Yield Prediction from Soil Fertility Management Parameters

Fearnside (1980) has done an effort to predict pepper productivity based on soil fertility and management parameters in the pepper growing areas along the transamazon highway of Brazil. According to this author, in Brazil black pepper is "doomed as a long term mainstay of colonist cash cropping due to its susceptibility to a number of devastating diseases." Fearnside developed a regression equation of yield on fertility (Y=-12.119+0.292A+0.382B-0.0552 where Y=pepper yield, A=pH of soil, B=carbon (per cent dry weight) and C=phosphate ppm), and that regression equation was found to be highly significant (p<0.0001). The prediction model was developed after taking into account the soil fertility, fertilizer application and related factors. But the author stresses the point that the ultimate fate of pepper in the area is hinged on the disease problem, as pepper life span is seriously cut short by Fusarium wilt. Chemical treatments can slow the progress of disease, but cannot stop it completely. The colonists there, were playing a losing battle using fungicides, and in that process, several farmers suffered chemical poisoning. Any pepper yield prediction should also take into account the Fusarium wilt incidence. The following parameters have been suggested for modeling the incidences (Fearnside 1981):

1. The entry of the disease into a virgin area in any given year;

2. The attack of any given patch of healthy pepper within the area in any given year, given that the disease has already entered the area;

3. The death of a patch of pepper in a given year, given that it is diseased;

4. The availability of a new resistant variety, given that the resistance of the current variety has been broken.

In addition, for yield prediction, the proportion of pepper production expected from diseased plants should also be estimated.

The first of these parameters can be calculated from the equation P=1-0.5 1/t, where P=the yearly probability of the disease entering a virgin area, and t=the average number of years needed for the disease to make its first appearance.

The probability for the second parameter will also depend on how many other patches of pepper have been attacked. Fearnside has estimated around two years. The third probability also varies with time, and an estimate of three years has been made. The probability for the fourth parameter is very remote. The probability for pepper production from diseased plants is around 0.5, assuming that the pepper plants in a patch are killed at a constant rate during the disease incidence, and that the plants are killed instantaneously. The parameters estimated by Fearnside (1981) for Fusarium incidence is given below.

Table 4.1A1 Parameters for disease incidence*

* Source: Fearnside (1981)

It was also assumed for prediction, that the pepper plants reach full production potential by fourth year (the proportion being 0.000, 0.40, 0.80 and 1.00 for 1, 2, 3 and 4 years). The productive life expectancy is 10-15 years (because dead standards are used), but Fusarium wilt prevents many of the plants from entering into this age group.

All the parameters were used by Fearnside in an AGRISIM model for developing the yield prediction. The author concluded that the prospects for pepper in the transamazon colonization areas are bleak.

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