Implications of selecting for persistency on hydroponics in timothy (Phleum pratense L.)

Summary

Twenty four populations of timothy (Phleum pratense L.) with varying persistency were grown on a nutrient flow system and in soil. Growth analyses showed that seedlings grew faster on nutrient solution than in soil but this was only temporary. After the fourth cutting, regrowth of plants in soil was faster than on hydroponics, probably because the optimal growth conditions and the relatively high temperatures in the nutrient solution led to a depleted storage carbohydrate pool, necessary for regrowth.

Non-destructive growth analyses were carried out by monitoring the amount of acid needed to compensate for carbohydrate extrusion by the roots in exchange for nitrate uptake. It was assumed that regrowth was proportional to the NO₃ ^- incorporated in the plants. The calculated growth efficiency on hydroponics, averaged over all populations, ranged between 4.4 and 5.4 gram dry matter per megajoule photosynthetic radiation absorbed. The populations responded significantly differently to a frequent cutting regime. As a function of harvest number, the competitive ability of some populations decreased compared with the mean of all populations, while that of others increased or remained stable. The coefficients of genetic variation for shoot regrowth ranged between 0.16–0.22 for different harvests. For root regrowth and tillering the coefficients of genetic variation were even higher: 0.21–0.25 for the roots and 0.18–0.35 for the tiller number. Dry matter production was closely correlated with tiller formation (r=0.95).

The application of nitrogen to the nutrient solution was controlled by a simple computer model, which was based on the incoming radiation and which calculated momentaneous growth of the plants on a minutes time base. Thus an equilibrium between nitrogen application and the demand of the plants was maintained. During the last regrowth period, the nitrogen supply was limited to 30% of the optimal addition rate. The production of different populations under limited supply (sixth harvest) was closely correlated with that under optimal supply (fifth harvest), (r=0.7).