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Maize (Zea nuJys L.) forage producers need more information on how N management affects dry matter (OM) yield, forage quality, and residual soil NO; -N concentrations. Studies were conducted in New York to evaluate three hybrids under different sidedress N rates (0, 56, 140, and 255 kg N ha-• at the V4 stage) and timing (70+ 70 kg N ha-• at V4 and V8 and 75+75+75 kg N ha-• at V4, V8, and R1 stages). The OM yields, which averaged 25% lower in 1991 (12.3 Mg ha-') compared to 1990 (16.9 Mg ha-1 ), responded curvilinearly to N rates with maximum economic yields of 140 and 160 kg N ha-•, respectively. Whole-plant neutral detergent fiber (NOF), acid deter· gent tiber (ADF), and N concentrations responded linearly to N rates in 1990 indicating that forage quality improved with each additional increment of N. Higher N rates, however, increased residual soil NO;-N concentrations in the upper 0.3 m soil depth in 1990 (0, 3, 30, and 32 mg kg-') and 1991 (0, 0, 17, and 17 mg kg-' for the 0, 56, 140, and 225 kg N treatments, respectively). Split·N applications compared to respective single rate N applications did not increase OM yields, Improve forage quality, or decrease residual soil NO;-N con· centrations. When applying higher rates of N fertilizer, maize forage producers must balance potential benefits of higher OM yields and improved forage quality with the potential risk of increased residual soil NO;·N concentrations.

Coffee (Coffea canephora var robusta) is grown in Southwestern Togo under shade of native Albizia adianthifolia as a low input cropping system. However, there is no information on carbon and nutrient cycling in these shaded coffee systems. Hence, a study was conducted in a mature coffee plantation in Southwestern Togo to determine carbon and nutrient stocks in shaded versus opengrown coffee systems. Biomass of Albizia trees was predicted by allometry, whereas biomass of coffee bushes was estimated through destructive sampling. Above-and belowground biomass estimates were respectively, 140 Mg ha À1 and 32 Mg ha À1 in the coffee-Albizia association, and 29.7 Mg ha À1 and 18.7 Mg ha À1 in the open-grown system. Albizia trees contributed 87% of total aboveground biomass and 55% of total root biomass in the shaded coffee system. Individual coffee bushes consistently had higher biomass in the open-grown than in the shaded coffee system. Total C stock was 81 Mg ha À1 in the shaded coffee system and only 22.9 Mg ha À1 for coffee grown in the open. Apart from P and Mg, considerable amounts of major nutrients were stored in the shade tree biomass in non-easily recyclable fractions. Plant tissues in the shaded coffee system had higher N concentration, suggesting possible N fixation. Given the potential for competition between the shade trees and coffee for nutrients, particularly in low soil fertility conditions, it is suggested that the shade trees be periodically pruned in order to increase organic matter addition and nutrient return to the soil.

Proper N management is important to optimizing profit and minimizing N loss. The efficiency of N use may be improved in humid regions with a reliable soil test to guide fertilizer N recommendations. Recently, a presidedress nitrate soil test (PSNT) has shown promise as a means of quantifying the size of the potential mineralizable organic N pool in soil. This study was conducted to determine if the PSNT could be used for corn (Zea mays L.) production to identify N responsive and non‐responsive sites, predict the economic optimum fertilizer N rate, and improve the current fertilizer N recommendation procedure. The PSNT gave a useful and defined critical level of 21 ppm nitrate‐N, delineating N responsive from nonresponsive sites. The success rate for making the correct decision about N responsiveness was 84%, indicating a good relationship between the PSNT and the ability of the soil to supply N. The PSNT was less precise in determining the economic optimum fertilizer N requirement (R1 = 0.50) for sites below the critical level. This probably was due to the inability of the PSNT to quantify organic N mineralization. The standard N recommendation, based on estimates of N availability from organic sources, was a slightly better predictor of the fertilizer N requirement (R2 = 0.67) than the PSNT. There is a need to further improve the methodology used for formulating fertilizer N recommendations. Research Question Proper N management is important to optimizing profit and minimizing N loss. The efficiency of N use may be improved in humid regions with a reliable soil test to guide fertilizer N recommendations. This study was conducted to determine if a presidedress nitrate soil test (PSNT) for corn could be used to identify N responsive and nonresponsive fields, predict the economic optimum fertilizer N rate, and improve the current fertilizer N recommendation procedure. Literature Summary Traditional fertilizer N recommendations are based on N credits from soil organic matter, crop residues, animal manures, and residual N carryover. The precision of the fertilizer recommendation is often variable owing to the difficulty in estimating N mineralization rates and N losses. Recently, a PSNT procedure was developed to measure the amount of soil nitrate in the surface 12 in. of soil when the corn is 6 to 12 in. tall. The PSNT has shown to be reasonably well correlated with the ability of the soil to supply N. Improvements in the fertilizer N recommendation through the use of the PSNT seem apparent. Study Description The study was conducted at 78 locations across New York from 1986 through 1991. Locations were selected to typify crop rotational sequences and N management practices. Multiple rates of fertilizer N were applied at 29 of the locations for the purpose of calculating economic optimum fertilizer N rates. The PSNT was correlated with relative yield at all sites. The relationship between the economic optimum fertilizer N rate, PSNT value, and the standard fertilizer N recommendation was compared. Applied Questions W...

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