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Assessment of net primary productivity of maize (Zea mays L)‐based agroecosystems is dependent on both above and belowground dry matter production that is ultimately returned to the soil as residue and decaying roots. Root to shoot ratio (R/S) is a parameter often used to estimate root biomass (RB) when shoot biomass is measured or estimated. The labor intensive nature of root sampling and wide variety of sampling techniques has lead to a paucity of maize RB data in the literature, and few researchers have endeavored to characterize R/S throughout an entire growing season. In this paper, the results of 45 maize root studies published in 41 journal articles are summarized and the data used to generate estimates of maize RB and R/S versus days after emergence (DAE). The data from these studies indicate that on average, RB was maximized just after anthesis at approximately 31 g plant−1 (13.6 g C plant−1) and that average R/S varied from a high of 0.68 at emergence to a low of 0.16 at physiological maturity. Net rhizodeposited C as a percentage of total net root‐derived belowground C at time of sampling (%NRC) was reported for 12 maize studies and varied between 5 and 62%. The wide variation in the %NRC was shown to be highly correlated with an index combining irradiance level, photoperiod, and ambient temperature, suggesting a strong dependence of net rhizodeposited C on rate of photosynthesis and soil respiration. The net belowground C deposition at maize physiological maturity is estimated as 29 ± 13% of shoot biomass C for maize that has not experienced stress.

An understanding of the effect of fertility management on soil surface fluxes of CO2, N2O, and CH4 is essential in evaluating C sequestration measures that attempt to increase the amount of crop residue returned to the soil through increased fertilizer inputs. In this study, soil surface CO2 flux was measured over a 27‐mo sampling period in continuous maize (Zea mays L.) plots managed under either an intensive fertility regime (M2) or recommended best management (M1). Flux was significantly higher in the M2 treatment on only 2 d during the first growing season. Annual estimates of soil surface CO2 flux, based on a modified exponential equation that incorporates leaf area index (LAI) to predict temporal changes in soil respiration, averaged 11550 kg C ha−1 yr−1 for both treatments (approximately 31.64 kg C ha−1 d−1 on average). Within row soil surface CO2 flux was, on average, 64% higher than between row flux. Plant population did not significantly affect measured soil surface CO2 flux. While fertility management had no significant effect on CH4 flux, N2O flux as measured on 3 d during the 2000 growing season was significantly higher in the M2 treatment. In 2001, no significant differences in N2O flux were observed, possibly due to changes in N management and irrigation method. Electrical conductivity measured during the 2000 and 2001 growing seasons was significantly higher in the M2 treatment while pH measured during the 2001 season was significantly lower for M2.

To help make decisions on shifting of crop species in water management strategies, information is needed on comparative water use characteristics of the principal row crops. The objective of this study was to compare the water use characteristics of six row crops grown in a replicated and randomized field experiment. Crops were corn (Zea mays L.), grain sorghum (Sorghum bicolor (L.) Moench), pearl millet (Pennisetum americanum (L.) Leeke), pinto bean (Phaseolus vulgaris L.), soybean (Glycine max (L.) Merr.), and sunflower (Helianthus annuus L.). Crops were grown near Manhattan, KS, on Muir silt loam (Cumulic Haplustoll) in 1981 and on Eudora silt loam (JFiuventic Hapludoll) in 1982, and near Tribune, KS, on Ulysses silt loam (Aridic Haplustoll) in both 1981 and 1982.Soil water content was determined to the 3.1-m soil profile depth by the neutron attenuation method. Measured evapotranspiration (ET) was calculated as the sum of soil water depletion, rainfall, and irrigation. Reference ET was calculated by using the original Jensen-Haise equation. The maximum value of measured ET /reference ET was greater for sunflower (1.35) than for the other five crops (ranged from 1.05 to 1.15). The mean daily water use rate of sunflower (6.1 mm d-1 ) was 22% greater than the mean of the other five crops (5.0 mm d-1 ). The mean dry matter water use efficiency was 17.5 Mg ba-• m-• for the group of C 3 crops (pinto bean, soybean, and sunflower) and 33.3 Mg ba-• m-• for the group of C 4 crops (corn, grain sorghum, and pearl millet). Sunflower depleted significantly more water from deeper soil depths (0.99-1.60 m) than the other five crops at Manhattan in 1981 and 1982. Our findings consistently showed that sunflower bad a greater daily water use rate than the other five crops.

Soil electrical conductivity (EC) is a useful indicator in managing agricultural systems, but tools for convenient and inexpensive measurements in the field are generally lacking. Handheld conductivity probes were designed to evaluate in-field naturally occurring and human-induced total soluble electrolyte levels in soil and water. The probes were used to survey and monitor EC in the field and to assess soil and water quality as related to environmental stability and sustainable food production. A pencil-sized 16-cm probe (PP) was connected to a handheld Hanna (DiST WP 4) conductivity meter, resulting in an economical, compact, and easy to use device. The tool provided accurate and precise results compared with laboratory instrumentation under standardized conditions of soil water content and temperature. Soil samples, varying widely in texture and organic matter content, and having ECs ranging from 0.13 to 2.32 dS m 21 were used for comparison. Mean values and coefficients of variation were similar for the PP and the commercial laboratory EC meter with values determined with the two instruments being strongly correlated (r 2 ¼ 0.96-0.99). The handheld and PP probes effectively replaced expensive and cumbersome laboratory and field instruments used to measure EC in water and soil samples. The 2271 probe measurements were useful alternatives to conventional methods as they enabled accurate and precise measurement of EC, were a manageable size for field use, and were reliable and economic. The utility of EC as an indicator of soil health, plantavailable N, and environmental quality is also presented.