Niveles de nitrógeno y edad de corte y sus efectos sobre el valor nutritivo y características fermentativas del maíz (Zea mays L.)

The experiment consisted of two dates of planting [in September (D1) and February (D2)] of maize (Zea mays L.) DKC 67-60, to evaluate the effect of four N fertilization levels (0, 56, 112 and 185 kg/ha) and three ages at harvest [70, 77 and 84 days after planting (DAP)] on dry matter yield (DMY) of the leaves, stem, ear and of the entire plant; and as indicators of nutritive value [crude protein (CP) and neutral detergent fiber (NDF)] of harvested material prior to ensiling. In both plantings, the levels of N affected (P<0.05) DMY of leaves, stems, ears and entire plant, exhibiting both a linear and a quadratic response, and suggesting that the optimum N application rate is between 112 and 185 kg/ha. Age at harvest date affected (P<0.05) DMY of stems, ears and entire plant, but not that of the leaves. Greater DMY was observed at 84 DAP for all components. The CP concentration was greater in the forage of the first planting (D1). Increasing N application rates increased CP, but had no effect on NDF concentration. Age at harvest had no effect on CP, but progressively increased NDF. Both pH and organic acid concentrations in the silages were similar with the four N levels; all of the silages showed good fermentation characteristics.El experimento consistió de dos fechas de siembra [FS; en septiembre (F1) y febrero (F2)] de maíz (Zea mays L.) DKC 67-60. En cada fecha se evaluaron los efectos de cuatro niveles de fertilización con nitrógeno (0, 56, 112 y 185 kg/ha) y tres edades de madurez [70, 77 y 84 días después de la siembra (DDS] sobre el rendimiento de materia seca (RMS) de las hojas, tallos, mazorcas y la planta entera; y como indicadores de valor nutritivo [proteína bruta (PB) y fibra detergente neutro (FDN] del material antes de ensilar. En ambas FS los niveles de N afectaron (P<0.05) el RMS de los componentes hojas, tallos, mazorcas y de la planta entera, exhibiéndose una respuesta lineal y otra cuadrática, por lo que la dosis óptima pudiera estar entre los niveles de 112 y 185 kg de N/ha. La edad de corte afectó (P<0.05) los rendimientos de tallos, mazorcas y de la planta entera, pero no el de las hojas. Los mayores RMS de todos los componentes se obtuvieron a los 84 DDS. La concentración de PB fue mayor en F1 que en F2. A medida que se aumentó la fertilización nitrogenada la concentración de PB también aumentó, pero la concentración de FDN no varió. La edad de corte no tuvo efecto en la concentración de PB, pero sí en la FDN (aumentando con la edad). El pH y los ácidos orgánicos de los ensilajes fueron similares con los cuatro niveles de N; todos los ensilajes mostraron características propias de un buen proceso de fermentación

PRESENCIA DE NEMATODOS EN PATRONES DE CÍTRICOS EN ISABELA, PUERTO RICO

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Yield, Decomposition, Mineralization and Nitrification of Annual Legumes in an Oxisol

Knowledge about seasonal and litter bag soil position effects on litter decomposition (k value), mineralization and nitrification rate of annual legumes in Puerto Rico is limited. This study determined dry matter yield (DMY), k value of litter bags placed below and above the soil surface, mineralization and nitrification rates of Lablab purpureus cv. “Rongai” and Mucuna pruriens (Velvet bean) seeded in the wet and dry season in Oxisol soils (Typic Eustrustox). There was an interaction (p < 0.05) for season and legumes on DMY, k value and N content. “Rongai” DMY was higher for the dry than wet season while Velvet bean had an opposite seasonal response. Higher k value occurred in the wet season for legumes, but “Rongai” had higher k than Velvet bean. For both legumes, N content was higher on litter bag placed below-ground in both seasons. However, in the wet season, there was less N in the above ground litter position. Higher inorganic N was observed at 90 days of soil incubation (DOI) suggesting that N was not available prior to 42 DOI. Nitrification rate was higher for “Rongai” at 22 DOI and lower at 42 and 90 DOI for both legumes. Both legumes enhanced inorganic N, but, regardless of season, Rongai supplied nutrients to the soil faster than Velvet bean. “Rongai” because of its higher k value than Velvet bean is recommended for fast growing row or vegetable crops in Puerto Rico

Carbon and Nitrogen Dynamics Affected by Drip Irrigation Methods and Fertilization Practices in a Pomegranate Orchard

Knowledge of carbon (C) and nitrogen (N) dynamics under different irrigation practices in pomegranate orchards is novel and essential to develop sustainable production systems. The aim of this research was to determine the effect of high-frequency drip irrigation and different rates of N fertilizer on C and N distribution in the soil and N uptake by pomegranate fruit and leaves. The main treatments were surface drip irrigation (DI) and subsurface drip irrigation (SDI), and the sub-treatments used were three initial N rates (N1, N2, and N3). As trees grew larger, the N application rate increased. From 2013–2015, trees received the following rates of N: 62–113 (N1), 166–263 (N2), or 244–342 kg/ha (N3). Soil and leaf total C (TC) and N (TN), soil dissolved organic C (DOC), soil nitrate (NO3−), and total N uptake by fruit were evaluated between 2012 and 2015. Soil samples were collected to 120 cm depth at 15 cm increments. DI resulted in higher concentrations of TN, TC, NO3−, and DOC in the upper 75 cm depth than SDI. The N3 treatment resulted in higher concentrations of TN, TC, NO3−, and DOC under both DI and SDI. Neither DI nor SDI at the N1 or N2 levels increased TN and NO3− concentrations at 105–120 cm soil depth, indicating reduced leaching risk using high-frequency drip irrigation. Higher N uptake by fruit was observed in SDI than in DI in 2014 and 2015, and in N2 and N3 treatments compared with N1 in 2013 and 2014. The data indicate that the application rate at 166–263 kg/ha (N2) provided sufficient N for a 4–6-year-old pomegranate orchard and that high-frequency SDI is a promising technology for achieving higher N use efficiency and minimizing leaching loss of NO3− and DOC

Long-rotation sugarcane in Hawaii sustains high carbon accumulation and radiation use efficiency in 2nd year of growth

Sugarcane has been a major agronomic crop in Hawaii with an unique, high-yield, two-year production system. However, parameters relevant to advanced, cellulosic biofuel production, such as net ecosystem productivity (NEP) and radiation use efficiency (RUE), have not been evaluated in Hawaii under commercial production. Recent demand potential has rekindled interest in Hawaiian grown biofuels; as such, there is a need to understand productivity under changing climate and agronomic practices. To this end, we established two eddy covariance towers in commercial sugarcane fields in Maui, Hawaii to evaluate the carbon balance and RUE of sugarcane under contrasting elevations and soil types. We combined the tower observations with biometric and satellite data to assess RUE in terms of net biomass accumulation and daily gross primary production. High, sustained net NEP was found in both fields (cumulative NEP 4.23–5.37 103 g C m2 over the course of the measurement period). Biomass RUE was statistically similar for both fields (1.15–1.24 g above ground biomass per MJ intercepted solar irradiance). Carbon accumulated in both fields at nearly the same rate with differences in cumulative biomass due to differing crop cycle lengths; cumulative gross primary productivity and ecosystem respiration were higher in the lower elevation field. Contrary to previous studies in Hawaiian sugarcane, we did not see a large decrease in NEP or increase in ecosystem respiration in the 2nd year, which we attributed to suppressed decomposition of dead cane stalks and leaves due to drip irrigation and drought. Biomass RUE also showed little decline in the 2nd year. The results show that Hawaiian sugarcane has a higher productivity than sugarcane grown in other regions of the world and also suggests that a longer (\u3e12 months) growing cycle may be optimal for biomass production

Effect of Long-Term Continuous Fumigation on Soil Microbial Communities

High value crop producers in California rely heavily on soil fumigation to control a wide array of soil borne pests including nematodes, pathogens and weeds. Fumigants with broad biocidal activity can affect soil microbial communities that contribute to nutrient cycling and plant nutrient uptake which can impact soil health. It is often thought that soil microbial communities make a relatively rapid recovery following fumigation. However, recently it has been found that repeated application of fumigants over time can have greater and longer lasting impacts on soil microorganisms than single fumigation events. Therefore, the main objective of this study was to determine the effect of long-term repeated application of fumigants on soil microbial communities and compare them with non-fumigated and organic sites. Soil samples were collected from fields in Watsonville, CA. Chronosequence sites were defined by number of years of annual fumigation (yaf) with methyl bromide (15, 26, 33, 39 yaf) at the time of sampling, and representative non-fumigated sites were also included for comparison. Phospholipid fatty acid (PLFA) analysis was used to analyze the samples. The canonical variate analysis showed that microbial communities in sites with a longer history of fumigation (33 and 39 yaf) were similar to one another; however, they differed significantly from 15 yaf site and further analysis concluded that non-fumigated sites were significantly different than fumigated sites. This study showed that the proportion of arbuscular mycorrhizal fungi (AMF) was lower in all fumigated (15, 33 and 39 yaf) sites as compared to their non-fumigated counterparts, which could be a threat to sustainability since AMF plays a major role in soil health and quality

Alfalfa Responses to Gypsum Application Measured Using Undisturbed Soil Columns

Gypsum is an excellent source of Ca and S, both of which are required for crop growth. Large amounts of by-product gypsum [Flue gas desulfurization gypsum-(FGDG)] are produced from coal combustion in the United States, but only 4% is used for agricultural purposes. The objective of this study was to evaluate the effects of (1) untreated, (2) short-term (4-year annual applications of gypsum totaling 6720 kg ha−1), and (3) long-term (12-year annual applications of gypsum totaling 20,200 kg ha−1) on alfalfa (Medicago sativa L.) growth and nutrient uptake, and gypsum movement through soil. The study was conducted in a greenhouse using undisturbed soil columns of two non-sodic soils (Celina silt loam and Brookston loam). Aboveground growth of alfalfa was not affected by gypsum treatments when compared with untreated (p > 0.05). Total root biomass (0–75 cm) for both soils series was significantly increased by gypsum application (p = 0.04), however, increased root growth was restricted to 0–10 cm depth. Soil and plant analyses indicated no unfavorable environmental impact from of the 4-year and 12-year annual application of FGDG. We concluded that under sufficient water supply, by-product gypsum is a viable source of Ca and S for land application that might benefit alfalfa root growth, but has less effect on aboveground alfalfa biomass production. Undisturbed soil columns were a useful adaptation of the lysimeter method that allowed detailed measurements of alfalfa nutrient uptake, root biomass, and yield and nutrient movement in soil

Effect of Long-Term Continuous Fumigation on Soil Microbial Communities

High value crop producers in California rely heavily on soil fumigation to control a wide array of soil borne pests including nematodes, pathogens and weeds. Fumigants with broad biocidal activity can affect soil microbial communities that contribute to nutrient cycling and plant nutrient uptake which can impact soil health. It is often thought that soil microbial communities make a relatively rapid recovery following fumigation. However, recently it has been found that repeated application of fumigants over time can have greater and longer lasting impacts on soil microorganisms than single fumigation events. Therefore, the main objective of this study was to determine the effect of long-term repeated application of fumigants on soil microbial communities and compare them with non-fumigated and organic sites. Soil samples were collected from fields in Watsonville, CA. Chronosequence sites were defined by number of years of annual fumigation (yaf) with methyl bromide (15, 26, 33, 39 yaf) at the time of sampling, and representative non-fumigated sites were also included for comparison. Phospholipid fatty acid (PLFA) analysis was used to analyze the samples. The canonical variate analysis showed that microbial communities in sites with a longer history of fumigation (33 and 39 yaf) were similar to one another; however, they differed significantly from 15 yaf site and further analysis concluded that non-fumigated sites were significantly different than fumigated sites. This study showed that the proportion of arbuscular mycorrhizal fungi (AMF) was lower in all fumigated (15, 33 and 39 yaf) sites as compared to their non-fumigated counterparts, which could be a threat to sustainability since AMF plays a major role in soil health and quality

Soil Carbon and Nitrogen Stocks of Different Hawaiian Sugarcane Cultivars

Sugarcane has been widely used as a biofuel crop due to its high biological productivity, ease of conversion to ethanol, and its relatively high potential for greenhouse gas reduction and lower environmental impacts relative to other derived biofuels from traditional agronomic crops. In this investigation, we studied four sugarcane cultivars (H-65-7052, H-78-3567, H-86-3792 and H-87-4319) grown on a Hawaiian commercial sugarcane plantation to determine their ability to store and accumulate soil carbon (C) and nitrogen (N) across a 24-month growth cycle on contrasting soil types. The main study objective establish baseline parameters for biofuel production life cycle analyses; sub-objectives included (1) determining which of four main sugarcane cultivars sequestered the most soil C and (2) assessing how soil C sequestration varies among two common Hawaiian soil series (Pulehu-sandy clay loam and Molokai-clay). Soil samples were collected at 20 cm increments to depths of up to 120 cm using hand augers at the three main growth stages (tillering, grand growth, and maturity) from two experimental plots at to observe total carbon (TC), total nitrogen (TN), dissolved organic carbon (DOC) and nitrates (NO−3) using laboratory flash combustion for TC and TN and solution filtering and analysis for DOC and NO−3. Aboveground plant biomass was collected and subsampled to determine lignin and C and N content. This study determined that there was an increase of TC with the advancement of growing stages in the studied four sugarcane cultivars at both soil types (increase in TC of 15–35 kg·m2). Nitrogen accumulation was more variable, and NO−3 (<5 ppm) were insignificant. The C and N accumulation varies in the whole profile based on the ability of the sugarcane cultivar’s roots to explore and grow in the different soil types. For the purpose of storing C in the soil, cultivar H-65-7052 (TC accumulation of ~30 kg·m−2) and H-86-3792 (25 kg·m−2) rather H-78-3567 (15 kg·m−2) and H-87-4319 (20 kg·m−2) appeared to produce more accumulated carbon in both soil types