize grain yield (kg/row) for the 3 maize rows inside the Cassia alleys.


Hybrid 511 that was planted in the SR 88 season is a longer maturing variety compared to the Kkatumani B composite and is usually grown in the wetter areas. The rainfall received during this season was, however, higher (515 mm) than the normal average for the area (350 mm), and was also well distributed throughout the growing season (Table 1). This ensured that the hybrid maize grew to maturity and yielded well (produced approximately 4 Mg/ha of grain as opposed to the 2 Mg/ha for Katumani composite). Though the hybrid did better than the Katumani composite in terms of total yields, the controls of the hybrid increased more than the treatments when the LR and SR were compared. The hybrid was apparently able to exploit the control area more effectively while in the treated plots competition with Cassia siamea hedges diminished that advantage.

Since the hedges occupied approximately 30% of the cropland, alley cropped treatments should have produced more than 30% yields compared to the controls to be able to compensate for the cropping area lost to the trees. Unfortunately, in our present study, the yields for the LR just managed to break-even (32% increase of the treated plots over the controls), whereas the SR 88 season difference of 12% was not sufficient to compensate for the land lost. The relative advantage of prunings application did not therefore make up for the area occupied by the hedges. The small amount of prunings incorporated into the soil during the two seasons (1.8 and 1.2 Mg/ha for LR and SR seasons, respectively (Mugendi, 1991), as opposed to the 8-10 Mg/ha production reported in the humid tropics (Young, 1989)) was too little to bring about appreciable differences between treated and control plots. The low biomass production and competition for water and nutrients (that usually exceeds the beneficial fertility effects) have been cited as some of the major drawbacks limiting the potential of alley cropping in semiarid areas (Jama and Nair, 1995; Sanchez, 1995).

The two maize rows (eastern and western) next to the cassia hedge performed better than the middle row with the eastern row out-performing the western row in both seasons (Fig. 2). This phenomenon that had also been observed in other previous seasons could be explained by the soil temperature distribution profiles that precisely followed this yield pattern (eastern < western < middle) (Mungai, 1992). Another factor contributing to this phenomenon was the slope aspect. The trial was located on a gentle slope running on a west-east direction. The hedges therefore acted as barriers trapping soil, nutrients and water thereby benefiting the crop at the lower level immediately above the hedge (eastern row) (Mugendi, 1991).

Soil data collected at the end of the SR 88 growing season (Table 4) revealed an overall increase in nutrients in the plots that received prunings compared to those that did not. The results corroborates those of Yamoah et al. (1986) and Kang et al. (1990) who reported that soil applied prunings resulted in increased soil organic matter and higher N, P, K, Ca and Mg.

The study indicated that using Cassia siamea loppings as green manure could improve the yields (on a per row basis) and the nutrient levels of the soil and accompanying maize crop. However, when the total area was taken into account, the relative advantage of application of prunings did not compensate for the area occupied by the hedges. This was due to low biomass production of the shrubs and competition for water and nutrients between cassia hedges and maize crop in the system. Because of these factors, the advantages of alley cropping in semiarid areas, aimed at sustainably increasing yields, appears not as promising as in the more humid areas.


The authors are grateful to the International Development Research Dentre (IDRC) of Canada for providing the bulk of financial support to this research. The work was a supportive study to Ph.D. research within the Traditional Techniques of Microclimate Improvement (TTMI) project, funded by the Netherlands government. Support from the Kenya Forestry Research Institute (KEFRI) and the International Centre for Research in Agroforestry (ICRAF) is greatly acknowledged. The authors are also grateful to Ir. F.C.T. Guiking, Wageningen Agricultural Aniversity, for his advice on sampling techniques prior to the start of this research. The comments of the anonymous reviewers are greatly appreciated.


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Copyright 1997 The African Crop Science Society

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