Cornell University

Forage sorghum is not always harvested for the highest yield, sometimes the quality of the sorghum is also an important factor that farmers will consider when making the decision of harvest. Time of harvest can decide trade-offs between yield and quality, so I paid attention to this topic in my summer internship.

Generally, the sorghum yield tends to increase as the harvest time is delayed. This increase might be attributed to the longer time of dry matter accumulation in sorghum tissues. However, the yield will finally reach a plateau where the later harvest does not result in a significant increase in yield due to the maturity of the plant.

On the other hand, the change of sorghum quality may have different trends. The crude protein content tends to decrease as the sorghum reach maturity, while the lignin content tends to increase as the harvest is delayed. The crude protein is important to the nutritious value of the feed, high crude protein content in sorghum feed may relatively reduce the need of other protein supplement. The lignin content partly determines the digestibility of the forage, too much lignin will reduce the digestibility and thus lower the quality of feed.

To balance the yield and quality, farmers need to decide the time of harvest to gain the most suitable forage according to their own needs. For example, when there are other available sources of crude protein, the crude protein in sorghum forage might not be that important. Then farmers may choose to pursue higher yields by waiting longer. Yet if farmers do treasure the crude protein in sorghum and want higher digestibility, then they may sacrifice certain amount of yield in exchange for better quality.

Anyway, farmers will make decisions according to their own situations. What I can do in my summer intern is to figure out trends of yield and quality change as the harvest time changes. By offering some information that can help to the process of decision-making, I can also slightly contribute to the actual production.

This summer the Tompkins county suffered drought, for almost a month there was no decent rainfall and the water was really deficient for vigorous crop growth. One of our sorghum fields was located in Varna, and it took nearly the whole June for those sorghum seeds to emerge from the soil. The sorghum was usually viewed as a drought-tolerant crop that did not need much water for survival, yet extremely drought after planting would still delay the emergence since seeds could not well germinate without certain amount of moisture.

The corn at the Musgrave experimental farm also showed obvious symptom of water deficiency. By the early July, the corn had reached the V8 to V9 stage and the average height was around. Due to the drought, newly-developed leaves rowed and older leaves turned yellowish. Rolling leaves could reduce transpiration of water from the leaf surface, yet it also reduced the solar radiation intercepted by the canopy for photosynthesis. Less photosynthesis would result in insufficient accumulation of biomass. Besides, limited moisture in soil would restrict the roots’ absorption of nutrients. Hence the corn yield might be lower than normal years.

Since the water is usually abundant in New York state during the growing season, not much attention would be paid to irrigation issues, especially in corn and hey production. To increase the crop’s resistance to drought, adjusting planting date and improving soil health are two important methods. By adapting reduced-tillage, leaving more residues on the soil surface or planting cover crops, the soil’s water holding capacity can be increased and thus benefits crops during drought.

I hope there would be more rainfall in the following days. Hang in there, my sorghum seedlings !

Crop canopy sensing technology has been increasingly used in precision agriculture. Imagine that if farmers are able to know the crop’s growth status just by scanning leaves, then the field management will be much more convenient and accurate. Since I am interested in precision agriculture technology, the canopy sensing is really attractive to me. And in my summer internship, I get the chance to experience this fascinating technology.

The canopy sensing technology I use is called GreenSeeker®. It is an active sensing device which contains a light emitter and a receiver. The emitter emits certain wavelengths of light towards the crop canopy, and the receiver measures the light that is reflected by leaves. By comparing the intensity of different wavelengths in reflection, the GreenSeeker can calculate the extent of canopy absorbance of light, which can be use as an indicator of crop growth status. In my case, the normalized difference vegetation index (NDVI) is calculated by the relative absorbance of near-infrared and visible light. High NDVI value (close to 1) indicates vigorous growth, while low NDVI value (close to 0) suggests that the crop is in stress.

To gather the NDVI data at different crop growth stage, field scanning was conducted for many times during my intern. I carried the GreenSeeker and held the sensor above the canopy, walked through the field with my finger pressed on the trigger that controlled the emission of light. The track of my walk was captured by the GPS and was shown on the PDA attached to the GreenSeeker, so I also needed to notice the screen to make sure that I walked in relatively straight line. The sensor emitted one pulse of light per second, so the final results were lines of data points across the field.

Each data point carried lots of information include speed, direction, GPS location, calculated NDVI value, etc. With the GIS software (ArcGIS), we got a scanning map that showed the distribution of NDVI values in the scanned area. The difference in NDVI value indicated the uneven growth status of crops in the field. Such uneven pattern could be explained by the spatial variability of nutrients content in soil, for example, the nitrogen was abundant in some area but deficient in other parts of the field. Then according to different levels of need for nutrients, farmers can adopt variable rate application of fertilizer to maximize the nutrient use efficiency. In this way, farmers could save fertilizer from plants that already had enough nutrients supply from the soil, and thus reduce nutrient losses caused by excessive application.

In the first week of my internship, I helped to harvest the triticale at the Musgrave experimental station at Aurora. The triticale was planted as part of the double cropping system trial, which involved both triticale and sorghum grown in consecutive order on the same land. Compared with conventional monocropping of corn, the double cropping system of triticale and sorghum tends to have higher total yield. It also spreads the risk of crop failure, that even if one crop suffers from diseases or environmental stresses in its growth period, farmers may still have the other crop to rely on.

To evaluate the performance of double cropping system in NY state and provide suggestions about nutrient management for farmers, the field experiment was conducted to measure the yield and forage quality of triticale-sorghum double cropping system and to figure out the effect of residual nitrogen that previous triticale left on the following sorghum. The triticale field was divided into 4 blocks, and each blocks had 4 replications. Each replication was then divided into 5 plots that received different rates of nitrogen treatment. So there were 80 plots of triticale for us to harvest.

The harvest of triticale in each plot was completed by a forage harvester. It also recorded the weight of harvested forage in each plot. I walked after the harvester and measured the length of harvested area. The width of the harvester was fixed, so with length and weight we could calculate the fresh yield of each plot. After the harvest, I took triticale samples in each plot for quality analysis.

It took us about 4 hours to complete all the harvest and sampling. Fortunately, the weather was not hot and the breeze in field kept us comfortable. The harvester created pathways that went through the 5 plots in each replication, and I enjoyed sitting in the middle of the plot, where I was surrounded by waves of green leaves that moved as wind blew. It was a such a relaxing experience that I even forgot the time to leave.