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There is an increasing interest for use of cover crops in orchards; however, the species that are most likely to be successfully implemented and their impact on yield and soil productivity have not been fully explored under Maritimes climate. This study investigated the effect of various cover crops treatments on organic apple (Malus domestica Borkh cv. Honeycrisp) yield and leaf nutrient concentrations in Nova Scotia over 3 years. Various cover crop mixtures including legumes, cereals, and grasses were planted using a modified Swiss Sandwich System (SSS). The cover crops treatments did not affect apple yield. In 2012, the input of biomass to the soil was 89%and 144%greater for alfalfa (ALF) and other cover crop treatments than unseeded (CON) treatment, respectively. The pea, oats, vetch mixture (POVM) contributed 24% higher biomass N to soil compared with average of other cover crops in 2012. Soil available K concentration in the tilled strip was increased in the 3rd year of the study compared with the initial values across cover crop treatments. The red clover oats mixture (RCOM), POVM, and Triple Mix (TM) treatments appeared to add the greatest amount of available K to the soil among treatments. The CON, TM, and ALF treatments resulted in higher leaf Mn concentration inonly 2012 and CON, sweet clover and oats mixture (SCOM), and ALF resulted in higher leaf P concentration in 2014, compared with other treatments. Cover crops did not compete with apple trees and their most beneficial and consistent contribution was to total C, total N, and K input to the soil. [ABSTRACT FROM AUTHOR]

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Livestock manure is an important source of N for forage grass production. The long-term effects of semisolid beef manure application to forage grass on potentially mineralizable N (N 0), mineralizable N pools, and field estimates of soil N supply were evaluated in dike-land (heavy textured, poorly drained) and upland (medium-textured) soils in Nova Scotia, Canada. Treatments included an unfertilized control, annual spring application of 100 kg N ha-1 mineral fertilizer or annual applications of 75, 150, or 300 kg total Kjeldhal N ha-1 as manure (M75, M150, and M300, respectively) from 1995 to 2004. Soil samples collected in fall 2004 were used to estimate N0 using a 44-wk aerobic incubation at 25°C. The N0 values were 62 and 49% higher in the M300 treatment (324 and 480 kg N ha-l) than the other manure treatments (199 and 323 kg N ha-1) for the upland and dike-land soils, respectively. The mineralization rate coefficient ranged from 0.045 to 0.082 wk-1 Manure application increased the readily mineralizable N pool (Pool I); higher rates of application resulted in higher values in both soils. The intermediate and stable mineralizable N pools were increased only by the M300 treatment in the upland soil but not in the dike-land soil. Long-term manure application of the M300 treatment resulted in high N0 with no yield benefits, which can increase the risk of N losses to the environment in both soils, whereas Pool I was responsive to all manure application rates. [ABSTRACT FROM AUTHOR]

Accurate estimation of soil nitrogen (N) supply in the field is required to optimize fertilizer N management and to minimize environmental N losses in humid environments. Laboratory-based measures of N availability were evaluated as predictors of field-based indices of soil N supply within potato production systems. Pre-plant soil samples (0–15 cm) were collected from a series of forty treatments in established potato trials located in Atlantic Canada and Maine, USA. Total plant N uptake at topkill with no fertilizer N applied (PNU0N), PNU0N plus soil mineral N to 30 cm depth at harvest and relative yield were considered as field-based indices of soil N supply. The potentially mineralizable N (N0) was determined by aerobic incubation at 25°C and periodic leaching for 24 weeks. A series of laboratory-based measures of soil N supply were measured in soil samples. Pre-plant soil nitrate or total mineral N at 0–30 cm depth was the best single predictor of PNU0N ( r = 0.67 and 0.71, respectively) and relative yield ( r = 0.58 and 0.61). The ultraviolet absorbance of 0.01 M NaHCO3 extract at 205 nm (NaHCO3-205) was suitable as a predictor of PNU0N and relative yield in each growing season, however, the relationship between this parameter and PNU0N or relative yield varied somewhat among years. A combination of pre-plant mineral N plus N mineralized in the first 2 weeks period of incubation after re-wetting is proposed as a more robust measure of N availability compared with use of mineral N alone. [ABSTRACT FROM AUTHOR]

Information on nitrate uptake kinetic parameters, and their variation among cultivars, is lacking for potato. A growth room solution culture experiment with five potato cultivars (Atlantic, Chieftain, Red Pontiac, Russet Norkotah and Shepody) at three sampling dates [10, 17 and 22 days after transplanting (DAT)] and three replicates was conducted to investigate the variation in nitrate uptake kinetic parameters among cultivars and with plant age during vegetative growth. Potato plantlets from tissue culture were grown in a re-circulating hydroponic system. On each sampling date, depletion of nitrate concentration in 3 L of nutrient solution by a single plant was measured over a 360-min period. Nitrate influx parameters were calculated from depletion curves. Root length (RL), average diameter and root/shoot ratio were determined and relative growth rate and plant N demand per unit of RL were calculated. The maximum influx ( I max) ranged from 1.30 to 3.65 pmol cm−1 s−1 and was significantly different among cultivars. Russet Norkotah and Atlantic had the highest values of I max at 22 DAT. Values of the Michaelis constant ( K m) and minimum concentration ( C min) were not significantly different among cultivars except for Red Pontiac which had the highest values of K m and C min. The I max of all cultivars decreased over time. There was a strong negative correlation between I max and RL. The plant N demand per unit of RL explained more than 50% of variation in I max among the cultivars at 17 and 22 DAT. The results suggest that I max in combination with root morphology may be important in controlling differences in N uptake efficiency among potato cultivars. [ABSTRACT FROM AUTHOR]