Proceso Productivo de la Achira en los Municipios del Departamento

Rainfall is undoubtedly the most important climatic factor to be taken into account when considering growing peas (Gane et at., 1 984). Heavy and prolonged rain is not required, but showers during flowering are likely to i n c rease yield while rainfall at the e n d of the floweri n g period is detrimental because it encourages moribund leaves to stick to young pods and become colonised by Botrytis which reduces yield and quality (Gane et a/., 1 984).

Acute deficiencies in moisture supply resulting from temporary but severe drought can have disastrous effects, especially during the seed development period, because they interru pt see d development and result i n light,

shrivelled seed (Del ouche, 1 980). The pea is very sensitive to moisture stress at both flowering and pod filling but i t will also not tolerate waterlogging (Logan, 1983; Gane et al., 1 984; Gane, 1 985).

Ordinary leafed pea plants have been shown to be extremely susceptible to injury by soil waterlogging (Jackson, 1 985). Stomatal closure after 24 h of waterlogging is one of the earliest symptoms and is presumably responsible for slower transpiration and at least some of the loss in dry weight gain suffered by fl ooded plants, alth o u g h flooding may also disturb the biochemistry of photosynthesis (Bradford, 1983). Concomitant increases in the concentration of ABA suggest that an accumulation of this hormone may be the cause of stomatal closure.

The foliage of waterlogged plants begins to lose its turgidity after about 6

days which is closely associated with membrane damage that disrupts the osmotic relations on which the retention of water by the leaves depends.

\

The cause of this membrane injury is unknown but phosphorous toxicity

may be partly responsible (Jackson, 1 985). Leafless peas are more resistant

to waterlogging compared with leafed peas (Jackson, 1985).

Irrigation rarely increases yield when applied before the start of flowering and petal fall, because it depresses growth (Salter, 1963). Peas should not be irrigated before flowering unless:

1 . The seed bed is very dry and adequate germination would not otherwise occur.

2. Increased haulm length is required on short strawed cultivars to

facilitate harvesting.

3. The crop is severely wilted because of drought (Gane et al., 1 984).

Irrigation is needed at the commencement of flowering when the peas are most responsive because the root system has ceased to grow, making the plan t more vu lnerable to water shortage (Gane et at. , 1 9 84). Y ield increases can be very substantial, up to 50%, because more pods and more peas per pod are produced, and the haulm weight is increased (Gane, 1 985).

response being due to the occurrence of a slight renewal of root growth (Gane et al., 1984). Irrigating peas at the pod swelling stage increased the yield by up to 20%, due to an increase in the number of peas per pod and mean seed weight.

In New Zeal and , irrigati on is used in garden pea production for the following reasons (Freeman, 1987):

1 . Under the garden pea pricing formula, which is based on machine dressed weights, a farmer could have a very substantial dressing loss if peas are not irrigated for maximum pod fill.

2. Irrigation is done twice before budding to promote vine growth for easier harvesting.

3. Irrigating once at the flowering stage and once or twice at the pod filling stage increases yield and reduces the risk of undersize peas. Therefore drier climates for pea production are preferred, because of the ease of irrigation management, and the absence of wet ground due to rain which can result in stunted growth, poor colour and high mildew incidence (Freeman, 1 987). Under Canterbury, New Zealand conditions, irrigation every 1 4 days with an application of 50 mm at each pass is practiced (Freeman, 1987).

In an experiment on a dry Canterbury soil, irrigating peas at flowering and pod swelling increased green pea yield by 84% and seed yield by 78%, because of increases in pod plane 1 , peas pod- 1 and pea weight (White et al., 1982).

With irrigation, peas pod- 1 increased at populations of 83 to 1 09 plants m-2 but were not significantly different at 1 35 plants m-2 (Anderson and White, 1 974). Stoker ( 1 975) found that under dry land conditions, the optimum population density was 7 1 plant m-2 but with irrigation this could increase to 104 plants m-2, and finally to 1 2 1 plants m-2 with more frequent border dyke irrigation.

These experiments provided a basis for recommendations in New Zealand (Stoker, 1 975). Without irrigation, 70 plants m-2 would seem to be the optimum on shallow soils (Stoker, 1975), increasing to 90 plants m-2 on deeper soils (Anderson and White, 1 974). With irrigation, these densities can be increased to 1 20 - 1 3 0 pl ants m-2 (Anderson and White, 1 974; Stoker, 1975).

H owever, moisture has a deleterious effect on pea seeds during harvest. Seeds harvested after periods of heavy rain appeared to have reduced percentage viability and increased percentage mortality in soil (Flentje, 1 964 ; Matthews, 1 973). Th is effect of rainfall on seed moisture content could have occurred through an increase in the uptake of moisture by the plant from the soil or b y the more direct effect of rain on the pods (Matthews, 1 973). Aside from these reports, there are as yet no studies concerning the effect of moisture on seed quality in garden peas.