A COMPARISON OF SOIL CORE SAMPLING AND MINIRHIZOTRONS TO QUANTIFY ROOT DEVELOPMENT OF FIELD-GROWN POTATOES

Root growth of potato (Solanum tuberosum L.) is sensitive to soil cond itions. A reduced root system size can result in reduced uptake of wat er and/or nutrients, leading to impaired crop growth. To understand th e mechanisms by which soil conditions affect crop growth, study of tem poral and spatial development of roots is required. In field experimen ts, effects of soil temperature, soil compaction and potato cyst nemat odes (Globodera pallida) on root growth of potato cultivars were studi ed using two methods: core sampling and vertically oriented minirhizot rons. Minirhizotrons showed relatively more roots in deeper soil layer s than core sampling, probably because of preferential root growth alo ng the tube. Spatial distribution of roots should therefore be analyse d by core sampling. To eliminate differences in spatial distribution, total root systems as measured by both methods were compared. Nematode s, cultivars and time did not affect the relationship between both met hods. Soil compaction, however, affected it because of a strong respon se of root length in bulk soil and small differences in root number ag ainst the minirhizotron, suggesting that soil coring has to be used to study effects of different bulk densities. With both methods, sequent ial measurements of roots give the net effect of root growth and decay . Data on root turnover can only be obtained with minirhizotrons by co mparing video recordings of different dates. Other information obtaine d with minirhizotrons is the average orientation of roots. Moreover, t he minirhizotron method has the advantage of demanding less labour.