Rainfall erosivity in south-central Nigeria

Rainfall data collected from 1986 to 1990 at Okomu (6° 25′N; 5° 12′E; 76 m above mean sea level), a humid forest area near Benin City, southern Nigeria, were used to evaluate erosivity characteristics. The average annual rainfall was 2048 mm and the distribution pattern was unimodal. 49% of rainfall amount fell at 7.5-minute intensities exceeding 25 mm/h. A maximum 7.5-minute intensity of 240 mm/h was observed at the site. The median rain drop size (D₅₀) was 2.3 mm. The mean monthly kinetic energy, using the Wischmeier and Smith (1978) recommended procedure, ranged from 1.5 to 87 MJ/ha; whereas the values ranged from 1.5 to 140 MJ/ha using the Kowal and Kassam (1976) equation. These results suggest that equations developed in the tropics would estimate kinetic energy higher than those developed in the temperate regions. The annual value of erosivity was 18510 MJ·mm/ha·h by the EI₃₀ index, 216 MJ/ha by the KE ≥ 25 mm/h index and 1329 cm²/h by the AI_m index. The study indicates that rainfall of small and large amounts are capable of causing soil erosion at the site because they often fall at erosive intensities and contain big drops. The complementary role of the small- and large-amount storms made the cumulative erosivity of the rains at the study site very high. The information provided in this study shall be useful in estimating the erosive nature of rain in similar environments and will augment other available information in drawing an iso-erodent map for Nigeria. Furthermore, the erosivity factor for soil loss estimation on monthly basis in the area of study can be quantified by selecting the appropriate index values for soil loss equations.     

Iso-erodent map of Zambia: Part I: The calculation of erosivity indices from a rainfall data bank

The first stage in the establishment of an iso-erodent map of Zambia is the development of a Zambian rainfall data bank, the calculation and discussion of three erosivity indices and correlating the erosivity indices with rainfall amount.The data bank is made up of 10 years of data from eight different meteorological stations representing the different rainfall zones in Zambia. The data bank includes

• 1.1. total rainfall amounts split into component rainfall amounts with constant intensity
• 2.2. kinetic energy calculations
• 3.3. the erosivity indices.

Three erosivity indices have been calculated: E130 (WISCHMEIER 1959), KE (KINNELL 1981) and ΣN_pI_p (LAL 1976). Daily amount of rainfall explained 96, 95, and 89% of the variation in those indices respectively.Although the three indices are of comparable value, advantages and disadvantages of each of them are discussed.This work will be the basis for modelling the monthly erosivity and finally for making the iso-erodent map of Zambia (see part II, this volume).     

Reduction in soil loss from erosion-susceptible soils amended with humic substances from oxidized coal

Soils that pose high risk of erosion require amendment with either natural or synthetic soil conditioners to reduce soil loss hazards. The objective of this study was to evaluate the potential of using coal-derived humic substances (as soil conditioners) to reduce runoff erosion on erosion-susceptible soils. Surface (0–20 cm) samples of severely degraded soils from Principina in Tuscany (Orthic Xerofluvent) and Bovolone in Venice (Udic Ustochrept) in Italy were used to assess the effects of five rates (0, 0.05, 0.10, 0.50 and 1.00 g/kg) of humic acids (HA) on soil loss and other hydrological parameters. A rainfall simulator was used to apply approximately 40 mm/h intensity rain for 1 h on soil beds of dimensions 2 m × 0.5 m × 0.01 m, packed at a bulk density of 1.20 Mg/m³ and inclined at a slope of 15%. The amount of soil eroded (E) and the time to initiate runoff (Rt) and drainage (Dt) were related to changes in the water-holding capacity and aggregate stability of the soils following the HA treatments. In the control treatments, the values of E, Rt and Dt were higher in the Principina than Bovolone soil. Increasing HA rates generally delayed Rt, accelerated Dt and reduced E substantially on both soils. On the Principina soil a reduction of about 36% in soil loss was obtained by adding only 0.05 g/kg of HA (equivalent to 100 kg/ha). On the sandier Bovolone soil, the same magnitude of reduction was achieved with 0.10 g/kg (200 kg/ha) of HA. Improvements in Rt and Dt from the HA amendments explained between 58 and 81% of the variation in E from both soils. Furthermore, improvements in the water retention capacity more than in the aggregate stability of these soils accounted for the reduced runoff erosion. These results show that amending erosion-susceptible soils with low rates of coal-derived humic substances is a potentially effective soil management practice for reducing erosion rates.     

Stabilizing steep slopes with geomembranes

The effects of five types of geomembranes, placed at the soil surface, on runoff and erosion on steep earth slopes were studied under laboratory and field conditions. In the laboratory, the soil samples were packed in boxes held at a 50% slope and subjected to three consecutive simulated rainstorms of 120 mm each. The membranes dissipated the drops' impact and reduced runoff significantly compared with the control. There was no significant difference among the membranes regarding their effect on the runoff. In the field, the membranes lined earth dikes of 33–60% slope and 12–20 m length, during 2 years. There was no runoff and erosion from the lined plots compared with 80–125 tonne ha⁻¹ of erosion in the control plots. No considerable wear and tear of the membranes was observed.     

Non-regular spatial patterns of plants and their effect on several agronomic traits per area

Based on several simplifying assumptions, a stochastic approach is developed that allows an estimation of the effects of non-regular spatial patterns of the distribution of individual plants on the mean value (K) of trait per area. In this approach, two random variables are attached to each plant: single plant trait measurement (E) and individual space per plant (A). The latter is estimated by the area of Thiessen polygons. K is calculated theoretically by the expectation of the ratio E/A. Appropriate approximations of this expectation depend on the means (Ē and Ā), coefficients of variation (v_E and v_A) of E and A and their correlation (r_EA). K can be decomposed into two additive terms: the first term gives the commonly used estimate Ē/Ā. If a functional relationship, E=h(A), between E and A is assumed, this first term is h(Ā)/Ā. In this study, the two relationships E=k₁+k₂ ln A and E=A/(k₃+k₄A) were used (with appropriately chosen constants k₁, k₂, k₃ and k₄). The second term in the decomposition of K can be interpreted as the effect of variable individual plant spaces on K.In this paper, these theoretical concepts were applied to 17 experimental data sets of three cultivars of winter oilseed rape (Brassica napus L.) with single plant measurements for the traits grain yield, number of pods, grain yield per pod, total dry matter, harvest index, 1000-grain weight, number of seeds and number of seeds per pod. The means, standard deviations and coefficients of variation of the individual plant areas exhibit a large variability. The differences within cultivars are larger than the differences between cultivars. The correlation coefficients between E and A can be positive and large (for grain yield, number of seeds and number of pods), small (for 1000-grain weight and number of seeds per pod) or intermediate (for total dry matter, harvest index and grain yield per pod). There were no significant differences in the goodness-of-fit for either of the tested relationships between E and A, although the logarithmic relationship seems to be slightly superior. There were only a few data sets where negative values were found for the percentage (K=100%) of the second term in the decomposition of K. This indicates an overestimation of K by the commonly used estimates Ē/Ā and h(Ā)/Ā, respectively. These overestimations, however, are less than 5.2%. In all other cases with positive values for the second term, K is underestimated by the common estimates with values from 0 up to 40%. With regard to the numerical amount of the second terms, the eight traits can be clearly partitioned into two distinct groups: group 1={grain yield, total dry matter, number of pods, number of seeds} with small percentages for the second term and group 2={1000-grain weight, harvest index, grain yield per pod, number of seeds per pod} with large percentages for the second term. The Spearman rank correlation coefficients of second term percentages (based on replications=data sets) for pairs of traits belonging to the same group are positive and large with larger values for group 2 than for group 1. The correlations between traits belonging to different groups, however, are intermediate or small.     

Effect of rice straw biochar and irrigation on growth,dry matter yield and radiation-use efficiency of maize grown on an Acrisol in Ghana

In order to determine whether the current low productivity associated with rainfed cultivation on degraded soils in Ghana can be improved by biochar amendment and irrigation, field experiments with maize were conducted over two seasons in 2017 and 2018. Rice straw biochar at rates of 0 t/ha (B₀), 15 t/ha (B₁₅) and 30 t/ha (B₃₀) was combined with irrigation regimes of full irrigation (I₁₀₀), deficit irrigation (I₆₀) and no irrigation (I₀). The I₁₀₀ treatment was irrigated to field capacity every 3–4 days according to time domain reflectometry measurements while the I₆₀ treatment received 60% of the irrigation amount given to I₁₀₀ but with the same irrigation frequency. The I₀ treatment was not irrigated. In both seasons, the B₃₀ treatment recorded the highest total dry matter yield (TDMY), intercepted photosynthetically active radiation (IPAR) and radiation-use efficiency (RUE) and these were significantly (p ≤ .05) higher than B₀ except for RUE in 2017. Irrigation regimes did not significantly affect TDMY, IPAR and RUE in 2017 but compared to I₁₀₀, I₀ significantly reduced TDMY, IPAR and RUE in the relatively dryer 2018 season. Measured ratio vegetation indices differentiated biochar treatments earlier in the 2018 season than during 2017 and increase of leaf chlorophyll content indices with biochar rate in both seasons indicated that biochar amendment improved nitrogen uptake. Our study demonstrated that rice straw biochar is capable of increasing TDMY, IPAR and RUE of maize grown on degraded soils in Ghana. The study further showed that TDMY, IPAR and RUE of deficit irrigated maize for two seasons were similar to the counterpart fully irrigated maize and may be a viable water management option for farmers in Ghana to save irrigation water resources.     

Irrigation and Nutrient Effects on Growth and Water–Yield Relationship of Wheat (Triticum aestivum L.) in Central India

Increasing production of wheat from a limited water supply can result from efficient irrigation and nutrient management. A 3‐year field experiment was conducted at the Indian Institute of Soil Science, Bhopal, to study the growth, yield, seasonal evapotranspiration (ET) and water use efficiency (WUE), and the water–yield relationship of wheat in a soybean–wheat cropping system on vertisols. Three levels of irrigation, viz. I₀, no post‐sowing irrigation; I₁, two irrigations [crown root initiation (CRI) and flowering stage]; and I₂, three irrigations (CRI, maximum tillering and flowering stage) and three nutrient management treatments, viz. F₀, control (without fertilizer/manure); F₁, 100 % NPK (100–21.5–24.9 kg ha^?1); and F₂, 100 % NPK + farmyard manure (FYM‐10 t ha^?1) were tested in a split‐plot design with three replication. It has been established (through anova ) that the year effect was rather negligible and the interaction effects of irrigation and nutrient management on the growth parameters, ET, yield components, yield and WUE were significant. Plant height, progressive leaf area index, dry matter accumulation and crop growth rate were higher in I₂F₂, and I₂F₁ and I₁F₂ were statistically at par. The seasonal ET increased significantly with the increase in water supply in every nutrient treatment and it was highest in I₂F₂ and lowest in I₀F₀. The highest grain yield was obtained in I₂F₂; and a similar yield was recorded in I₃F₁ and I₂F₂. This shows a strong interaction effect between irrigation and nutrients. Yield components, viz. number of ears m^?2, number of grains ear^?1 and 1000‐grain weight were significant. The higher number of ears m^?2 containing greater number of grains with relatively heavier weights appeared to have contributed to the higher yield in I₁F₂, I₂F₁ and I₂F₂. The highest WUE obtained in I₀F₂ did not correspond to the highest yield and maximum ET, but a WUE of 10.43 kg ha^?1 mm^?1 in the I₂F₂ combination corresponded with the highest yield and the seasonal ET requirement was 391.8, which was 137 % greater than the water use at maximum WUE. The ET–grain yield relationship was linear, with a lowest regression slope (i.e. marginal WUE) and elasticity of water production (E_wp) in F₀ and a considerably higher slope and E_wp in F₁ and F₂. As the E_wp is positive and close to one in 100 % NPK treatment, the scope of improving WUE and yield with only inorganic fertilizer is very little, and relatively greater scope exists in the integrated management of organic manure and inorganic fertilizer. The results suggest that integrated nutrient management (100 % NPK + FYM) in conjunction with three irrigations maximized yield of wheat with concomitant improvement in ET and WUE under limited water availability.     

Severe erosion on agricultural land in east Sussex,UK October 1987

Severe erosion occurred as a result of heavy rainfall on 7 October 1987 and subsequent storms. Rates of erosion were highest on land drilled with winter cereals in the previous three weeks but erosion also occurred on ploughed land. In an area of c36 km² some erosion was recorded on all cereal fields. Several fields suffered losses >50 m³ ha⁻¹ and rates reached>200 m³ ha⁻¹ on one field. This is the most serious erosion on agricultural land recorded in Britain.In autumn months heavy rain on erodible, silt-rich soils prone to crusting inevitably leads to runoff and high rates of soil loss but a number of factors contributed to the severity of this event: the amount of bare, recently drilled land; the timing of drilling; the size of fields, steepness and length of slopes; the rolling of drilled fields, and the prevalence of wheelings.     

Cropping systems effects of a newly-cleared ultisol in Southern Nigeria

A 4-yr. study was conducted to investigate the effects of five cropping systems on soil erosion, earthworm activity and crop production on an Ultisol in southern Nigeria. Five cropping systems were casava-based, oil palm-based alley cropping, plantain and traditional farming system. The traditional farming system for this region involves cultivation of vam (Dioscorea sp.) and several other crops grown in partially cleared land. The first four systems were tested on mechanically-cleared plots, and the traditional system was evaluated on manually-cleared plots with partial clearing and intact stumps. Soil erosion was observed only during the first year after clearing. Soil erosion was high in the oil-palm- (170 kg/ha/5 months) and plantain systems (157 kg/ha/5 months), and was negligible in the forested control (0.4 kg/ha). During the rainy season, earthworm activity was the highest in traditionally-farmed plots and the lowest in the forested control. Earthworm activity significantly decreased in all systems during the dry season. On the basis of agronomic yield, cassava-based cropping system was the most productive (10.8 Mg/ha/yr. of produce) followed by traditional farming (8.0 Mg/ha/yr.), and the plantain system was the least productive (0.74 Mg/ha/yr.). Measured in terms of the calories output, productivity of different cropping systems followed the other cassava-based > alley cropping > traditional farming > oil palm-based > plantain. Results indicate that Ultisols can produce high yields of cassava, yam and maize, provided that soil degradation and fertility depletion are minimized by practicing no-tillage, returning crop residue to soil at harvest, and maintaining favorable nutrient status through supplemental application of fertilizers.     

弱光下生长的高产小麦品系PH01-35旗叶光合机构对不同光强的响应

为了解弱光下生长的小麦叶片在不同光强下PSII和光合电子传递链的工作状态,解释其突然转入强光下时发生光抑制和光破坏的原因,以PH01-35为材料,采用大田人工遮光的方法,测定了小麦旗叶叶绿素含量、光合特性参数及快速光曲线。弱光处理15 d后,旗叶叶绿素含量明显上升,净光合速率、光补偿点、光饱和点、表观量子效率、羧化效率均出现不同程度的下降。与250 μmol m^-2 s^-1的弱光适应3 h相比,1 200 μmol m^-2 s^-1的强光适应3 h后,弱光下生长叶片的快速光曲线初始斜率下降幅度较大,曲线下降部分的斜率、最大相对电子传递速率、半饱和光强的上升幅度均小于自然光下生长的叶片,光能利用能力较低,其非光化学猝灭系数NPQ也明显低于自然光下生长的叶片,为自然光下生长叶片的87.5%。弱光下生长的小麦叶片光能吸收能力增强,但较低的光能利用能力和过剩光能耗散能力是其转入自然强光后易发生光抑制甚至光破坏的主要原因。     

Characterizing bulk density and hydraulic conductivity changes in a potato cropped field

Soil samples were taken at two depths from a potato field during the months of May and July of 1990 to determine the variation of bulk density and saturated hydraulic conductivity with time, depth and machinery traffic. Saturated hydraulic conductivity was measured with the falling head permeameter. In general, conductivity decreased with depth, whereas bulk density increased with depth. Saturated hydraulic conductivity (k_sat) at the surface decreased from 6.6 cm/h in May for untracked soil to 0.6 cm/h in wheel tracks in July, while bulk density increased from 1.31 to 1.51 g/cm³. At 20–30 cm depth, k_sat decreased from 3.6 to 1.2 cm/h during the same time period, while bulk density increased from 1.44 to 1.71 g/cm³. In some instances, higher values of k_sat were observed at lower depths. This could be due to compaction and weakening of soil structure in the upper 10 cm soil layer.     

Hybrids of Bread Wheat (Triticum aestivum) with Thinopyrum scirpeum (4x) and Thinopyrum junceum (6x)

Hybrids were obtained by crossing Thinopyrum scirpeum (4x) and T. junceum (6x) onto Triticum aestivum cv, ‘Chinese Spring’. An average meiotic pairing of 24.44^I+ 5.07^II+ 0.14^IIIin the ‘Chinese Spring’×T. scirpeum hybrid (ABDE₁E²) is attributed to two similar genomes from T. scirpeum (E₁E₂E₃E₄). An average meiotic chromosome pairing in the other hybrid (ABDJ₁J₂E₃) was 31.70^I+ 3.80^II+ 0.90^III and is attributed to autosyndetic pairing between the three genomes of T. junceum.     

Comparison of soil and sediment properties of a loamy sand soil

Ten 25 m² runoff plots at the Hilton experimental site, east Shropshire, UK, have been used to compare the physicochemical properties of loamy sand plot soils and sediment eroded from the plots over one year. Sediment contained more sand (2 mm–60 μm) and less clay (< 2 μm), silt (2–60 μm) and coarse fraction (> 2 mm) than soil. Erosion rates increased with slope and proportionally more silt and particularly clay were eroded on steeper slopes. Selective clay depletion has serious implications for soil structure and fertility. Correlations existed between the organic matter contents and particle size distributions of soil and sediment, but the sediment had less organic matter and lower pH values than soil. Sediment also contained lower concentrations of calcium, iron, potassium, magnesium, manganese and phosphorus than soil. Relationships between erosion and soil textural change appear to be partly technique-dependent, which suggests more uniformity in approach would be beneficial in studies on the effects of erosion on soil fertility.     

Coupling a sugarcane crop model with the remotely sensed time series of fIPAR to optimise the yield estimation

The objective of this study was to assess the efficiency of the assimilation of the fraction of intercepted photosynthetically active radiation (fIPAR) data derived from Satellite Pour l’Observation de la Terre SPOT images into the MOSICAS sugarcane crop growth model for estimating the yield at field scale on Reunion Island. Over 3 years, time series of SPOT satellite imagery were used to estimate the daily evolution of NDVI for 60 plots located on two climatically contrasted farms. Ground measurements of the fIPAR were performed on 5 reference fields and used to calibrate a relationship with the corresponding NDVI values. Forced and not forced simulations were run and compared with respect to their ability to predict the final observed yield. Forcing MOSICAS with fIPAR values derived from SPOT images improved the accuracy of the model for the yield estimation (RMSE = 12.2 against 14.8 t ha⁻¹) closer to the 1:1 line. However, underestimations of the yield by the forced model suggest that some of the model parameters were not optimal. The maximal radiation use efficiency parameter (RUE_m) was optimised for each field, and an analysis of variance showed the significant effect of the ratoon number of the field, of its cultivar and of the farm where it is planted. Accordingly, the RUE_m was recalibrated for each cultivar for the number of ratoons and farms. New RUE_m values ranged from 3.09 to 3.77 g MJ⁻¹, and new computations were run using the optimised values of RUE_m. The results indicate that recalibrating the maximal radiation use efficiency according to the number of ratoons improved the yield estimation accuracy by as much as 10.5 t ha⁻¹ RMSE. This study highlights the potential of time series of satellite images to enhance the estimation of the yield by a forced ecophysiological model and to obtain better knowledge about the ecophysiological processes that are involved in crop dynamics with the recalibration method.     

The effects of bioturbation on sediment transport on an intertidal mudflat

Laboratory flume studies were conducted to determine the relative importance of various biological and physical factors controlling sediment erosion threshold and transport rate on an intertidal mudflat in the Bay of Fundy. Studies were conducted in a July period of maximum solar exposure. The upper and mid-intertidal stations of the flat were dominated by silt-clay sediments, while the lower intertidal was dominated by very fine sand. The tube-dwelling amphipod Corophium volutator was the most abundant infaunal species with densities exceeding ∼1300 ind·m⁻² based on counts of burrow openings. Sediment-penetrometry and water-content measurements indicated no change in unconsolidated shear strength and porosity, respectively, along the intertidal transect. Despite the apparently cohesive nature of the sediment, erosion occurred as small ripples. Critical shear velocities (u_crit) for erosion determined with intact cores in a laboratory flume were relatively consistent between stations and sampling dates (mean = 2.1 cm·s⁻¹ ± 0.2 SD), with no relationship to Corophium density, sediment chlorophyll a, or physical variables. Field-treatment of sediment with formalin did not cause an obvious change in u_crit as determined by flume experiments. Corophium seemed to have little effect on erosion thresholds because incipient motion could be observed between tube burrows, beyond the local influence of the amphipod. In contrast to erosion thresholds, sediment-erosion rates measured with bedload traps were negatively correlated with density of small Corophium, probably due to binding of sediment into burrows and the ambient sediment microfabric, all of which reduce the availability of sediment for transport. Adult amphipods, which occurred at low density probably due to territorial/competitive interactions, had no obvious effect on erosion rate since only a small proportion of the sediment surface was impacted by their bioturbation. Although a portion of the amphipod population exerts a stabilizing influence on sediment-erosion rates, concurrent studies at the site indicate that Corophium seasonally reduces the sediment-erosion threshold by grazing on microflora which would otherwise inhibit the initiation of grain motion. Due to this decoupling of erosion rate and threshold, it is necessary to measure both processes in assessing the effects of benthic biota on sediment transport.     

Peach ripening: Segregation at harvest and postharvest flesh softening

The peach melting flesh cultivars ‘Ryan Sun’ and ‘Sweet September’ and the non-melting, ‘Kakamas’ were harvested according to their visually assessed ground color and divided into four, ripeness classes (M1, M2, M3, and M4). The following aspects were determined: fruit mass, soluble, solids content (SSC), ground skin hue angle (h°) and chroma (C*), the absorbance difference at 670 nm and, 720 nm index (I_AD), and the texture (fruit firmness measured with a needle, flesh firmness measured, with a 7.9 mm plunger, and uniaxial compression strength). Considering that in peaches, the h° of the, ground color and the I_AD are maturity indicators closely associated with ripeness and particularly with, flesh firmness, the texture parameters and their relationship to h° and I_AD were examined. The visual, assessment of the ground color was validated as the criterion for sorting the ripeness levels in peaches, as confirmed by h° and I_AD. Fruit firmness assessed with the needle and that with the 7.9 mm plunger, were highly correlated with each other and with the h° and I_AD, whereas the compression strength, exhibited less correlation with the optical properties of the skin. The non-melting ‘Kakamas’ showed, the poorest correlation between texture and h° and I_AD. Comparing both optical properties, the I_AD, showed a higher correlation with texture features than the h°. In a second experiment, fruit from the M3 ripeness class was maintained in a ripening chamber (20 °C, and 80% RH) until the flesh was softened for consumption. During postharvest, the first two principal, components of a principal component analysis explained 85% of the total variance of the texture, components and the optical properties of the skin. PC1 (67.2%) was defined positively by the texture, parameters and I_AD. The h° of the ground color was negatively related to all texture parameters, and, I_AD. PC2 (17.8%) was associated positively with the juice content, and this parameter proved to be, independent of all others.     

Soil nitrogen availability indices as predictors of sugarcane nitrogen requirements

Nitrogen recommendation systems for sugarcane (Saccharum spp.) generally does not consider the N supply from soil. Identifying a reliable soil test for estimating N availability is crucial to avoid yield losses or environmental pollution. Therefore, the objective of this study was to correlate and calibrate N availability indices with field–based measures of soil N supply. Between 2006 and 2013, 15 trials for rate–response to N fertilizer by sugarcane ratoons were performed in São Paulo, the main sugarcane–producing state in Brazil. The following indices were tested: KMnO₄ oxidizable C, hot KCl extractable N, phosphate–borate buffer distillable N, NaOH distillable N, Illinois Soil N Test, organic C, total N, mineral N, anaerobic incubation, soil respiration, substrate–induced respiration, microbial biomass C, metabolic quotient, microbial quotient, and gross N mineralization. The indices were then correlated with sugarcane yield (Y_0N) and N content of the crop (N_0N) in N–unfertilized plots, relative yield (RY), and the N rate predicted to achieve 90% of the RY (NR 90%RY). Although weak correlations were found between Y_0N with anaerobic incubation, total N, and soil respiration, as well as between N_0N and anaerobic incubation, no index correlated with RY or NR 90%RY. Grouping sites based on soil texture or byproduct management did not improve prediction of RY. Therefore, we concluded that none of the fifteen laboratory indices is a reliable predictor of soil N supply, and hence could not be used to adjust N fertilization rate for sugarcane.