ABSTRACT
Three field experiments to investigate the partial nutrient balance (N and K) in cassava/soybean intercrop system were conducted at University of Nigeria, Nsukka in a derived Savannah location of South Eastern Nigeria. Effect of fertilizer rate, residual fertilizer and soybean residue management on growth and yield of soybean and cassava and soil nutrient reserve were studied. Soybean growth and yield were significantly affected by their varieties, fertilizer rate and cropping system but not by cassava variety. Application of fertilizer at 50 Kg ha-1 fertilizer rate gave the highest soybean total dry matter (898.24 Kg ha-1), highest grain yield (156.91 Kg ha-1) and highest fresh cassava tuber yield (30.7 t ha-1) at 12 months after planting (MAP). Intercropping cassava variety (NR 8230) with medium maturing variety of soybean, (TGX 1894-3E) gave the highest grain yield of soybean (133.60 Kg ha-1), highest fresh tuber yield of cassava (30.8 t.ha-1) at 12 MAP, highest N and K balances (+44.06 and +72.70 Kg.ha-1), highest LER of 2.71 and ATER of 2.10 at 50 Kg K.ha-1 fertilizer rate. The effect of residual fertilizer on soybean plant height, litter weight and shoot dry weight was highest at 45 Kg N.ha-1 and 50 Kg K.ha-1 fertilizer rate, while soybean grain yield of 204.1 Kg.ha-1 was highest at residual 50 Kg K.ha-1 fertilizer rate. Also, cassava leaf-N (4.05%) and cassava stem-K (2.8%) were highest at residual 45 Kg N.ha-1and 50 Kg K.ha-1, while cassava tuber yield at 12 MAP was highest (24.27 t.ha-1) at residual. 50 Kg K.ha-1 Soil nitrogen increased from 0.04%N to 0.34%N and soil- pH from 4.2 to 6.6 at sole soybean. In sole cassava, soil-N decreased from 0.04% initial soil-N to 0.03%N but soil-N under 3 year natural fallow was unchanged. Residual fertilizer affected nitrogen balance of sole cassava which was negative, while intercrop had positive nitrogen balance at all residual fertilizer rates. Potassium balance was positive with intercrop at all residual fertilizer rates except at no fertilizer. Incorporation of soybean residue into cassava/soybean intercrop system increased cassava tuber yield and soil nutrient status and resulted in positive N and K balances. Analysing of nutrient stock: balance (NSB) ratio revealed that fertilizer rate of 50 Kg K ha-1 in the first year of cassava/soybean intercrop followed with incorporation of residue in the subsequent year (without further application of fertilizer) gave the highest dynamic reserve of 310.6 Kg N ha-1 and 311.64 Kg K ha-1. Under sole soybean, production can be sustained for 15 years (NSB ratio 14.58), while under intercropped system production can be sustained for 9 years for nitrogen and 9 years for potassium (N balance of +62.64 Kg ha-1 and K balance of +87.66 Kg ha-1). Sole cassava without fertilization and no residue incorporation can be sustained for one year with NSB: ratio of 0.88.
TABLE OF CONTENTS
TITLE PAGE – – – – – – – – i
CERTIFICATION PAGE – – – – – – – ii
DEDICATION – – – – – – – – iii
ACKNOWLEDGEMENT – – – – – – – iv
ABSTRACT – – – – – – – – – v
TABLE OF CONTENT – – – – – – – vi
LIST OF TABLES – – – – – – – – xv
INTRODUCTION – – – – – – – – 1 LITERATURE REVIEW – – – – – – – 5
Environmental Sustainable Development – – – – – 5
Nitrogen – – – – – – – – – 6
Nitrogen Fixation – – – – – – – – 7
Biological Nitrogen Fixation (BNF) – – – – – – 7
Nitrogen Assimilation – – – – – – – – 9 Residual Effect of BNF – – – – – – – 10
Role of Legumes – – – – – – – – 11
Integrated Soil Fertility Management (ISFM) – – – – 12
Soil Nutrient – – – – – – – – – 13
Potassium – – – – – – – – – 13
Nutrient Balance – – – – – – – – 15
Nutrient Stock Balance – – – – – – – 18
Soybean – – – – – – – – – 18
Cassava – – – – – – – – – 20
Relative Crowding Coefficient (RCC) – – – – – 22
Aggressive Index (Al) – – – – – – – – 23
The Relative Yield Total (RYT) – – – – – – 23
The Competitive Ratio (CR) – – – – – – – 24
Land Equivalent Ratio (LER) – – – – – – 24
The Land Equivalent Coefficient (LEC) – – – – – 24
Area x Time Equivalent Ratio (ATER) – – – – 25
MATERIALS AND METHODS
Experiment 1 – – – – – – – – – 26
The Effect of Fertilizer Rate (N and K) and Cropping System on Growth, Crop Yield, Nutrient Content and Soil Nutrient Reserve in the Cassava and Soybean Intercrop
Experiment 2 – – – – – – – – – 27
Residual Effects of Fertilizer and Cropping System on Soil Fertility and Follow-up Crop Yield
Experiment 3 – – – – – – – – – 28
Effects of Cropping System and Soybean Crop Residue Management on Growth and Yield of Soybean, Cassava and Soil Nutrient Reserve
Methods for Plant Analysis – – – – – – – 29
Nitrogen Content – – – – – – – – 29
Potassium Content – – – – – – – – 29
Land Equivalent Ratio (LER) and Area x Time Equivalent Ratio (ATER) – 29
Partial Nutrient Balance Method – – – – – – 30
Definition of Input-Output processes – – – – – – 30
Nutrient Stock: Balance Ratio – – – – – – 31
Experimental Design – – – – – – – – 32 Experiments 1 and 2 – – – – – – – – 32 Linear Additive Model – – – – – – – 32 Experiment 3 – – – – – – – – – 32 Linear Additive Model – – – – – – – 33 Data Analysis – – – – – – – – – 33 RESULTS
Some Meteorological Information of the Experimental Sites for 2004, 2005 and
2006 – – – – – – – – – – 34
Soil Characteristics – – – – – – – – 36
EXPERIMENT 1:
The Effect of Fertilizer Rates (N and K) and Cropping Systems on Growth and
Yield of Cassava and Soybean Varieties at Intercrop, Nutrient Uptake,
and Soil Nutrient Reserve – – – – – – – 38
Soybean Plant Height – – – – – – – – 38
Shoot Dry Matter – – – – – – – – 41
Litter Dry Matter – – – – – – – – 44
Soybean Stover – – – – – – – – 46
Total Dry Matter – – – – – – – – 48
Grain Yield – – – – – – – – – 50
Effect of Fertilizer Rates and Cropping Systems on Cassava Tuber Yield (t.ha-1)
at 4 12MAP – – – – – – – – – 52
Effect of Fertilizer Rates and Cropping Systems on Cassava Tuber Yield
(t.ha-1) at 8MAP – – – – – – – – 54
Effect of Fertilizer Rates and Cropping Systems on Cassava Tuber Yield
(t.ha-1) at 12MAP – – – – – – – – 56
Effect of Fertilizer Rates and Cropping Systems on Cassava Leaf-N (%) at
4 MAP – – – – – – – – – – 58
Effect of Fertilizer Rates and Cropping Systems on Cassava Leaf-N (%) at
8 MAP- – – – – – – – – – 60
Effect of Fertilizer Rates and Cropping Systems on Cassava Leaf-N (%)
at 12 MAP- – – – – – – – – – 62
Effect of Fertilizer Rates and Cropping Systems on Cassava Leaf-K (%) at
4 MAP – – – – – – – – – 64
Effect of Fertilizer Rates and Cropping Systems on Cassava Leaf-K (%) at
8 MAP – – – – – – – – – 66
Effect of Fertilizer Rates and Cropping Systems on Cassava Leaf-K (%) at
12 MAP- – – – – – – – – – 68
Effect of Fertilizer Rate and Cropping System on Soil-Nutrient Reserve at
12 MAP- – – – – – – – – – 70
Soil –N Réserve – – – – – – – – 70
Soil – K Reserve – – – – – – – – 70
Soil- NO3 Reserve – – – – – – – – 71 Nitrogen Balance – – – – – – – – 73
Potassium Balance – – – – – – – – 76
Effect of Fertilizer Rate and Cropping System on Nutrient Stock: Balance
Ratio (NSB) – – – – – – – – – 79
Nitrogen – – – – – – – – – 79
Potassium Nutrient Stock: Balance Ratio – – – – – 81
Effect of fertilizer rate and cropping system on Land equivalent
ratio (LER)- – – – – – – – – – 83
Effect of fertilizer rate and cropping system on Area x Time equivalent ratio
(ATER)- – – – – – – – – – 86
EXPERIMENT 2:
Residual Effects of Fertilizer Including Fallow and Cropping System on Soil
Nutrient Content and Yield of Cassava (NR 8230) and Soybean
(TGX 1894-3E) as Follow up Crop- – – – – – – 88
Soybean Plant height – – – – – – – – 88
Litter Dry Matter – – – – – – – – 90
Shoot Dry Matter – – – – – – – – 92
Soybean Stover – – – – – – – – 94
Grain Yield – – – – – – – – – 96
Cassava Leaf-N – – – – – – – – 98
Cassava Leaf-K – – – – – – – – 101
Stem-N – – – – – – – – – 103
Stem-K – – – – – – – – – 106 Tuber Yield – – – – – – – – – 108
Tuber-N – – – – – – – – – 111
Tuber-K – – – – – – – – – 113
Effects of Residual Fertilizer Including Fallow and Cropping System on Soil
Properties- – – – – – – – – – 115
Soil-pH – – – – – – – – – 115
Soil-N – – – – – – – – – – 115
Soil-organic matter – – – – – – – – 115
Soil-NO3 – – – – – – – – – 117
Soil-K – – – – – – – – – – 117
Effect of Residual Fertilizer Including Fallow and Cropping System on N and K
Balance – – – – – – – – – 118
EXPERIMENT 3
Effect of Soybean Residue Management and Cropping System on Growth and
Yield of Cassava and Soil Properties – – – – – – 121
Yield of soybean and Cassava – – – – – – 121
Effect of Soybean Management and Cropping System on Soil Property after the
harvest of Cassava and Soybean – – – – – – 123
Soil pH – – – – – – – – – 123
Soil-N – – – – – – – – – – 123
Soil-K – – – – – – – – – – 123
Organic Matter (OM) – – – – – – – – 125
Nutrient balance – – – – – – – – 126
DISCUSSION – – – – – – – – 128
The Effect of Fertilizer Rate (N and K) and Cropping System on Growth,
Crop Yield, Nutrient Content and Soil Nutrient Reserve in the Cassava
and Soybean Intercrop.- – – – – – – – 129
Vegetative Growth in Soybean – – – – – – 129
Soybean Grain Yield – – – – – – – – 130
Cassava Tuber Yield – – – – – – – – 131
Nitrogen Nutrition – – – – – – – – 132
Potassium Nutrition – – – – – – – – 133
Soil Nutrient Reserve – – – – – – – – 134
Land Equivalent Ratio and Area x Time Equivalent Ratio – – – 135
Nitrogen Balance – – – – – – – – 136
Potassium Balance – – – – – – – – 138
Nutrient Stock : Balance Ratio (NSB) – – – – – 139
Residual Effect of Fertilizer Including Fallow and Cropping Systems on
Soil Nutrient Content and Yield of Cassava and Soybean as Follow – up
Crops – – – – – – – – – – 140
Soybean Vegetative Growth – – – – – – – 140
Residual Fertilizer Effect on Grain Yield – – – – – 141
Residual Fertilizer Effect on Cassava Plant Growth – – – – 142
Cassava Tuber Yield – – – – – – – – 143
Residual Soil-Nutrient – – – – – – – 143
Effect of Residual Fertilizer on Nitrogen Balance – – – – 145
Effect of Residual Fertilizer on Potassium Balance – – – – 145
Effect of Cropping System and Soybean Crop Residue Management
on Yield of Soybean and Cassava and Soil Nutrient Reserve- – – 146
Growth and Yield of Cassava – – – – – 146
Soil Nutrient Changes – – – – – – – – 147
Nutrient Balance – – – – – – – – 148
CONCLUSION – – – – – – – – 149
Suggestions for Further Research – – – – – – 151
References – – – – – – – – – 152
Appendices – – – – – – – – – 161
I: Partial Nutrient Balance Estimate for Medium Maturing Variety of Soybean
TGX 1894-3E Intercropped with Cassava NR 8230 at N0K50 Fertilizer Rate 161
II: Partial Nutrient Balance for TGX 1894-3E (Medium Maturing Variety
of Soybean) Intercropped with Cassava NR 8230 at N0K0 Fertilizer Rate – 162
III: Partial nutrient balance in Experiment 2 – – – – – 163
IV: Summary of the Effect of Residual Fertilizer and Cropping System on
Dry Matter of Soybean, Cassava Tuber Yield and Soil Nutrient in Experiment 2 164
V: Partial Nutrient Balance for the System with Retained Soybean
Residue (CRT) – – – – – – – – 165
VI: Partial Nutrient Balance for the System with Removed Soybean
Residue (CRM). – – – – – – – – 165
VII: Properties for Calculating Nutrient Balance – – – – 166
VIII: ANOVA Table for the Split Plot Design – – – – 167
IX: ANOVA Table for RCBD – – – – – – 167
X: Agronomic Characteristics and Source of the Cassava Varieties – – 168
CHAPTER ONE
INTRODUCTION
Nutrient monitoring (NUTMON) is an integrated methodology that targets different factors in the process of managing soil nutrients and other natural resources in agriculture (Vlaaming et al., 2001). With the NUTMON methodology, farmers and researchers analyse the environmental and financial sustainability of farming systems. A quantitative analysis generates important indicators such as nutrient flows, nutrient balances, cash flow, gross margins and farm income. Both the quantitative and qualitative analysis are then used to improve or design new technologies that tackle soil fertility management problems and can help improve the financial performance of the farm. Manipulation of nutrient ‘stock and flows’ of farm lands is vital in the derived Savannah zone. Soil organic matter (SOM) in the farms, which accounts for the major cation exchange capacity and nitrogen content of the soil are not often replenished as they decline from crop cycle to crop cycle. The soil therefore becomes rapidly degraded and highly weathered especially where inorganic fertilizers become the major methods for soil nutrient replenishment. According to FAO (2003), agricultural intensification without adequate restoration of soil fertility threatens the sustainability of agriculture. A nutrient input-output balance analysis will therefore help in predicting the sustainability.
Guillard et al. (1995) reported that traditional farming system is a concept that will be developed. This concept is mostly based on ecological principles of constant utilization of all tropic levels. Some approaches to the concept have been reported by Defoer et al. (2000) as integrated nutrient management (INM) and integrated soil fertility management (ISFM). Both concepts included intercropping and biological nitrogen fixation (BNF) as part of input data. By the application of these concepts in any agricultural system, the system should maintain sustainable mineral availability in the soil and results in a balanced nutrient management system (BNMS), (IITA, 1997).
A good knowledge of possible changes of nutrient stock of a system involves balancing of nutrient input and output in the system (nutrient flow analysis). Nutrient flow analysis using an approach based on “balance” is one of the possible ways to estimate the diversities in the sources and flows of nutrient content of a system (applied fertilizer, fertility in soil, plant mineral uptake and crop residue). It quantifies the whole system management method together with their cost and time. However, nutrient balances involving flows of few nutrient elements are considered “partial balances” because they basically show only a portion of what the farmer takes out of the system and what they put back (Browner and Powell, 1993). They do not include the farmers’ action while managing the farm in terms of cost and time rather helps to understand the status of soil fertility. When the nutrients extracted from the soil roughly equals the nutrient brought back, it would be assumed that the system is in equilibrium. A large negative or positive difference is cause for concern and will require some form of correct action. Nutrient accumulation occurs only when more nutrients are added than removed. A negative balance means that the production system is being degraded as the store of available soil nutrient is depleted. Nutrient stock: balance ratio (NSB) which is an indicator for sustainability gives a more accurate indication on the length of time in years farming can continue in the same way, given the available nutrients.
Ledgard, (2001) noted that intercropping promises sustainable plant production Aggarwal et al. (2002) suggested that to select and integrate legumes into various production systems should maintain a non-declining mineral trend from crop cycle to crop cycle. The rate of replaced nutrient within or between cropping cycles must at least equal the rate of removable during the previous cropping. Benefiting effect of succeeding crops after legumes which were recorded by many workers (Touchtors et al., 1982; Thimonier et al., 2000; Alewell et al., 2000; Krajiek, 2001) were traced to the decomposition of litter deposits and sloughed off dead nodules left in the soil (Bohra and Singh, 1990).
The challenge therefore, is to sustain soil fertility over time. It requires judicious system management and integration of crops for biological mineral fixation to achieve favourable nutrient balance. The use of soybean in legume/non legume crop production system has been sparingly exploited with cassava. There is need to identify legume (soybean) cultivars capable of near maximum levels of N fixation and dry matter accumulation in our soils and utilizing them in such intercropping system. Results from work carried out by the International network on soil fertility and fertilizer evaluation for rice (INSFFER) indicate that incorporation of one crop of Azolla anabena increased rice yield as does the input of 30 Kg urea ha-1 (Watanabe, 1987). In addition, repeated incorporation of Azolla improved soil structure significantly (Lumpkin and Plucknett, 1982). Likewise, inclusion of soybean in cassava-based cropping system improved chemical properties of the soil (Umeh, 2002). Repeated incorporation of soybean residue into the soil over .a period of time should have also the potential to improve soil structure as does Azolla spp. The incorporated plant residue absorb soil nitrate, reduce leaching and stimulates yields of non-nitrogen fixing crop (Ladha and Reddy, 2003). It has been reported that potential contribution of cowpea to a subsequent crop increased with maturity class of cowpea (Abaidoo et al., 1999). Soybean mineral contribution to associate crop may increase also with maturity class of soybean and influence the nitrogen balance of the soil for both accompanying and subsequent crops. Letting legume crop residue ploughed-in or recycled into the soil should increase soil humus content, stabilize C/N ratio and thereby reduce volatilisation of minerals during decomposition. Low C/N ratio favours high rates of mineralization and volatilization (Ladha and Reddy, 2003).
The increasing world population and limited availability of energy has prompted a recent surge of interest in cassava, not only for traditional use as a human food, but also for specialised starches, animal feedstuff and then industrial uses. Cassava, which has been reported as the 4th most important energy staple of the tropics, providing food and income for more than 750 million people annually (FAO, 1992) is still cultivated on small farms, with little technology. Nigeria being one of the leading nations of the world in cassava production has depended largely on use of chemical fertilizer. Leihner (1988) noted that cassava removes about 90 Kg N ha-1 from soil in a cropping season. Within the derived Savannah ecology, cassava fertilizer K and N recommendation of 112 Kg K ha-1 and 120 Kg N ha-1 was for optimum productions in pure stands (ARTS, 1994). Since the mid 1990’s it has been suggested that to argument this fertilizer need for the higher yield of cassava and to sustain the growing human population without further degrading the soil, this integration of biological nitrogen fixation and nutrient stock balance are needed (Aggarwal et al., 2002). Very few studies have pursued this suggestion. The objectives of this research were to
(1) select soybean variety most suitable for intercropping with cassava, and determine the combined effects of fertilizer (N and K) on the growth and yield of the crops.
(2) determine N and K levels in the crop and soil at different cropping systems and predict sustainability using nutrient stock: balance ratio,
(3) determine the cropping system efficiency from land equivalent ratio and Area x Time equivalent ratio and
(4) determine the effect of soybean residue management on cassava yield and soil properties.
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