Root and Foliage Growth of Oats at Several Levels of Fertility and Moisture

The effects of fertility and moisture on root and shoot gorwth of oats (Arena sativa L.) were studied in potculture experiments. An experimental unit was a 75-liter garbage can filled with low-fertility Thurman sand, embedded 0.6 m deep in the soil. Forty-eight can were covered with a plastic shelter to permit controlled moisture regimes. A factorial set of fertilizer treatments using two levels each of N (0 and ]40 kg/ha), P (0 and kg/ha), and K (0 and 93 kg/ha) were applied at seeding time. At the initiation of stem elongation, wet (field capacity) and dry (wilting coefficient) moisture regimes were imposed across all fertility treatments. Traits measured on the plant tops were plant height, number of tillers, number of spikelets per panicle, dry weight and stem diameter. Weights were taken on roots extracted from 0.007-m³ soil samples from the 0-15-, 15-30-, 30-45-, and 45-60-cm soil depths. The root and shoot growth responded more to fertilizer application when moisture was adequate than when deficient. Nitrogen and phosphorus, applied alone and in combination, gave more shoot and root growth than any other element or combination of elements. Shoot growth responded to added fertilizer in both the high and low moisture regimes, but root growth responded only in the wet regime. Leaching of the nutrients with surface irrigations caused maximum root response to N in the 30-45- cm zone, but for P, which resists leaching, maximum response was in the 0-15-cm zone. Reduced root-top ratios resulting from added moisture and fertilizer elements were due largely to large increases in top growth without concomitant increases in root growth. Increase in shoot weight from added fertilizer under the dry regime was not accompanied by increased root weight. We concluded that root response to added fertility could not be responsible for oat plants utilizing subsoil (30-60-cm depth) moisture to produce increased shoot weights.