Bibliography
T RIAL 2: L EGUME COVER CROP TO INCREASE SOIL NITROGEN AND INCREASE YIELDS
It is assumed there are two cropping seasons per year, the legume is sown in the first cropping season, eliminated as a cover crop at the pod-filling stage, and the grain crop is sown at the beginning of the second season.
Materials required:
Machinery, implements, and inputs required for land preparation, sowing, fertilisation, manuring, weeding, and control of pests and diseases for the grain and legume crops, machete or contact herbicide, stakes, spring balance or scales.
Procedure:
1. Select a field which is typical of the soils, cropping and management history of the area, and which is known to suffer from nitrogen deficiency.
2. Prepare the land according to normal farmer practice, and mark out adjacent treated and control
plots of 200 m2 (10 m x 20 m) in a representative part of the field.
3. Sow the legume in the treated plot only at the recommended spacing, and sow the control plot to the same first season (non-leguminous) crop as the rest of the field.
4. If the soil is phosphorus-deficient, incorporate P fertilizer at the recommended rate to the whole field at the time of sowing so that N-fixation is not inhibited. Apply the usual fertilisation, manuring, weed, pest and disease control practices.
5. When the legume reaches the beginning of the pod-filling stage, observe the degree of nodulation, then eliminate it by cutting with a machete, mowing, rolling and cutting (using a rollofaca) or by applying a contact herbicide.
6. Harvest the crop in the control plot and the rest of the field following normal farmer practice. 7. Prepare the land for the subsequent grain crop in the control plot and the rest of the field
following normal farmer practice. Leave the residues on the surface of the treated plot. 8. Sow the entire field including the two plots with a grain crop that responds well to nitrogen. A no-
till seeder will probably be needed to sow the treated plot.
9. Apply the normal fertilization, manuring, pest and disease control practices to the whole field. Weed control in the treated plot will be by herbicide applications whereas either herbicides or mechanical control may be used in the control plot and the rest of the field.
10. During the growth of the grain crop, visit the site every 2-4 weeks, and monitor the following indicators for the treated and control plots:
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crop appearance (foliage colour, nitrogen deficiency symptoms),•
crop growth (height, vigour),11. Harvest and record the yields of the grain crop from the treated and control plots.
12. Evaluate the legume cover crop treatment in terms of crop yield, profit (gross margin), and nitrogen supply. Discuss advantages and disadvantages of the practice and for what types of soil and crops the practice will be feasible.
Note: It is assumed that low levels of nitrogen fertiliser are applied; if optimum nitrogen rates are applied, the fertilizer applied to the treated plot may be reduced by about 40 kg N/ha depending on how much nitrogen the legume is expected to fix and release to the next crop.
Note: Darker green foliage in the treated plot should be taken as evidence of greater nitrogen availability. Encourage participants to identify nitrogen deficiency symptoms in the control plot using the key to foliar nutrient deficiency symptoms given in Annex 6.
Annex 1: Examples of discovery-based exercises and trials 70
TRIAL 3: COMPOSTCOMBINEDWITHMINERALFERTILIZERTOOVERCOMENUTRIENTDEFICIENCIESANDINCREASEYIELDS Materials required: Machinery, implements, and inputs for land preparation, sowing, fertilization,
manuring, weeding, and control of pests and diseases, compost for 200 m2, stakes, spring
balance or scales, paper and markers, blackboard and chalk.
The procedure presented here assumes that fertilizer recommendations exist for the cropping system, and so the treatments to be tested are:
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the recommended nitrogen application rate as inorganic fertilizer (Plot A),•
the recommended nitrogen application rate, part supplied by inorganic fertilizer and part bycompost (Plot B),
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no fertilizer or compost (the control - Plot C).The phosphorus and potassium fertilizers are applied at the recommended rates as a basal application.
Procedure:
1. Select a field which is typical of the soils, cropping and management history of the area, and which is used for horticultural crops. Decide which crop is to be sown for the test.
2. Prepare the land following normal farmer practice, and mark out with stakes three plots of 100-
200 m2 each, referred to as plots A, B and C, ensuring that all plots are representative of the
dominant soil type, cropping and management history of the field.
3. Apply fertilizers and compost at the recommended rates and according to the treatments given above. Follow normal farmer practice in terms of the timing of application, i.e. how much of the inorganic nitrogen fertilizer is applied as a basal dressing, and how much as top or side dressings, and the method of applying the basal dressing, e.g. by broadcasting and incorporating or by placing in bands to the side of crop rows.
4. Sow the field, including the three plots, to the agreed crop. 5. Apply normal weed, pest and disease control practices.
6. During the growth of the crop, visit the site every 2-4 weeks, and monitor the following indicators for each plot:
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the appearance of the crop (colour of the foliage, foliar deficiency symptoms, crop height,vigour, number and size of the fruits),
7. Harvest the plots separately, and record the yields.
8. Evaluate the two fertilizer/compost treatments by comparing the yields, evidence of nitrogen deficiency, and profits (gross margins) with those of the control.
TRIAL 4: DEEPCULTIVATIONTOENCOURAGEDEEPERROOTING, GREATERSOILW ATERAVAILABILITYANDHIGHERYIELDS Materials required: Spades or hoes, pickaxe, subsoiler or paraplough, machinery, equipment
and inputs for land preparation, seeding, weeding, harvesting and the application of fertiliser, manure, herbicides and pesticides, stakes, spring balance, paper and markers.
Procedure:
1. Select a field where problems of restricted water availability due to dense subsoil layers impeding root penetration are known to occur. The soil should be representative of the soils of the area in terms of morphology, cropping and management history.
2. Confirm the presence of these dense root-restricting subsoil layers by digging a soil pit in the field. Examine the soil profiles and determine the depth to the upper and lower boundaries of the dense root-restricting layer.
3. Decide which crop is to be sown; it should be a crop that is sensitive to moisture stress and which responds well to deep tillage.
4. Select and mark out with stakes two similar plots - treated and control plots, of not less than 50 m x 20 m each, which are representative of the whole field in terms of soil characteristics, cropping and management history.
5. Prior to normal land preparation when the soil is dry to slightly moist, use a subsoiler or “paraplough” to loosen the subsoil in the treated plot only. The depth of penetration should be approximately 10 cm deeper than the lower limit of the dense root-restricting layer, and the spacing of the subsoiler shanks should equal the depth of subsoiling for narrow-spaced crops, or correspond to, and coincide with, the row spacing for widely spaced crops.
6. Prepare the land for the whole field using normal farmer practice, and avoid excessive tractor passes as this may cause compaction and offset the benefits of the subsoiling; greater benefits are likely to be obtained with minimum tillage for land preparation.
7. Sow the whole field with the agreed crop, and apply the same fertilisation, manuring, weed control, pest and disease management practices to both treated and control plots.
8. Visit the site at 2-4 week intervals during the period of crop growth and monitor the following soil and crop indicators:
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the appearance of the crop (degree of wilting during dry periods, height, vigour),•
depth of rooting * (determine at flowering and during pronounced dry periods),•
soil moisture within and below the rooting zone (determine at flowering and duringpronounced dry periods),
9. Harvest the two areas separately, and record the yields.
10. Evaluate the deep tillage treatment by comparing the depth of rooting, soil moisture contents during dry periods, yield and profit (gross margin) with that of the control plot.
* To observe the depth of rooting, dig a small 50 cm-deep pit of 1 metre length, parallel and close to the crop rows in both the treated and control plots. Compare the depths of rooting and soil moisture contents above and below the root-restricting layer in the plots.
Annex 1: Examples of discovery-based exercises and trials 72
TRIAL 5: LIMINGACIDSOILSTOREDUCEALUMINIUMTOXICITY, INCREASE P AVAILABILITY, PROMOTEDEEPERROOTING,