Soil Depth Coupled with Soil Nitrogen and Carbon can Improve Fertilization of Rice in Arkansas

Abstract

Success of alkaline bydrolyzable nitrogen (AHN) to predict N fertilizer needs when soils were sampled over the effective rooting depth of the crop rekindled an interest in more traditional soil procedures including soil total nitrogen (STN) and total carbon (STC). The benefits of a N soil test that can accurately predict N fertilizer needs are not solely about optimizing economic or agronomic returns, but include making environmentally sound N fertilization decisions. This paper presents the results of a study assessing the ability of STN and STC to predict the N fertilizer needs of direct-seeded, delayed-flood rice (Onza saliva L.) produced on silt loam soils in Arkansas. Twenty-five N response trials were conducted from 2004 to 2008 to correlate STN and STC with rice response parameters such as total nitrogen uptake (TNU), check plot grain yield, and percent relative grain yield (RCY) and calibrate STN and STC to predict the fertilizer N rate required to achieve 95% RGY. Relationships with the selected parameters were evaluated for both methods over a series of soil depth increments using linear regression models. Soil TN was significantly and positively correlated with all rice response parameters except check plot grain yield at the 15-to 30-and 45-to 60-cm depths. Coefficients of determination were greatest for percent RGY at the 0-to 45-cm depth for STN (/-= 0.62) and STC (/-= 0.33). Calibration of the fertilizer N rate to achieve 95% RGY mimicked correlation of rice response parameters with soil depth, but with higher /-values. The highest coefficients of determination were observed in the 0-to 45-cm depth where STN explained 74% and STC explained 54% of the variability in the fertilizer N rate required to achieve 95% RGY. These relationships indicate the importance of proper sampling depth for successful correlation and calibration of soil analytical methods.Abbreviations: AHN, alkaline hydrolyzable nitrogen; DSD, direct steam distillation; ISNT, Illinois soil nitrogen test; RGY, relative grain yield; STC, soil total carbon; STN, soil total nitrogen; TNU, total nitrogen uptake. N itrogen fertilizer represents the primary input cost for most crop production systems and most crop plants are often deficient in N especially in the absence of N fertilizers. To prevent N deficiencies and improve crop yields soil fertility .specialists have attempted to predict N rates required to optimize crop yields and maximize economic returns using sound research based on crop response to N fertilizer. To date the majority of N recommendations are based on yield goal approaches (Lory and Scharf, 2003; Dahnke, 1973) that do not account for the N supplying power of the soil which can have extreme variability from site to site within a relatively small geographic region (Stevenson and Cole, 1999). Research has proposed many direct and indirect methods to estimate potentially mineralizable soil-N; however, residual or inorganic-N testing is the only index of N availability that is used on a wide scale (Dahnke and Johnson, 1990).

Strengths and Limitations of Nitrogen Rate Recommendations for Corn and Opportunities for Improvement

“…We suggest that a more in-depth understanding of BBC, with its recognition of the importance of plant-soil-weather interactions, can help improve field testing of proposed soil N mineralization tests and thereby improve N recommendations for corn. Nitrogen recommendations in irrigated systems, as shown in irrigated rice systems (Roberts et al, , 2012, are more accurate and precise because predicting the N dynamics in the plant-soil-weather conditions of a field are less complex due to almost complete elimination of uncertainty caused by rainfall. Predicting the total amount of plant available N and its timing of release in relationship to crop needs over a growing season is substantially more difficult due to the interaction of rainfall with soil properties, soil management practices, and rotations.…”

Soil tests for predicting nitrogen supply for grassland under controlled environmental conditions

“…These fundamental requirements of a soil N test have contributed to the development of numerous chemical N tests in an effort to find suitable alternatives to the biological N tests (Griffin 2008;Ros et al 2011). Worldwide, the most prominent chemical index of N availability is testing for soil mineral N levels (Dahnke & Johnson 1990;Roberts et al 2012). However, under humid and high rainfall climates, these tests are of limited value as soil mineral N pools are too dynamic and transient for making even short-term predictions (Keeney 1982).…”

Evaluation of Soil Tests for Measuring Potentially Mineralizable Soil N in Southern Idaho Soils

“…The DSD soil test measures alkaline-hydrolyzable N (i.e., NH 4 -N, amino sugars, and some amino acids) and has been successfully correlated and calibrated in Arkansas and is now widely used within the state for fertilizer N recommendations for rice producers where flooded conditions alter N mineralization dynamics (Roberts et al, 2013). In addition to specific soil tests, sample depth in combination with soil N and C has been shown to be an important but sometimes overlooked factor (Roberts et al, 2012). Roberts et al (2016) recently patented a novel technique for measuring potentially mineralizable N based on measured ASN that uses a standard 2 M KCl extract and fluorometric principles to quantify amino sugar compounds.…”