The absence of an effect of the na/ca ratio on sodium chloride uptake by rice (Oryza sativa l.).

The effect of the Na/Ca ratio in the growth medium on the response of the salt-sensitive crop species Oryza sativa L. to NaCl salinity was investigated. No effects on growth or salt concentration in the shoot were found over a range of Na/Ca ratios (5 to 25) considered likely to be commonly encountered in saline situations in the field, and even at extreme Na/Ca ratios (100 to 500) there were only marginal increases in NaCl entry to the shoot. Increasing the Ca concentration in the growth medium over a wide range did not, therefore, ameliorate the effects of salinity on rice seedlings. Polyethylene giycol at low, osmotically negligible, concentrations reduced the movement of CI to the shoot by 60 to 70% even in the presence of adequate (3.5 mol m−3) Ca. It is concluded that membranes of rice roots respond weakly to Ca and that they are capable of better permeability control than is evoked by Ca ions. The relevance of this to the salt sensitivity of rice is discussed

Soil test calibration for predicting corn response to phosphorus in the northeast USA

The consensus of soil fertility specialists working in the northeast USA was that soil testing and recommendation systems for P needed to be reexamined because of recent changes in soil testing methodology in the laboratory and com (Zea mays L.) production technology in the field. Soil tests (M-COL, MM-COL, B-ICP, M1-ICP, and M3-ICP) were performed by either colorimetry or inductively coupled plasma (ICP) emission spectroscopy on samples from soil test calibration studies conducted daring 1998 to 1999 at 51 experimental sites chosen to represent a range of soils, including Ultisols, Spodosols, and Alfisols, in northeastern states (Connecticut, Delaware, Massachusetts, Maryland, Maine, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and West Virginia). The mean P measured by M-COL, MM-COL, B-ICP, M1-ICP, and M3-ICP was 8.3, 6.6, 148, 66, and 121 mg P kg-1, respectively. Production practices followed local state extension recommendations at each site and included P fertilizer treatments: none, 15 kg P ha-1 banded, or 60 kg P ha-1 broadcast. Combined analysis of variance over sites showed that plant height at 35 d after planting, silk emergence, grain yield, and grain dry down were enhanced by the broadcast P treatment. There were yield increases (P \u3c 0.10) to the band treatment at only four sites and to the broadcast treatment at nine sites. Cate-Nelson statistical analysis of relative yield in relation to soil test P failed to identify soil test P critical levels for any of the soil test methods. The percentage of experimental sites that had soil test P levels below the currently used critical levels in the region ranged from 14 to 65% of the sites. Results showed that 17 to 47% of those sites testing below the critical level exhibited a yield increase (P \u3c 0.10) to broadcast P. Some of the yield responsive sites had soil test P above currently used critical levels. The calibration data obtained from the present study and the relationships examined between soil test P and relative yield do not necessarily validate the currently used soil test P critical levels nor does the data enable much refinement. This study shows that the current critical levels frequently permit both types of errors in soil test prediction; indicating a need for P fertilization when it may not be needed and not indicating a need for P fertilization when it may be needed. The second type of error is usually avoided by recommendations for crop removal rates of P. © American Society of Agronomy