The effect of irrigation and time of harvest on maturity, yield, and gross return of four vining pea cultivars

Abstract

Four vining pea (Pisum sativum L.) cultivars 'Tere', 'Piri', 'Pania', and 'Greenfeast 68' (Gf.68) were grown either with irrigation at start of flowering and pod fill, or without (natural rainfall). Harvesting began once peas reached tenderometer (TR) 90 and continued daily until TR 140 was exceeded. Harvested samples were threshed in a mini-viner, and green pea yield, TR and average sieve size were measured. Subsamples were analysed for alcohol insoluble solids (AIS), total solids (TS) and weight per pea. Botanical characteristics, yield components and total vine yield were also measured.

TR was highly correlated with AIS and found to be a fast and reliable method for measuring maturity of peas, although the TR-AIS relationship varied between treatments. AIS and TS would be useful methods for measuring maturity when a tenderometer is not available.

Irrigation prolonged flowering, delayed harvest, and reduced the rate of TR advance during the first four days of harvest. Irrigation also prolonged the harvest period for all cultivars except Pania. The effect of irrigation treatments on green pea yield was confounded by a period of heavy rain which caused waterlogging and subsequent yield depression in irrigated treatments of Piri, Pania, and Gf.68. In contrast, the pea yield of the natural rainfall treatments was enhanced by the rainfall. The heavy rain prevented measurement of the differences in the yield response of cultivars to irrigation treatments. Total vine yield, stem length, and number of peas per pod were also adversely affected by waterlogging. Pea yield of Gf.68 was also reduced by vining difficulties attributed to the pointed pod of this cultivar. Tere, the earliest cultivar, was not adversely affected by the heavy rain. Irrigation enhanced green pea yield of Tere by 20% due to increases in the number of peas per pod and pods per node. Yield increased with maturation but the rate of increase became smaller with advancing maturity. The curvilinear yield-TR relationship became linear when yield was plotted against log(TR-75). Differences in yield-TR relationships were measured by comparing regressions of relative yield (yield at TR 105=100) against log (TR-75). The respective relationships for natural rainfall and irrigated treatments of Tere were:

Y = 27.5 + 49.1 X, and Y = -21.7 + 82.4 X, where Y = relative yield and X = log(TR-75).

The four cultivars did not differ from each other in their yield-TR relationships within each irrigation treatment. The yield-TR relationships of Piri, Pania, and Gf.68, in contrast to Tere, were unaffected by irrigation, although the period of heavy rain probably influenced these results.

The gross return-TR relationship was similar for all cultivar x irrigation treatments, indicating that one payment scale may be equally applicable to newer cultivars as it is to older, less determinate cultivars (e.g. Gf.68). Gross return was negatively correlated with maturity, and was highest for peas harvested below TR 100. The smallest gross returns for most treatments were for peas at TR 120 to 130.

Yield calculated from yield components over-estimated vining pea yield and was found to be unreliable as a method for yield prediction. This was attributed to problems associated with the early growth stage at which the yield components were measured.