 |
| About Bioline | All Journals | Testimonials | Membership | News |
|
||||||
|
||||||
Vol.5. No.2, pp.175-188, 1997 Response of castor cultivar "Hale" to rate and method of nitrogen fertilizer application in different environments of Zimbabwe
D. HIKWA and L.M. MUGWIRA
Agronomy Institute and Chemistry and Soil Research Institute
(Recieved 7 February, 1995; accepted 25 March, 1997)
Code Number: CS97023
Sizes of Files:
Text: 48.6K
Graphics: Line drawings (gif) - 9.7K
ABSTRACT
The effects of different rates and methods of N fertilizer application were assessed at five sites over two seasons (1987/88 and 1988/89). Fertilizer rates of 0, 30, 60, 90 and 120 kg N ha^-1 were applied in a single dose at planting or in two splits, half applied at planting and the other half as topdressing at primary floral initiation. The sites at Makoholi, Mlezu and Matopos were on sandy soils in low rainfall areas while those at Kadoma and Panmure were in sandy clay loam soils in higher rainfall areas. There were significant interactions between N rate and season on seed yield in the sandy soils except at Makoholi. The effect of N rate on these parameters contrasted at each site between the two seasons, indicating that the amount of N fertilizer needed for castor (Ricinus communis L.) on the sandy soils depended on the amount of rainfall. Application of N in a single dose did not significantly increase seed yield when available soil N was medium to high (> 24 ppm) except at Kadoma where application of 30 kg N ha^-1 increased yield when soil N status was rated as medium. Yield responses to N applied at planting in 1987/88 at Matopos and Panmure and in 1988/89 at Makoholi and Mlezu indicated that 60 kg N ha^-1 was the optimum application rate for castor. When compared to a single dose, splitting N application enhanced its effectiveness in increasing yield in 1987/88 at Mlezu and Matopos, and at Kadoma in two seasons. These results suggest that split N applications are beneficial to castor when seasonal rainfall is greater than 700mm.
Key Words: Nitrogen rate, rainfall, Ricinus communis L., soil type
RESUME
Les effets de differentes proportions et methodes d'application d'engrais azote ont ete evalues dans cinq stations au cours des saisons 1987/88 et 1988/89. Les proportions du fertilisant de 0, 30, 60, 90 et 120 kg de N ha^-1 ont ete utilisees. Elles ont ete appliquees soit a dose unique aux plantes et l'autre a dose dedoublee dont une partie aux plantes et l'autre a l'initiation de l'epanouissement floral primaire. Les stations de Makoholi, Mlezu et Matopos etaient situees sur des sols sablonneux dans des regions a faibles precipations. Celles de Kadoma et de Panmure etaient, par contre, situees sur des sols sablo-angileux dans des regions a fortes precipitations. Les interactions entre la teneur en N et la sason sur la production des graines se sont sevelees hautement significatives dans des stations a sols sableux sauf a Makoholi. L'effet de la teneur en N sur ces parametres variait a chaque site en fonction de la saison. Cela monre que la quantite d'engrais azote souhaitable pour la poivriere (Ricinus communis) sur des sols sablonneux est fonction de la quantite de pluies. L'application de N a dose unique n'a pas augmente de facon significative la production des graines lorsque l'azote disponible du sol etait de moyenne a eleve (> 24 ppm) sauf a Kadoma. Dans ce dennier cas, l'application de 30 kg de N ha^-1 augmentait la production quand le statut de l'azote du sol etait considere comme moyenne. Les reponses de la production a l'azote applique aux plantes en 1987/88 a Matopos et Pammure et en 1988/89 a Makoholi et Mlezu a montre que 60 kg de N ha^-1 etait la proportion optimale pour la poivriere. Contrairement a la dose unique, le dedoublement de l'application de l'azote a accru son efficacite. La production a donc augmente a Mlezu et Matopos en 1987/88 et a Kadoma au cours des deux saisons. Ces resultats montrent bien que les applications de l'azote a dose dedoublee sont benefiques a la poivriere loisque les precipations saisonnieres sont superieures a 700mm.
Mots Cles: Proportion d'azote, precipitations, Ricinus communis, type de sol
INTRODUCTION
The castor plant (Ricinus communis L.) is native to the tropics, including Zimbabwe. Castor grows in soils of wide ranging fertility, but varieties of the species may respond differently in growth and yield to similar levels of nutrients (Weiss, 1983). This necessitates determination of soil nutritional levels for each variety that are needed to produce the maximum yield at economic levels of fertilizer input.
Nitrogen is one of the limiting nutrients for crop production in most soils. According to Weiss (1983), excessive nitrogen tends to promote vegetative growth of castor, while reducing resistance to drought. Insufficient nitrogen may culminate in stunted plants, firing of older leaves and premature senescence, thereby reducing yield. Research work on fertilizer requirements of castor in Zimbabwe conducted for two seasons in Matabeleland and Midlands Provinces showed overall seed yield increases of between 23 and 45% and between 30 and 60 %, when 14 and 29 kg N ha^-1 were applied, respectively (Donovan and Landsberg, 1963). Elsewhere, seed yield increases have been reported with applications of up to 90 kg N ha^-1 (Muthuvel et al., 1987; Saran and Giri, 1987; Rao and Ventateswarlu, 1988).
The information base on fertilizer requirements of castor under various Zimbabwe conditions is inadequate and needs to be broadened. Determination of optimum levels of specific fertilizer nutrients such as nitrogen and phosphorus is imperative. Exploratory field experiments of 1986/87 had shown that there were hardly any interactions between N and P applied, while responses to N application were apparent (Agronomy Institute, 1991). Since castor is a long season crop, there was need to compare effects of single dose to split N application on performance of the crop. Therefore, the objective of this study was to assess how spliting N application compared to a single dose application impacted on performance of castor, particularly seed yield.
MATERIALS AND METHODS
The experiment was conducted during the 1987/88 and 1988/89 seasons in fields at Matopos Research Station (Matopos), Mlezu Agricultural Institute (Mlezu), Cotton Research Institute (Kadoma), Panmure Experiment Station (Panmure) and Makoholi Experiment Station (Makoholi). The Matopos, Mlezu and Makoholi locations were on medium-grained granitic sands with 8% clay and more than 85% sand, while the Kadoma and Panmure locations were in medium-grained sandy clay loam soils with 20-40% clay and less than 45% sand (Chemistry and Soil Research Institute, 1989). Selected soil test values on these sites are shown in Table 1. Matopos and Makoholi are in Natural Region (NR) IV, with a long term mean annual rainfall of 570 and 650mm, respectively, Mlezu is in NR III with a range of annual rainfall between 675 and 700mm, whereas Kadoma and Panmure are in NR IIb, with a long term mean annual rainfall of 726 and 721 mm, respectively. The location elevations are 1204, 1200, 1338, 1157 and 881 metres above sea level for Makoholi, Mlezu, Matopos, Kadoma and Panmure, respectively (Whingwiri et al., 1987). TABLE 1. Available nitrogen, phosphorus and potassium in soils at the different sites in 1987/88 and 1988/89
-------------------------------------------------------
Location pH^1 Mineral N^2 P^3 K
(ppm) (ppm) (me/100 g soil)
--------------------------------------------------------
1987/88
Makoholi 4.8 18 VL 19 A 0.08
Mlezu 4.9 32 M 16 A 0.23
Matopos 5.0 35 M 15 A 0.26
Kadoma 6.2 44 H 16 A 0.27
Panmure 5.5 21 L 16 A 0.36
1988/89
Makoholi 4.8 17 VL 22 A 0.07
Mlezu 4.7 15 VL 5 D 0.09
Matopos 4.9 21 L 11 MR 0.12
Kadoma 6.3 30 M 11 MR 0.19
Panmure 5.4 24 L 14 A 0.17
Legend:VL = Very low, D = Deficient, L = Low , MR = Marginal, M =
Medium, A = Adequate , H = High (Chemistry and Soil Research Institute ,
1989)^1 A 0.01M CaCl2 solution (1:5 soil: solution ratio) was used in determination of pH. ^2 Soil N after laboratory incubation for 14 days ^3 Resin extractable P --------------------------------------------------------------------------- The N rates studied were 0, 30, 60, 90 and 120 kg ha^-1, applied as ammonium nitrate (34.5% N). These rates were based on results of an exploratory field experiment on both heavy and light sandy soils (Agronomy Institute, 1991) which showed responses of N up to 120 N ha^-1 at the same locations. The nitrogen applied at each rate was either a single dose at planting or was split, with half applied at planting and the other half as top-dressing at primary floral initiation. Uniform dressings of 100 kg ha^-1 of single superphosphate (8% P, 12% S) and 50 kg ha^-1 potassium chloride (50% K) were applied at planting at all locations in both seasons. The open pollinated dwarf-internode cultivar "Hale," developed in the USA, was used.
A factorial combination of treatments in randomised complete blocks (RCB) design with four replicates was used. A gross plot consisted of five 10m long rows, spaced at one metre apart with an in-row spacing of 0.5 metres. The net plot, from which seed yield was estimated, comprised three middle rows of 8.5m long. The average number of racemes per plant was based on a mean of five plants randomly selected in the net plot. Days to maturity of the primary racemes were estimated at about 80% physiological maturity of the plants in the plot. Analysis of variance (ANOVA) was performed on the data.
Daily rainfall amounts were monitored and recorded using a rain gauge at each site (Figs. 1 and 2).
Figure 2 - Cumulative precipitation (mm) in five day periods (pentads) from Nov. 1 - April 30 at the five sites in 1988/89 season. RESULTS
Overall, the 1987/88 season was wetter than the 1988/89 one at all sites. The cumulative rainfall amounts received in 1988/89 season were 44, 58, 46, 41 and 28 % less than those received in 1987/88 at Makoholi, Mlezu, Matopos, Kadoma and Panmure, respectively (Figs. 1 and 2). Table 2 shows the amount of rainfall accumulated at intervals from November 1 to planting date, flowering and crop maturity.
TABLE 2. Rainfall amounts accumulated between the periods November 1 and planting date, flowering and crop maturity in both seasons
------------------------------------------------------------------------
Interval From Nov.1 Makoholi Mlezu Matopos Kadoma Panmure
------------------------------------------------------------------------
1987/88
Planting date 48.0 49.0 34.0 34.0 58.0
Flowering 261.0 292.0 289.0 481.0 341.0
Maturity 558.0 775.0 736.0 780.0 747.0
1988/89
Planting date 5.0 32.0 53.0 12.0 12.0
Flowering 84.0 131.0 332.0 153.0 202.0
Maturity 327.0 318.0 412.0 530.0 727.0
--------------------------------------------------------------------------
Effects of applied N rate and season. There were significant effects of interactions between the rate of N applied and season on number of days to physiological maturity and on seed yield at Mlezu and Matopos, and on days to physiological maturity at Makoholi (Tables 3, 4 and 5). Although there were no significant interaction effects, the average number of racemes/plant were 18, 15 and 10 % less in 1988/89 than in 1987/88 at Mlezu, Kadoma and Panmure, respectively. At Matopos, 20 % more racemes/plant were attained in 1988/89 season. At Makoholi, the difference in number of racemes between the two seasons was negligible (Tables 3, 4 and 5).
Makoholi. At Makoholi, plants took an average of 41 days longer to mature in the wetter 1987/88 than in the drier 1988/89 season. In 1987/88, no marked differences in duration to maturity among the N rates were observed at this site. However, in 1988/89, the plots with zero N rate had the shortest (P<0.01) duration to maturity when compared to the plots where N was applied (Table 3). TABLE 3. Effects of interactions between N rate and season on average number of racemes/plant, days to maturity and seed yield (kg ha^-1) in 1987/88 and 1988/89 seasons at Makoholi
---------------------------------------------------------------------------
Nitrogen Racemes/plant Days to maturity Seed yield, kg ha^-1
rate ----------------- ------------------- --------------------
(kg ha^-1) 1987 1988 Mean 1987 1988 Mean 1987 1988 Mean
/88 /89 /88 /89 /88 /89
---------------------------------------------------------------------------
0 4.9 4.9 4.9 202 151 176 1 338 615 977
30 6.0 6.7 6.4 199 158 178 1 218 729 973
60 5.1 6.0 5.6 200 161 180 1 149 867 1008
90 6.6 5.9 6.2 199 158 178 1 304 802 1053
120 8.5 6.5 7.5 198 164 181 1 516 867 1193
Mean 6.2 6.0 6.1 199 158 179 1 306 776 1041
SEm SEm SEm
Interaction means 0.7 1.4 127.4
Season means 0.3 0.6 57.0
N Means 0.5 1.0 90.1
SEm = Standard Error of mean
---------------------------------------------------------------------------
TABLE 4. Effects of interactions between N rate and season on average number of racemes/plant, days to maturity and seed yield (kg ha^-1) in 1987/88 and 1988/89 seasons at Mlezu
---------------------------------------------------------------------------
Nitrogen Racemes/plant Days to maturity Seed yield, kg ha^-1
rate ----------------- ------------------- --------------------
(kg ha^-1) 1987 1988 Mean 1987 1988 Mean 1987 1988 Mean
/88 /89 /88 /89 /88 /89
---------------------------------------------------------------------------
0 10.1 6.9 8.5 144 119 132 1756 1411 1583
30 9.6 8.1 8.9 147 115 131 1670 1662 1666
60 10.2 9.4 9.8 147 114 130 1761 1825 1793
90 11.0 8.9 9.9 146 109 128 2036 1873 1955
120 10.9 9.4 10.1 148 114 131 1714 1994 1854
Mean 10.4 8.5 9.4 146 114 130 1787 1753 1770
SEm SEm SEm
Interaction means 0.7 1.4 86.3
Season means 0.3 0.6 38.6
N Means 0.5 1.0 61.0
SEm = Standard Error of mean
---------------------------------------------------------------------------
There were no effects of interactions between rate of N and season on castor grown at Makoholi (Table 3). However, at the 30 and 60 kg N ha^-1 rates, 36.7 and 22.2 % more racemes were attained than where no N was applied, in the drier season (1988/89), while 34.5 and 73.5 % more were realised with the 90 and 120 kg N ha^-1 rates in the wetter season (1987/88) at this site (Table 3).
Mlezu. At Mlezu, effects of interactions between rate of N applied and season on days to maturity were similar to those of Makoholi in that plants also took longer (mean of 32 days) to mature in the first than in second season (Table 4). In the wetter season (1987/88) application of N lengthened duration to maturity by three days when compared to the zero N rate. However, in the drier season (1988/89), the 60 to 120 kg N ha^-1 rates significantly (P<0.01) reduced the period to maturity when compared to the zero rate (Table 4). Although no significant interaction effects on number of racemes/plant were observed at Mlezu, the number of racemes increased progressively from the zero rate up to 60 kg N ha^-1 in 1988/89. However, main effects of season were significant, with the 1988/89 season having 18 % less racemes than the 1987/88 season (Table 4).
The significant effects of interactions between N rate and season were mainly a result of seed yield response to applied N during 1988/89. In 1987/88, there was no yield advantage in applying N to the crop (Table 4).
Matopos. In 1987/88, no significant differences were observed on duration to maturity among the various N rates applied. However, in 1988/89, the period to maturity decreased significantly (P<0.05) when 30 kg N ha^-1 was applied to the crop (Table 5). Differences in days to maturity among the 30, 60 and 90 kg N ha^-1 rates were insignificant (Table 5). TABLE 5. Effects of interactions between N rate and season on number of racemes/plant, days to maturity and seed yield (kg ha^-1) in 1987/88 and 1988/89 seasons at Matopos
---------------------------------------------------------------------------
Nitrogen Racemes/plant Days to maturity Seed yield, kg ha^-1
rate ----------------- ------------------- --------------------
(kg ha^-1) 1987 1988 Mean 1987 1988 Mean 1987 1988 Mean
/88 /89 /88 /89 /88 /89
---------------------------------------------------------------------------
0 4.5 6.7 5.6 149 149 149 845 1174 1010
30 5.7 7.1 6.4 151 144 148 1300 1497 1399
60 6.7 7.2 7.0 150 146 148 1746 1493 1619
90 5.9 7.1 6.5 147 147 147 1456 1401 1428
120 7.2 7.7 7.5 149 148 149 1752 1425 1588
Mean 6.0 7.2 6.6 149 147 148 1420 1398 1409
SEm SEm SEm
Interaction means 0.5 1.2 120.7
Season means 0.2 0.5 54.0
N Means 0.3 0.8 85.4
SEm = Standard Error of mean
---------------------------------------------------------------------------
Even though interactions between rate of N applied and season on number of racemes/plant were not significant, main effects of season and those of N were apparent at Matopos. At each N rate applied, higher numbers of racemes were attained in the drier 1988/89 than in the wetter 1987/88 season.
When compared to the zero rate, all rates of N applied in the 1987/88 season enhanced seed yield. The seed yield increased progressively and significantly from zero N up to 60 kg N ha^-1, after which the trend was broken. When compared with the seed yield obtained at 60 kg N ha^-1, seed yield was depressed at 90 kg N ha^-1 and remained the same at 120 kg N ha^- 1. In the seacond year, the effects of aplying N on seed yield were not significant (Table 5).
Kadoma. At Kadoma, there were no significant interactions, but significant effects of season were observed on the measured parameters. On average there were 25 % less racemes in the second than in the first season. The plants also matured earlier by some 22 days in 1987/88 compared to 1988/89 (Table 6). Generally, yield differences between the two seasons were highly significant at each N rate applied, with an average of 137 % more being produced in the wetter 1987/88 than in the drier 1988/89 (Table 6). TABLE 6. Effects of interactions between N rate and reason on average number of racemes plant, days to maturity and seed yield (kg ha^-1) in 1987/88 and 1988/89 seasons Kadoma
---------------------------------------------------------------------------
Nitrogen Racemes/plant Days to maturity Seed yield, kg ha^-1
rate ----------------- ------------------- --------------------
(kg ha^-1) 1987 1988 Mean 1987 1988 Mean 1987 1988 Mean
/88 /89 /88 /89 /88 /89
---------------------------------------------------------------------------
0 7.1 5.5 6.3 112 132 122 1798 669 1234
30 6.6 4.9 5.7 111 133 122 1785 933 1359
60 6.7 4.9 5.8 113 138 126 1850 674 1262
90 6.7 5.2 6.0 110 133 121 1577 760 1168
120 6.4 4.6 5.5 113 134 123 1745 661 1203
Mean 6.7 5.0 5.9 112 134 123 1751 739 1245
SEm SEm SEm
Interaction mean 0.4 1.6 124.6
Season means 0.2 0.7 55.7
N Means 0.3 1.2 88.1
SEm = Standard Error of mean
---------------------------------------------------------------------------
Panmure. Just as for Kadoma, interaction effects between N rate and season on the measured parameters were also not significant at Panmure. However, the seasonal effects were such that more racemes were produced in the wetter 1987/88 than in the drier 1988/89 season (Table 7). In both seasons, fertilizer application resulted in early maturity of the crop. Seed yield was neither influenced by season nor by the N rate applied (Table 7). TABLE 7. Effects of interactions between N rate and season on average number of racemes/plant, days to maturity and seed yield (kg ha^-1) in 1987/88 and 1988/89 seasons at Panmure
---------------------------------------------------------------------------
Nitrogen Racemes/plant Days to maturity Seed yield, kg ha^-1
rate ----------------- ------------------- --------------------
(kg ha^-1) 1987 1988 Mean 1987 1988 Mean 1987 1988 Mean
/88 /89 /88 /89 /88 /89
---------------------------------------------------------------------------
0 7.7 6.7 7.2 99 149 124 1312 1174 1243
30 8.5 7.1 7.8 97 144 121 1286 1497 1392
60 7.2 7.1 7.2 95 147 121 1357 1401 1379
90 7.2 7.1 7.2 95 147 121 1357 1401 1379
120 8.1 7.7 7.9 96 148 122 1422 1425 1423
Mean 8.0 7.2 7.6 96 147 122 1376 1398 1387
SEm SEm SEm
Interaction means 0.6 1.0 99.4
Season means 0.3 0.5 44.5
N Means 0.4 0.7 70.3
SEm = Standard Error of mean
---------------------------------------------------------------------------
Effects of method of N application and season. At two (Makoholi and Matopos) of the three sites on sandy soils, effects of method of N application on number of racemes/plant were affected by season only (Table 8). However, duration to maturity and seed yield were not affected by interactions between method of N application and season. TABLE 8. Effects of interactions between method of N application and season on average number of racemes/plant at the sites with sandy soils
---------------------------------------------------------------------------
Method of N Makoholi Mlezu Matopos
application ------------------- ------------------ --------------------
1987 1988 Mean 1987 1988 Mean 1987 1988 Mean
/88 /89 /88 /89 /88 /89
---------------------------------------------------------------------------
Sole 7.1 5.9 6.5 10.2 8.2 9.2 5.3 7.5 6.4
Split 5.3 6.1 5.7 10.5 8.8 9.7 6.7 6.9 6.8
Mean 6.2 6.0 6.1 10.4 8.5 9.4 6.0 7.2 6.6
SEm SEm SEm
Interaction means 0.5 0.4 0.3
Season means 0.2 0.3 0.3
Method means 0.3 0.3 0.2
SEm = Standard Error of mean
---------------------------------------------------------------------------
In 1987/88, split application of N at Makoholi resulted in significantly (P<0.05) fewer racemes/plant than when N was applied in a sole (single) dose (Table 8). However, in drier 1988/89 season, the method of N application did not affect the number of racemes/plant.
At Matopos, split N application produced a significantly (P<0.01) greater number of racemes/plant in 1987/88, while in 1988/89 the difference in the number of racemes/plant between the two methods was insignificant. In 1988/89, when N was applied as a sole dose, the number of racemes/plant was higher than that of 1987/88 by 42 % (Table 8).
At Mlezu, one of the three sites on sandy soils, neither sole nor split N application affected raceme production in both seasons (Table 8). Not withstanding this, there were 24 and 19 % more racemes with sole and split N application, respectively, in the wetter 1987/88 than in the drier 1988/89 season.
The interactions between method of N application and season were not significant for the measured parameters over the two seasons on the heavy soil sites of Kadoma and Panmure (data not presented).
Interactions between rate and method of N application. Effects of interactions between rate and method of N application on days to maturity were realised only at Matopos and on yield at Mlezu and Matopos (Tables 9 -14).
In both seasons, crop maturity period at Makoholi and Mlezu were not affected by the interactions between rate and method of N application (Tables 9 and 10) and neither was seed yield at Makoholi (Table 12). TABLE 9. Effects of interactions between rate and method of N application on days to physiological maturity at Makoholi
--------------------------------------------------------------
1987/88 1988/89
N rate(kg ha^-1) --------------------- --------------------
Sole Split Mean Sole Split Mean
--------------------------------------------------------------
0 - - 202 - - 151
30 200 198 199 160 157 158
60 201 198 200 164 159 161
90 199 198 199 160 156 158
120 198 198 198 164 164 164
Mean 200 198 199 159 157 158
SEm SEm
Interaction means 1.0 2.6
N means 0.7 1.9
Method means 0.5 1.2
SEm = Standard Error of mean
---------------------------------------------------------------
TABLE 10. Effects of interactions between rate and method of N application on days to physiological maturity at Mlezu
----------------------------------------------------------
N rate 1987/88 1988/89
(kg ha^-1) ------------------- -------------------
Sole Split Mean Sole Split Mean
----------------------------------------------------------
0 - - 144 - - 119
30 149 146 148 117 114 226
60 147 147 147 113 115 114
90 146 146 146 109 110 109
120 146 151 148 116 113 115
Mean 146 147 146 114 114 115
SEm SEm
Interaction means 1.6 2.4
N means 1.1 1.7
Method means 0.7 1.1
SEm = Standard Error of mean
---------------------------------------------------------------------------
Table 11. Effects interactions between rate and method of N application on days to physiological maturity at Matopos
---------------------------------------------------------
N rate 1987/88 1988/89
(kg ha^-1) ------------------- -------------------
Sole Split Mean Sole Split Mean
----------------------------------------------------------
0 - - 149 - - 149
30 151 151 151 146 143 144
60 148 151 150 147 145 146
90 153 141 147 147 147 147
120 154 145 149 148 148 148
Mean 146 152 149 147 146 147
SEm SEm
Interaction means 1.7 1.6
N means 1.2 1.1
Method means 0.8 0.7
SEm = Standard Error of mean
-----------------------------------------------------------
TABLE 12. Effects of interactions between rate and method of N application on seed yield (kg ha^-1) at Makoholi
-----------------------------------------------------------
N rate 1987/88 1988/89
(kg ha^-1) ------------------- -------------------
Sole Split Mean Sole Split Mean
----------------------------------------------------------
0 - - 1338 - - 615
30 1282 1155 1218 849 608 729
60 1177 1120 1149 918 816 867
90 1214 1394 1304 729 875 802
120 1697 1340 1519 797 938 867
Mean 1380 1231 1305 775 778 776
SEm SEm
Interaction means 237.5 92.4
Nitrogen means 167.9 65.3
Method means 106.2 41.3
SEm = Standard Error of mean
----------------------------------------------------------
TABLE 13. Effects of interactions between rate and method of N application on seed yield (kg ha^-1) at Mlezu
------------------------------------------------------------------
N rate 1987/88 1988/89
(kg ha^-1) ---------------------- ------------------------
Sole Split Mean Sole Split Mean
------------------------------------------------------------------
0 - - 1 756 - - 1 411
30 1 528 1 812 1 670 1 575 1 748 1 662
60 1 424 2 099 1 761 1 861 1 788 1 825
90 1 860 2 212 2 036 1 864 1 882 1 873
120 1 758 1 671 1 714 1 977 2 011 1 994
Mean 1 702 1 873 1 787 1 724 1 782 1 753
SEm SEm
Interaction means 139.5 101.8
Nitrogen means 98.6 71.9
Method means 62.4 45.5
SEm = Standard Error of mean
--------------------------------------------------------------------------
TABLE 14. Effects of interactions between N rate and method of N application on seed yield (kg ha^-1) at Matopos
---------------------------------------------------------
N rate 1987/1988 1988/89
(kg ha^-1) --------------------- ----------------------
Sole Split Mean Sole Split Mean
---------------------------------------------------------
0 - - 845 - - 1174
30 1451 1150 1300 1439 1555 1492
60 1683 1809 1746 1332 1654 1493
90 1219 1693 1456 1591 1212 1401
120 1362 2141 1752 1468 1382 1425
Mean 1429 1698 1420 1457 1451 1398
SEm SEm
Interaction means 164.8 176.5
Nitrogen means 116.5 124.8
Method means 73.7 78.9
SEm = Standard Error of mean
----------------------------------------------------------
Significant (P<0.01) effects of interactions between rate and method of N application were observed for period to crop maturity at Matopos in 1987/88. At the 30 and 60 kg N ha^-1 rates, there were no differences between the sole and split N application. However, at the 90 and 120 kg N ha^-1, when N was split, the delay in crop maturity was up to 12 days (Table 11). In 1988/89, the period to maturity was not influenced by method of N application.
At Mlezu and Matopos, the rate and method of N application interacted positively to influence yield performance in 1987/88 season (Tables 13 and 14). However, the differences between sole and split N application were only significant at the 60 and 120 kg N ha^-1 rates at Mlezu and Matopos, respectively, while in 1988/89, the seed yields at both sites were not influenced by these interactions (Tables 13 and 14).
Main effects of method of N application on yield were only realised at the heavy soil site of Kadoma, but there was no effect at the other heavy soil site at Panmure (Table 15). At the Kadoma site, splitting N application was highly favourable, in both seasons, compared to applying all the N at planting. Yield advantages of split over sole N application were 18 and 17% in 1987/88 and 1988/89, respectively, at the latter site (Table 15).
TABLE 15. Effects of method of N application on seed yield (kg ha^-1) at the heavy soil sites
---------------------------------------------------------------------
Method of N Kadoma Panmure
application -------------------------- --------------------------
1987/88 1988/89 Mean 1987/88 1988/89 Mean
---------------------------------------------------------------------
Sole 1 580 673 1 126 1 342 1 409 1 376
Split 1 922 806 1 364 1 410 1 387 1 398
Mean 1 751 739 1 245 1 376 1 398 1 387
SEm 106.9 31.2 55.7 41.0 78.9 44.5
SEm = Standard Error of mean
---------------------------------------------------------------------
DISCUSSION
The performance of castor at the five sites was greatly influenced by amount of rainfall. In the wet 1987/88 season, there was a higher number of racemes/plant than in the dry 1988/89 season and this was positively related to seed yield at Mlezu and Kadoma, but the same relationship between the two paramenters was not apparent at the other sites. However, since seed yield at Mlezu (364 mm rainfall) and Matopos (436 mm rainfall) in 1988/89 was not depressed by rainfall which was lower than that of 1987/88, while being depressed at Makoholi (300 mm), differences in the yield performance could also be attributed to seasonal precipitation. However, in terms of rainfall distribution, the results of this study indicated that seed yield in a low rainfall season was negatively related to the amount of rainfall between flowering and maturity, suggesting an earlier critical rainfall requirement for castor cv "Hale" (Table 2). The 364 mm rainfall (Fig. 2) which maintained seed yield at Mlezu in 1988/89 (Table 4) is comparable to the minimum of 375 mm reported by Van der Merwe and Clarke (1977), to be able to support a castor crop.
Besides the differences between the two seasons in the performance of castor noted above, there were significant interactions between season and N rate on maturity period and seed yield only at the sandy soil site at Makoholi, Mlezu and Matopos. At Makoholi, there was no seed yield response to N rate in both seasons. In the case of maturity period, however, responses to N rate at each of the three sandy soil sites in the second season was directly the opposite of that obtained in the first season. These contrasting responses to N between seasons were also obtained in the response of seed yield at Mlezu and Matopos where there was response only in 1988/89 at the former site but only in 1987/88 at the latter site. These trends suggested that the amount of N fertilizer needed for the production of castor on sandy soils was influenced by the amount of rainfall. Increasing N fertilizer rate significantly increased the number of racemes at Makoholi and Matopos, delayed maturity at Makoholi, while shortening it at Matopos and Panmure, and increased seed yield at Mlezu and Matopos.
The yield responses of 54 and 28 % due to applications of 30 kg N ha^-1 obtained at Matopos were within the range previously reported by Donovan and Landsberg (1963) in similar environments of the country. These researchers had reported yield responses of 30 to 60 % from application of 27 kg N ha^-1 at various sites in 1958/59.
There was little interaction between method of N application and season on the performance of castor. The only significant interactions showed that split N application reduced the number of racemes at Makoholi while increasing them at Matopos in 1987/88, when compared to sole N application. The only significant interactions between rate and method of N application were obtained on seed yield at Mlezu and maturity and seed yield at Matopos in 1987/88. Split applications of 60 kg N ha^-1 at Mlezu and 120 kg N ha^- 1 at Matopos had yield advantage over sole N application. Split application of 90 and 120 kg N ha^-1 delayed crop maturity at Matopos. However, split N application had overall yield advantage at Kadoma in each of the two seasons.
The responses to split N application appeared to be primarily due to the status of available N in soils and the amount of rainfall. These responses coincided with medium status of available N in the soils at Mlezu and Matopos or high N status at Kadoma (1987/88) and medium N status in the case of Kadoma in 1988/89 (Table 1). Furthermore, the response of castor to split N in the wet 1987/88 occurred only when cumulative rainfall, up to crop maturity, was greater than 700 mm as was the case at Matopos, Kadoma and Mlezu, respectively (Fig. 1), but not at lower rainfall at Makoholi (580 mm) and Panmure (480 mm). However, in 1988/89 split N had yield advantage over single N application at Kadoma under medium N status in the soil but a cumulative rainfall of 530 mm. The results of the two seasons suggest that thresh-holds for yield benefit from split N application were a minimum of medium N status in the soil and about 700mm rainfall to crop maturity in a good rainfall season such as 1987/88 or medium to high N status in the soil, supported by at least 500 mm of rainfall in a relatively dry season such as experienced in 1988/89.
Yield increases from split application at two of the sandy soil sites tended to improve with N rate, reaching a maximum of 47 % at 60 kg N ha^-1 at Mlezu in 1987/88 (Table 9), while the largest increments at Matopos were 57 % at 120 kg N ha^-1 in 1987/88 and 24 % at 60 kg N ha^-1 in 1988/89 (Table 12). In a similar study carried out in Andhra Pradesh (India), Sarma (1985) reported that spliting 40 kg N ha^-1 resulted in a 25.8 % yield increase of castor compared to a single application, on sandy loam soils. The results obtained in this study are within a similar range or above. Comparisons of the performance of castor "Hale" at the different sites indicated that the highest yields (>1700 kg ha^-1) were obtained at Mlezu in both seasons and at Kadoma in 1987/88. The lowest yields were obtained at Makoholi and at Kadoma in 1988/89. Otherwise yields were fairly uniform across the five sites during the two seasons and ranged between 1300 and 1400 kg ha^-1. These values suggest that comparable yields of castor may be expected on sandy and clay soils provided seasonal changes do not severely limit yield.
The average number of racemes/plant and duration to maturity of the primary raceme were measured in consideration that they could be used as good indicators for seed yield. Generally, no set pattern between these parameters and seed yield were observed in this study.
The observations mentioned above suggest three possibilities; firstly; that the number of racemes per plant on its own, is not a good indicator of the plant's yield potential. In future work, additional information may be generated if an assessment is done on how number of racemes, size of raceme (length and number of capsules on it) and weight of capsules interact to influence overall yield performance. Secondly, duration to maturity of only the primary raceme does not indicate overall yield potential of a castor plant. At the same time, it is rather difficult to establish the cut off point in maturity days in castor due to the sequential ripening of racemes from primary, at the bottom, through secondary to tertiary at the top. In the variety "Hale", sequential sets can vary from three to five depending on the season length and rainfall situation.
The results obtained in this study, suggest that out of the several factors that affected yield, the amount of rainfall exerted the greatest effect. This was shown by yield reductions of 41 % at Makoholi and 58 % at Kadoma as rainfall decreased by 53 and 32 %, respectively, from the wet 1987/88 to the drier 1988/89 season. Furthermore, the yield advantage of split over sole N application was dependent on the amount of rainfall, particularly in a good season.
CONCLUSION
A major difficulty in assessing castor performance across the different sites was the fact that the sandy soils were all located in the drier agro-ecological zones, Natural Region III (Mlezu) and Natural Region IV (Makoholi and Matopos) while the fine-textured soils were located in a more humid region, Natural Region II. Neverthless, there were several important trends that were observed in this study.
In a good rainfall season the mean yields (1306, 1787 and 1420 kg ha^-1) of castor "Hale" obtained on sandy soils at makoholi, Mlezu and Matopos, respectively, were comparable to those obtained on clay soils (1751 kg ha^- 1 at Kadoma and 1376 kg ha^-1 at Panmure). Furthermore, in a drier season, the lowest yields obtained on sandy soils (776 kg ha^-1 at Makoholi) were comparable to those obtained on clay soils (739 kg ha^-1 at Kadoma). The yields remained remarkably constant at the other sites during the two seasons indicating a rather high drought tolerance ability by castor, particularly at Mlezu and Matopos which had cumulative rainfall of 330 mm and 420 mm, respectively, at maturity in 1988/89.
There was an indication that castor can tolerate "low" levels of available N. Splitting N application had seed yield advantage on the sands over single application in a good rainfall season under medium to high initial N in soils. The increased efficiency of such split N application was shown by the highest yields which were achieved at 60 kg N ha^-1 at Mlezu instead of a minimum of 90 kg N ha^-1 in single N application in 1987/88, while split N application increased average yield above that achieved from single N application at Matopos in 1987/88 and at Kadoma in both seasons.
ACKNOWLEDGEMENTS
The authors would like to express their gratitude to the Crop Productivity Units (CPUs) at Matopos, Makoholi, Kadoma/Mlezu and Panmure Experiment Station (under the leadership of Messrs C. Ndebele, H. H. Dhliwayo, M. Chisenga and J. Karambwe, respectively), for meticulously recording the field data. Many thanks to T.P. Kachidza for drawing the final graphs and to Sarah Musariri for typing the script.
REFERENCES
Agronomy Institute. 1991. Annual Report, Summer 1986/87 and Winter 1986. Department of Research and Specialist Services, Harare, Zimbabwe, pp. 83-85.
Chemistry and Soil Research Institute. 1989. A Guide to the Meaning of Soil Analysis. Department of Research and Specialist Services, Harare, Zimbabwe, pp. 4-5.
Donovan, P.A. and Landsberg, J.L. 1963. Castorbean investigations at Matopos Research Station. Rhodesia Agricultural Journal 60:53-56.
Muthuvel, P., Sivasamy, R. and Subramanian, V. 1987. Studies on nitrogen and phosphorus requirements of rainfed castor. Madras Agricultural Journal 74:26-28.
Rao, C.M. and Ventateswarlu, M.S. 1988. Effect of irrigation, nitrogen and plant density on yield attributes and yield of castor varieties. Indian Journal of Research, Apau 16:37-39.
Saran, G. and Giri, G. 1987. Effects of seeding time and nitrogen on summer castor. Indian Journal of Agronomy 32:155-157.
Sarma, D.A. 1985. Effects of varieties and levels of nitrogen on the yield of castor. Research Note. The Andhra Pradesh Agriculrutal Journal 32:133-134.
Van der Merwe, J.J. and Clarke, P.F. 1977. Growth requirements of the castor oil plant. Bulletin 2, Farming in South Africa.
Weiss, E.A. 1983. Castor. Chapter 3:53-62 in Oilseed Crops. Tropical Agriculture Services. Longman, London and New York.
Whingwiri, E.E., Natarajan, M., Kanyanda, C.W. and van Lindert, H.J.A. 1987. Agroclimate and soil characteristics of the research centres in the Department of Research and Specialist Services. Zimbabwe Agricultural Journal 84:37-53. Copyright 1997 The African Crop Science Society
The following images related to this document are available:Line drawing images[cs97023a.gif] [cs97023b.gif] |
| |||||||||
